Musings and Experiments on the Art and Science of 3D Printing

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First week with the Prusa MM Quad Extrusion Kit

By Michael Hackney → Saturday, June 24, 2017

Last Sunday I had a leisurely afternoon to myself – a rare occurrence around here! I took the opportunity to upgrade my Prusa i3 MK2/S with the MM (multi material) kit. The job was straight forward and took about 3 1/2 hrs start to finish. The kit includes four new extruders that use Bondtech dual drive gears, here they are:
This is the cool Prusa Super Switch – it interfaces to the mini RAMBo card and drives the four new extruders by multiplexing their step and direction signals over the original E0 connector. Clever.

The kit includes filament racks for four spools of filament along with a new E3D V6 hot end that was customized for the MM kit. Once it was all together, this is what it looks like from the top:
The filament racks are paired, so there are two of them. The four new extruders sit on top of the Prusa arch – again in pairs. The filament is delivered to the Y Splitter via four short Bowden tubes (ironically, I've been working to eliminate Bowden tubes from my delta printers!) you see in the lower half of the photo and here is a closeup view. The four filaments feed into the top of the Y Splitter and the g-code orchestrates the dance to advance the active filament and withdraw the retiring filament.
Other than the space required for four spools of filament, the setup is very compact.

Like anything new, there is a bit of a learning curve required. It is highly recommended that you have solid experience with single extrusion on your i3 before doing the MM upgrade. There are just too many new variables to control and without a firm foundation of success I fear frustration will be your friend.

For my first attempt I decided to print the MM g-code for the Gear Bearing Prusa provides. I chose green, blue, white and orange filament. I have a lot of experience printing the green, blue and white but not much with the orange and it was a little persnickety at the time. This is important! I highly recommend finding four filaments that print very well with your stock i3 before diving into quad extrusion. In my case, I understand filaments and extrusion well enough that I believed I could deal with a relative newcomer filament. How wrong that assumption was!

And the reason for that is buried in the details on how the MM kit does its magic. Conceptually, filament changes are made by removing the active filament and then advancing the new filament. That's easy enough. But deep in the bowels of the hot end and Y Splitter things are not so simple. Are is a cutaway drawing based on my understanding of what's going on:
Assume that the printer is printing your first color – red in the drawing. When it's time to change to the next color the nozzle is moved to the prime block. The nozzle is simply moved back and forth the length of the prime block as the filament is withdrawn up into the special PTFE tube (light blue). This tube is special in several ways – it is not standard 2mm PTFE, it has a precision 1.9mm ID. You can not replace this tube with standard 2mm PTFE and get good results. The lower end of the PTFE is tapered to help shape the soft filament as it is retracted up through the heatsink. The filament retract  continues until the tip of the filament is inside the steel tubing. This tube is a good heat conductor and quickly cools off the filament so it retains its shape – a precise 1.9mm diameter. While it is cooling, it appears that the g-code is jiggling the filament back and forth a little to keep it moving it as it cools. This prevents it from sticking to the tubing.

When the red filament is completely withdrawn into its steel sheath, the next filament (blue in this case) is advanced. The upper end of the PTFE is tapered to guide the filament in. The filament continues its journey to the heat block where it is extruded on the prime block to purge the old color and prime with the new.
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An update: Peter(PJR on the Prusa forums mentioned below) emailed me after reading this post with a few well made comments. I'll just quote him, no use trying to wordsmith a clear description!
The Y-Splitter is actually a multiplexer, although technically it should not be called that it does perform that function.

The "SuperSwitch" is actually a demultiplexer.

During the tool change, about 10mm of the previous filament is "rammed" into the hot end which has the effect of cooling the tip of the filament for clean withdrawal.  Withdrawal must be fast, but not too fast such that a ball of filament is left behind (below the MUX).  If the temperature is too high, then stringing will occur causing a blockage.

A steady (or better, slowly increasing) purge speed allow the best possible purging of filament and uses about 60mm of filament.

I have a feeling that the cooling tubes are actually 1.95mm internal diameter.  The primarily tip forming is carried out by the PTFE.  Early beta tests were using standard 2mm PTFE and 1.85mm cooling tubes; the tip forming was then carried out by the tubes.

The problems may start when the PTFE start to wear.
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Simple right! What could possibly go wrong? It might be better to ask "how does this thing even work?" It does and quite nicely – once you understand the mechanics described above and the properties of the filaments you are using. PJR on the Prusa forums posted a well done Blockage troubleshooting thread that is a must-read for anyone upgrading to the MM kit.

During my first print, the extruders were sounding out that tell-tale click-click-click of skipping steps. This is virtually unheard of for Bondtech dual drive gear extruders so something must be seriously wrong! Even a Bondtech extruder can't push filament through a wall – and that's the clue. In my case, that orange filament was not retracting cleanly and leaving a long string as it was pulled up into the steel tube (this is somewhat hypothetical although I did disassemble the Y Splitter several times during failed test prints to find a blob and string of orange filament in the bottom of the splitter). This blocked the next filament from entering the hot end. I replaced the problematic orange with a known good gold filament and was off and running making some reasonably nice multi color test prints.

The above illustrates why its good to have some printing experience under your belt and choose four filaments that perform very well. The filament must be well behaved as it melts and cools during the change-over process – extruding at elevated temperatures is the kiss of death and will likely result in blockages as described in PJR's post.

I don't have a lot of experience yet but I am over the initial learning curve and I'm starting to slice my own MM objects. Prusa provides a post processor for Slic3rPE but I'm using KISSlicer (the unreleased 1.6 beta 1 that should be out in the next week or so) and a post processor written by the same PJR mentioned above. It works beautifully. Here's a 12 hour MM snake I printed last night in gold, white and red PLA. This gold is known to string at higher temps and I forgot about that when I sliced. So I did have a fair amount of stringing of the gold. Next time I'll reduce extrusion temperature to 190° or 195°C for it. This print was 200°C, 3 perimeters, .1mm layers and 50% straight infill.

Here's the belly of the snake, not a bad first layer.




Six months with the UltiBots D300VS delta printer

By Michael Hackney → Tuesday, June 20, 2017
A few years ago I built an UltiBots K250 delta printer from printed parts and a hodgepodge of purchased parts from UltiBots. I wanted a smaller delta to take to my presentations on 3D printing and it was the perfect size. This printer was also my original test platform for trying out the Duet .6 controller and David Crocker's dc42 RepRapFirmware. It turned out to be a perfect storm of delta nirvana! The K250 was the most reliable and most precise delta printer I've owned, period (until now).

So flashing forward, I came across the new UltiBots D300VS delta printer kit introduced in November last year (D=delta, VS = V-Slot). This printer's build of materials list read like a whose-who of top-notch printer components. Here's what I mean:

  • Duet WiFi controller with RepRapFirmware
  • Authentic E3D V6 all metal hot end
  • FSR sensors and JohnSL board for probing (delta auto-calibration)
  • all metal (aluminum) frame and corners assembles quickly and precisely, the towers are 20x40 extrusions for excellent rigidity
  • OpenBuilds Delrin carriage wheels
  • Hadyn Huntley's carbon fiber with magnetic ball delta arms
  • .9° stepper motors offer 2x the precision over the standard 1.8° steppers
  • Kapton bed heater with an aluminum heat dissipator and borosilicate glass build plate
  • 24VDC power supply
  • UltiBots' direct drive Micro Extruder - no Bowden tube!
  • top mounted filament spool holder
  • LED lighting
The Duet, .9° steppers, FSR probing and all metal frame caught my attention. But my main interest in this printer was its massive size - 445mm Z x 290mm bed diameter (it's actually a bit larger than that). The only "must have" not included is a PEI print surface – but one is available and can be purchased with the kit.
I ordered my D300VS kit not realizing it was one of the first sold and documentation was sparse. No worries though, I've built a lot of 3D printers and the only unique item was the Micro Extruder. I was actually on the fence about it and my initial plan was to swap it out for a Bondtech QR extruder and Bowden. Brad (UltiBot's owner) convinced me to give it a try for a few weeks and I'm glad he did!

I started to document my build with a lot of photos with the plan to help document the build. But as I got into the build, my excitement grew and I wanted to get this printer commissioned as soon as possible.

Once I had the printer commissioned and operational it was time to take a test run. Most who read this blog and my forum posts know that I am into fly fishing and developed a 3D printed fly fishing reel. I like to use it – nine printed parts – to test extruders, hot ends and printers because they can be challenging parts to dial in. So I loaded up the models and sliced an entire platter of all nine parts. This is the 3D printing equivalent of a Hail Mary, especially for a first print! I carefully prepared the new PEI surface, brought everything up to temperature and allowed to stabilize for 15 minutes then crossed my fingers and clicked Print...

As soon as auto-calibration completed (I run auto-calibration in my g-code header for nearly everything I print) and the first layer started I could tell this was going to be a special printer. And that's the precise moment that I fell in love with the D300VS! Take look at the photos below. These parts are each challenging on their own and even more so combined into one platter and printed simultaneously. As you can see, the first layers went down flawlessly. Two of these parts are printed with an "open mesh" that is very challenging to print reliably and flawlessly. The D300VS printed them flawlessly the very first time!

Here are the completed parts. Let me describe these and the challenges they present to the printer (and operator).
Starting at the upper left is the foot – that long skinny object. It is the part that attaches the reel to the fly rod. This part has very little surface area to stick to the print bed and is always a challenge.

Below it are two disks with a central post. These are the side plates and are the parts with the open mesh design. Here's a photo of one printed in pink PLA so you can see the detail more clearly. These parts are the most challenging to print. If the first layer height is off even a little it significantly affects the aesthetics (smoothed weave is obvious and looks horrible) or the part peals from the bed (layer too thick). These parts are perfect.
To the right of the spool pates are three cylindrical parts. They have very little contact area with the bed and must be printed very precisely to hold their dimensions. The larger of these has a gear-like feature you can see clearly in the photo of the pink parts. Those teeth are a major challenge to print flawlessly.

Below these is a large ring. Nothing significantly challenging on this part or the small part at the lower right. 

In the lower left is the reel back plate. This part has all sorts of challenges to print. The tall pillars are magnets for stringing and are a real test of extrusion and filament. They also create havoc for layer registration and part cooling for most printers.

The D300VS has continued to perform like this from the very first print. I knew what to expect from the Duet, .9° steppers, FSR bed leveling and other features but the Micro Extruder was an unknown entity. I've now done enough printing and testing to come to understand that direct drive extruders blow Bowden filament delivery out of the water on these large delta printers. I have been so impressed with part quality and the ease of dialing-in slicing to eliminate strings and blobs that I've gone on a mission to eliminate Bowden tubes from ALL my delta printers. I'm glad Brad convinced me to give it a try and now with six months of continuous use I can say the Micro Extruder has been very reliable and trouble free.

Sidebar: I'll post details about this later – shortly after building my first D3000VS several other direct drive extruders have become available. The E3D Titan Aero, the Bondtech BGM, the Zesty Nimble (remote direct drive) and of course the Flex3Drive (remote direct drive) has been available for a couple of years. I've spent a lot of time learning to get the best performance from Bowden filament delivery using 1.8mm ID PTFE tubing, Bondtech QR extruders and a host of slicer tricks. It wasn't until I saw (and experienced) the results from the Micro Extruder that I realized just how big of a compromise Bowden filament delivery really is. For small deltas like the Mini Kossel and K250 the length of the Bowden is manageable but the loooonnnggg Bowden's on large deltas like the SeeMeCNC Rostock Max and UltiBots D300VS have significant limitations. Over the next few months I'll post about these options. Back to the D300VS...

The only significant criticism about the D300VS was the lack of good build documentation. This is not an issue for experienced builders but is a bit of a non-starter for folks looking for a first 3D printer. Recognizing this, Brad asked if I'd write a professional build guide for the D300VS and I agreed. He sent me a new kit to use to photograph and document the build. The UltiBots D300VS Build Guide is now complete and getting great reviews – and more importantly, helping a lot of first time 3D printer builders get off to a great start.

At the end of the day, the D300VS is an excellent delta printer with top-notch features. It's geometry lends itself to precision construction and printing. The Duet WiFi controller is excellent and its stepper drivers are are dead quiet. Everyone always comments on how quiet my D300VSes are. The RepRapFirmware with its integrated Duet Web Control interface is the best open source firmware there is, especially for auto-calibration performance, usability and overall print quality. And the D300VS is a great value too with its quality components and construction and print build volume.

I'll leave you with a few more photos showing what the D300VS is capable of doing.








When it rains, it pours: Prusa multi-material quad kit arrived!

By Michael Hackney → Friday, June 16, 2017
Last week I got the Mosaic Palette to explore printing with four colors of PLA on one of my large delta printers. Yesterday I got the Prusa quad multi-material kit for the Prusa i3 MK2(S upgrade) I ordered with the printer last October. In fact, the only reason I bought the Prusa was to get my hands on the quad extrusion kit! Turns out the i3 MK2 itself is not a bad little printer within the limitations of its 8bit RAMBo mini controller and firmware. But it produces nice prints reliably (not as nice as those from my delta printers running Duet Wifi and RepRapFirmware, but nice).

Here's what arrived in a Tyvec package:
And here's what's inside the main box, the motor and multiplier pox has 4 steppers and Prusa's innovative multiplexer/driver:
Under all of the parts were the two components I was most interested in. Shortly after I ordered my kit last Oct. Prusa announced a shipping delay because they were not happy with extrusion and hot end. The net result was, they worked with Martin at Bondtech and decided to use the excellent Bondtech dual-driven drive gears in their extruder update. The magic here is the Bondtech dual drive do very little damage to the filament surface. I've been talking about this for several years so it's great to see an application where this is critical. Prusa is sourcing the drive gears from Bondtech.

They also worked with E3D to address the issue they discovered with the hot end that affects the quad kit but not normal V6 operation. This is because the quad kit does its magic by pulling the active filament completely out of the hot end in order to insert the next color in! That's a lot of movement, especially when the end of the filament is a molten blob that can get unglanceable up as it cools and solidifies. 

So I anxiously removed bags of parts until I found these. The Bondtech drive gears - they are as beautiful in a Prusa bag as they are in a Bondtech QR or BGM extruder!
 
And the E3D V6 hot end:
So it will be a fun weekend of tearing apart my i3 MK2 again (I had to tear it down for the "S" update last month) to install the quad system. I'lll post photos, impressions, results as they come. Meanwhile, take a look at these prints from Prusa, if these don't make your heart skip a beat (except for those unbearable Benchies) you are either 1) dead or 2) disinterested in FFF 3D printing!
(photo linked from http://www.prusaprinters.org/update-multi-material-upgrade-2)





Mosaic Palette - the journey begins

By Michael Hackney → Wednesday, June 7, 2017
I've been watching the Mosaic Palette since its Kickstarter and have come close to buying one on four occasions. But each time I hesitated and moved on to other projects and challenges – a little gun-shy from the shipping delay and lack of time. So what, you might be asking, is the Mosaic Palette?
(photo used with permission)
That 290mmx170mmx140mm (11.4"x6.7"x5.5") white box above is what it looks like in case you haven't seen one. But the all-important question is "What does it do?"

In a nutshell, you feed four different colors of filament into Palette and it chops them up into short segments and fuses them back together to make a single multi-colored filament. Here's a little graphic to show the concept:

The length and position of the colored segments are calculated from an object's g-code file. It delivers this sequence of chopped up colored segments to your 3D printer, with its standard extruder and hot end, so it can print objects in up to four colors. If that isn't difficult enough, it does the cutting and fusing in near real time as the object is printed. It's a fascinating concept and it isn't difficult to imagine the technical challenge to pull it off. Is it art, technology or black magic (or a combination)? Over the next few months I am going to find out.

Due to a combination of a successful Kickstarter campaign and some last minute technical challenges, Palettes were scarce with a long waiting list. That was one of my deterrents for jumping on board; I tend to be opportunistic due to my very busy "life schedule". I can't predict what I'll be doing and how much time I'll have next week let alone six months from now! But while I faltered Mosaic stuck to it, resolved the technical issues one by one, and finally caught up shipping to backers and those patient early buyers.

I was a bit surprised when I made my monthly pilgrimage to the Mosaic web site this week and found they were offering a 25% discount to the first 50 new customers. That was just the extra kick I needed - well, that and having seen Jetguy's Palette at the Midwest RepRap Festival in March. I knew it was just a matter of time before I got my hands on one to see exactly what it can do with visions of four-color 3D printed fly-fishing and spinning reels dancing in my mind. I placed my order at 12:45pm yesterday and today at 12:30pm this package arrived at my door:
An amazing feat when you realize that Mosaic is in Toronto, Canada and I'm in Boston, MA USA. The tracking showed my package routed through Cincinnati, OH! Less than 24hrs from order to delivery - your mileage may vary :)

Inside the box, packed in paper any molded foam, is this purple box (one of my favorite colors):


Inside the purple box is the Palette. It might be a good omen that a postcard from my all-time favorite filament designer – Proto-pasta – greeted me when I opened the box!
Over the next months I'll post updates on my progress, tests and prints as I install and learn how to use this unique device. My plan is to commission it on an UltiBots D300VS large delta printer modified with an E3D Titan Aero direct drive extruder. The Aero should provide very precise filament delivery without the issues of Bowden hysteresis - an issue that some early delta Palette users have discussed on the SeeMeCNC forum.

Please be patient though! I have a lot on my plate so progress might be slow. But I'll get there... 

Friend's don't let friends use oil...

By Michael Hackney → Friday, June 2, 2017

Back in the dark ages when humans knew not the subtleties of FFF 3D printing, many tried elixirs, potions, broths, salves, incantations, and many other unscientific and unproven so-called remedies.

It was a dark and dangerous time – especially for those unknowing and unenlightened followers. The "oil myth" started in the early days (circa 2013) of the full metal hot end; that which we know and love today called E3D (taking a bit of liberty here, historically, the oil treatment was developed by a Replicator 2 user as best I can tell. But the word spread fast to the delta community who were grappling with those long, filament-strangling Bowdens). The early E3D was a slightly different beast than the then-current J-head state-of-the-art hot end. And many unwittingly assumed the E3D and other all-metal hot ends of its ilk would work exactly the same, but only better. They did not understand the subtleties of a short melt transition zone that is the hallmark of these all metal designs.

So they continued to blindly slice with long and rapid retracts. And lo, as they printed, the filament – most notoriously, PLA – would jam. "It can't be my beloved slicer or filament or my lack of understanding so it must be this cursed hot end" proclaimed many. "We must lubricate it into submission. If it wants to jam, then let's oil the darned thing." And oil they did - Canola, peanut, corn and many other oils were used. And "good results" were exclaimed by those silly enough to go down this path. Until, that is, until other, more challenging problems arose – first-layer adhesion problems, inter-layer adhesion problems, gummed up extruder drive gears and a general unkempt appearance on and about the 3D printer.

Meanwhile, a few brave and hardy soles were determined to study and understand the problem. They invested 1000s of hours collectively (and some of us individually) to hypothesize and test – you know, the scientific method that seeks truth above all else. And lo, these pioneers discovered that retracting molten filament past the short melt zone and into the heat exchanger is bad, very bad. And more importantly, does not fail catastrophically 100% of the time so the unwitting could not correlate the results to its cause with certainty. However, those brave and determined few DID correlate the results to the cause. They dissected hot ends and nozzles and heat breaks by slicing them latterly after quenching in liquid nitrogen. They invented the "cold pull" test (blush) to study the shape of the melt zone and nozzle geometry, and they came up with theories, testable theories, to determine once and for all what was really going on.

Meanwhile on the forums and groups, the oil-mongers propagated their myth at a time when many, many new 3D printer users were entering the field. Not knowing the hows or whys, these noobs saw the exuberant claims made by the oil-mongers and fell prey to them. Creating a new cycle of perplexed and frustrated users.

It was just at that time when the results of all the hard and scientific work were made known after much collaboration and cross-checking and verification. The cry went out "No oil, no oil good people! It is not necessary and actually creates more problems than it solves." Data and results and explanations were shared. And the nascent hot end manufacture took note and rather than get defensive they embraced, welcomed, understood and appreciated the work and dedication to truth and understanding. They tested and verified the results on their own and went the extra steps to make changes, changes that would later propel them to the top of the hot end market for performance, reliability(!) , functionality, innovation and design aesthetics. They realized the minor flaws in their earlier designs that might lead users down the slippery oil-covered path and fixed them, saving countless others from the "oil myth" of 2013-2014.

You can read about this here: E3Dv6 Release Announcement & Design Details. And the all-important quote that tickled and caused this author to blush slightly:

• Fix niggling reliability issues.

v5 has a great track record of reliability with less than a fraction of one percent of users experiencing issues due to manufacturing issues, however we really wanted to eliminate any chance of future defects.

1.75mm Bowden users were experiencing a disproportionate amount of problems, which was traced back (with much help and hard work from Michael Hackney) to nozzle geometry in certain situations needing high extrusion pressures that resulted in starvation of filament flow.

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The first reference I can find to the use of oil for preventing PLA jams was posted on the MakerBot Operators Google Group on 1/14/13. I have not found an earlier reference, if you do please let me know!


Everything you wanted to know about the Zesty Nimble remote direct drive (RDD) extruder

By Michael Hackney → Tuesday, May 30, 2017
I've been a "delta fanatic" for over 4 years. Like all things in life, delta printers have tradeoffs compared to their Cartesian counterparts. In exchange for very fast movements in all three dimensions, the extruder is mounted remotely and the filament delivered through a long PTFE tube called a Bowden tube, typically 2mm ID for 1.75mm filament.

Delta Musings
The early delta printers were fairly small (Mini Kossel) and the length of the Bowden was not too problematic. But as delta sizes increased - like the SeeMeCNC Rostock MAX and the more recent UltiBots D300VS - the length of the Bowden also increased. Long Bowden tubes have more friction for the extruder to overcome, especially if the extruder roughens the filament surface with its drive gear. Another issue is that long Bowden tubes introduce more hysteresis into filament retracts due to their inner diameter being much larger than the filament diameter. This results in print quality issues like excess stringing and blobbing.

Several years ago I recognized these problems and developed a solution to combat them with a combination of using 1.8mm ID PTFE tubing and Bondtech QR extruders. This combination greatly improved my print quality and is highly reliable (1000s of hours of printing without a single problem). The 1.8mm ID tubing has less issues with hysteresis, the primary contributor to print quality issues. But, any significant filament diameter issues or surface damage from the extruder drive gear results in jamming and filament starvation. This is where the Bondtech QR extruder comes to play. It's dual opposing drive gears exert much greater extrusion force with far less filament damage than the common single drive gear/pressure bearing extruders. The combination was very successful.

Then last year I added an UltiBots D300VS large format (300mm D x 445mm Z) delta printer to my stable. My intent was to build the D300VS stock and then replace the UltiBots Micro Direct Drive Extruder with my tried and true 1.8mm Bowden and Bondtech QR extruder. But after a couple of test prints I was so impressed with the results that I decided to put the extruder through its paces. This experience really punctuated the tradeoff we delta fanatics make with Bowden filament delivery - even with more advanced solutions like mine.

The Zesty Nimble

It was exactly at this time that I first learned of the Zesty Nimble remote direct driver (RDD) extruder. This is a different filament delivery mechanism that places the stepper motor (the primary contributor to extruder mass) remote and powers the drive mechanism via a rotating cable - also a type of Bowden. This has the advantage of removing significant mass from the delta effector while powering the filament delivery right at the entry to the hot end like a direct drive extruder system.

I backed Zesty's unsuccessful KickStarter campaign in October, 2016. KickStarters are hit and miss from a funding perspective and to Zesty's credit, Brian and Lykle persevered to bring their super light extruder to market. I kept in contact with the founders through late 2016 and ultimately they asked if I would be interested in testing the Nimble once they had a pre-production unit ready to test. I couldn't say no to that!

I received the pre-production Nimble on March 16, 2017 just a week before I had to leave to attend the 2017 Midwest Rep Rap Festival (MRRF) in Indiana. I was determined to get the Nimble installed and printing so I could bring it to show the crowd. Little did I know when I received it that mine was the very first (and only) Nimble in the wild.

I decided to replace the Bowden setup on a mid-size K250 delta printer powered by a Duet .8 controller and dc42 firmware (my gold standard delta firmware) with an E3D V6 hot end and standard .4mm nozzle. I have 1000s of hours of printing on this printer so I know it inside and out. Rather than print a new mag ball effector (which would actually have been the effector and all three carriages because I only used matched sets printed at the same time to eliminate dimensional issues) I modified the effector simply by drilling two holes for the Nimble mount.

The Nimble is remarkably small and light (appropriately named!) and mounting it was surprisingly easy as you can see here.
 
In addition to its diminutive size, the Nimble's design and engineering are remarkable. The extruder is ambidextrous - meaning that it can be mounted either left- or right- handed. And, it features a really convenient "breech loading" system - the red lever you see in the photo below is the breech lock.

And here's a photo of the remote stepper and drive shaft.
Before continuing, here are the basic stats for the production Zesty Nimble:
  • 23.5mm x 39mm x 28.5mm (WxDxH)
  • less than 28gm
  • 1.75mm filament standard, 3mm is possible
  • 30:1 gear ratio

And now for the part I'm sure you've been waiting for - testing!

My 3D printed fly fishing reel is a great torture test for hot ends, extruders and printers. There are 9 printed parts and each has unique challenges to print perfectly. The reel back plate with its 4 thin pillars and central shaft is a very difficult part to print without excessive stringing. I've spent an inordinate amount of time printing and studying this part and I've become very proficient in diagnosing printer issues with it. So, of course, it was the first part I printed with the Nimble.

My initial experience was a little mixed but understandable. With its 30:1 gear ratio, retracts require a little forethought. I typically retract PLA at 20mm/s but this speed stalled the stepper. A few back and forth emails with Zesty resulted in lowering retract to 10mm/s. The gears in my pre-production Nimble were 3D printed and the production gears would be much smoother and allow faster retracts. I didn't have high hopes that 10mm/s retracts would be sufficient to prevent stringing but I forged ahead. Here is the very first part I printed:
A very respectable part that many would be very happy to produce. But, as you can see at the red arrow, there was some stringing between the pillars. I've printed 100s of these with this PLA filament and know its extrusion characteristics inside and out. This was not a temperature issue, it was a retract issue due to the low retract speed. Otherwise the part was great with smooth, even and well registered layers. I printed a few of these in several PLA filaments with similar results.

For my next print I decided on a gear vase of my own design. I planned to print this at MRRF. It is not extremely challenging but stringing can be an issue for long Bowden delivery systems. This part turned out near perfect.

I printed in the neighborhood of 40 parts with this setup before, during and the week following MRRF. I gave a lot of thought to how to mitigate or improve the slow retract speed. The "solution", I thought, might be to use a Duet Wifi and decrease the micro steps from 16 to 2. This would reduce the steps/mm from 3100 (1.8° stepper) to 387.5 steps/mm - very much in line with a good extruder steps/mm range. During this time, Brian was experimenting and tweaking acceleration and jerk settings. He was getting much higher retract speeds - up to 80mm/s. He shared his test results and settings. Here's what he came up with:

extruder acceleration: typically 1000mm/s^2 - reduced to 50mm/s^2
jerk (speed changes): typically 600mm/min - reduced to 500mm/min

I made these changes in my config.g and loaded the reel back plate I use to test. This time I sliced with 20mm/s retract. I'm pleased to say that the Nimble performed perfectly with no stringing or other extruder related print artifacts. I continued to test prints and filaments including NinjaFlex (Nimble is excellent for this difficult filament), ABS, PETG, CF filled PLA, CF filled PETG, BronzeFill and WoodFill. Overall the Nimble performed very reliably and produced some excellent looking parts.

Filament changes are a breeze with the breech loading system. My only minor point on this is the breach lock (the red lever) does require a short break-in period. This won't be noticed by many users but if your delta printer is equipped with magnetic ball arms, you have to be careful in order not to pop off the joints. Not harmful but annoying. But after several dozen loadings, the parts break in nicely and I suppose the user develops a process that works without separating the mag joints.

During this time I've kept a relatively low profile about my Nimble results - not because it wasn't performing nicely but because 1) it was not a production unit and 2) I never endorse any product that I haven't personally put through the wringer with testing, testing and more testing. It's easy to develop a product that gives good results "most of the time", it's much more difficult to develop a product that produces great results with 100% reliability. I'm looking for products with 100% reliability to use on my 3D printers.

The Production Nimble
In late April, Zesty sent me a production Nimble to test - again the first one in the wild. There were a number of changes to the extruder body so a complete new kit arrived on my door step. It was a 10 minute job to change over to the new kit. I've printed over 100 of my fly reels (all 9 parts) and countless (well, at least 150) other models to test the Nimble under a variety of conditions and filaments. I am really happy with it's performance and can speak to its reliability over several months of continuous and heavy printing (5+ hours a day).

Here is a photo of the fly reel back plate printed in Hatchbox translucent blue PLA (one of the more stringy filaments I've come across) yesterday. This is an as-is photo still on the print bed untouched and un-retouched.

This is the level of perfection I seek in all of my 3D printed parts and the Zesty Nimble delivers admirably.

Results in a Nutshell
Nimble Pros:
  • very low mass (<28gms): reducing effector mass is critical for a delta printer. Mass contributes to "ringing" - overshooting corners results in imperfect layer alignment
  • very small (23.5mm x 39mm x 28.5mm (WxDxH)): effector space is typically very tight, especially on smaller delta printers. The petite Nimble can fit virtually anywhere.
  • simple filament loading: the breech loading system gives Nimble one of the easiest filament loading systems available.
  • ambidextrous mounting: the Nimble's design allows it to be mounted in either left or right hand orientations.
  • flexible filament: Nimble is the first really good extruder for printing flexible filaments on a delta printer that I've used. 
A Con or two:
  • removable breech lever: the red breech lever detaches easily from the extruder body. If you are careless, you might lose it or drop it during filament loading.
  • price: although not the most expensive extruder on the market, the Nimble comes in at €85.50 ($95.75 as of 5/30/2017). However, for this you get a very well engineered product that does the job and does it well. If you require low mass, small size and the ability to print flexible filaments, it is an affordable option.
Final Remarks
It's taken Zesty longer than many would like to finalize production of the Nimble. But to the company's credit, rather than rush an product not ready for prime time out the door they took their time to refine, test and deliver a well engineered and produced extruder. I give them a lot of credit for that - I know it was frustrating and expensive for them.

Along the way to production, Zesty has developed mounts/adapters for over a dozen printers for their single and dual Nimble extruders and are committed to developing adapters as needed. They've also refined their documentation for assembling, calibrating, tuning firmware and caring for the Nimble. 

The Zesty Nimble produces excellent results with a variety of filaments including flexibles. Flexible filaments are the bane of Bowden tube delivery so not many delta owners have been successful printing them. The Nimble will change that. 

Disclaimer
Although my pre-production and production Nimbles were provided by Zesty, I remained unbiased throughout testing and provided critical feedback to the company. Frankly, I test so many products that I purchase or that are sent to me that I do not feel obligated to provide a good review if the product does not perform remarkably. I have very high standards for quality, reliability and my integrity and I evaluate everything I test to those standards. The Nimble met or beat all of my expectations. 

I am so impressed with the Nimble that I just purchased (full price) the Dual Nimble Upgrade kit so I can test it with the E3D Cyclops dual in-one out multi-filament hot end. 

Understanding Probing and Trigger Z Height

By Michael Hackney → Monday, May 1, 2017

Background

Before digging into probing it's useful to take a look at what happens at the beginning of a print. After the printer homes the firmware needs to know exactly where the bed surface is located, called Z=0 by convention, so it can position the nozzle for the first layer. This distance, called Z height, is configured in the firmware. The firmware uses the Z height and subtracts the layer height to position the nozzle above the bed, as shown below for a typical 0.20mm first layer.
Printing the First Layer

To recap, Z height is the total distance the nozzle must travel from the home position (top of printer) to where it is just touching the bed (Z=0) as shown in the diagram to below. Z height is an important parameter as it's what determines whether the first layer is too thin, too thick or just right. In a perfect world, you would set Z height once and be done. In the real world Z height is not static; thermal expansion and contraction can change the position of the bed slightly and the frame and delta mechanics can also change ever so slightly on a day-to-day basis.
Z Height

In the Early Delta Days (EDD) (pre-probing) you determined the Z height empirically and set it in the firmware. This was a chore and caused countless problems for newcomers. So the quest for auto-probing (or simply probing) ramped up to simplify setting the Z height as part of more comprehensive delta printer calibration.

Probing

The probe, or more precisely Z probe, is a device that accurately and precisely reports its Z position. In the hypothetical perfect world the probe would trigger just at the point where the nozzle tip touches the print surface and report the actual Z height. In practice, such a probe is not practical and there will likely be an offset from the nozzle tip to the bed surface. In RepRapFirmware and Smoothieware, this offset is called trigger Z height. The IR Probing diagram below shows this offset as 5mm.

Raise your hand if you knew that you have to calibrate your Z probe for delta auto-calibration to work properly. You do and I'll explain why and how in this post. As we learned above, real world probes do not trigger precisely at Z=0. This implies that some probes trigger with the nozzle above the bed surface and others trigger with it below the bed surface – and this is indeed the case. Probes that trigger with the nozzle above the bed surface include inductive probes, IR probes and the early simple effector-mounted mechanical switches. Probes that trigger with the nozzle below the surface typically function by pressing the nozzle into the bed and some small movement is necessary to trigger the probe. FSR (force sensitive resistor) probing is a typical example. 

I'll look at each of these two cases in detail below using the IR probe as the example for probes that trigger with the nozzle above the bed and FSR probing for probes that trigger with the nozzle below the bed surface. Let's start with the simplest case to understand, the IR probe.

IR Probing Example

IR Probing
Conceptually, an IR probe works by shining a beam of IR light from an LED at the bed surface. If the bed is IR reflective, some of that light bounces back and is detected by an IR sensor. The time it takes for the beam to make this round trip can be used to calculate the height the sensor is above the print bed. As you see in the diagram, the IR probe is mounted with its lens a few millimeters above the tip of the nozzle and it is designed to trigger before the nozzle hits the bed. The height the nozzle is above the bed when the probe triggers is called the trigger Z height. Let's assume that the tigger Z height is 5mm as shown in the diagram.

If you simply ran delta auto-calibration (G32) after installing the IR probe, without telling the firmware how to adjust for this gap (trigger Z height), the firmware would think that Z=0 is 5mm above the bed and would start your print in the air. It's hard to get a first layer to stick 5mm above the bed (actually, 5mm plus the thickness of your first layer, so 5.20mm above the bed).

Now you can see that some adjustment, or calibration, is needed to let the firmware know where Z=0 actually is. In RepRapFirmware and Smoothieware, G31 is used to set the trigger Z height – the height of the nozzle when the probe triggers. In this case that is 5mm. Think about what this means in relation to the Z height described earlier. When the printer probes, it triggers with the nozzle 5mm above the bed. The distance the probe (and nozzle) traveled is called the probed Z height. Knowing this, you could set the correct Z height using the M665 H parameter simply by adding "5" to the H value. This works as expected but the next time you probe you have to remember to reset M665 H again. This is tedious and error prone.

This is where trigger Z height comes in; the firmware sets the trigger Z height with the G31 Z parameter.  The G31 Z value is added to the probed Z height to calculate the actual Z height. Makes sense, right?
Z Height Calculation for Trigger ABOVE Bed

FSR Probing Example

Now that you understand the simple case where the probe triggers above the bed surface, let's take a look at FSR probing where the trigger point is below the bed surface.

A typical FSR probing system consists of three FSRs positioned evenly (120°) around the perimeter to support the print bed. These FSRs are connected to an interface board that converts the resistance signals into a simply binary on/off signal so the system behaves like a simple endstop switch to the controller (Duet). This board is the infamous JohnSL controller and is really the magic that makes FSRs practical to use.

Watch this short video showing how the nozzle pushes the bed slightly to trigger the FSRs.



We saw earlier that the IR probe triggers with the nozzle above the bed surface, here the FSR probe triggers with the nozzle just slightly below the bed surface – exactly the opposite. Here's a still view of the situation, lets assume the trigger point is 0.5 mm below the bed – greatly exaggerated for illustration.
FSR Probing
Now we should be able to apply what we learned about setting the trigger Z height for the IR probe in the example above. In this case the probed Z height is longer than the actual Z height so we need to subtract the trigger Z height from probed Z height to calculate the correct Z height.
Z Height Calculation for Trigger BELOW Bed
Again, it makes sense.

Ok, that's all great, how do I determine the Trigger Z Height?

Now that you know you have a problem (you need to calibrate your Z probe trigger Z height) you can learn how to fix the problem. The Duet Wiki has a nice procedure for doing this but I'm going to recommend a slight modification to the process and I'll explain why.

Setting trigger Z height

  1. Position the nozzle until it is at Z=0 – this is where I deviate from "standard practice" of using the paper snag test. Typical notebook or printer paper (20#) is about 0.1mm thick (see photo below), about half of a typical 0.20mm first layer height. An old machinist's trick is to use cigarette rolling paper; it is remarkably thin (~0.02mm) and tears easily when snagged. I recommend buying a pack or two and using it for all your Z=0 testing.
  2. Set this height to Z=0 with G92 Z0.
  3. Move the nozzle up a centimeter or so, just to get it out of the way and clear of the bed.
  4. Now run a single probe that doesn't update the printer's coordinates with G30 S-1.
  5. Finally, get the Z height using M114. This is the value to put in the G31 Z parameter in config.g. This will be positive for probes that trigger above the bed surface like the IR probe and negative for probes that trigger below the bed surface like FSR probes. 
Here's a photo showing the thickness of common 20# printer paper, 0.10mm.
20# Printer Paper is 0.10mm thick

Tweak, tweak

Once you've determined and set the trigger Z height you should make a test print to ensure your first layer height is what you expect. I like to use my SingleLayerTest model to do this, it is simply a 75mm diameter disk that is one layer height tall (0.20mm is typical). Run the delta auto-calibration and print the SingleLayerTest. Once the part has cooled, peal it off the bed and carefully measure its thickness with a micrometer or caliper. It should be very close to your layer height – 0.20mm in this example. If it is not, you need to tweak the G31 Z parameter to compensate. Here's where it gets fun and where a lot of users get confused and frustrated – especially those who are using FSR probes!

Probes that trigger above the bed (IR probe)

This one is easy. Remember the Z Height Calculation for Trigger ABOVE Bed drawing above? The Z height – which is the value the firmware cares about – is calculated by adding the probe Z height to the trigger Z height. If your SingleLayerTest is too thick, you need to increase trigger Z height to move the nozzle closer to the bed. Conversely, if the SingleLayerTest was too thin, decrease trigger Z height. The way to think about this is from the perspective of the desired Z height. The probe Z height is fixed as long as you don't physically alter the probe or its mount. So if a first layer is too thick, your goal is to increase the Z height, thereby moving the nozzle closer to the bed. You do this by increasing the trigger Z height (since probe Z height does not change).

Probes that trigger below the bed (FSR probe)

Look at the Z Height Calculation for Trigger BELOW Bed drawing above. In this case, if the SingleLayerTest is too thick the probe Z height must change in the positive direction (a smaller negative number). If the SingleLayerTest was too thin, probe Z height must change in the negative direction (a more negative number). This might seem a little counterintuitive until you consider that the direction and magnitude of the change is relative to the probe Z height. Let's take a concrete example so it sticks in your mind:

Assume you have 0.20mm layer height and FSR probe with G31 Z-0.15 to let the firmware know the probe triggers slightly below the bed surface.

Now you print the SingleLayerTest and measure it at 0.16mm thick. This is 0.04mm thinner than you expected. What this says is that the Z probe height is longer than the desired Z height so you need to make it shorter. You've already told the firmware to move -.15mm with the G31 Z-0.15 but that wasn't enough, so to move back more, subtract 0.04mm from the Z height offset (-.15m) to get -0.19mm. Set G31 Z-0.19 in config.g and auto-calibration should result in a perfect Z height and perfect first layer thickness the next time you print.

Or the easy way with RRF 1.18 Baby Stepping

RepRapFirmware v1.18 introduced a new feature – M290 baby stepping – and Duet Web Control v1.15a supports it with new buttons on the Print Status page.
Baby Stepping Buttons
With baby stepping, you can actually move the nozzle up or down to change the first layer height while the printer is printing the first layer. So for the example above, if the first layer was printing too thin you could click the Up button to make the layer thicker by the set increment – in my case it is 0.02mm per click. Make note of the Current Offset value shown above the buttons. Once the print has completed, subtract the Current Offset value from the Z height offset and update the G31 Z. For the example I would have clicked the Up button twice to increase the 0.16mm first layer to get the 0.20mm layer height I expected. The G31 Z value was -0.15 so I subtract 0.04mm from it:

-.015 - .04 = -0.019mm

Set G31 Z-0.019 and you have corrected your Z height offset.

Conclusion

I realize this is probably more detail than most would like but I wanted to capture this so I don't have to repeat myself. I receive a lot of questions about probing and bad first layer heights. Many times, the simple explanation and answer is that delta auto-calibration does require calibrating the probe itself – Z height offset!



E3D Online V6 hot end drawing used with permission.

emmett's amazing Knotted Orbit print

By Michael Hackney → Saturday, April 15, 2017
A member of the UltiBots delta printer Facebook group posted a challenge two days ago to see if anyone could print emmett's Knotted Orbit. I decided to take the challenge "just because". This particular model was not designed to be printed on an FDM 3D printer but with an understanding of how to configure a slicer to deal with the many curves of small radiuses and lots of supporting structure, it can (almost) be done. I say "almost" because this print really is an exercise in support, support removal and cleaning up the print.

I chose Atomic Aqua Gemstone PLA filament as I love its color and translucency. I sliced the model for .1mm layers, 3 perimeters, 3 shells, and 20% grid infill using Slic3r Prusa Edition and its new improved supports. Here are some mid-print photos.




 




I used every post processing trick I know including my secret weapon, Otter Butter (a product I manufacture for fly fishing but use for all sorts of things). Here are the results along with a tray full of broken off support.





Printed on an UltBot D300VS delta printer. 22hrs 59min 14 sec