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

Recent Posts

emmett's amazing Knotted Orbit print

By mhackney → 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

Delta Arm Joint Musings

By mhackney → Thursday, April 6, 2017
I see (and participate) in a lot of discussions about delta arm joints (or rod ends) - the connections between the ends of the arms and the effector at one end and the carriages on the other. An example appears in the photo below. These joints have the unenviable task of allowing unconstrained motion in three dimensions while not allowing play or backlash in the mechanism. Twelve joints are required for a delta printer. Four joints for each of three sets of parallel arms. The photo shows the six joints (three sets of parallel arms) at the effector end. The other end of each pair of arms is attached to the carriage that controls positioning of the effector.


First I'll present a bit of history, then I'll give my assessment of the strengths and weaknesses of each.

A little joint history

In the early days of delta printers, most builders used Traxxas rod ends – they are inexpensive and they work. When SeeMeCNC released their first Rostock MAX delta printer in 2011 they used their own "Universal Joint" made of aluminum and injection molded parts. The in 2013 a poster, Werner Berry, on SeeMeCNC's forum showed his all-custom delta printer with magnetics and metal balls for the end joints. To the best of my knowledge, this was the first public post showing magnetic ball joint ends. This was not a new idea, magnetic joints like this were used in other fields but Werner certainly pioneered their use on delta printers. The results were obvious and spectacular (more later). More recently (late 2015 I recall), SeeMeCNC released an all-new "Ball Cup" joint on several models of delta printers.

This makes up the four primary families of joint types used for delta printers, to recap:

  1. ball rod ends like the Traxxas rod ends
  2. universal joint rod ends
  3. magnetic ball rod ends
  4. ball cup rod ends
Now let's look at these in more detail.

Joint review

1) Traxxas ends (the name brand) are functional and inexpensive but they are not manufactured to high tolerances. New ends often have excessive play (or lash or backlash). They also wear relatively quickly, again introducing play. By "play" I mean the ball is not held firmly in its socket and can wiggle around easily. This wiggle – or backlash – results in imprecise movement during a print and leaves tell-tale print artifacts like visible layer shifts and overshot layers at sharp corners. This is their primary weakness and they have no built-in ability to eliminate this backlash. There are higher precision ball rod ends but, of course, they cost significantly more. Precision costs, how much do you want to spend?

2) SeeMeCNC's universal joint ends required a fair amount of tweaking and tuning to eliminate excess friction while not introducing backlash. Over a few years of iterations the molding technology and design improved and they were serviceable. I put them on par – arguably a little more reliable and longer lasting – with Traxxas ends.

3) When the delta world was introduced to Werner's magnetic ball ends it was like the veil of backlash had been lifted from our eyes. Werner's early print photos were spectacular. And there was good engineering reason for this – magnetic balls have built-in backlash prevention. The design uses a magnet mounted in a hemispherical cup – a type of ball-in-cup joint. The magnet attracts the steel in a precision bearing holding it in the cup. The ball is free to move – not much unlike your hip joint (which is a type of ball-in -cup joint) – but the magnet holds it tightly in the cup so there is no excess play. It's brilliantly simple.

4) More recently SeeMeCNC introduced their ball cup ends. These are another type of ball-in-cup joint and they also eliminate backlash. Interestingly, the ball cups are mounted perpendicular to the axis of the rod arm whereas magnetic ball ends are in line with the arm. This allows for a spring to pull the cups into the ball as shown in the photo above. Like magnetic ball end, ball cup ends give excellent print results.

The nitty-gritty

So now the Big Question "which type is best?" The answer, of course, is "it depends." I won't be so cruel as to end here, I'm going to give you my opinion and testing results on this. I've owned and tested delta printers with all of these end joint types so I assert I'm in a good position to make comparisons.

First off, the original SeeMeCNC universal rod ends (#2 in the list) have been replaced with much better alternatives and for good reason. Now we're down to three. The ball rod ends (#1) are actually quite good if you purchase precision parts. The Traxxas brand ends are fine for small Mini Kossel types of delta printers where high print resolution and high print speeds are not a requirement. They are easy to make or inexpensive to purchase and are a great beginner option. The higher end rod ends are quite nice but at the end of the day, they do not have built-in backlash prevention and they do wear. But, the one thing ball rod ends have going for them is they are secure – they hold the rods to the carriages and effector so they can't dislodge. This means that if the print nozzle hits a bump in the print or jerks quickly, the ball rod ends will hold everything together. We'll see why this is important next...

Magnetic ball rod ends (#3) result in much better print quality due to their ability to eliminate backlash. They are a little more difficult to fabricate the arms, effector and carriages but these parts are available and there are many STLs available to print your own. The one criticism about magnetic ball rod ends is that they can separate. Sudden jerks, hitting a plastic bump on a printed part, printing with a heavy(ier) direct mounted extruder, or simply working on the hot end like polishing the nozzle tip or removing plastic drool can result in inadvertant spontaneous separation. This is their one weakness. Some have tied the carriage to the effector with elastic strips to pull them together in an effort to prevent separation. I haven't tried this myself.

This leaves us at solution #4, ball cup ends. I really like them, especially the red after-market cups that Trick Laser manufactures. To me, they have the best characteristics of magnetic ball end (backlash elimination) and ball rod ends (secure fastening) with none of the negatives of either. They are well suited to large deltas with effector mounted direct extruders like the E3D-Online Titan Aero or Bondtech BMG extruders (more on these in the next few posts). The one "weakness" they have is they are single sourced from SeeMeCNC – at least the molded balls. The cup ends with carbon fiber tube arms are available from Trick Laser made to length and the injection molded "barbells" can be purchased cheaply ($6 for an entire set). I predict this will change in the not too distant future as more people become aware of them and their benefits.

On my delta printers I use either magnetic ball rod ends or the Trick Laser ball cup ends. I do have. preference for the Trick Laser ball cup ends and carbon rods, they are well made, secure and have no backlash.







www.sublimelayers.com is now active!

By mhackney → Friday, March 31, 2017

After a year of successful blogging and sharing information I decided to take the plunge and register the domain sublimelayers.com. I'll be able to setup email so folks can reach me easier and have a web site associated with my blog so I can organize information and downloadable files. Stay tuned but in the meantime you can get here via http://www.sublimelayers.com.

Post 3: Core X-Y Musings...

By mhackney → Tuesday, March 7, 2017
It's been 4 months since my last update Post 2: Improved Z Screw Bearing Blocks so time for an update. Things were going a little (ok, a lot) slow because I was getting caught up in analysis paralysis and over design-itis - primarily because of the hgh cost in both materials and time for the aluminum parts I planned to make. But recently I discovered Atomic Filament PETG-carbon fiber. This stuff is really nice, it prints beautifully, has great dimensional stability and print accuracy and is quite stiff. So, my new plan is to print all of the parts in this PETG-CF and get the printer operational. I can always come back and replace with machined parts if needed. This allwos me to do fast design and test print iterations (with PLA) and then a final print for the machine.

I also have a home for the printer so it is up off the floor–where it was really difficult to work on.
There it is squeezed between RazMaTazz (my Taz 4) and a Terk (a mini Kossel).

This makes working on it much easier. And the new plan is working. Here are some of the parts in PETG CF:

X and Y stepper mounts


Bearing mounts for ballscrews with angular contact bearings


Segment-less Delta Movement

By mhackney → Monday, March 6, 2017
This post comes from a post I originally made on the SeeMeCNC forum in December, 2015. I find myself referring to that post often and repeating it in multiple places so I'm adding it here where I can keep it updated.
----
updated 3/6/2017

Segment-less Delta Movement
A little know secret to most delta (and Cartesian) printer owners is that path movement for all firmware except David Crocker's dc42 RepRapFirmware is actually broken up into short straight segments. In other-words, a curve is actually "drawn" as a series of short lines and not a smooth arc like you might expect.

These other firmwares are interpolating movements into short line segments so, in theory, there is a negative impact on print quality. There are other factors at play too though - hence the reason for "in theory". By it's very nature, 3D printing starting with an STL file sacrifices some resolution depending on how the original CAD model was converted into an STL (most profound is the # of triangles in the final model). Here is an example of how this works...

Imagine you have a CAD drawing of a 20mm diameter sphere. The CAD tool uses sophisticated math to calculate the geometry and display it. It looks like a perfect sphere on screen. Now, let's run that perfect sphere through the meshing process to create STL versions. To demonstrate I am using 5 different resolutions that generate a low number of triangles to a high number of triangles. When you download an STL from Thingiverse, you have no control over this, the original author made the resolution choice for you. And frankly, most of the folks uploading to the shared services really don't know how to create high quality meshes. Anyway, back to the example - here I've meshed to create a "sphere" with 48, 224, 960, 16128 and 99856 triangles (from left to right). You can see that the far left sphere is course and the one on the far right is reasonably smooth.

Now to take this one step further, imagine your slicer creating g-code from these STL models. To illustrate, I created an imaginary slicing plane 12mm above the base that is .02mm thick and took a cross section of the model at that plane. This is the red line you see inside each model. I projected these slices up above the models so you can see them clearer (black). The 48 triangle model has a slice with 8 sides - pretty low resolution. You can see as you move left to right, each slice has more line segments. These will result in a finer/higher resolution print all things being equal. But they are not! In addition to the slicer converting curves into short line segments, the firmware also imposes its own line segmentation on top of that - that is all of them EXCEPT dc42 RepRapFirmware. dc42 draws each point along the way completely tracing the original path it was given. Smoothie, Repetier, Marlin and the others actually break the path up into short line segments and draw those. This does not always match the original path exactly.

As you can see, if the STL had a low triangle count, you are going to get a course print whether or not your firmware does segment-less movements. Increasing the triangle count will improve the print quality until you reach the segmentation threshold of the firmware, at which point, increased # of triangles won't have an effect and might actually make things worse. That is except dc42, which will faithfully trace each of the tiny line segments exactly point by point.

But, there are other factors that come into play like stepper resolution (1.8° vs 0.9° steppers) and a host of others. Will segment-less moves make all your prints look fantastic? No. But if you design your own parts and optimize output for high quality meshes, I assert you will be able to see the difference. This difference is minute and impossible to photograph, I've tried for over a year. But, parts in hand 10 out of 10 test subjects will pick the part printed with segment-less moves as the best quality part.

I posted Musings on Impact of STL Triangle Count in Jan, 2016 if you'd like to get more info.


The Tusk Fan Shroud

By mhackney → Saturday, March 4, 2017
I don't understand why many people feel they must blast their part, hotend and heated bed with lots of air. Consider this: blasting a large area with a lot of air can create more problems than it solves - problems like part warping, hot end temperature fluctuations, beds that can't reach and maintain higher temperatures and a host of others. A much better approach - particularly for common filaments like PLA, ABS, PETG, etc - is to direct the minimal amount of air as precisely as possible with laser focus.
I started experimenting and writing about this a few years ago. See Strat

New FSR Plate mounting system

By mhackney → Thursday, February 9, 2017

I've posted quite a bit about FSR probing along with my previous mounting system. I've been using FSRs for probing for coming up on 3 years.

2 Drawer Cabinet for SeeMeCNC Rostock MAX V3

By mhackney →
My friend Chris Androsoff came up with a great idea to replace a Rostock MAX V3 base panel with a drawer. I saw it when I visited him in Calgary a few weeks ago. I liked the idea but wanted a drawer to organize my nozzles and small tools so I revised it with two drawers as shown here. I've posted the STLs on my Thingiverse account.