Playing with Bearing free Axis's on a printer (UHMW plastic)


So I am building a large printer. Started off with the hypercube CoreXY plans but decided for the size I have scaled it too. That a lack of parts and price made it unfeasible. So basically starting from scratch besides a bunch of the similar parts. Mostly lots of Tslot.


In the process i realized that using skateboard bearings or most metal bearings in general added to much weight. I down own a mill, or lathe, so trying to do as much with as little as possible. If you look at alot of larger CNC machines for industrial automation, you notice the use of UHMW to remove backlash and play and provide a slippery sliding surface.

Like I said before I don’t own a mill. But in the process for looking for semi cheap and usable UHMW, I found UHMW tape on amazon. So I picked up a roll of it and decided to give it a shot.


So yeah so far the test piece works, its got about 100microns of play. So the plan for now is to try to build this beast with just UHMW against the Tslot. Which slides nicely and is very quiet.



So after about a week of work playing around with tolerances and parts, and printing problems. I now Have a working Y axis for the new printer. All with UHMW plastic for the surfaces to ride on.


The part even prints without supports believe it or not. The interesting thing is that when you let the bearings slide by themselves just under gravity. The air flow between the surfaces slows it down so it looks like its getting caught. But under weight and being pulled by the belts it seems to work (in theory). Might even hook up the electronics and see how it works with the test carriage.



Hopefully this helps anyone having a hard time understanding what i am talking about, and my design. You can clearly See the UHMW tape in this picture.




Interesting project for sure, does the tape have any elasticity to it to allow to to press fit onto the extrusion?

Those skinny arms maybe look like trouble since you said you printed without supports. It seems the only angle you could have printed without support would leave layer lines running parallel to the belts, which would create a weak point on those arms.



the tape is pretty rigid, the adhesive on the tape has a odd tolerance when mating to the prints but if you apply some pressure to it with the extrusion it flattens out and bonds well. I have been playing with the tolerances a good deal. I would like to come up with something that applys a light amount of tension to keep tolerences inline, while not having to be as accurate while printing.

The part is definitely capable of printing without support, however I have been in a hurry to print so i add some supports to it,partly cause i am printing at a peak of 150mms (i do all my supports at 150mms ). This has caused those arms to break while removing supports or not print very clean. However I am using abs and they are clean breaks, so a drop or two of acetone and its back together nice and strong. I will find out soon if the belt tension on those parts requires me to rethink the design. But for now everythings been holding up to the abuse i have been throwing at them (including the hammer as some parts are pressfit in the design).



Update 9/2/2017 part 1

I made a mistake with the design (again), I forgot to stagger the idlers on the Y axis to make up for the loop of the belt that hits the servos. A new design was made to save time and parts to keep track of I extended the arms out and added a second set of screw holes. I added some additional stiffness on the lower arm also.

Belt binding from V2

V3 design

I had also noticed at this point that I seemed to still be playing with tolerances that where to tight. So I opened up the clearances on either side of the channel again. Thinking this would solve things.

While the new parts where printing I finally uploaded marlin to the arduino and set about configuring that. I also realized I needed to get some barrel connectors for the MKS TFT2.8 I picked up to use as a display/controller. I also starting making the Cables for the stepper motors and endstops.

Next I went through the process of removing the old parts and installing the new ones. Clearances where much better this time seemed like I was going to be good. Set about making sure everything was moving on the correct plane then went about Installing the Y axis channel and test carriage.

Unfortunately it seems as if the Y axis’s are still binding, further more the parts have warped enough during printing that they are several degrees off on the alignment between the two. I spent a bunch of time checking alignments and squareness. I also decided to fire things up and see how the first moves went. The carriage moves great in the X axis but there is no Y axis movement, the steppers just skip steps or jump the semi loose belts. After alot of checking stuff I decided to walk away for a bit and come up with a new plan of attack. After all you need to stumble a bit in the process of experimenting, I wasn’t ready to just give up yet.

I decided to try lubricating the Channels after testing it with some scrap and previous revisions of parts. This did help some but not enough to allow the steppers to move things in the Y direction . After investigating more it appears that the channels might be binding in the corners. I also had incorporated a small step in certain places to make it easier to align the size of tape a bought (the tight varied in size quite a bit larger than it was advertised at (I am glad i didn’t buy the larger size).

This also brought to my attention another flaw in my design. That its a pain in the ass to swap parts for the Y axis. As it requires the disassembly of top section of the frame, and removal of the stepper motors and idler assemblies each time. So Version 4 of the Y axis slider will likely be a multiple piece assembly. To allow for changes without that level of disassembly and realignment. I also know that the tape will wear over time. How quickly i am not sure. So it would be wise to address this sooner than later if this proves to be a working method of design. This should me remove the few degrees that the X axis is off due to warpage.

My other thought is that i am possibly adding an additional twisting force to my design with the current X axis placement in the design. Since the Bar sits above the Y axis. 23mm or so. When you look at the deign specs on you see that he does a much better job of keeping the forces in line better, when it comes to the carriage and Y axis’s. So i might need to investigate that method of doing things. (i have known about the twisting issues in the hypercube design. However I had hope the Tslot extrusions would counter this issue.

I still think Tslot is the better/more affordable option when it comes to accessibility. So I am not ready to give up on it anytime soon. The idea of paying 65$-100$ per ground 12mm rods in suitable lengths for larger format FDM printers is painful on the wallet. Compared to 25-35$ I payed for annodized 2020 Tslot from McMasterCarr in 8’ Lengths.

I will try to post a video later of the current movments.



How about putting the tape on the slots?

It may mean making a part with some sort of a bearing surface on the slider.

I like the experimental approach.

Don’t take this as a criticism I am just throwing the idea in the ring :wink:



I actually tried that. I been trying to get my office cleaned up enough to do some filming to make a video about this experiment. Cause I have learned a ton and I want to pass the information along to everyone Working with and playing with printer designs. I also learned alot about CoreXY’s. The problem is I am doing a lot of work on my house, in perpetration to list it. So my office has become the catching point for everything besides about a decade worth of Computer hardware and parts (and four printers).

I found that UHMW against UHMW actually doesn’t slide well, it causes a increase of friction and then starts galling (I think that is the correct term) and eroding the mating surfaces.

The ultimate conclusion for now is that UHMW doesn’t work well when the surfaces experience compression. If you use the UHMW to large amount of compression for whatever reason it seems to loose its lubricating properties, and just binds. I will likely try building a Cartesian at some point with UHMW bearing surfaces. But I am short of funds right now.