Working up to building a CoreXY/Hypercube variant. Got my 500mm 2020 extrusions from Misumi. Lots of other bits arriving, ordered off Amazon.
As a point of information - the surface of anodized aluminum is essentially a gemstone. Makes for a pretty good bearing surface, at least for light duty.
As an experiment, printed PLA sliders to travel along the anodized extrusions. These work surprisingly well. Might be good enough for the Z-motion of the print bed, as it slowly drops in Z, during the print.
Note that I am massively skeptical of these printed PLA sliders as precise bearing surfaces … but if they work …
Had a conversation on this topic with my (retired) father. He spent his working life as an aerospace engineer, building things that were borderline impossible. (This was primarily for military contracts, where cost was lesser concern.) He recommended Delrin as having very low static friction. As Delrin is a thermoplastic, might be possible to 3D print with Delrin. But as Delrin has a chemistry based on formaldehyde … I am not going to try that experiment without a lot(!) more information.
If I can make PLA work well enough, that will greatly simplify the design. Another alternative would be to use Delrin for the bearing surfaces (as simple inserts into the PLA frame).
I think you will find that it works perfectly. It’s slow moving, not weight bearing, and should last for a good long time.
The TrueUp design over on Openbuilds uses nylon insert guides, later changed to teflon rod I believe, but the prototype used all PLA and it’s still running just fine months later, from what I understand.
Acetal is a poor print filament choice because the shrinkage is enormous, four times that of typical ABS. I second the recommendation of try Igus Tribo filament.
I am printing POM (delrin) - can tell you it is the worst printable material you will find. But when you manage it - the mechanical properties are quite wonderfull. Don’t worry too much about CH₂O (formaldehyd) it is not that big problem as you might think … You will smell it at low concentrations of 0.05 ml/m³ - (your body produce 50g of it per day and within your breath you have up to 0.01 mg/m³) I never smelled anything while printing. If you will try - give me a shout, i might have some usefull tips for you.
I’d say if you’re really interested into using aluminum extrusions as linear guides, just go with Openbuilds v-slot rail–their integrated system uses v-profiles and v-wheels for an adjustable, preload-able and fairly simple-to-implement system
FWIW, my experiments are in OnShape. Not claiming these are sterling examples of design, as I am still on the CAD learning curve. Also the designs are tweaked for my current (not perfectly calibrated) FDM printer.
Also, I soaked the slider with a silicone/teflon spray (generic stuff from the local hardware store) before testing. These is a case where a slightly-porous print is useful.
Hey Preston. As suggested by your Dad, delrin should work way better that PLA. In my experience with Delrin, i highly doubt the toxicity of its composition. Also the light loads are unlikely to cause enough friction/temperature to bring Delrin to is melting point.
However, PLA will turn molten at 220C and malleable right around 190C.
@mfalme254https://en.wikipedia.org/wiki/Formaldehyde is the main component of POM (polyoxymethylene or Delrin) and classified as toxic - but aslong you are not going too hot or burn it - it will not decompose and you are safe. BUT you must not ignore that it could harm!
In that part, make (semi)holes to hold a PTFE tubes in place along the rubbing areas. If precise enough, your durability concerns are (somewhat) gone, at least after parts are settled in. If you have doubts about the aluminium durability (small area/footprint of the tubing) you may place the holes at an angle to increase the rubbing area. If your printer is well calibrated this should be easily attainable.
Fwiw, I used pla bushings on misumi’s “clear coating” surface finish when I designed my 3d printer and it worked amazingly well, with less sliding friction than some linear bearings.
PLA just can’t be run very fast or the friction will soften it.
Can’t believe no one has mentioned nylon. Printed nylon bushings work GREAT, nearly as well as POM will work, but is widely available and a lot easier to print.
@Ryan_Carlyle I’ve been running using PLA on coated extrusion for 2 years. Softening is not a problem even in the slightest. Gentle erosion over time is a concern; I end up with maybe 100 to 200 microns of additional slop every few months. I replace most of my bushings every 4 to 8 months, which isn’t much of a problem since I’m constantly upgrading my design.
Since nylon is softer than PLA at working temperature, I’d expect nylon to erode faster than PLA.
Nylon is low friction and very high abrasion resistance. PLA is higher friction (particularly if it warms up) and pretty low abrasion resistance. It’s about the polymer molecular structure, not hardness.
There’s different schools of thought on polymer bearing design… performance depends a lot on load versus the material’s load capacity (e.g. PV rating). Igus actually designs theirs to wear a lot during initial bedding-in, thus leaving behind a microscopic dry powder film that fills the surface roughness and provides polymer-on-polymer contact thereafter. For that reason, igus bearings work best on somewhat rough surfaces like anodized aluminum, while typical plastic bearings last longer on hard polished steel. It’s not a cut-and-dried selection/design exercise.
@Ryan_Carlyle with misumi’s polymer coated (not anodize, not powder coated) extrusion, my pla bushings have low enough static friction to function as a crude level. My experimental printer is a prusa-style Cartesian bot; I run it at about 90 to 120 mm/s depending on how impatient I feel. The machine isn’t nearly rigid enough to handle the dynamic forces, but my parts are rarely cosmetic so I can tolerate artifacts in exchange for print speed.
Here’s a picture of an earlier iteration. I built the thing as a proof of concept for both the bushings and also as a sub-$200 device. No corner left un-cut. Except the e3d extruder. That’s legit. missing/deleted image from Google+
