We are looking to sandwich a 625 bearing between the two printed wheels, joined using a self-tapping screw for plastics, through the middle, and then suspend a bracket below the 625 bearing which would wrap around its outer race. Need about 200-300 sets, so it’s worth spending a bit of time to minimise material and maximise yield/print reliability.
It printed OK on the bed but the first few layers spoiled the curved profile and it couldn’t fit in the curved grooves of the track. I printed on the bed because the amount of support material for 200 would be wasteful and I would really like to find a geometry that can print on bed but also won’t mess up the curve which needs to not extend past the profile of the track groove. So I tried a revision, which also hollowed out the part and had plenty of anti-cupping drains:
But we get predictable failures of prints because the surface area significantly increases after the first few layers, causing the print to detach from the build plate and adhere to the tank film:
I’m happy to keep plugging away at this but thought I’d see if the community had any tips, given that this is one of the rare occasions I have quite a bit freedom to control the design and it’s a good exercise in designing for the constraints of the printer.
You’ll need to adjust for not only elephant foot here but also set early layer merge to 0 and also compensate for early layer compression. Preforms compression compensation is buggy so don’t do it in preform, you’ll need to do it in CAD.
I bet you can print this without a cupping vent if you enable Cup mitigation in the print settings
Lastly if you have adherence issues you can up the first layer exposure to make it stick harder (it may cause more elephant foot which you can tune by changing your offsets)
Overall definitely a part you can print direct on the BP.
I’m not sure this is a problem for my use case - as I understand it, early layer compression would actually decrease the effective radius of my wheel’s outer profile, which would prevent it from clashing with the track groove. For a perfect fit, yes, I should address this. But for “hits the bottom of the groove” I think this can wait until other settings are dialled in.
Good point. I will try this next.
Done - just did a custom default profile with solely this parameter changed. You can see I have removed the cupping vent in the base (but left the other ones in as I think they help to wash excess resin out afterwards (newer rev is in green box):
I also shrunk the diameter of my screw head recess, as this helps create more surface area on the BP. I removed the step and went for a much shorter overhang of 15 degrees from the radius of the wheel outer profile to the flat face on the BP. On the top side, I opened out the slots more, to aid washing and minimise material use (this is Tough 2k V2, btw).
While this version is doing a test print, I might try putting the spokes at an upward angle, to minimise the amount of material I need in the spacing section above them.
The fit in the track grooves is pretty good. I just need to increase the space between the two wheels by another 0.5 mm or so. At 2.2 ml for the pair, they are pretty good value! I should be able to fit 24 pairs on the BP at once, and print time is around 40 minutes per batch, so 5-6 hours of printing should get me the 200 sets I would want and cost under £100. The bearings will cost more!
I will probably look at making the centre bracket/hanger on the Form4 next.
parts turned out great 