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jens

Printing realy tiny things with even tinier details?

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Hi there,

 

I want to print bearing cages for axial ball bearings from PETG - that would basically be a washer with a bunch of spherical holes around its circumference (with all the holes' axes parallel). I'd like to post a picture here, but there is just no (visible) option to attach something to a posting, is there?

Now, for the problem, the cages I am talking about are really small, say, for micro micro micro ball bearings (micro referring to the balls). Something like

 

  • Inner diameter 4..5 mm
  • Outer diameter 7...10 mm
  • Diameter of the ball holes around 0,5 mm

 

I've tried some settings and my results range from

 

  • Ok for washers, but the tiny holes were missing - you could clearly see where they were supposed to be, just that there weren't actual holes

to

 

  • Just a blob of plastic, pretty much like a piece of chewing gum (too low speed, I guess)

So, (1) is something this tiny printable at all and, if so, (2) what settings would one need?

 

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Unfortunately uploading images to the forum is clumsy, but this is how to do it:

http://umforum.ultimaker.com/index.php?/topic/4525-how-to-upload-an-image-to-the-forum/

As for your print. I'd say, no, don't waste your time. Think of it this way to put things in scale, the nozzle on the printer is 0.4mm in diameter and you're trying to produce details that are 0.5mm. I'm sure it could be done, but it would take a long time to dial everything in just perfect and the slightest variation would ruin things. A single itsy bitsy tiny bit of stringing accidentally getting in the hole would ruin it. I'd say you'd be better off drilling the holes, it would be far more accurate.

Maybe you could print the washer solid (that shouldn't be a problem) and create some sort of drilling jig to create the holes?

edit: Wait, would a straight hole even work? Would it need to have a curve so that the balls are held captive? If so, forget about printing it right away.

 

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Yes, the holes wouldn't have to be just straight but kind of spherical (sort of a pop-in fit, so to say). Well, it was worth a try.

Maybe I'll tinker with the design a bit to avoid the tiny holes ...

Talking of tiny things. I ran into the blob-problem a lot trying to print structures with a small cross sections, say, a shaft-/bolt-/rod-like structure (printed standing upright on the bed) with a diameter smaller than 4 mm. The plastic just wouldn't cool quick enough or the nozzle keep re-melting too much of the already deposited plastic - not sure which it is. Are there ways to avoid that (other than not printing one at a time)?

 

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Well you said it, the plastic doesn't have enough time to cool, so you have to give it that time. You can either do that by printing more stuff at once (preferable) or activating something like cool head lift which will move the nozzle away from the print to let it cool. The problem with the latter is that it just sits there and potentially oozes a bit.

I guess you could experiment with adding more external cooling. Maybe putting a funnel on a big fan that you can aim at the top of the print? :)

 

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Using my UM2 any small holes print smaller than designed, and the percentage increases with the smaller the holes, at about 1mm the holes disappear but leave a dimple where the hole should be!

Anything small, like for instance, small diameter spacers, need to keep the temps low, pla I use 190~195 else you end up with a bunch of toffee!

I have to side with IRobertI on this one, trying to print any object that small, with any detail will lead to frustration!

 

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