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3D Printing Ergonomic Knobs with a Resin Core

Hack your tools for greater efficiency

By Rain Noe - August 22, 2017

in 3D Printing | Digital Fabrication | DIY | Videos

If you're making something for yourself and casting it in resin, you can probably live with the inevitable air bubbles that appear in the object. But if you're an industrial designer prototyping something a client's going to see, bubbles are a no-no. That's why professional prototypers like Eric Strebel use pressure casting. That's when you do the casting inside a pressure tank, hooking it up to a compressor and setting the interior at 60 p.s.i. or so, which'll squeeze those bubbles out of the resin.

Some pain points for Strebel are the lousy wingnut-handled screws on his pressure tank's clamps. So here he shows you how he whips up some more ergonomic knobs using 3D printing, urethane resin and the original clamp screws:

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Nigel Alcorn

7 years ago

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Take care when doing this - depending what epoxy you use the heat produced from curing can warm the printed part to where it begins to deform. It's happened to me!

Increasing the wall thickness of your print and using an epoxy that doesn't cure too warm is probably a good idea.

If you have a good recipe this is a really nice fabrication technique!

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- Eric Strebel
  
  Nigel Alcorn
  
  7 years ago
  
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  I am using a urethane resin, it's get slightly warm but nowhere near hot enough to melt any plastic.
  
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Noodle Time

7 years ago

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been using epoxy and urethane to backfill FDM parts for years. helps when you have a production line that uses large quantities of the stuff. The epoxy from EFI always sets smooth, and only bubbles are internal, which can be removed via vibes.

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Mrten Boi

7 years ago

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Aren't you making the bubbles "too small to see" instead of "squeezing them out"?

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- Eric Strebel
  
  Mrten Boi
  
  7 years ago
  
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  When I cast anything, the resin is always degassed in a vacuum tank first, then for additional strength and security I place the part in a pressure tank to crush any remaining bubbles. There are never really any left other the initial vacuum degassing. I find the parts are much stronger after being cured in a pressure tank. There are other advantages to the pressure tank as well as mine is temperature controllable. The parts come out looking like production injection molded parts. Absolutely, essential and fantastic if you are making working prototypes and simulated preproduction parts. The attached image is a SwingLink golf wearable product (soon to launch on Kickstarter) the part looks like a production part. You can't get that if you don't use the right process and equipment. I have other videos that show the process of of how to make silicone molds the right way too.
  
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  - Mrten Boi
    
    Eric Strebel
    
    7 years ago
    
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    Thank you for that reply! Is the resin you use particularly slow setting? I ask because Rain linked to a video from Diresta a couple of months ago who explicitly stated that vacuum was a lot harder to use than overpressure (too slow to build up perhaps? Could be equipment related). Live and learn!
    
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  - Eric Strebel
    
    Eric Strebel
    
    7 years ago
    
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    Marten, with very fast setting resins there is not enough time degas them properly. So, the only option is to put them under pressure. I don't use resins like that. There are lots of resins out there, I usually chose something with a minimum of 5-6 minutes to 15 min working time so I can use them correctly. You get much better results, patience....
    
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Nathan D.

7 years ago

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Demonstrably more efficient: https://www.mcmaster.com/#machine-component-knobs

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- Eric Strebel
  
  Nathan D.
  
  7 years ago
  
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  Possibly, but not really as cool or fun, as designing and using something of your own design.
  
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