How do I make a mold for these parts?  

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Mike
 Mike
(@mike-6)
Active Member

I'm not sure if this is the right place to ask this so please let me know where a better place would be.  I would like to cast some printed parts in some other material like urethane or epoxy.  Unfortunately I can't figure out how to make a mold for these and keep the internal features intact.  Can someone tell me how to make a mold for this and what material would be best for the mold?  I'd like to be able to reuse the mold if at all possible.  For scale, the internal hole is 1/8" (3 mm) diameter.  Thank you.

Housing A Section

Housing A

Housing B Section

Housing B

Posted : 18/03/2021 4:39 am
Dan Rogers
(@dan-rogers)
Honorable Member

Just from the one picture - I think it could be done.  It's probably 3 parts - a split outer casing for the main part external shape, and a snap-in core that does NOT have the threads (those are better off cut as part of final finish).  You'll probably also need some clamps or braces to hold things stable, center the core that makes it hollow.  

Why split outer case?  So you can get it out.  It will leave a seam that you'll after-finish away.

I would recommend starting with PLA - depending on the curing temp of whatever you choose - PLA is very un-sticky so it'll help not bond your mold into a permanent fail.  The challenge though is your internal surfaces on your mold will need to have a MIRROR finish - no layer lines - if you leave much of a rough surface you risk your casting material infusing into the layer lines.

One thing that might work the BEST is make a wax positive using your plastic mold (hot wax - means switch to PETG) - casting wax is soft enough you can get the wax part out, clean it up with an exacto, and then cast using lost wax process in a more traditional plaster/wax mold approach.

 

Posted : 18/03/2021 9:17 pm
Mike
 Mike
(@mike-6)
Active Member

Thank you for that.  I was fixating on molding the part with the threads intact but as you said it would be best if I tap them.  For reference, if you right click on the broken images you can view them in a new window.  

Posted : 19/03/2021 1:14 am
Dan Rogers
(@dan-rogers)
Honorable Member

PTFE Coupler?  I'm assuming you're already printing these directly - and want to speed things up.  If you try the 3 part mold approach w/Epoxy be sure to apply a good release agent to the mold before pouring.  You'll also want to think about how you'll introduce the casting liquid and expel excess air - channels.  Since you've got the design for those halves, making a pure negative inside a solid block should be a cake-walk.  Then peel apart the outer and inner, split the outer after giving it some clamping rims that you'll split when you split it.  Make it open at the top and sealed by the part that will frame the inner core (which you'll need to extract).  Think about a finish step involving drilling that center hole afterward and the "get it apart" part will get a whole lot simpler (no long plunge tube to extract).  Remember, leave extra meat where you'll be cutting the threads. 

Sure sounds like a fun project.

 

Posted : 19/03/2021 3:20 am
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