How do I mold this?

[RSloan76]

Hello,

I'm having trouble coming up with how to make the mold for this part (cylinder for a revolver).


Essentially it's a cup shape with a small hole through the bottom. I can't figure out where to have the pour hole.

At first I considered this two-part mold, but of course, there's no pour hole.


Next, I considered this, but I don't know how to solve for the inevitable void there will be around the top. Vent holes won't work because the void area would be the entire top surface.


I don't have a pressure pot, nor access to one so that's out.

Here's what I'm working on:


All the parts have been smoothed out and molds have been made for almost everything except the cylinder and the barrel, which poses almost the same molding problem.

 

[Zlurpo]

I'd try this:



In the T shaped mold, Have two channels coming up and out. Easy enough to add them before you make the mold, even if you are just using straws or clay or whatever to make them. Pour the resin into one, air escapes from the other. It's better if you don't fill up to the funnels because the mold can't slide off then, but either way I'd recommend letting it cure completely, and then just breaking the pour channels off as you de-mold.

 

[RSloan76]

Assuming you mean like this:

Won't there still be trapped air along the rest of the top surface?

 

[krispikarim]

Assuming you mean like this:
View attachment 514279
Won't there still be trapped air along the rest of the top surface?

there wouldnt get air trapped if u just roll the mold when you pour with that set up

 

[cavx]

I'd try this:

View attachment 514268

In the T shaped mold, Have two channels coming up and out. Easy enough to add them before you make the mold, even if you are just using straws or clay or whatever to make them. Pour the resin into one, air escapes from the other. It's better if you don't fill up to the funnels because the mold can't slide off then, but either way I'd recommend letting it cure completely, and then just breaking the pour channels off as you de-mold.

He could probably have more than 2 vents. Maybe upto to 4.
Also given he won't have a vacuum chamber or pressure post, he might be able to roll some resin inside the mold first to help coat the surface. Resin pending, tapping the side should then release any trapped air.

Surface finish pending, use talc first.

 

[Darksyde13]

One could also try the very first pictured mold with no pour holes. Put in just a touch more resin than is needed in the bottom and then close it up. The plug should push out the liquid and fill the mold. A little messy but on paper it should work.

 

[RSloan76]

there wouldnt get air trapped if u just roll the mold when you pour with that set up

I was thinking about that, but I wasn't sure how sure I could be that it could come out ok. I'm tired of having molds where I have to cross my fingers before demolding!
I think I'll try it this way. -And add a few more thin vents as cavx suggested.

One could also try the very first pictured mold with no pour holes. Put in just a touch more resin than is needed in the bottom and then close it up. The plug should push out the liquid and fill the mold. A little messy but on paper it should work.

Clever idea! I can actually try this too since having the vent holes and double pour holes will just contain the "mess" a bit.