For the molding/casting gurus

[Fizbin]

I have a gun barrel that needs to be cast in resin, but I can't figure out the best way to do it. Here's the item in question:

The smaller barrel needs to be hollow at least down to the begining of outer barrel. The hole in the bottom of the larger barrel is only about 1/4" deep, so there's no real problem there.

I imagine that I'll need to make a 3-part mold:
(a) Two vertical halves of the entire item.
(b) One for the depth of the smaller barrel, that rests on top of the two vertical halves.

Unfortunately, if I build the mold as mentioned above, I don't see where any vents can be made to prevent massive air bubbles in the casting.

If anyone has a suggestion, you'd be saving me a ton of wasted silicone and quite prossibly whatever little hair I have left on my head. :lol Thanks.

 

[clonesix]

As I see it, the issue is the hollow center. The probably is no draft to it. If it is a common pipe size size, that can be incorporated into the mold. The internal pipe would need to be removed from the mold while the casting is still "Green" to insure that it doesn't lock itself in the casting. A good mold release and some elbow greese usually do the trick.

As for the rest of it, build a box around it and pour the RTV as one piece. After it has cured, run a utility knife down the side to open it up anough to get the casting out. It should pop out while still attached to the center pipe. Grab the casting and give it a twisting pull to remove the core and get a finished piece.

 

[micdavis]

Add two sprues to the part as shown.

Place in box or cup as shown.

Pour the rubber over it.

Pour resin in one sprue hole wait for the bubble to get chased out the other.

Cut along dotted line at the top and down the sprue side just enough to pull the part out from the top.

One piece split mold. No need for Multiple piece mold.

 

[Steelblitz]

If the smaller diameter is a common pipe size you can use, cast them as part of your finished piece if it makes it easier for you.

Your pipe is not too far off my resin clone detonator caps I cast. It is a failry simple two piece mold. The seam I make at the very top surface and the top part of the mold only really serves as a plug to form the void in the main part of the cap. The cast caps are clean when coming out of the mold except for having to trim off the material from the vents. I have three small vent holes slightly smaller than the thickness of the wall of the caps.

The two round caps in the center of this picture are completely hollow underneath, and they have about 1/8 thick outer walls. They both slide right over the piece of PVC pipe behind them.

 

[Fizbin]

Awesome! Thanks for the help, I didn't realize there were so many simple approaches to this problem... that's what I get for not using my noggin. :rolleyes

Thanks again!!! :thumbsup