Post by jimholmgren on Apr 5, 2020 20:18:16 GMT -5
Hi Everyone, First time for me venturing into this realm. I'm in the process of restoring a 1970 arcade shooting gallery game (Midway Flying Carpet). The "trigger guard" is plastic and is held in place by a couple of roll pins. Mine has cracked. It seems like this would be an ideal part to either 3D print or to cast. 3D printing would take a fair amount of CAD time and I don't have easy access to a 3D printer in today's environment, so I thought I'd try my hand at casting.
Wondering what you folks would recommend for an approach to making a mold of this part? I can't wrap my head around whether to make it one-piece or two and if two, top/bottom or left/right. Any advice?
Last Edit: Apr 5, 2020 20:19:56 GMT -5 by jimholmgren: Added pictures
Make sure to glue the crack so that it's solid and the silicone doesn't get in it - the beauty of a liquid silicone is that it picks up the finest details but that also means it gets into every crack and crevasse. You can do a one piece mold but it will take a little work to set it up but demolding the copy will be easy.
1) First tape up the holes (a single piece of plain old tape will work) on the sides of the round part (hole #1) and then fill it with silicone and let it cure. Leave the tape there as you'll need it to keep the silicone from the outside from getting to the silicone in the hole. Silicone will only stick to silicone and you don't want it to go all the way through the holes as you would have to cut it to remove the original piece. Be sure to fill the hole up to the top.
2) Next put a thin wall of something (tape or clay) in the other hole (hole #2) so that the two sides of silicone don't form a solid piece that needs to be cut to remove the original.
3) Pour a layer of silicone on the mold box bottom and once the open time is almost up and/or the layer is firm enough to hold the weight of the original without the original sinking to the bottom of the mold box, put the original round edge down on top of the layer of silicone. Let that cure a little then pour the rest of the silicone. Make sure to not cover the long piece (in blue) as that will be where you pour the casting material.
You shouldn't have problems demolding the original but let us know if you do.
Post by jimholmgren on Apr 6, 2020 18:04:13 GMT -5
Wow - I cannot thank you enough for this Notoes, really - thanks! I never expected step-by-step instructions!
A couple of quick points of clarification. 1) I assume I should tape up the hole circled in red before I fill hole #1 with silicone. The circled red hole opens up to the larger hole (hole #1) to feed wires up through to the trigger switch. 2) When I pour the silicone you say not to fully cover the long piece. If I don't cover it, I assume I will need to mill out the small groove to the right of the red circle after I cast, as well as drill and tap the two small screw holes to the left of it in yellow? No big deal either way, just trying to figure out what to expect.
You're very welcome, I tend to over-explain things to be sure I'm explaining them enough.
1) No need to tape that hole, that will be the pour area so the top that you see will be open as it is and you won't have to worry about the silicone going all the way through.
2) Just fill it to the top of the long piece so that it is level with the top part. If the hole in red goes all the way through then the silicone will make the hole for you (you might need to add a little to get it all the way through and level with the long part) but if it doesn't then yes you'll need to mill it out. Same for the ones in yellow.
Post by jimholmgren on Apr 17, 2020 21:42:36 GMT -5
Took me a bit to get this done - made a rookie mistake and ordered way too little rubber for my mold,so I had to wait on another shipment.
They didn't turn out too badly, but yeah you definitely pick up every little imperfection. I can clearly also see the tape I used to seal the holes around the barrel, in retrospect, I should have put the tape on the inside. Rookie mistake.
Overall - pretty happy with the way they turned out, I did two castings with different amounts of dye just to play around. The first one is the middle in in the picture and just by dumb luck I almost got the gray perfect.
I'll need to drill out some of the holes and remove the excess from the trigger area, but in general I'm happy with them. Thanks a bunch for the advice, really appreciate it.