Picture of JB Weld Casting
If you need a small part and you have access to the original then use some JB weld to get 'er done.

JB weld did the trick on a missing piece for my airsoft gun.

UPDATE - Make sure you check out all the awesome comments about how to go even further and reinforce the epoxy.
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Step 1: Playing with Playdough

Picture of Playing with Playdough
Take some kind of casting medium, I stole some playdough from my son. I think this would work even better if you used modeling clay or something made specifically for such an application. Who knows.

Step 2: Your Part

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Here was the part that I wanted to copy. It is the selector switch off of an airsoft gun. I'm sure you can buy these parts but I didn't feel like paying $10 + $10 shipping on ebay for such a silly part. Luckily I had a spare part from a buddy's gun that I could use to make the copy. Notice that there are some pretty finely machined areas of this part that were essential to fitting on the gun.

Step 3:

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This stuff isn't rocket science so I'm sure you could probably figure it out on your own. I just wanted to prove that it does in fact work. Or maybe you hadn't thought of it.

One trick I did learn was that for the really deep parts that it helped to fill them with the clay so that it would then adhere to the rest of the mold when you remove.

Also, try to make sure the top of your mold is even with the top of your piece to avoid too much excess.

Step 4: Mix it Up

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Mix up your jb weld and dump it into the mold. I had the quick setting type laying around. It would probably work better to use the slow setting, just leave it in the mold longer until it is hard. The original recipe is supposed to setup harder than the kwik version.
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llapdog6 months ago

I've been wondering about using JB weld to make a old-looking coin as a prop for a costume. My only worry is I don't how much it weighs. Could it be used to make a coin similar in weight to one made from iron?

DanTDM1 year ago

You can cast custom pipe fittings (like 4 inch to 1/8 inch bushings)

this stuff is the best! i just repaired the handle of a 150.00$ goat milker with it, it works great, and only cost $5.99. i've used it to fix auto interior plastic panels, even filling in pitting on aluminum intake manifolds. if you want more strength, embed finishing nails.
Goat milker?
Milks goats, I reckon.
a plastic, hand operated vacuum pump, with a milk container, and a teat coupler, to milk small numbers of goats. kind of like a one man brake bleeder pump. squeeze the handle to create a vacuum, which draws milk from the teat to the container, through a tube. the handle broke at the pivot . easy fix for an expensive piece of equipment.
808create5 years ago
You could use JB in both steps, instead of PlayDoh, to get a better mold. Let it dry and spray with WD-40 to keep it from bonding.
Using JB as the mold would be a great option, easily modified and mold could be tagged and put away for doing same mold again.
Capt. Kidd4 years ago
The only problem is, it makes a mirror copy of the original piece instead of an exact copy. I guess you could cast the copy to get the same thing as the original though. It just takes more JB Weld.
The playdough makes an inverted copy and the JB weld then inverts it again so it becomes the original.
hmm... right. DERP
jammin0 (author)  Capt. Kidd4 years ago
umm, it doesn't create a mirrored copy. That doesn't make any sense.
YOUR A GENIUS!!! i serioously wouldve never thought that would work with an mp5 selector switch, cuz theyre so intricate
dude i believe i have that same airsoft gun. its firepower brand mp5 right?
syco1235 years ago
I never go long distance hiking without JB weld. It's a lifesaver and worth it's weight, literally! I like this idea of casting with it. Hadn't thought of that.
ERCCRE1236 years ago
is that an MP5?
I think it might be a G3.
Nope, its an MP5. G3's have a very different upper receiver. They do look similar though, because they are both originally made by H&K.
jammin0 (author)  ERCCRE1236 years ago
You guessed it. Tokyo Marui
My brother used to have one and the selector switch looked exacly the same
rhughes6 years ago
Quite a while back I read an Instructable (I think) on casting small parts from homemade ABS plastic resin. The resin was made by grating/grinding or otherwise pulverizing a section of ABS pipe and dissolving the result with acetone. The result (a custom part for a car interior) turned out pretty good!
I have used the same method (acetone and styrne plastic) to mold a small part for model car once, work all right. I work close to a plastic molding plant and once in a while I get raw pellets to use, PVC pipe cleaner (MEK) works good to melt styrne also. Would like to build a home made injection molder using chems instead of heat, any ideals on that?
Check out, they've got a book on building your own plastic injection molder, and I'm will to bet it wouldn't take much to modify it to work with chems instead.
Just a thought, late but still a thought. the FDM or Direct Digital Modeling comes to mind it's the thing, molding with I'm old and slow.....must be early stages of oldtimers.........still going to check out the site.....L8R
Went and checked out the site, the tube book caught my eye because I work on radio frequency welders, RF Welder, Dielectric welder , what ever you want to call it. It shows the schematics for a radio and it is very close to what I work with, kind of like a radio station, only instead of music, we bond plastics together....
Alphonsus6 years ago
I'm Currently using this idea to fix some cosmetic problems on my motorcycle. there is a clip missing of one of the side panels so i used modeling clay to mold the other one.... waiting for it to dry now :D that has been bugging me for the last year!
jjprice6 years ago
that is cool i never thought about that
Marcos6 years ago
I'd like to see more instructions on technique, like how thick you rolled (cut?) the Play-Doh, did you level the surface of the mold, did you level the surface of the JB Weld or just let it stay above the surface of the mold and sand it off, etc.

Lots more info could be delivered here. So far you've shown what you did, but very little about how, which is often the critical part for those who want to repeat the process.
Marcos6 years ago
Great idea. I saw a guy at the Maker Faire who does product development, and he advocates doing rapid prototyping with epoxy by modifying existing products ( he showed me some scissors and something else he'd done), and also making new, functioning parts from epoxy.

That year he gave people who stayed for his talks a tube of Oatey epoxy putty. It's good stuff. made in the U.S. , the label is also in French and Spanish, so it may be available in other countries too.
PKM6 years ago
If only I'd known this when those igganunt fools in the drama department broke my prized Beretta all those years ago... do you know how strong the finished product is? I guess your switch isn't going to be under great mechanical strain, but could you cast a new trigger out of it? Or some part that takes a lot of local pressure?
jammin0 (author)  PKM6 years ago
I'm sure you could use this for a trigger as well. I used the quick setting stuff and it is probably about as hard as aluminum. If I gouge it with a screwdriver it will dent and scratch. However, I've heard that the regular JB weld is considerably stronger. Or do like kenbo suggests and add something. I'm thinking like metal shavings or something really fine. Dremel up some metal so that you get a fine metal powder to add.
maruawe jammin06 years ago
You can take aluminum foil and grind it in a coffee grinder, it will take a while to get it to a fine powder , I needed aluminum powder to make thermite and this worked quite well. cut or tear foil into strips for best results Grind and regrind several times to get a 400 grit on the aluminum .
whats thermite
Thermite is a combination of aluminum powder and iron oxide usually a one to two mixture that will burn through most anything. It is dangerous to use , i have a hole in my patio as evidence , before using thermite do a lot of research.
Pazzerz maruawe6 years ago
Don't pressure contain it either. Makes a devastating bomb and throws incendiary particles everywhere that will burn through your hand, etc.
maruawe Pazzerz6 years ago
What do you mean by pressure contain it .I have been working with thermite for over a year and never ever thought about pressuring it. Are you referring to a powder compression in an explosive or air compression.. Please clarify
Pazzerz maruawe6 years ago
What's to clarify?? I suppose I should have added the extra ingredients on the last comment, but I really don't want to blatantly tell everyone how to make a bomb. Obviously you are working with it in the way that it is supposed to be worked.
maruawe Pazzerz6 years ago
Bombs are good in their place, But the components that make bombs are useful in many ways and I kinda like to have me around in case I need me. So I am very careful about how I use chemicals......having had the training in explosives that I have been fortunate to get through out my life give me the knowledge to work with chemicals . My motto is: if you don't know ask questions till you do know and then be real careful. (See above statement).
research is the key to longevity.........
where can i get iron oxide
Leave some steel wool half submerged in slightly salty water, stir it every couple of days to break it up slightly. Add more steel wool when you can't see much shiny in the brown powder, and when you have enough rinse the salt out and crush with a pestle and mortar. You can then get residual iron out with a magnet.
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