Mold-Making Masterclass In Minutes – Hackaday

Making silicone molds seems easy, but there are a lot of missteps to be made along the way that can mean the difference between a great, reusable mold, and one that’s a sad waste of silicone. If you’re helpless to know the difference, then check out [Eric Strebel]’s 9-minute masterclass teaser video on making a two-part mold for resin casting, which is also embedded below.
Even if you already know how to do this, there’s probably a good tip in here somewhere. One of them being that you should always pour your silicone from one place and let it coat the piece being copied. Otherwise, there might be lines on the mold. Another tip is for DIY mold release made from petroleum jelly thinned with naphtha.
Our favorite tip has to do with the way [Eric] makes this a reusable two-part mold, which is more akin to injection molding. To pour silicone for the second part and get it to separately nicely, [Eric] uses sprues made out of resin rods that were cast inside of drinking straw molds. These he chamfers against a belt sander to minimize the contact with the cast part, which makes them a snap to break off. [Eric] says this is just the beginning, and there are more videos to come that will break down the steps.
There’s more than one way to make a mold, especially for casting in metal. We’ve seen everything from 3D-printed molds to kinetic sand.

I nearly missed a deadline by using petroleum jelly as mold release and ending up with sticky surfaces. The real stuff is cheap compated to the other materials you potentially ruin. I cheaped out and paid the price, a mistake I won’t make twice.
Most silicones are cure inhibited by oils, especially petroleum products. Enamel paints are also not a good surface to cast silicone against, even with several layers of hi-temp mold release wax. If you must work with a master item that’s painted with enamel, the paint has to be *old* so it’s fully cured. Or if you can spray clear lacquer on it, that will work.
If you’re spending the money on platinum cure silicone, don’t cheap out trying a homebrew mold release. A spray can of release agent made to work with silicones is cheaper that wasting silicone and time on a fail.
I don’t use tin cure silicones. They’re not that much cheaper and they shrink a bit, also the molds will slowly deteriorate just sitting around. I have some platinum cure molds near 20 years old that I still use.
Anybody else find that guy a little bit weird and creepy? Neighbor.
Don’t get me wrong though he’s a damned genius at his craft.
So it’s not just me that finds “soothing” voices just a bit grating on the nerves? “I know you’re trying to sooth me and sound all comfy. Stop it!” 😉
He was doing Misterogers. It may not have come out as intended.
I didn’t discover Misterrogers’ Neighborhood until adulthood, but he had some really good “how it’s made” segments. The first one I saw was on blowmolding.
sorry but making the mold part of a project is not the difficult. getting a workable positive to create the mold with is the really difficult part IMHO. nice video but doesn’t really teach much useful information IMHO
Try making a mold from a 50+ year old plastic lens that spent a lot of its existence being baked from inside by an incandescent bulb. The slightest bit too much pressure and it’ll shatter like a dropped egg. Has to be consolidated, primed and sanded several times, painted and sanded several times, polished and buffed, inside and out. All the while its still super fragile. There’s also figuring out how to reconstruct bits that just aren’t there.
Then there’s making the first half of the mold and sweating it that the lens will survive. Whew! It does! The second half is no big deal because if the original (which is useless for original purpose anyway) goes *pfft* it’s fine because the mold is done. Of course I did the important side of the mold first.
Yup, the lens fell apart into tiny pieces but now I can make new ones that should outlast the rest of the car. Some old Iso and Ferrari owners are very happy with their indestructible dome lamp lenses.
I do make some decent $ on low volume and one-off parts for classic cars. Some of my work has been on cars at Hershey and other Councours d’Elegance shows.
Do the dome light lenses you make require much polishing?
I made a 3 part series about urathane casting from 3D prints. This shows me making an electrical enclosures for a short run production. Eric makes great videos but I added a bit more depth.
Part 1:
Part 2:
Part 3:
Let me know what you think. 
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