Injection Molding

I need to repair some base molding in a house. The molding is no longer available. I want to mold a casting around a good piece of the molding, then attach this molding to the damaged part and inject some sort of paintable substance to fill in the complex shape.

does anyone know where materials for making molds like this can be bought as well as the injectable product to fill the defect?

I had a friend that did something like this making unavailable plastic parts for an old Lancia.

 

Uro,

go to http://www.smooth-on.com/

There are a few ways you could do this... I would definitely use a medium hardness rubber molding compound on the good base material. Be sure to tape it off very well (smooth-on makes molding compounds specifically for architectural use, designed not to damage the original part and be easy to clean up, etc). You may want to look closely at their silicone molding putty - no drips or smears, just knead is like Play Doh and smoosh it onto the good molding then let it harden. I would recommend molding in a straw or some type of tube which will be the part through which you inject your repair resin, and also put a piece of wire at the highest point of the mold (which, when removed, will serve as a vent hole to let the air out as you fill with resin).

Then you could attach your new mold to the damaged part. As for filling it, it depends on how large an area and how complex a shape we're talking about, but I would personally most likely go with a 2-part epoxy. Abatron makes epoxies specifically designed for wood repair (often includes wood pulp in suspension) but honestly, if it was in any way hard to find wood epoxy, you could go with regular epoxy. Go with a long-setup time (like 30 minute epoxy at least) and just get the clear 2-part stuff you can get at home depot or even West System marine clear epoxy. They are both pretty low viscosity and runny enough to give nice detail and able to be injected. Pick up some syringes too (if you can't find any, I have some at work with epoxy nozzles which are just very large diameter needles and I'll send you some). Mix up the epoxy, suck it up with the syringe and inject into your mold. Make sure the mold is already affixed, of course. It's not a bad idea to put vaseline on the back of your casting mold so it doesn't stick and a thick coat of vaseline will also help seal it against the wood and prevent the epoxy leaking out of the cavity you're trying to fill - just be sure not to get vaseline in the cavity where you want epoxy or it won't stick!

Also make sure you have that air vent hole at the highest part of your mold so that the air has somewhere to escape when you are injecting in the epoxy. When you squirt it in, and epoxy comes out the top, that means it's full... just walk away and let it set up.

You will have 2 sprues (bits of epoxy sticking up from your air vent and your injection hole). You can cut those off, then sand them flat. Epoxy will take paint fine and will be indistinguishable from the natural wood. It will soak into the pores of the wood and won't come out or fracture even with lots of heat/cool cycles.

I have no affiliation with any of the products mentioned!

If you want to get really ambitious, use your rubber mold of the good section and cast a plaster reproduction of the piece. Then just cut-out the bad part and insert your plaster replica, or if you want to get super fancy, use a pantograph with a router or dremel type tool and make a copy out of wood from your plaster cast replica part

 

Wow! thanks for the info!!!!!

 

Mike got it all right !

I also use Smooth-On products at my effects and toy company

 

If it's a small area you can purchase an alginate kit (similar to the stuff dentists use to cast your teeth).

 

No worries... I'll just hit you up for a free colonoscopy in a few or twenty years!