Rubber Casting repro parts.

[BRENT in 10-uh-C]

Do we have anyone here that has some experience with casting Rubber? I lost my local liaison who was very knowledgeable, and now I need to make some small runs of certain rubber items that are out of production or on 'terminal backorder'.

One is the rubber pieces that clamp windwings. I will likely 3D print molds using the reproduction rubber pieces as samples, but I have a little observational experience at using epoxy to form a mold. If anyone has experience in this, I would like to chat by phone.

[ModelA29]

I think the rubber parts will need to be heat cured so you'll need metal molds. Lots of youtube videos on making small molds. Plaster and lost wax may work well for a small run of these parts. For 100s you'd want to invest in a permanent mold. If you can find who was making the repops they may be willing to sell the tooling if continued production is no longer profitable for them.

[alexiskai]

I wonder if there would be economies of scale from combining parts. For example, you could purchase tooling for a single molded piece that combined, e.g., several windwing clamps, the inserts for the VE28 rumble seat step, and the plug for the phaeton top rest mount. Then you'd get multiple pieces out of each run for nearly the same cost. I'm sure there are other unproduced rubber parts I'm not thinking of.

[Tacoma Bob]

MMM long shot Brent. Check out Metro Molded Rubber Parts. They are in Minnesota. I just looked at their website briefly. I dealt with them many years ago. Worth a shot unless you already tried them.

[nkaminar]

Traditional rubber needs to be cured at high temperature but there are rubber like compounds that cure at room temperature. Silicone gasket sealant is one. Polyurethane is another. There are many other polymers.

I have cast polyurethane for a machine that I was designing. First I made the plug that is the male part used to make the mold. Then I cast silicone to make a mold. Then I cast the polyurethane into the mold. I made a few parts. The material that I used does not shrink so the plug can be the final size and shape.

The mixed components used for the mold and for the part have to placed in a vacuum chamber to de-air them.

It takes a while for the polyurethane to set but that maybe could be sped up with some moderate heat.

[BRENT in 10-uh-C]

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Neil, you are correct about the curing. The product I was exposed to has a small curing process at 140° for about 30-45 minutes. I think the resins have changed this process immensely, and it has been a couple of years since I had someone that was versed helping me. I am assuming technology has changed in that time.

Colin, I probably will only make a small run for our own use on customer's vehicles. The correct size/shape/detailed Battery Cable Support Grommet was never produced exactly in the commercial market and just before Doc Kalinka passed, I purchased about 15-20 from him. I have 2 left, so I want to replicate those. The reproduction Steering Column Anti-Rattle rubber is not correct, and so if i could cast those with the reinforcement cloth imbedded, that would be nice. The same with the Wind Wing Mounting Rubber. Again, just some small one-off production pieces to use inhouse.

Thanks everyone for the thoughts & comments!!

[denis4x4]

You might search for companies doing reproduction rubber for motorcycles.

[mikem]

New member here. I have done lots of rubber molding etc. The molds must be made out of steel or aluminum with thick wall to withsatnd the molding pressure and heat.
Real rubber usually outlasts urethane rubber.

[nkaminar]

Mike M, Welcome to the Barn. Where are you located and how many Model A's do you own?

[TomInCologne]

Maybe it‘s worth having a look at 3d-printing? In our company we are manufacturing more and more parts on our own 3d printers. They are cheap enough to just get one and try it and there‘s loads of material to try out, including carbon fibre strenghend materials.

If you need some assistance with preparing 3d-files, just contact me.

[BRENT in 10-uh-C]

Originally Posted by mikem

New member here. I have done lots of rubber molding etc. The molds must be made out of steel or aluminum with thick wall to withsatnd the molding pressure and heat.
Real rubber usually outlasts urethane rubber.

Welcome to the 'barn, -and thank you for your response.

What I am doing is making small runs for one-off pieces where we cast pieces in polyurethane rubber that sets around 70 to 80 range (depending on application). Several years ago (i.e.: 8-10??) a friend of mine helped me cast some hood bumpers for a 1958 Buick Roadmaster that I could not find. Those were cast using an epoxy mould that we made using a hood bumper as a sample. To this day, the cast pieces have held up well. Since then, we have cast several other small pieces, but unfortunately my friend is no longer with us. Additionally, I am sure the casting technology has improved somewhat, and I was hoping I could speak with someone who actually does casting frequently enough to know what the latest technology was. I appreciate your thoughts though.

Originally Posted by TomInCologne

Maybe it‘s worth having a look at 3d-printing? In our company we are manufacturing more and more parts on our own 3d printers. They are cheap enough to just get one and try it and there‘s loads of material to try out, including carbon fibre strenghend materials.

If you need some assistance with preparing 3d-files, just contact me.

We have a small 3D printer inhouse that we do use make fixtures, tooling, or moulds, and I have debated using the printer for two items I am going to cast where a two-piece mould will be required. Mostly what we use is PLA and PETG filiment. As for modeling, we presently are using Fusion inhouse. We got our start with SolidWorks but the seats have become too expensive to justify the costs.

[TomInCologne]

Originally Posted by BRENT in 10-uh-C

We have a small 3D printer inhouse that we do use make fixtures, tooling, or moulds, and I have debated using the printer for two items I am going to cast where a two-piece mould will be required. Mostly what we use is PLA and PETG filiment. As for modeling, we presently are using Fusion inhouse. We got our start with SolidWorks but the seats have become too expensive to justify the costs.

Okay, so you already have that experience. I am printing several parts for my A, last one was a trim ring for my dash panel to put a 1.28" round Display in instead of the amp-meter. The Touch-Display will show Current, Voltage, Time or rpm.


We are using Inventor, as an engineering company we have no choice...

[mikem]

Brent
Could you post a picture of one of the items your looking at making ?

[CT Jack]

If your are capable of printing the desired shape into a solid you could then use this to make a mold in silicone (RTV). I would look at using a urethane elastomer that has the desired durometer and color for your application. Selecting the proper RTV for your mold will enable thermally curing the final cast urethane part. If this approach is feasible for your application it would be in my view should be the least expsensive method.