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crazyjim

Need molding/casting help

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I'm trying to mold and cast Pegasus disk brakes because they cost so much and I use lots of them. I've gone through 4 or 5 molds and cana't get it right. I've tried using clay as a base and making a 2 piece mold from there. The disc brake was laying flat. Should I be standing the disc brake up, bury it halfway into clay and start a 2 piece mold that way? I could really use some help here, anyone.

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I wouldn't use clay. Lay the backside onto a piece of packaging tape. Build your mold box around it. Pour your silicone. When it dries pop your pieces out and pour some resin!

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Also, I'd do a 1 piece unless you want the detail on both sides. If you want a 2 piece do what I said above, pell the bottom off, apply mold release, but new walls from the bottom up, pour silicone, and your done.

If you still have trouble I'll be glad to help you make the molds, or make them for you.

Edited by ian ashton

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I agree unless you want the details on both sides just to a flat relief mold.

I'd help ya too, I am just in the process of setting up my pressure pot vacuum chamber to do more advanced molds and castings. I should be up and running in a few weeks.

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I want the detail on both sides. I had a thought just before going to bed last night. Cutoff the axle flanges, glue/tape the caliper down in an upright position. Let the mold dry. Flip the mold over and pour the resin. This way the caliper would be on top and with no flanges, the unit should (hopefully) come right out. I can then use Evergreen tubing for the flanges. I plan to try this version out today. Wish me luck.

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That idea didn't work. The rotors were paper thin and most times the caliper broke off when coming out of the mold. Maybe I'm not doing molds correctly. I just take a cleaned yogurt cup, hot glue the bottom of a part, and pour the silicone. I let it set up, remove original part, and pour the resin. This method works great for the bucket seats I've been doing. This is quite a bit of excess resin when I remove the part that I just sand away. I'm not very good at pouring just right amount into the mold and always get overflow.

I don't understand about just taping a part to the bottom and pouring silicone, especially for Pegasus disc brakes. Wouldn't the silicone just cover everything? How would the part be removed?

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Get some foam board, the kind that is like poster board. Strip the paper sides off. Get some modeling clay. a hot glue gun and some hot glue sticks, build your mold box alittle taller. Take the modeling clay, fill the bottom of the mold box up oh say 1inch with the modeling clay. Make sure you pack the clay into the bottom of the mold box. Now take and lay your part flat ways onto the clay and firmly press it down into the clay to your likings. Now take and use a pencil or something to make afew hole indents in the modeling clay. Now take and have some release agent on hand and spray the mold box down good on the inside. Pour your casting compound in, leave set over night. Now here is where it can kinda get tricky at, just remove the bottom of the mold box real easy, pick out all the modeling clay "without moving your part" and after you have the modeling clay all removed, take and use the mold release agent again by giving that side a good spraying. Then mix up some casting compound and pour. Wait at least 24 hours and then check, if good start demolding easy. Now when pulling the two half's apart, they might at first seem like they are one but alittle presure of pulling easy they will come apart. The hole indents you make before will act as arms for when you place the two half's of the cast togother as they will line up correctly without any guess work. I hope this info might be of help to you.

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Pics might help, Ian.

I did that exact procedure on the second or third mold attempt, Moparman. Even had an air vent and pouring shoot. The part came out extremely thin and worthless.

Thanks for the info guys.

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Pics might help, Ian.

I did that exact procedure on the second or third mold attempt, Moparman. Even had an air vent and pouring shoot. The part came out extremely thin and worthless.

Thanks for the info guys.

What kind of rubber are you using? You might need a more rigid rubber. Or is it the resin is not filling up the mold all the way?

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I'm using Smooth-On OOMOO-30 for the molds and their casting stuff too. I discovered a problem with the 2 piece mold in that the pour tube went to the caliper and the resin wasn't able to go around it to the rotor. I tried cutting another pour tube and it's setting up now. If this works -great, but then I hit another problem. I'd like to be able to cast 4 disc brakes at one time.

I'm wondering if I was in too much of a hurry for the resin to set in the 1 piece mold, so I poured again and will wait a couple of hours before checking the results.

This project of trying to save a couple of bucks on building materials is starting to be a money losing proposition.

Edited by crazyjim

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I'm using Smooth-On OOMOO-30 for the molds and their casting stuff too. I discovered a problem with the 2 piece mold in that the pour tube went to the caliper and the resin wasn't able to go around it to the rotor. I tried cutting another pour tube and it's setting up now. If this works -great, but then I hit another problem. I'd like to be able to cast 4 disc brakes at one time.

I'm wondering if I was in too much of a hurry for the resin to set in the 1 piece mold, so I poured again and will wait a couple of hours before checking the results.

This project of trying to save a couple of bucks on building materials is starting to be a money losing proposition.

Probably work just fine if you pressure cast it. It had to do a two part mold casting on the bench.

Your mold is probably leaking.

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Getting the equipment to pressure cast is way more thatn I want to get involved in casting. The resin is still setting out there.

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Sorry for the slow reply, hectic day with with work yesterday.

At any rate, this is how I make 2 piece molds (I thought I had more pictures, but they are now lost)

Lay tape flat (sticky side up) on your working surface giving you a decent amount or room around where your part will go. Then, place your part in the center, face up. Next, build your mold box around the part. I just fold cardboard, place it on the tape, then fold the tape edges up onto the side walls. I'll add a little more tape to prevent leaks, then I'm ready to pour the silicone;

IMG_3085.jpg

When the silicone dries flip the box over and peel off the tape - this should leave your part in the mold, with an exposed bottom, and the rest of your mold. Next, tape more cardboard onto the sidewalls, essentially making the mold now go in the other direction. Paint on your mold release, let it dry, then pour your second half. Once the second part of the mold is dry peel off the cardboard side walls and carefully seperate your molds.

I wouldn't worry about putting any 'ports' into the mold, I'd just pour and 'squish' the top of the mold on, as its likely that you won't need any additional resin for the details on the backside, you just need the mold there to form the details.

That is exactly how I make the hoods - it took me a few tries to get the casting process right, but now I've got it down to a science.

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Thanks. Ian. That's about wht I've been doing except using hot glue instead of the tape. I tried another 2 piece mold and forgot to use release agent. I ruined the mold cutting it apart and that was the last of my OOMOO 30 mold stuff. I've ordered some but will probably take at least a week to get here.

And thank you, Mark. I sent you a PM.

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I gave up on the Pegasus disc brake molds. Marc sent me some Brembo units and they're much easier in a 1 piece mold.

Can you guys tell me how you pour the resin? I've been mixing the 2 parts in a small dixie cup and then squeezing the top to make a spout. That doesn't work very well when trying to pour into a small mold. I have a tiny poly funnel but was afraid that it would get clogged and ruined after the first use.

A guy at JaxCon told me to heat the molds and add baby powder before pouring. I was out yesterday looking for a cheap microwave but $60 was the cheapest and I didn't buy it. I'm going to try a heat lamp and/or hair dryer. I got the baby powder.

Appreciate your thoughts on pouring/heat/baby powder.

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Get some pipettes and decant from your primary mix container. rinse the pipettes acetone or MEK so you can reuse them. Eyedroppers also work,and you can spray the tube and bulb with release to make cleaning easier.

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