Poor Man's Carbon Molding

[HyperSpeed]

So I have one guy telling me I need to get a $400 vacuum bagging kit. Saying it's what I need.

But I have never conventionally "vacuum" formed. I have always used some type of pressure from an object formed like I want and clamping or weighting it on the carbon, using underneath a quick peeling ply like 4-6 mil clear plastic from the farm store, or wax paper, if I am NOT oven curing; which will melt the wax in the wax-paper into the epoxy.

Now by conventional standards, this is becoming an odd approach I am using, but still think that the extra time for assembling the vacuum bag material could be a problem for me with the breather mat, pump, and etc.

The new thing I have seen is guys using plastic sheets, a box they build, a frame on top, and the top of the box is supported pegboard. The holes in the pegboard allow them to lower a frame containing the hot plastic sheet, which their shop-vac generates the suction to pull the plastic down while hot, it hardens, and then they have a female mold.

What if say I want to mold very basic curved planes, to make thin sheets of carbon for R/C buggy body guards for my buggy, and I have carbon and West System epoxy, but I want to do it all without having to order anything? I do have a Menards and Home Depot nearby. My thoughts were, at one of the hardware stores they sell different sized sheets and types of plexi-glass. Polycarbonate sheet, and acrylic I believe. Would I be able to heat them up in an oven or with a heat gun, and drop one on a lexan RC body to get a rough mold? Or would the thin lexan likely warp?

I do only desire a simple shape for some small squares of carbon, to use as mud guards or body protectors on a 1/8 scale RC buggy. The molds for the carbon do not need be sucked down perfect replicas of the buggy body, just mainly along the top sloping curve of the body they should be a similar curvature and smoothness. My theory is that by using a full new clean body the same as what the carbon will be made and cut out and to stick onto, it would be necessary to heat the plastic mold material sheet enough to become very soft, then quickly lay it down upon the supported lexan. If needed, the lexan mold-use body could receive a support with composite material like fiberglass on the underside itself for the original male mold. I then wish to take the piece formed as mold #1 from the experiment when cooled, and repeat the process upon it, with another piece of thin plastic sheet. I would finish, by placing carbon + epoxy into mold #2 which is female, then take the plastic made from mold #1, and use it to sandwich the carbon/epoxy in between the two outside layers, then clamp or weight them.

Does this sound just like a bad idea, or is there hope in my two pieces of plastic? Should I use the poly, or the acrylic, if either?

 

[mkadams001]

Sounds like a lot of work.

I would be easier to make a fiberglass mold of the part you want to duplicate. Rather than try to explain the process it is better to search for videos showing the process. I have seen some good instructional videos for making parts and it is the same method that I have used.

Heating and draping plastic over something will not give you what you want. It may or may not follow your contour. You would have to use a vacuum. The problem is crushing your original part from the vacuum.

It is easy to make a vacuum table to vacuum form plastic. There is a lot of diy for that as well on the web.

Bottom line from me is: Search for and watch some videos on the process that you are trying to do. My advice is marginal at best. You will get enough differing suggestions and explanations that you will be more confused than when you began by the end of the day. Finally, sometimes it is better to just jump in and see what happens, you will figure it out from there.

 

[GregGleason]

I wouldn't mess with vac forming or vac bagging on something like this. Especially for "one off's".

I would use something like this instead:

https://shop.hobbylobby.com/products/mold-putty-881540/
​

Then use a mix of chopped carbon and milled fiber in epoxy laminate. I might even use some lightweight fiberglass cloth. At least that is what I would try first

Greg

 

[HyperSpeed]

So say I use putty to make a mold. How would it be easiest to make the second male mold that is not the part I'm copying? In other words, if I need to sandwich the carbon to pressurize it, I can't make an exact duplicate male of the female, or the carbon and epoxy will not fit in between. So I need the male to be like 0.06" smaller in all dimensions, to account for layers of carbon and epoxy, right?

And...the same concept as this technique. https://www.youtube.com/watch?v=KfZFw2zc3sc

I bought the materials to build the box similar only I bought aluminum bar stock to machine a clamp frame, I'm just not sure of how to make TWO molds since the second needs to differ a little so that it's planes are all parallel to the first with carbon in between. To better explain, I couldn't copy a cube, because the second cube mold would not slide in with carbon wrapped around the first cube, that's what I'm saying.

I suppose maybe I could suck another sheet down inside my first female mold to act as a spacer, then remove it, and my mold would contain a spacing pocket. Am I looking at it correctly at this point?

 

[GregGleason]

Ah. I should have just directed you to this link:

https://www.alumilite.com/
​

They have all of the materials for the molds and mold material (negatives and positives).

If you have the original, you can usually mold it.

I would contact the folks at Alumilite and ask their advice. At this point, their opinion is much better than mine.

FWIW, compression does help build strength in composites, but I am not sure that you need that level of strength. A good layup, with the correct proportions of epoxy and amendments, will be adequately strong for most hobbyists.

Greg

 

[bobkrech]

Vacuum forming is a well known process. The Vac-u-form was one of my favorite toys in the early '60s.

See the pictures and video below.

[YOUTUBE]aat5m46RE1s[/YOUTUBE]

For what you want to do, I would make a larger vacuum former, and make a cavity mold. Plans are easily found on the internet.

Then do a hand layup for outside in just like they make real boats.

Bob