Questions on skinning

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#1

I am trying to skin some very simple shaped interior car parts, but the carbon does need to wrap around the edges a bit.

I first tried skinning without a vacuum bag, but the fiber lifted from the edges thus making the parts not usable.

So I got materials to do this with a vacuum bag but I’m having some troubles and I am looking for help.

In my first vacuum bagging attempt I used a perforated release film over the part, but when it cured the epoxy dimples caused the surface finish to look pretty poor. I sanded too deep and ruined the twill.

In the second attempt, I used standard release film. The problem is that the film itself wrinkles easily, and any wrinkles translate to the finish. Also, this process seemed to leave more trapped air, and thus bubbles in the finish. So this didn’t work.

Lastly, the vacuum bagging tends to cause creasing around the edge of the part, which leaves an uneven epoxy finish.

Any suggestions on how to get a better surface finish? Should I just use peel ply instead? I thought that may leave a worse surface finish, but I’ve yet to try it.

#2

Also, the process I used is to tint some resin, apply it to the part, then once the resin is tacky, lay down the fabric.

I feel like there must be a better way because for one you have to wait ~45 minutes for the epoxy to get tacky, and at that point it may not be tacky enough to stick nicely to the edges.

I tried super77 spray, but that actually shows through the fabric since I’m only doing one layer.

Anything else I should be using?

BTW, I’m using West System 105/207 if that matters any.

#3

Sounds like you already have some experience. There’s a lot of info already on the forums about this. Do a search for overlay. If you have any questions though feel free to post in this thread.

http://www.compositescentral.com/search.php?searchid=32458

#4

Best advice I can give is to keep very specific records of what you do, how you did it, what worked and what didnt. Everyone here will probabley agree that composites are very process intensive. slight deviations to a process that worked before can junk a new part/style of part. Repeating mistakes can be a real bummer too. Even if I have made something several times I still go to my book to ensure my steps are being followed exactly. Good luck

#5

What he said ^ x10.

#6

Get plenty of over lap and tape the fabric dry on the backside of the panel. Then brush epoxy on the dry fabric. Build up epoxy then block sand smooth. Clear coat with a urethane.

#7

Thank you all. I was just getting frustrated, glad to hear that it’s not as easy as it looks. I’ll just keep tweaking what I have until it’s solid. I made the mistake of being overly enthusiastic and did my first few runs on actual parts. I would just like to point out that stripping a part back down is a major PITA so doing test runs is worth it’s weight on gold.

#8

Well lots of pictures and constant updates and we will help you through it!

#9

OK, well I thought I had the process down, then on the next part I proved that to be wrong, LOL.

The main problem I have is getting the carbon to stick the part prior to vacuum bagging.

I have been covering the part with resin, wait for it to tack up, then apply fabric. The problem is that it’s a bit of a pain to wait 45 minuts for the resin to tack up - and then secondly when it does tack up, it’s not always at the right level of stickiness. The process window to make it work seems small.

So I have some 3M super 77 spray. I feel like that will show through the fabric since I’m doing one layer. Are there any better tack sprays?

I am using an epoxy resin as well. I have done some searching on sprays, but I couldn’t really find what’s the best one to use for skinning where I may have issues with seeing the base layer.

Thanks

#10

Essentially you have to bond the carbon to the plastic first. I never bagged carbon while doing overlays. Doesn’t really make sense unless your really good at using and tailoring a stretchy nylon peel ply. Thi is how I do it. Scuff the plastic part with 180 grit and clean… Then get a 5-7 minute epoxy and brush it on the part. Use a liberal amount so you don’t wet out the part with it but use enough that it holds. Then let cure. Then you brush on resin. Scuff and brush a second coat on block sand and clear coat.

Lay the carbon then trim after it dries to the five minute epoxy.the fibers will not distort or pull out.

You could, when wetting the fabric with resin, apply peel ply and perf and some breather vacuum bag it to pull out excess resin. Smooth sand the surface texture and clear coat. I’ve never tried this approach but might save time and a better part if executed well. Fabric peel ply perf and breather would need to be tailored extremely well so the least amount of print is left on the surface.

#11

Thank You! I don’t know why I didn’t think of using the quick set epoxy as you mentioned - that would really resolve my issues.

I had only used the vacuum bag because the carbon was floating up and not laying flat, especially on some non flat surfaces. Your method sounds way easier for what I am trying to accomplish and should allow me to do this much faster.