Im currently making a bike frame as a non work related project and have the typical cheapo approach where im laying on top of a structual foam core. Ill be vac bagging carbon over the top of it in the next few weeks and then will be doing the dredded sanding to finish the outer surface off.
But, I can imagine the outer surface being up and down like the rockies just due to the nature of male tooling etc and the inevitable wrinkling from vac bagging it. I plan to debulk as much as possible to reduce wrinkles obviously, but has anyone any ideas to make the outer surface as smooth as possible and reduce effects of the bag/breather on the surface finish?
I basically dont have time to go making intensifiers as its a 1 off part, but would something like a 1-2mm silicone sheet below the breather help or something like that? Would it work in the tight corners and can you even get such a sheet?
thanks in advance
Try to cut the peel-ply to long narrow stripes and wrap it tightly on the laminate.
While doing this, try to avoid wrinkles of the laminate.
Thanks Roberto, Ill be doing that anyway, that’s for sure! I still think I would need some medium on the top of it though
You could shrink tape it instead of bagging it. Gives more control.
Shrink tape needs a lot of heat to do the job. And it’s a pain on the Y shaped parts.
shrink tape is pretty much a no go as the radii changes. it will always apply more pressure to the smaller radii and far less as the radii decreases.
the trick is carful lamination with minimal bulk and even more carful application of the bagging materials. you want to avoid any bagging material getting pulled into the “unavoidable” wrinkles in the bag itself. so slow vacuum while working it all out.
again, the neater and tighter your peel/release/breather, less will get pulled into the wrinkles.
also, the noob tendency is to over saturate the laminate with resin. this will worsen your issues as it adds bulk. so watch for this.
ps. shrink take can actually add more ugliness than bagging in my experience.
Nick,
Any photo’s of your peel ply, breather process, I’m alway’s looking for little hint’s to lessen the prospect of wrinkles. It’s been suggested to me to try making a latex form. I agree with the shrink tape comment. Sarto and Billato used to use some type of rubber to compact there joints with a finish layer once all the initial finish sanding was done. As Nick say’s, you always end up with compromised compaction on the sides of the joints.
For the record, Nick is the king of tube to tube bicycle construction, he has raised the bar over the years in both technique and finish.
Bill
Yeah, I think Shrink tape is a no-go due to the shape of the frame. Looks like its just coming down to a bit of careful lamination then.
thanks v much
hey mate, havent done a bike frame but made a chair (similar principle) a few years ago. bagged and bled the structural laminate, unis, then skimmed with microballoons then did a non bagged cosmetic wrap. may be a bit on the heavy side for what youre after but it did come out mint.
Shrink tape, yes Dunstone makes good shrink tape that is heat activated. I was thinking someone needs to make shrink tubing. this way no spiral print left on the composite finish… but perhaps there is a way to not have spiral print as a byproduct.
I would think by now a company will have invented a shrink tubing for composites. That would be ideal.
John Soller sells treated shrink tubing. http://www.solarcomposites.com/composites/carbon%20fiber%20sleeves.html#Shrink
It doesn’t consolidate as much as shrink tape. The only hard part I’ve had with it is getting the tube over the wet fabric without distorting the fabric. When you heat it you want to use a heat gun at first and start in the middle to “push” any air bubbles out the ends. Then you can put it into a oven for final cure.
You can get treated-for-composites heat shrink tubing up to 2" in diameter. Soller composites sells some.
The challenge with tubing is that the tubing itself can prevent the excess resin from escaping the system. If the tubing at the ends shrinks before the center (happens in an autoclave) then the resin in the center of the tube gets trapped. The tubing has to be shrunk from the center out. This can be carefully done with heat gun.
Dang, Rotorage, beat me by 7 minutes. 
thanks for the kind words Bill. i am not much of a shutter bug but would say the application of peel and breather should be as or more thoughtful as the prepreg itself.
Gotcha Nick, No substitute for experience and repetition. Generally speaking each one I do is better than the last, but I know I pick up so many ahaa moments looking at what others are doing.
Bill
…just throwing this out there, I have never done a bike before but I’ve used this technique with success. If it’s a round tube, cut a piece of PVC in half on a table saw, release the crap out of it, laminate then put the two halves on your tube, bag-it. Remove the pvc after cure. It may be more trouble than it’s worth, I don’t know.
not a bad idea! unfortunately my shapes arent round though - typical 
well again not seeing what your working with I don’t know if it’s possible but what about metal flashing. …or Mylar tape? or PTFE paper. also I’ve seen these plastic cutting boards they are paper thin, nothing should stick to them either and easy to cut, they would work in bigger area, but the smaller areas would still be a PITA I’m sure.