Bike Forums

Bike Forums (http://www.bikeforums.net/forum.php)
-   Framebuilders (http://www.bikeforums.net/framebuilders/)
-   -   Stripping carbon? (http://www.bikeforums.net/framebuilders/929478-stripping-carbon.html)

Kimmo 01-11-14 04:39 PM

Stripping carbon?
 
Can anyone say with certainty what the best method is?

Soda blasting?

Mark Kelly 01-11-14 06:15 PM

Hand sanding.

In practice it's very easy to see where the finish ends and the carbon matrix begins.

Canaboo 01-11-14 11:54 PM

Definitely by hand. Why do you want to strip it? If you just want to refinish you are probably better off just taking the gloss off and smoothing any nicks rather than trying to get right down to the carbon unless the original coat is really flaky.

seankanary 01-12-14 05:43 AM

I was wondering this as well. I've hand sanded a fork just to prep for paint so nothing more than a quick scuff and squirt. Say I was to have a frame with a bad paint job and I wanted to have it as just a satin clear coat, what grit paper should I go? Start with 220, finish with 500? Finer? Sorry for the hijack btw.

Kimmo 01-12-14 07:20 AM

1 Attachment(s)
Why no blasting? Surely there's a blasting medium that's okay for carbon.

The decals and red have to go.

http://bikeforums.net/attachment.php...hmentid=359208

And I think so does the clear, because I want to do a tricky half-silver clear over it and remains of the old clearcoat could conceivably interfere with the finish.

Andrew R Stewart 01-12-14 09:30 AM

I think the issue is that the media that cuts the paint layers will also attack the epoxy that's part of the carbon layer. And with a power tool the ability to discern when this boarder (between paint and body) is a hard skill to get right every square inch.

What type of paint are you considering using that would have a reaction with the original? Why couldn't just spray primer over the hand sanded surface? And then do a paint job as usual? Seems to me (and I don't play a painter even in my dreams but did pretend many years ago) that the more complex the top coats get the more prep and consideration the under coats need. Andy.

Kimmo 01-12-14 10:25 AM

It occurred to me that epoxy is precious little harder than paint, but I see ads for soda blasting saying it won't harm plastic and fibreglass...

But anyway, when you think about it, carbon itself is appreciably tougher than epoxy and there's a 3k weave pressed hard against the surface, so even if the outer layer of epoxy was removed I doubt that'd matter with paint in its place...

I'd say with the right blasting medium it should be easier to do without damaging the carbon than by sanding... I want to preserve the weave (ie not start to go through it at all), because I want to paint it a translucent silver, to kinda match a polished and grey-anodised frame. I'm thinking any traces of the original clear might be visible, I dunno.

Going for a trick yet subtle look that'd be totally compromised by a half-arsed job. So I guess nobody has any inside info on how Calfee strips carbon to do repairs?

reddog3 01-12-14 11:16 AM

If you're looking for the easy way out I can almost guarantee it's going to turn out a mess. Get out the sandpaper and spend a couple evenings- it's only time. I strip a lot of carbon parts of their logos and ugly graphics (by hand) and it's well worth the effort.

Some carbon parts have the logos and graphics applied on top of the clear. Others have them buried underneath loads of clear. You think at the outset that you'll never get there, but a couple hours later you've almost got a "bare" part. It's the last remains of the graphics that are tough, and the temptation to sand only these areas is strong. Resist. Continue to sand evenly or you'll likely end up cutting through the clear under the logos. Most have a clearcoat- graphics, and more clear.

Some of the logos are applied very heavy, and you'll be able to feel those in the finish. Then I use a sanding block to even out the surface. A lot of the time the logo is "almost" completely removed. Then I sand the entire surface evenly being careful not to cut through to the carbon. Recoating is usually not necessary, unless you want to add color. I start with 320 "wet." Finish with a dull piece of 500 "wet" and it's as smooth as you'll need for either color, more clear, or polishing.

When blasting it would be tempting to remove the logos/graphics first, at which point you'll be sanding anyway to flatten the surface. Quit being lazy. Go buy a piece of sandpaper. It'll last through several forks.

Canaboo 01-12-14 06:00 PM

I wouldn't say carbon is tougher than epoxy... Carbon on its own will turn to dust if you look at it wrong.
You can readily find pictures of a Calfee carbon repair but that's not the same as what you want to do.
They have to grind/sand away all the damage and feather the edges to the old finish. The very perimeter of the repair is about what you want to do to the whole frame.

Kimmo 01-12-14 09:25 PM

Quote:

Originally Posted by reddog3 (Post 16404148)
If you're looking for the easy way out I can almost guarantee it's going to turn out a mess.

No, I've stripped carbon before, and found it difficult to ensure I wasn't sanding into the carbon; NBD with a UD finish or if it's getting a solid colour, but it totally spoils a weave.

Discovered that I could scrape down to the carbon pretty reliably with a sharp blade at just the right angle, which is when you can feel the carbon being tougher than epoxy... but that's a bit too sketchy here; this fork cost me $400 (it's 1").

Canaboo 01-12-14 10:09 PM

That's the carbon/epoxy matrix you are hitting. It's not one or the other. Scrape a piece of dry carbon and then scrape a block of epoxy if you want to compare toughness.

Mark Kelly 01-12-14 10:37 PM

Quote:

Originally Posted by Canaboo (Post 16405715)
That's the carbon/epoxy matrix

It would help if we used the recognised terminology. The carbon fibres and the epoxy matrix (and the interface between them) make a carbon epoxy composite.

Kimmo 01-12-14 10:43 PM

Quote:

Originally Posted by Canaboo (Post 16405715)
if you want to compare toughness

Have you ever done anything destructive with carbon?

This is in the context of possible blasting, where the removal of any surface epoxy isn't a concern so long as the carbon isn't damaged. Presumably this would lead to a slightly textured surface as the weave isn't going to be perfectly flat despite the pressure that was on it when it was fixed, but obviously the paint can be sanded smooth instead.

The point of this thread is to determine the optimum stripping method, not so much getting into the idle speculation and tedious argument...

Canaboo 01-12-14 11:20 PM

[QUOTE=Kimmo;16405808]Have you ever done anything destructive with carbon?

[QUOTE]
Well I have to sand down the carbon lugs on my bamboo bikes so you could say I have probably destroyed far more carbon than most.. I've also re-finished several where I had to remove clear coat on top of carbon.
I think you may find that most carbon frames are not actually coated in epoxy but rather just clear coat.
The carbon epoxy composite of a commercial frame is going to be as smooth as the inside of the mold it was formed in. The weave won't actually have texture.
However I don't think my experience is telling you what you want to hear so I'll step aside now and let the experts advise you.

Mark Kelly 01-12-14 11:42 PM

Quote:

Originally Posted by Kimmo (Post 16405808)
The point of this thread is to determine the optimum stripping method,

Hand sanding.

Kimmo 01-13-14 02:44 AM

Quote:

Originally Posted by Canaboo (Post 16405888)
The weave won't actually have texture.

It certainly won't if you sand it... but since we're talking about a twill of clumps of fibres that are more than 0.00mm thick, there have to be low spots filled with resin every place weft emerges from under warp and vice versa. Trek's OCLV doesn't stand for Optimum Compaction, No Void. I used to work at a joint where we made carbon yacht masts, and I've seen surface voids follow the twill pattern.

Seems reasonable to assume even the most optimal choice of blasting medium might remove these bits of epoxy along with the paint...

But anyway, I'm perfectly happy to sand if the consensus is that there's little chance the remaining clear (I don't fancy my chances of sanding it all off down to the surface and stopping there nice and even over the whole fork) will show through under a tinted clear - that means one less challenge, I don't have to find someone to blast it.

Canaboo 01-13-14 09:41 AM

The key is that the little "divots" in the weave should be filled with resin so that the surface is smooth, the same way a fiberglassed wooden boat should appear smooth.
I actually assumed the low void part of OCLV meant a low number of air voids rather than voids with excess resin. Cut up a few carbon frames and you will surprised how many air gaps there are in the matrix of fibers. That includes an OCLV frame.
You seem to be set on the idea that blasting a carbon composite will selectively remove all those little dots of epoxy in the weave and leave the higher spots of carbon alone because they are "'tougher". Carbon really does have exceptionally poor abrasive resistance. Really.

fietsbob 01-13-14 12:21 PM

Seems , U just dont like the fork company logo & paint highlight?

Yea I'd like an advertising payment, like google,
every-time a brand name on my stuff was seen.

problems over lettering and Color,

just get it painted Black , Mick jagger..

a small 600 grit wet-sanding , like done between paint coats in the auto painting

Your Corvette , Ferrari or McClaren is what the procedure is..

Kimmo 01-13-14 03:33 PM

1 Attachment(s)
Canaboo, I kinda fudged 'void' interchangeably there to save on grammar, but anyway it's pointless conjecture in the absence of someone who can tell me about throwing bits of walnut shell or whatever at it. If you google up some blasting sites, they claim to be able to blast all kinds of stuff with different media...

This isn't just some boring fiets, Bob. This is a hotrod, and the finish is the toughest part.

http://bikeforums.net/attachment.php...hmentid=359529

This won't do.

MassiveD 01-13-14 03:51 PM

I've never blasted, but I don't see the problem. The process just needs to be dialed down to where it isn't cutting too fast. When the decals are gone there is always lots of overcoating, and epoxy to go. You can screw it up by hand or with power. The only difference is that with blasting the medial is always fresh, with paper it wears and may load so it isn't as consistent. I have abraded lot of stuff right into the carbon, to get a better bond. The carbon is easier to sand than epoxy alone, or not so much different that one notices, but I would say easier.

Andrew R Stewart 01-13-14 10:45 PM

Every blasting tool i've used has had a variation in the pressure and media stream/density of media in the stream. Andy.

Kimmo 01-14-14 02:10 AM

Let's say I sand it, and here and there I've gone through the clear.

Is there any chance that would show through a tinted clear above it?

fietsbob 01-14-14 02:12 AM

Any chance? no guarantees ..

Andrew R Stewart 01-14-14 08:04 AM

Kimmo- Why don't you just plan of applying a base coat of clear before going onto your "color/top" coat? Andy.

Kimmo 01-19-14 09:08 PM

Hey, I guess that'd minimise it.


All times are GMT -6. The time now is 01:37 PM.