I am going to skin an existing panel and want to create the symmetrical matching effect down the middle.  As I am using dry carbon fibre how do you cut and align the edges to ensure you can get a perfect match. 

I was thinking of using some very light tack tape to hold the weave whilst I cut the carbon to size (Otherwise it just frays and you end up with loose strands).  Once I have applied the base coat and its got tacky, then lay on the carbon and pull off the tape.

Is there any other way this could be done ?

I would not use tape. It's unlikely that you don't mess up the cloth while removing it. Or the adhesive strength is so low, that it doesn't protect the cloth from fraying.
If you work positive, I would get a light glass cloth like 100g and spraytack it to the back of our carbon cloth. And then just leave it there.

Along similar lines to MarkMK's suggestion is to use some hairspray onto the dry carbon fabric before you attempt to cut it. Whilst this wouldn't exactly be best practice in structural situations it does work well when you're more concerned with the cosmetics (such as in this case). This was something that we did sometimes for some of the Carbon Mods products that we made when we needed to get a neat 'prepreg-like' cut line in the fabric. As others have suggested, using a 240g carbon cloth helps too as the tows are more closely packed and so the fabric is naturally more stable, a combination of the two should give you a material which you can get a good sharp edge on.

Have you considered using our ProFinish stabilised carbon fibre cloth? - This is designed specifically for this purpose and already features a binder which lots the tows in the fabric and makes it perfectly cut-able.

I hope this helps.

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Thanks for all the replies guys.

As its only cosmetic, I think a little bit of hair spray will do the trick. (I'll pitch some off the missus when she's not looking).

I will check what carbon I have ordered previously, if i haven't got the profinish I might think of getting some.

Lenny. To get a symmetrical patern similar to what I think you are trying to achieve I would use the 220 profinish. I find this gives a more marked patern. I give just a flash of adhesive where I want the joint and makes it easier to position. Across the joint I have used 3 or 5 rows of cf tow again with a whiff of adhesive on to stop it fraying. As an alternative to the adhesive I have used some clear transparent tape just overlapping the last row I want to use and cut to this. It goes tape down so it doesn’t show.

When this is given a good polish finish it looks fantastic.

Best of luck on the learning curve.