Carbon question

[Anonymous]

Allow me to show my ignorance regarding carbon fiber 😯 I saw somewhere that someone was selling “carbon shears”. Is carbon fabric that incredibly tough to cut? I was thinking it was more like fiberglass and less like Kevlar?

I’ve never laid up any carbon. I’m going to use some for my M altitude attempt.

JW

[Doug GerrardParticipant]

I use Fiskar’s scissors. I like to seal the edge with CA first but I’ve had no problem cutting it.

Doug

[Ken PlattnerParticipant]

I use something similar but they are kitchen shears – heavy duty and they cut through CF with ease.

[Art HoagParticipant]

A good sharp pair of scissors will do just fine.

Art

[Warren B. MusselmanModerator]

I use a “pizza cutter” for fabric, a steel staightedge, and a cutting mat and get perfect cuts everytime. If you put anything on the cut edge to hold the fabric together like CA or Fray-Check, the epoxy will not absorb there so make sure you cut plenty of overlap so that you can trim off all edges that you use CA or Fray-Check on. John, you’ve laid up some carbon with me if I recall right – weren’t you there when I laid up the UprOar fins?

Warren

[Bruce R. Schaefer]

I use a pair of “scissors” that will cut pennies… or a pair of garage scissors that are not exactly sharp. Just hold the fiber and cut at 90 degrees, just try not to fray it. No big deal. Warren, my wife has a number of those cutters with replacement blades… hmmmm…

[Anonymous]

John, you’ve laid up some carbon with me if I recall right – weren’t you there when I laid up the UprOar fins?

Warren

I was there to wet the fabric and apply the material, but was not there when it was cut.

My plan is to do this:

– lay a strip perhaps 1.00-1.50″ wide over the fillet
– lay a piece that is a bit wider on top of that
– lay one last piece that goes tip to tip

I’m still wrestling with whether to go all carbon or use some glass. Also, I have always gone with the LARGEST piece of fabric first, then gone with the next largest, and so on – ending up with the smallest piece going on last. I may still do that. I haven’t lost a fin yet, and I’ve built over a dozen minimum diameter rockets this way. I am aware most folks start with the smaller pieces and then go with the next largest and end up putting on the largest piece last. I, personally, have never done it that way.

These fins are really tiny. They are also pretty thin. This will be my first mach 2 attempt. I want them to stay on 😮

[Art HoagParticipant]

John, either of the orders in which you decide to lay up your fabric won’t make a real difference as far as structure goes. It would make it a lot easier to finish if you start with the smallest layer and go to the biggest layer last, it will also look better

I would consider one thin layer of glass over the top of your carbon for sanding purposes only. That way the fins can be sanded and shaped without cutting into the structure of the carbon fiber.

Art

[Anonymous]

Good advice, Art – I’m going to feel bad if I cover this stuff up with primer 😯 That said, I’m going to go all out for performance here. I’d rather have it go a wee bit higher vs. looking pretty.

I’m using convolute wound glass for the airframe.

I’d like to set a TRA altitude record (so that Tony can break it shortly thereafter…)

[Chris LaPanse]

Carbon is very similar to fiberglass in ease of cutting (kevlar is a pain in the rear), but from my experience it does fray more easily than any glass I’ve worked with. Be careful of the stray fibers, and you shouldn’t have any trouble. The harder part is knowing when it is fully wet out – unlike glass, there is no obvious transition, you just sort of wet it until it looks good.

[Author]

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