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Old 16-03-2021, 08:22   #1
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Cutting Kevlar

I want to cut openings for deck lockers on my foredeck.
Construction is Kevlar over Nomex.

On a previous project to install a gas locker the (expensive) metal saw blade I used was dull after a single cut.
The cut edges were frilled with Kevlar stubble requiring shaving (safety razor) before laminating.

Does anyone have a technique for cutting Kevlar?
I'm considering a diamond tipped dry masonry blade and would welcome suggestions.
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Old 16-03-2021, 08:48   #2
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Re: Cutting Kevlar

I used a hot knife. Kevlar is very hard to work with, it wants to stay wrinkly even with a lot of resin, it was on a skiff where the skiff keel met the trailer bow stop. For deck lockers I do not see the point of using kevlar, which is great for abrasion resistance or maybe to stop bullets but why not use plain old fiberglass cloth and chop strand mat so much easier.
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Old 16-03-2021, 09:20   #3
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Re: Cutting Kevlar

The Kevlar that needs cutting is the existing deck structure.
(Kevlar over Nomex)
I need to cut a squarish hole to create lids.

Circular saw for the long cuts jig saw for the corners would be my weapons of choice.

P.S. Using lots of resin is not the solution for the wrinkles.
Prepreg and / or vacuum bagging is better.
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Old 16-03-2021, 09:35   #4
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Re: Cutting Kevlar

Haven't used them on Kevlar, but diamond cutting blades seem to work better than carbide tipped on fiberglass.

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Old 16-03-2021, 10:08   #5
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Re: Cutting Kevlar

Well that is a different matter, cutting through the deck and not fashioning a hatch. You are going to dull some blades, preferably diamond blades.

We will all be impressed by your skills if you vacuum infuse resin at home. Just the vacuum pump alone for a DIY runs $300+. It would be fun to experiment with that and I confess I have daydreamed of making carbon fiber hatches or car hoods with vacuum bagging. At least with those projects you can visually confirm the material is adequately wetted out, unlike a hull where you have to trust the engineers and workers get it right.
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Old 16-03-2021, 14:09   #6
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Re: Cutting Kevlar

Have you tried Carbide blades in a saber saw?? Don't know if it will work on Kevlar but solved the problem with quickly worn out blades cutting holes for ports in fiberglass. Could only get through about 1/2 an opening before regular steel sabre saw blades got so dull they would only cut with great force pushing the saw. A fiberglass glass guy in the yard saw me struggling and said to get a carbide blade. Finished cutting the rest of the ports with that blade and it's still in my blade storage compartment waiting for the next cut.
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Old 16-03-2021, 14:58   #7
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Re: Cutting Kevlar

Agricultural vaccum pumps for milking cows have successfully been repurposed for vaccum bagging.

You do not need a 300$ pump for it. I have for example successfully made a dolphin striker and mast foot for an 8m racing cat in the past, the pump was about 100.

Btw. Kevlar wrinkles because it's got a low density and tends to "float" in the resin when hand laminating it.
Besides vaccum bagging you can sometimes improvise by cutting the cloth larger and duck tapping all edges, than strapping it down with tape.

Cut Kevlar cloth with serrated scissors.

When you use Kevlar put a 100g/m2 glass cloth on top, when finishing you abrade the glass not the Kevlar.

Last not least, diamond blades are the way to cut fully cured Kevlar. If it's semi cured you can sometimes cut it with a razor knife.
Avoid any cutting method which lifts/pulls up and away from the surface when cutting it. Sabbersaw is not great, angle grinder is better.

Kevlar is quite heat resistant, a hot knife does not work very well with it.

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Originally Posted by Azul View Post
Well that is a different matter, cutting through the deck and not fashioning a hatch. You are going to dull some blades, preferably diamond blades.

We will all be impressed by your skills if you vacuum infuse resin at home. Just the vacuum pump alone for a DIY runs $300+. It would be fun to experiment with that and I confess I have daydreamed of making carbon fiber hatches or car hoods with vacuum bagging. At least with those projects you can visually confirm the material is adequately wetted out, unlike a hull where you have to trust the engineers and workers get it right.
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Old 16-03-2021, 15:29   #8
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Re: Cutting Kevlar

I use a saber saw with grit blades to but kevlar composites. They're marketed as "ceramic cutting" blades; they have no teeth, only grit strongly blued to the leading edge of the blade.
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Old 16-03-2021, 16:04   #9
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Re: Cutting Kevlar

had pretty good results with carbide tipped composite cutting jigsaw blades like these long ones 100mm,see link
or the ceramic cutting blades but much slower,and the blades are quite short if there are more layers of core than 50mm
https://www.ebay.co.uk/itm/153660585...0aAiRDEALw_wcB
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Old 16-03-2021, 16:08   #10
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Re: Cutting Kevlar

https://www.fiudi.com/?product=discs-cut-grind
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Old 16-03-2021, 17:17   #11
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Re: Cutting Kevlar

My vacuum bagging setup is based on a 40$US surplus store Gast fractional hp pump. It's not infusion but if you weigh cloth and resin you can get pretty close without much wasted resin.

Beware of pumps that known to spray oil out of their output ports, cheap A/C service pumps and recycled fridge pumps and the like.

The key is to have no holes in the bag or in the mastic on the seams.
I prefer 'real' bag film, breather, peel and perf ply, vacuum port, and mastic (butyl) versus garbage bags, paper towels, fabric, mustard bottle lids, and masking tape that is sometimes used by people to 'get by'. The few extra dollars per projects is worth it.
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