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Old 14-05-2008, 15:41   #1
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How to cut a Kevlar deck?

So, I just ordered 3 new offshore hatches. The trouble is that the required size for the cut out is approximately 8mm (5/16") bigger than the current hole. This is not a problem per-se; there is enough room. The problem is that the deck is kevlar and, where the hatches mount, not very thick.

The deck is about 4-5mm (5/32-3/16") thick, with 2 layers of Kevlar and a bit of fiberglass (and gelcoat on top). I'm just a bit worried about cutting it, since Kevlar is notoriously difficult to cut.

Optons under consideration at the moment are

Angle grinder with diamond cutting blade (for straights)
Jigsaw with fine toothed cutting blade (for radius')
Router (although this is tricky because ther is not really a big enough flat surface to work with).

Anyone have any experience with this type of work care to offer advice? Thanks.
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Old 14-05-2008, 16:31   #2
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I would start out by prefabricating a jig that is well secured to the boat that will guide your tools to exactly where you want to make the cut.
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Old 14-05-2008, 19:17   #3
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Jig saw will probably be easier to control, certainly easier than a router. If you look you might find very fine toothed jig saw blades for plastic. I've used them on lexan & plexy, fiberglass and carbon fiber. They should do a decent job on kevlar if you go slow. Mask off the area you want to cut because the baseplate of the jig saw will leave marks on the gelcoat.

Tape up some plastic sheet under your cutting area to prevent the kevlar dust from going everwhere. Respirator is a must cutting that stuff, it's nasty. The part you're cutting off isn't very wide. The deck might have a tendency to vibrate under the saw. If it gets out of control it might crack more gelcoat than you'd like. Make the long cuts first and leave the corners to last to support the cutoffs.

Good luck. Post some pics if you can.
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Old 14-05-2008, 19:31   #4
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Laminate Cutting Tools & Supplies - Fibre Glast Developments

Fibreglast has carbide saber saw blades and Kevlar router bits. Kevlar tends to leave a fuzzy edge when machined, you can get rid of most of the fuzz by wet sanding the edge with coarse wet sandpaper, say 40 grit. If the deck is thin, I might use the router bit, as the saber saw blade may vibrate and cause some cracking.
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Old 14-05-2008, 20:07   #5
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Don't cut it! Just center the hatch over the existing hole.
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Old 14-05-2008, 20:54   #6
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Quote:
Originally Posted by Joli View Post
Don't cut it! Just center the hatch over the existing hole.
It ain't that simple, the hatch flange is not flat, but, basically an angle section, so that it has a 25mm reveal (reveille?) that hangs down inside the hole.
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Old 14-05-2008, 22:53   #7
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Make a template and use a router.

Don't forget to re-gel the end of the exposed glass to seal it up.

-jim lee
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Old 15-05-2008, 02:53   #8
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I would be worried that """chater""" with the jigsaw might cause some delamination.
I'd probably go with the router
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Old 15-05-2008, 04:46   #9
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Ahhh. Makes things a bit more difficult. Can you exchange the hatchs for those that have a flat flange face? Also, is the deck flat or is there camber to contend with?

Quote:
Originally Posted by Weyalan View Post
It ain't that simple, the hatch flange is not flat, but, basically an angle section, so that it has a 25mm reveal (reveille?) that hangs down inside the hole.
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Old 15-05-2008, 05:17   #10
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There are some special router bits for cutting Kevlar (aramid) composites

CNC Routing Tools Catalog - solid wood and wood composite.

https://www.onsrud.com/xdoc/composites

I'd bet the diamond saw blade in your angle grinder would do a decent job on the straight runs.
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Old 15-05-2008, 16:20   #11
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Seems like its gonna be diamond wheel on a 4" angle-grinder for the straights and router with carbide bit for the corners... I'll let you know how I go (crosses fingers). Thanks for all the good advices.
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