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Author Topic: Cutting Holes in GRP  (Read 8461 times)

GaryM

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Cutting Holes in GRP
« on: June 08, 2008, 12:55:24 am »

Hi
I have to cut several holes (10mm approx. in dia.) in the hull for 'freeing ports' etc. 
After cutting holes for the running gear, I've found that the GRP 'chips' allot when drilling. 
I have a Dremel with a conical grinding bit, which I used for the running gear to open out the holes and was OK for this, as I could 'fill' the gap.
With the freeing ports I'm concerned that using the grinding bit will leave a 'tapered' hole and the inserts will not fit flush.
Any thoughts?

regards
Gary :)
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HS93 (RIP)

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Re: Cutting Holes in GRP
« Reply #1 on: June 08, 2008, 01:06:58 am »

If you drill a pilot hole you can use a round file , or drill a pilot hole and use your grinder from behind that will leave a nice vee to glue the port in with epoxy and you can Finnish flush , if you are going to file use a fine indelible pen to mark the hole and file to size,these pens make good markers for modeling these can de used on glass fiberglass good on metal/ brass

Staedtler Lumocolor 319 black permanent
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GaryM

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Re: Cutting Holes in GRP
« Reply #2 on: June 08, 2008, 01:20:51 am »

Thanks HS93

Gary
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barryfoote

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Re: Cutting Holes in GRP
« Reply #3 on: June 08, 2008, 07:38:37 am »

Gary,

Another way is to drill a series of holes....Start with the smallest drill you have and gradually increase until the hole is just smaller than required. Then finish with a file as HS93 suggests.

Barry
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nhp651

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Re: Cutting Holes in GRP
« Reply #4 on: June 08, 2008, 09:29:22 am »

if you want to get away with drilling without chipping, place masking tape over the area to be cut out, draw on the size of hole, and in your case use a 5mm drill bit in the centre of the area. then take a piece of what ever sanding paper you use( I use the yellow and green stuff from builders merchants sold on a roll at 40, 60 and 100 grade) and roll it very tightly around a piece of metal rod of about 1.8 mm dia until you have a round tube about 4 inches long and just diameter enough to go through the drill hole. then file out to your heart's content, getting a very smooth and none chipped edge to the whole recess.
lot cheeper than knackering your needle files with a grp compound that is basically what it is.... glass, and very hard in constituency.
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HS93 (RIP)

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Re: Cutting Holes in GRP
« Reply #5 on: June 08, 2008, 10:01:59 am »

Just a quick one on files , I use round files from B+Q designed for chain saw sharpening as they are are parallel , so once you get them in the pilot hole 1/4"  they do not jam, also they are only about £3  with a moulded in handle. also try to only put pressure on in the push strokefrom the face the gel coat side.

Hs93
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nhp651

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Re: Cutting Holes in GRP
« Reply #6 on: June 08, 2008, 02:57:58 pm »

Iuse those files too and very good they are, but for repetative work on grp soon become clogged and blunt because of their fine teeth.
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GaryM

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Re: Cutting Holes in GRP
« Reply #7 on: June 08, 2008, 09:02:56 pm »

Thanks Barry,NHP651 and HS93
I agree the needle files clog far too easily, I'll try the drill and sand paper method first.
When I was a pantographer / die sinker I used to have a tapered reamer which would have been ideal, as it only took a thin sliver of metal off at a time.

regards
Gary :)
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Bryan Young

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Re: Cutting Holes in GRP
« Reply #8 on: June 12, 2008, 12:45:10 pm »

Iuse those files too and very good they are, but for repetative work on grp soon become clogged and blunt because of their fine teeth.
File "de-cloggers" are available from decent tool shops...but in general I find a brass "suede" brush adequate. Only about 80p.
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Notes from a simple seaman

john54

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Re: Cutting Holes in GRP
« Reply #9 on: June 12, 2008, 08:00:07 pm »

Run the drill in reverse to get through the gel coat then off you go !
Done this many times without any chiping  O0
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justboatonic

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Re: Cutting Holes in GRP
« Reply #10 on: June 13, 2008, 10:37:52 pm »

If using a file to open up a hole, dont use the file on the 'in' and 'out' stroke (oo, er missus  {-)) Just use the file from the outside of the hull going into the hole. Also as has been mentioned, place some masking tape on the gel coat side of the hull and like the file, always go from the outside in.
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GaryM

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Re: Cutting Holes in GRP
« Reply #11 on: June 15, 2008, 10:49:16 pm »

Thanks Bryan - I have a brass brush and it does work good at DE clogging.
Thanks John54 and Justboatonic. 
I'm going to have a go soon - just keep on finding 'other things' to do first, and worried I'll end up with an oval hole!
(I have the small "needle files")

Has anyone had a go with a conical reamer?  I bought one from B & Q (2mm point dia to 10mm dia) hardened steel - fits into the drill chuck?

regards
Gary :)
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Tug-Kenny RIP

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Re: Cutting Holes in GRP
« Reply #12 on: June 17, 2008, 10:25:22 pm »


Yes Gary. 

It's great. I find this does not damage the gell coat if used on slow speed. Mine is in steps so there is no choice of gradually increasing the hole size, rather, it jumps up to the next diameter.
Hope this helps

Ken
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GaryM

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Re: Cutting Holes in GRP
« Reply #13 on: June 17, 2008, 10:29:50 pm »

Thanks Ken
The one I got was from B&Q "Bosch" 4 bits, the conical reamer has curvy edges from the point to the bottom.

regards
Gary :)
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sheerline

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Re: Cutting Holes in GRP
« Reply #14 on: June 18, 2008, 12:00:52 pm »

One way to prevent your needle files from clogging up with GRP is to keep it wetted with paraffin. Weve done a lot of this kind of thing and copious amounts fo paraffin will allow the file to stay clean and each time you dip it into the liquid the residue just floats off. An added bonus is that the GRP dust ends up as a wetted paste so a wipe with a cloth saves you blowing the dust around which is not good stuff to have airborne. Give it a try, it works for me. O0
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GaryM

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Re: Cutting Holes in GRP
« Reply #15 on: June 18, 2008, 07:26:07 pm »

Thanks Sheerline sounds good, I'll give it a go.

regards
Gary :)
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