Model Boat Mayhem
Technical, Techniques, Hints, and Tips => GRP & Epoxy => Topic started by: timbo on September 16, 2015, 01:06:42 pm
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Can any body put me in the right direction for the best hole cutter for fiberglass, I need to cut two holes in the transom of my speedline Severn for the exhaust out lets, I have been to my local diy store but everything I find look to heavy duty.
Tim
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Timbo
What diameter are the holes? I have a tapered reamer which will cut from 4mm to 12mm dia if you drill a starter hole and take it steady. Here's a similar one http://www.sloughrc.com/default.asp?WPG=SRCM_HomePage1&itemid=5532820 (http://www.sloughrc.com/default.asp?WPG=SRCM_HomePage1&itemid=5532820)
Larger than that you could use a round or half-round file to open out the hole to the correct diameter.
Permagrit also market various files and rotary tools; I use their flat sanding blocks and they make light work of trimming GRP.
One useful tip is to put masking tape over the position of the hole. It makes marking out easier and stops the glass from chipping away as you cut the hole.
DM
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seconded on the tapered reamer a small 2mm hole is all thats needed to start it off
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Its got be a 28.5 mm hole
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Would a step drill do it?
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I would tape up the transom, mark the holes and chain drill around the circumference with a 1.5 or 2mm drill and finish off with a rounded file, offering up the exhaust fittings as I progressed.
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Would a step drill do it?
Drilling a hole that size in GRP you'd be asking for trouble with the resin chipping away. I'm 100% with Dougal on his method for big old 'oles.
DM
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I've worked with GRP a lot before retiring, a good quality hole saw is what we used. :-))
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Not that big a hole, tape up area and mark with compass. Use a Fret saw take it nice and easy with the cuts.
You'll need to drill a pilot hole to get started P38 will repair any chipping.
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Well first one done, used a step drill by hand, so far so good :-))
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That looks good Timbo.
Cutting holes in hulls can be very traumatic
and you have found a method you are
comfortable with. :-)) :-))
Ned
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Yep to right, just patience and it is paying off.
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Getting there
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Are you fitting electric or IC? I don't know if those exhausts are practical or not. If they are you may need a gap around it, they can get very hot and paint damage is likely, possibly grp resin burning too.
A hole saw can be used with finesse, but usually only good ones. There's some out there that are split cylinders, fine for plumbing the house but less so for fine work, others are not concentric to the pilot, or even not round. Drill the pilots hole first and then introduce the holesaw gently at high rpm, that prevents the saw smashing into the surface when the pilot goes through, and the speed stops it from grabbing. Chipping will only occur through being clumsy, control the saw and it is fine. If you can come in from both sides then a clean hole will result. Chatter can be avoided by applying a very slight angle. However, in the absence of a range of quality holesaws, or just not having the right size, I find a rough hole enlarged by a sanding drum in a Dremel gives neat controllable results. Filing can force delamination, it's great that it worked for you though. Any method needs caution.