Cutting 80mm hole in fibreglass

[mordase]

Need to cut an 80mm diameter hole in a fibreglass panel moulding in the heads to fit a hot air duct outlet. Concerned that a hole saw may damage/splinter the fibreglass which is approx 5mm thick. Any advice would be very much welcome. Thanks.

 

[johnphilip]

Is it too obvious to ask if you can get to both sides of the hole with your drill? Drilling from each way once the pilot drill has set the centre should be straightforward

 

[sailorman]

cover the area with masking tape & cut slowly through the tape

 

[damo]

My method as follows.....

a) Get a proper 80mm hole cutter (not the horrible ones that fit into a slot)
b) Stick some thin ply over both sides the area you are going to cut (double-sided tape should do the trick)
c) Drill from each side towards the middle

The ply should help stop the gelcoat from splintering, especially if the initial contact with the saw is very gentle and the teeth are quite dull

 

[nimbusgb]

[ QUOTE ]
My method as follows.....

a) Get a proper 80mm hole cutter (not the horrible ones that fit into a slot)
b) Stick some thin ply over both sides the area you are going to cut (double-sided tape should do the trick)
c) Drill from each side towards the middle

The ply should help stop the gelcoat from splintering, especially if the initial contact with the saw is very gentle and the teeth are quite dull

[/ QUOTE ]

Starret or equivalent is what you are looking for.

To hold the ply really firmly in place you can screw through the ply into the glass in the area inside the 80 mm diameter

 

[roger]

Surely the flange on the heater outlet will cover a fair amount of splintering

 

[exfinnsailor]

Will be attempting same job next weekend .. Thought I might use a Dremil .. Used one at work for cutting holes in plastic boxes so with a new small cutter should do the job .. Like the idea of masking tape give you something to draw the hole on ..

 

[earlybird]

Assuming that you have adequate access, cut a hole rather less than 80mm dia. either by chain drilling or a hole saw. Use an abrasive flap-wheel in a drill to enlarge to a previously marked 80mm dia. line. This is quick, accurate and neat.

 

[tcm]

Um, 80millimetres is erm ooh over 3inches... the tip speed could be massive unless you have a really good low-speed drill. I would find a lump of fibreglass to try out on first?

Then, having found out that it'll be a right wrist-snapping mess, and/or that a decent hole saw exactly the right size costs loads even for just the one hole, I'd mark the hole first, rough it out undersize with a few smaller holes to get near enough, and then file and fit whatever you're planning to put there.

You still need to mask around the area with some stuck-down cardboard frinstance, cos the amateur filing type like me tends to let the file jump out of the hole and donk the fibreglass. But you can smooth those with rubbing compound, whereas a hole saw might dance about and wreck the heads in half a second.

 

[nimbusgb]

I have used a 110mm starrett hole saw in a hand held drill to cut f/g. No problems with a standard variable peed AEG drill.

 

[Strathglass]

A sharp hole saw will cut frp with no problems.
Use a very low speed.

I prefer to use a battery powered drill as I can limit the torque. This makes it much safer.

If you cannot get access to drill from both sides then you may require a backing piece. This can be a piece of say 12mm ply through bolted with three bolts at about 33mm radius centred on the final hole position. They will fit inside the cutter blade.

You can cover the outside face with masking tape if it has a gel coat finish, but I have never found this necessary with sharp blades.

Again - cut very slowly and hold the drill firmly.

Do not expect to cut many holes in frp with one blade.

Iain

 

[jimbouy]

I used a good quality hole saw when I fitted heating to my Centaur, which also has some thick old GRP to get through.

If you can go from both sides you will have a totally clean hole. But even if you go from the one side just don't expert to much pressure and you'll be fine.

The secret really is to get a good hole saw.


Jim

 

[maxi77]

Having just drilled a variety of larger holes in a variety of materials holesaws are the way to go. I used a 24V drill and even with the larger sizes with care there were no problems. If one is drilling from one side only some care is neaded at breakthrough but it is quite easy, with access from both sides perfect vevery time.