Whats the best method of cutting into GRP

[Thepipdoc]

I want to cut a rectangular hole in my dashboard to fit a battery monitor. Should I use a fine bladed jigsaw or is there another/better way?

 

[dovekie]

You can get carbide edged blades for jigsaws, which will do a neat job. Metal and wood cutting blades will blunt quite quickly and then cutting is slow, and less accurate.

 

[Pete7]

Angle grinder if you have a steady hand, Dremmel circular cutter is another option.

Pete

 

[saxonpirate]

I want to cut a rectangular hole in my dashboard to fit a battery monitor. Should I use a fine bladed jigsaw or is there another/better way?

As has been mentioned you can get carbide tipped blades for cutting GRP but they are expensive and not much good for anything else. I always use fine metal cutting blades at slow speed. GRP is very abrasive so the blade/s won't last that long, but I should imagine for the amount you'll have to cut and where you'll be cutting a couple will be fine.

Just be careful if you need a neat edge that can't be covered because the jigsaw blade is an upward cut and will chip gelcoat if present. Don't forget to wear a mask because the dust is dangerous and also itches like hell.....

 

[Matata]

I do lots of fine GRP work and those Dremel drums are wonderful for detailing. Keep a snorky vacuum cleaner beside you and wear a mask even for small jobs. I'd drill a hole at one corner of the template to get the job started and then use a Dremel router to continue or a jig saw. Nik

 

[Thepipdoc]

Thnks all.
I never thought of the Dremel. I have one of these little beauties so I reckon a dremel it is!

 

[Watson47]

Thepipdoc ... if your GRP has a smooth finish / gel coat, then mark the cutting line with a new craft knife blade / Stanley blade with a reasonable amount of pressure. This helps protect the gel coat edge from chipping.

In some cases it can also be beneficial to approximately mark out the cuttling lines - place masking tape centrally over these lines. Remark template cutting lines exactly with pencil on the masking tape and then cut with the craft / Stanley blade. Cut with slow speed, fine tooth jigsaw and carefully remove masking tape.

Then brew up cuppa & admire work ....

 

[Poignard]

You can get downward cutting jigsaw blades, I have some. But I don't know if they have tct blades and I ain't inclined to go out to the garage in the cold to find out just now

 

[Bobobolinsky]

You can get down cutting blades for jigsaws, for cutting laminates, just not from the likes of B&Q

 

[saxonpirate]

You can get down cutting blades for jigsaws, for cutting laminates, just not from the likes of B&Q

Your dead right you can get downward cutting blades but the pitch and blade width is not a lot of good for cutting GRP....I've tried em!

I tend to save up all my old blades (Bosh) metal, wood etc just for GRP jobs. They always come in handy.

 

[Ubergeekian]

Angle grinder if you have a steady hand...

Better still - imho - is a die grinder. Which for those who don't know, is like an angle grinder sized Dremel. Stick a 1/4" TC milling cutter in the collet chuck and you're away.

Last time I had to do something like this was a couple of big round holes for hatches into my dinghy's buoyancy compartments. Multiple holes with an electric drill and then a hole enlarger - like a drill but actually designed to cut sideways - did a very neat and very quick job.

 

[savageseadog]

You can use a Fein Multimaster (or one of the cheaper equivalents) with diamond blade or a diamond rotary blade in anything from a Dremel type tool to an angle grinder

 

[gjgm]

I want to cut a rectangular hole in my dashboard to fit a battery monitor. Should I use a fine bladed jigsaw or is there another/better way?

Rotozip. There was a clone too at one time. One of those tools you dont use very often but when you do..!!
Especially good as you preset the cutting depth, so nasty surprises.

 

[Egbod]

cutting GRP

I have done this with a Bosch PMF 180 E Multi. The machine takes a circular cutter with a bite taken out of it. The cutter is an extra - HM-Riff segment saw blade ACZ 85 RT (about £20 ). The edge has tungsten carbide bits on it. The blade moves (rotates) a few degrees one way and then moves back so it has a vibrating action.

This is brilliant. It is very controlable and cuts into the corners. A huge bonus is that the waste just falls down- it is NOT thrown everywhere by a rotating blade as in a grinder. I made several cuts inside the cabin. To start with I wore eye protection and face mask- I dispensed with those after the first cut and just vacuumed after every cut.

 

[prv]

You can use a Fein Multimaster (or one of the cheaper equivalents) with diamond blade

Yep - I saw the thread title and came here to say "no question - a multimaster clone". Obviously from the other replies there is some question

Last winter I had to make various cutouts, some in quite constricted places, and the Aldi multimaster-alike was by far the most effective way I could think of doing them.

I didn't use a diamond blade, just the normal fairly fine blades (both semicircle and plunge) that came with it.

or a diamond rotary blade in anything from a Dremel type tool to an angle grinder

It doesn't seem to be possible to buy a plain rotary saw for a Dremel in this country any more - I presume it falls foul of PUWER regs or similar. I've seen them for sale in the US. Here you can get a contraption like a handheld circular saw that plugs on the nose of a Dremel, but it looks a bit awkward to use in confined spaces.

Pete

 

[savageseadog]

Yes, I've used a Multimaster to do the same job on ceramic tiles. The blade I used may have been tungsten carbide or diamond, I'm not sure, obviously either type would do GRP and it's interesting to know the normal cutters will work on GRP. The big bonus with this type of tool is that although there's still dust it isn't blasted everywhere with a rotating disc, much safer too.

I have a small die grinder type air tool with a small diamond disc for difficult access work.

 

[Graham_Wright]

Easy;- ceramic cutting jigsaw blade. B&Q and they are cheap and last well.

 

[Cloven]

As has been mentioned you can get carbide tipped blades for cutting GRP but they are expensive and not much good for anything else. I always use fine metal cutting blades at slow speed. GRP is very abrasive so the blade/s won't last that long, but I should imagine for the amount you'll have to cut and where you'll be cutting a couple will be fine.

Just be careful if you need a neat edge that can't be covered because the jigsaw blade is an upward cut and will chip gelcoat if present. Don't forget to wear a mask because the dust is dangerous and also itches like hell.....

It is possible to get downward cutting jigsaw blades made for cutting laminate so less chance of splintering. However, you have to hold the jigsaw firmly down on the work-piece as it doesn't pull itself onto the surface as with upward cutting blades.

 

[saxonpirate]

It is possible to get downward cutting jigsaw blades made for cutting laminate so less chance of splintering. However, you have to hold the jigsaw firmly down on the work-piece as it doesn't pull itself onto the surface as with upward cutting blades.

Dave I've already mentioned these blades in an earlier post I think you'll find...

 

[aslabend]

I have done this with a Bosch PMF 180 E Multi......

I'll second that, they are very useful for plunge cuts and more controllable than a rotating blade.