What's the best holesaw for GRP (acrylic bath and GRP header tank)?

I'm building up a set of the Bosch holesaws but I'm worried they may either
chip GRP or the GRP will destroy the saw teeth. Are they OK or would a grit
edged one be better, eg:

http://www.toolstation.com/shop/Powe.../sd1530/p73155

or would one of these be better:

http://www.screwfix.com/prods/43887/...n-Holesaw-20mm

?

I have to ask because in both cases I cannot afford *any* mistakes(!)

Cheers

Tim

In article ,
Tim S wrote:
What's the best holesaw for GRP (acrylic bath and GRP header tank)?

I'm building up a set of the Bosch holesaws but I'm worried they may
either chip GRP or the GRP will destroy the saw teeth. Are they OK or
would a grit edged one be better, eg:

I used an ordinary (bi metal) one to cut holes in the grp bumper on my old
Rover for reverse sensors and it gave a perfect hole. I'd say it would be
ok on acrylic too - but keep the speed very low to avoid melting it.
Perhaps lubricate with water.

--
*I don't have a license to kill, but I do have a learner's permit.

Dave Plowman London SW
To e-mail, change noise into sound.

Tim S wrote:
What's the best holesaw for GRP (acrylic bath and GRP header tank)?

I have to ask because in both cases I cannot afford *any* mistakes(!)

I have used the standard BiMetal ones and they worked fine on a GRP
bath. Also with baths, most fittings will be designed with a flange that
would cover any chipping anyway.

--
Cheers,

John.

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Before you go mad on holesaws, consider a step drill?

They are a round drill thus avoid the 3-sided hole of normal drills
and self-centre so if you centre-drill a hole to begin with they do a
very good job of ensuring the resulting hole is where you want it. The
downside is their depth is limited to about 4.5mm (it varies, just
look at the engineering drawing of the tool if available). Wonderful
tools for enclosures, glass reinforced polyester, ABS, polycarbonate
etc.

js.b1 wibbled:

Before you go mad on holesaws, consider a step drill?

They are a round drill thus avoid the 3-sided hole of normal drills
and self-centre so if you centre-drill a hole to begin with they do a
very good job of ensuring the resulting hole is where you want it. The
downside is their depth is limited to about 4.5mm (it varies, just
look at the engineering drawing of the tool if available). Wonderful
tools for enclosures, glass reinforced polyester, ABS, polycarbonate
etc.

Thanks to you and John. My holesaws are bi-metal and in addition to Dave's
suggestion of water as a coolant, the bloke in Screwfix who's keen on kit
cars (much fibre glass) recommended applying tape over the surface too to
avoid chipping.

On the step drill front - I've never used on but it also sounds
interesting - I'll have a look into this.

Cheers

Tim

In article ,
Tim S wrote:
Thanks to you and John. My holesaws are bi-metal and in addition to
Dave's suggestion of water as a coolant, the bloke in Screwfix who's
keen on kit cars (much fibre glass) recommended applying tape over the
surface too to avoid chipping.

Again if you use a slow speed and don't push too hard grp shouldn't chip.
But as was said whatever you're fitting to it will have a flange to cover
the hole edge.

On the step drill front - I've never used on but it also sounds
interesting - I'll have a look into this.

Their main use is in sheet metal - they make a better hole than a normal
twist drill. I got a set at my local Sunday market for far less than most
charge - and wasn't expecting much of them. But they turned out to be very
good indeed.

--
*A cubicle is just a padded cell without a door.

Dave Plowman London SW
To e-mail, change noise into sound.