Hole saw type for drilling GRP

[BruceK]

What type of holesaw do people recommend for drilling a 45mm hole through GRP and gelcoat?

Forstner auger
Carbon steel ring with centre drill
Diamond
Step
other?

EDIT. This will be drilling from the outside in. i.e. gelcoat first

 

[Motor_Sailor]

The standard yellow Starrett holesaw will do it.

I think 46mm is the closest.

The black one will last longer if you've got loads to do.

You need a drill with a 1/2 inch chuck and go slowly with a good grip on the drill.

There are cheaper own brand versions that are good enough if you only have a few to do.
https://www.beal.org.uk/drill-bits-abrasives/holesaws-arbors/bi-metal-holesaw-46mm.html

 

[BruceK]

Thanks, I have two holes to make for davit supports. I am always a bit worried with that type despite the centre auger that an accidental slip might make an awful mess of the gelcoat. As the GRP is about an inch thick there, any tips on ensuring the hole saw remains on a perfect perpendicular alignment will be gratefully received or the plate may not sit flush.

 

[sprocker]

Top tip I was given years ago that does work very well in stopping any gelcoat chipping is:-

Drill the pilot hole first, then run the hole saw in reverse until you get through the gelcoat.
Once you're through the gelcoat you can run normally.

 

[BruceK]

Brilliant. Thanks Sprocker.

 

[savageseadog]

It's worth drilling part way on the reverse side for a clean finish, if you can.

 

[BruceK]

That will not be possible within the swim platform cavity.

 

[savageseadog]

That will not be possible within the swim platform cavity.

Right angle drill?

 

[oldgit]

Had to drill 2 x 120mm holes in glass fibre in order to gain access and release 30 years worth of corrosion to support brackets securing my old davits onto transom.
Although davits and visable bolts were stainless the internal stress structure and bracing studding was mild steel.
Had to cut into small bits to extract.
The hidden steel work is quite substantial and until removed it is difficult to see just how much is in there to prevent damage to stern due to constant movement of dinghy and outboard held well outboard of boat.
Kept the two plugs and fitted back in holes with white CT10.
Fortunately all is hidden behind seating.

 

[BB1]

The standard yellow Starrett holesaw will do it.

I think 46mm is the closest.

The black one will last longer if you've got loads to do.

You need a drill with a 1/2 inch chuck and go slowly with a good grip on the drill.

There are cheaper own brand versions that are good enough if you only have a few to do.
https://www.beal.org.uk/drill-bits-abrasives/holesaws-arbors/bi-metal-holesaw-46mm.html

You can get a 10mm arbor if required.

 

[Seastoke]

if you can I always drill a hole in a piece of ply , with your hole saw then either line it up with hole in gel coat and fix in position if pos ,or get some one to hold in position and it stops hole saw spinning off ,this is very use full when say making a hole bigger say 20mm up to 50mm as there is no where for pilot drill to go

 

[Momac]

I have a set of these for smaller holes in grp
https://www.screwfix.com/p/erbauer-...wFPGIUW_RyuC1Uct4u0aArliEALw_wcB&gclsrc=aw.ds
But from Alidi as they were cheaper.

 

[Scubadoo]

When I had to drill a larger hole, I simply applied a good layer of masking tape and kept the drill speed constant and made a nice clean cut.

 

[Andrew M]

if you can I always drill a hole in a piece of ply , with your hole saw then either line it up with hole in gel coat and fix in position if pos ,or get some one to hold in position and it stops hole saw spinning off ,this is very use full when say making a hole bigger say 20mm up to 50mm as there is no where for pilot drill to go

That's brilliant ! and will really help me where I'm replacing the transom shower head and mixer fittings but need to enlarge the holes to fit the new chrome capped fittings. Thanks.

 

[[165042]]

I use these: http://www.dk-holdings.co.uk/comp/holesaw2.html

 

[rubberduck]

Dremal with this attachment.

https://www.amazon.co.uk/Dremel-Line-and-Circle-Cutter/dp/B0035PTTCM