Drilling Fiberglass - Best Drill Bit

[exapp]

Hello,

What's the best type of drill bit to drill a 6mm hole in gel coat without chiping the gelcoat or pushing through the fibers on the far end of the hole being drilled. Only drilling about 30-40mm but need a very neat hole.

Regards,

Exapp

 

[Guest]

I always use HSS (for drilling metal) on the basis that GRP is incredibly abrasive when cutting .... Taken slow - mod speed and without pressing too hard ... let drill work its way through.

When using hole cutters ... though hull fittings etc. - I've blunted hole cutters more than once ...... GRP is something else.

If drilling from Gel side and bare GRP other side is not seen ... I've also used the wood bore bits ... flat sharp blade with spiked centre .... as they have a proud outer cut that scribes the circle into the gel before taking real bites out ...

 

[oldharry]

Keep it slow! Drill too fast and the heat can cause the drill to jam solid, possibly damaging the gel coat. As SBC says, HSS bits are best, except for staing on the gel coat when the centre spike wood bits ensure a neat start.

Let the drill do the work - not too much pressure.

 

[Guest]

It is hard to drill into old gelcoat and make a nice hole. It is even harder to keep it looking nice. The get coat will splinter off at a sharp edge.

If you want both ends nice you need to drill it once with a 4mm and then back drill both ends to half way through.

Cool the HSS or better drills with water. GRP will not remove the heat like metal and the drill cutting edges will melt.

Is it for wires? If it is going through such a distance is there a core? Could be a moulding joint so are there voids in the joint? Will water/damp penetrate into the void or foam?

I would get some glass fibre tube or tufnol and drill to its outside diameter and resin it in place after first masking the gelcoat etc. Once set carefully sand back excess tube to masking. If the gelcoat does splinter then it is easily filled back to the outer tube wall.

 

[exapp]

The hole is actually for a nylon grub screw to hold a rubber cutlass bearing so tapping should be fun too. Any tips here would be appreciated...

Thanks for the help so far.

 

[davidpbo]

Would applying Gaffa tape or PVC tape as per drilling ceramic tiles help?

 

[alldownwind]

[ QUOTE ]
If drilling from Gel side and bare GRP other side is not seen ... I've also used the wood bore bits ... flat sharp blade with spiked centre .... as they have a proud outer cut that scribes the circle into the gel before taking real bites out ...

[/ QUOTE ]
I've used these too with great success, drilling in from each side and meeting well inside of, and clear of, the gelcoat.

 

[Guest]

It is not that critical then. Drill a 4mm hole and countersunk the gelcoat to bigger than 6mm. Then drill the 6mm hole. I would not tap the gelcoat. The inside would just need cleaning up with a file.

Tapping is easy but make sure that you use a tight clearance drill than used on metal. Water helps to cool them also. Since it is not a blind end tap, it is easier with first tap.

Only fixed cutlass bearings on big steel yachts so no advice but 6mm nylon seems small. Mine does not have one!

 

[Talbot]

if you are tapping the hole, strongly recommend that you drill out the gelcoat to the max diameter + a tiny bit, as otherwise, there is a very high probability of chipping off the gelcoat when tapping the hole.

 

[Blueboatman]

I would be tempted to drill a 7 hole,insert epoxy resin and a wd 40 coated steel bolt in of the same thread as the nylon screw. Once cured,remove the steel bolt and insert the nylon-you will have cut a thread and sealed the raw fibreglass with little effort.Alternatively this is the back up plan if threadcutting into the bare grp doesn't quite work out!

 

[Guest]

Or .... over cut the hole to fit a proper threaded insert .... screwfix and various places do them .... local model shops do threaded inserts from tiny up to quite large specially for those blind / fiddly jobs that also have to look good ...

What ever happens - the hole cut has to be sealed with resin of some description ...... tip : If you want to get your eopoxy really runny to "soak" into those nooks and crannies ..... a hair-dryer played on it as you "paint it on" does the trick ..... but beware - it also speeds up the setting ....

Nylon screw is not the best to keep a thread in GRP or any other actually - why I think an insert would be a good idea ....

 

[tangofour]

[ QUOTE ]
The hole is actually for a nylon grub screw to hold a rubber cutlass bearing so tapping should be fun too. Any tips here would be appreciated...

[/ QUOTE ]

So this is going to be below the water? However you drill the hole if you are going to tap it and put a nylon bolt into it you will end up with some exposure of glass to H20. A few small chips wont matter either way. Drill it, tap it and then add some gel coat to seal the glass, screw the bolt into the wet gelcoat. It'll come out later no problem.

No-one is going to see it are they?