Drilling a hole in the dash

[stuartwineberg]

About to fit a Garmin fishfinder. To run the cables I need a 5/8 (16mm) hole in the top surface of the dash - seems a lot but it is because of the width of the plugs already on the ends of the transducer and power cables. The dash is (I think) gel coated fibreglass or very thick plastic (3 or 4 mm). The drill bit size is too big for the chuck of my small drill and there isn't enough vertical clearance above the surface to fit in a large power drill and the bit.

My current thought is to drill the biggest hole I can with a smaller drill and then open it out with a round file by hand. That said, I look to the assembled expertise for a cleverer and easier solution

 

[Tranona]

Hole saw from Screwfix. The arbor is from memory 6mm so will fit small cordless drill. will give a much cleaner hole than the alternative which is a a flatbit. Much shorter as well if clearance above the drill is an issue.

 

[vyv_cox]

As Tranona says, a hole saw is the best bet for the material you are drilling. A Forstner drill is great for plywood but possibly not for a brittle plastic that might chip.

 

[Trundlebug]

If you're struggling for room to get the drill in, get a 90 degree attachment like this
http://www.ebay.co.uk/itm/like/2511...ff11=ICEP3.0.0&ff12=67&ff13=80&ff14=83&ff19=0

Combined with the hole saw recommended above you'll be away no problem.
Can I suggest you buy the small hole saw kit from Screwfix, it comes in a nice little red plastic case and for the money is really good value.
Will be useful for years to come.
Unless you don't do many jobs!

 

[David2452]

The pilot drill is 6mm in most hole saws but many have 1/2" (13mm) arbor shanks to fit the chuck so be careful in your choice, Bosch power change is 10mm but I'm sure some others are small too. For GRP gelcoat a grit edged tile hole saw is best as you can easily chip the gelcoat with toothed ones. The nasty nest of hole saws al la B&Q will have the 6mm pilot drill continuing to the chuck so may be an option if used with great care, but not a real tool for regular use.

 

[stuartwineberg]

Thanks

As always good advice - thanks to all

Stuart

 

[cliff]

About to fit a Garmin fishfinder. To run the cables I need a 5/8 (16mm) hole in the top surface of the dash - seems a lot but it is because of the width of the plugs already on the ends of the transducer and power cables. The dash is (I think) gel coated fibreglass or very thick plastic (3 or 4 mm). The drill bit size is too big for the chuck of my small drill and there isn't enough vertical clearance above the surface to fit in a large power drill and the bit.

My current thought is to drill the biggest hole I can with a smaller drill and then open it out with a round file by hand. That said, I look to the assembled expertise for a cleverer and easier solution

http://www.toolstation.com/shop/Titanium+Coated+Step+Drill/p78333 (pick your size)
or
http://www.toolstation.com/shop/HSS+Titanium+Coated+Step+Drill+Set/p30591 (set of 3)

 

[Amulet]

I personally think you'll munge it up with a hole saw. They're pretty fierce things, the thin material won't hold the pilot steady, and hole saws that small don't work well anyway. I'm for Cliff's stepped drill, which I have used with success many times for jobs like this. Some think that it helps to put masking tape over the site and drill through it. I'd do so. Also I'd probably lubricate it with a bit of oil or detergent as it drilled. As for fitting in the space. I bought a Makita drill a bit like this Bosch one years ago (my model is no longer made).
http://www.axminster.co.uk/bosch-gwb-10-8v-li-cordless-angle-drill-driver-li-ion-in-l-boxx-2-0ah
It seemed like an indulgence at the time but it's been a godsend. Every boat owner should have one.

 

[stuartwineberg]

Thanks again

Thanks for the new word for my vocabulary. I have munged lots of stuff in my time but didn't know what to call the process!:encouragement:

I have indeed ordered the step drill which seemed the gentler option from those suggested. Appreciate the idea of the masking tape and using oil to cool/lubricate. The drill looks great but costs nearly as much as the fishfinder

 

[surekandoo]

I'd recommend a dremel hole cutter with suitable bit. I've used it to cut a very neat circular hole in the cabin roof for a circular vent. I found it very easy to use with a neat finish.

 

[Hadenough]

As Tranona says, a hole saw is the best bet for the material you are drilling. A Forstner drill is great for plywood but possibly not for a brittle plastic that might chip.

Forstner bit on slow speed to start is perfect.

 

[vyv_cox]

Forstner bit on slow speed to start is perfect.

I just tried a Forstner bit on some Formica. Definitely the wrong choice, the plastic is much too hard for it. I gave up before blunting the bit.

 

[Hadenough]

I just tried a Forstner bit on some Formica. Definitely the wrong choice, the plastic is much too hard for it. I gave up before blunting the bit.

Wow that told me didn't it!

With all due respect Vyv, I wouldn't post advice if it hadn't worked for me. The OP is wanting to drill a clean hole in GRP (I assume gel coated) or he thinks maybe plastic. I've drilled dozens through GRP and in plastic containment boxes with a Forsnter bit while re-wiring the boat. It worked for me. I suspect that formica is somewhat harder than GRP, although I've done that successfully too. Probably not too good for the bit but I was more interested in a clean cut than the life of a £5 bit. What I have found is that you need it angle the bit to get it started but that once it gets going, on a slow speed it will "shave" it's way through nicely. Perish the thought but I also use a flat bit for bigger holes. I have a 40mm bit with leading teeth on the outer diameter. Starts a very neat hole in GRP and as long as you can get to the other side to back drill works perfectly.