Cutting - and filling - access panel in GRP interior liner

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dunedin

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I think I need to cut an access hole in the thin (circa 1mm) GRP/plastic cabin roof liner to access some nuts holding the GPS receiver. Needs to be around 12cm diameter or square to get a hand in.

What is the best way / tool to do this?
- I suspect that a Jig saw would be too powerful/ rough to cut this cleanly (and don't have one on board). (And the emergency rigging cutting angle grinder is clearly staying in its box !!)
- is there a cutting tool that can be attached to a dremel type tool?
- other suggestions?

Also how best to cover the hole. Probably need to source a small peice of stiff thin white plastic sheet - but not a meter panel.
 
I think i'd cut it by hand with one of those little tools that you can clamp small saw blades in (they surely have a name?), and then tidy it up to being neat by sanding it. Not sure how best to create a final cover piece though - there are ready made access covers & frames, but maybe these are a bit bulky for what you want, they're often seen on sailing dinghies and such, screw thread lids. The construction industry use a lighter and simpler range of access panels... google Rytons to see a few - but I think all these are square or rectangular.
 
You can buy a 5" hole cutter from the usual suspects for not very much. You'll need a drill arbor to suit. Afterwards, glue ply strips inside over hole, glue cutout circle in and fill small gap. Unless you might want to be there again, in which case a circular access hatch. Cutter will come in handy next time you want to fit some speakers.

But how did the nuts get there in the first place? Are you sure they're not just self-tappers in to top surface? (But if it's a newish boat, it wouldn't surprise me to see inaccessible fittings).
 
Do you need to cut such a large hole just cut say a 1ins hole below the nut and use a socket on a extension bar and fill the hole with a blanking grommet,repeated for each nut.
 
I was thinking along the same lines as peteK. then all you need to finish the job is a grommet! Alternatively coopec's suggestion for a multi tool is a fantastic alternative. Once you have one you will find a million uses for it that other saws can't cover.
 
dunedin said:
I think I need to cut an access hole in the thin (circa 1mm) GRP/plastic cabin roof liner to access some nuts holding the GPS receiver.
Click to expand...

Is it really fixed with nuts and bolts? It would have had to be fitted in the factory before the roof liner was married to the deck moulding, which isn't usual procedure.
 
The GPS receiver definitely has nuts below it which need to be removed - and the much more tricky bit, refitted. And it was fitted post build - the fitter must have much smaller hands to get through a small access hole under the mainsheet winches 20 cm away. And the number of lost nuts shows how many attempts he took, before changing from nuts to thumbscrews but I can't reach the furthest one at all.

I have bought a circular hole cutter - like the one Rogershaw linked to (but 100mm as think that would be enough). However, good suggestion to perhaps just drill a smaller hole directly under the nuts, sized to allow a socket to get through.
Also good point if cut hole to glue something inside hole to take screws to attach a blanking plate. As the GPS batteries only last 5 or so years, further access will be needed hence the proposal to improve access (rather than bribe a small child with thinner hands/arms).
Thanks all
 
When I cut the rectangular holes for my yacht leg support blocks, see http://coxeng.co.uk/cruising/installing-yacht-legs/ I used a padsaw, as posted earlier, a handle to take half a hacksaw blade. In use set the blade to cut on the pull stroke, not push as with a hacksaw. For one use you could just wrap one end of a broken blade in duck tape.

This was in the days before multitools were available and today I might well use that instead.
 
dunedin said:
.....

I have bought a circular hole cutter - like the one Rogershaw linked to (but 100mm as think that would be enough)...
Also good point if cut hole to glue something inside hole to take screws to attach a blanking plate. As the GPS batteries only last 5 or so years, further access will be needed hence the proposal to improve access (rather than bribe a small child with thinner hands/arms).
Thanks all
Click to expand...


I used a hole cutter for the same job. You can get around the problem of the centre drill by drilling first and replacing it with a stubby length of plain steel.

If you use solid teak (or whatever matches the woodwork below) for a lipped blanking plug it can be neat enough to mistaken for an original feature. Try sticking the plugs with mastic (not around the plug but a big lump - touching the deckhead) and then the finish is not marred by screw holes, they tend to stay put and yet are easy to remove.
 
Agreed. I have overcome this by using a block of wood below the surface to be cut. Drill into the wood until the holesaw has cut a groove, then remove the arbour and allow the holesaw to cut throught the wood and the lining. The initial drilling into the wood can be done on the bench and then offered up to the surface to be cut.
 
Doing something similar (enlarging a hatch cover in a dinghy buoyancy tank), I found a drum sander in a power drill the best for tidying up a hole in thin GRP. It sands along the cut edge rather than twanging the flexible thin GRP or chipping the gelcoat. Very neat result quite quickly without buying any new tools.
 
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