Cutting rectangular hole in bulkhead

[eddystone]

Garmin having finally produced a software update for the GPSMap750, I’m toying with relocating it from a bracket mount at the chart table to flush mount on port bulkhead where there is a cable run to a soon to be obsolete depth repeater. (I have long lost the box but Garmin amazingly have a surface mounting kit!). I’m a bit concerned about using a power jig saw on thinnish grp and then have an even thinner layer to go through i.e. the one piece headlining- I’m afraid it will rip it. Is there a better technique to cut to a template?

 

[Fiddlesticks]

Something like this?
https://www.amazon.co.uk/dp/B00QEBOE0Q/ref=cm_sw_em_r_mt_dp_U_V380DbWT0QEE3

I used one to retro fit a flush mounted fog lamp into the bumper of my imported Mitsubishi Delica. Useful for loads of things though.

 

[coopec]

Not 100% sure of the problem but maybe a multi-tool is the answer? I often find it is the best tool for the job- very accurate.

https://www.youtube.com/watch?v=iZN_FOJS4RE

 

[prv]

I don't think you'll have a problem as long as you use a blade with reasonably small teeth - one advertised for cutting aluminium, for example, rather than ripping timber. However, other options would be a tile-cutting blade in your jigsaw, or getting one of the oscillating "multi-tools" that look a little like an angle-grinder with a chunk taken out of the disk. These are great for GRP especially into tight corners, and while they tend to be noisy they're very controllable - and have the unexpected benefit that they only cut rigid materials (soft ones just wobble back and forth) so if you catch your finger with it nothing much happens. Apparently they're actually used for cutting plaster casts off in hospitals

Pete

 

[vyv_cox]

When I have cut large holes like this in GRP and metal I drilled holes at the corners and connected them by hand using a padsaw. I think a multitool might be OK but a jigsaw can do too much damage for my liking.

 

[rogerthebodger]

I drill holes in each corner and the use on of these tools as below

 

[doug748]

The jig saw also needs a bit of depth to operate. Chain drilling, as above, is safe if a little more effort.
In very thin stuff you can use a small reamer (the engineers tool for making exact sized holes) in a drill to cut between the holes. They are hard, use goggles.

Doing holes in the boat I always have a good long think about it before acting.

 

[Fr J Hackett]

Use a Dremel.

 

[eddystone]

Use a Dremel.

That just occurred to me as I was reading replies and has the advantage I already have one - any thoughts on which tool?

Padsaw was what I was originally thinking (just couldn't remember the name!)

 

[prv]

The jig saw also needs a bit of depth to operate. Chain drilling, as above, is safe if a little more effort.

If you're concerned about something close behind then repeatedly poking a drill bit through seems like a lot of chances to poke a little too deep. Definitely the multi-tool in that case, you can make a cut exactly as deep or shallow as you want. And it will leave a reasonably neat straight edge, rather than postage-stamp perforations.

Pete

 

[Deleted member 36384]

I agree with the multitool as a great way of cutting holes in rigid materials. I would advise to be careful with the pressure, forcing the multi tool to cut faster by applying more force can cause the blade to wander off the line. Just use enough force to allow the tool to cut, I found this the hard way and wandered off the line, it happened quite fast, about 10mm thick ply, IIRC.

I didn't know about the soft material effect.

 

[Poey50]

Garmin having finally produced a software update for the GPSMap750, I’m toying with relocating it from a bracket mount at the chart table to flush mount on port bulkhead where there is a cable run to a soon to be obsolete depth repeater. (I have long lost the box but Garmin amazingly have a surface mounting kit!). I’m a bit concerned about using a power jig saw on thinnish grp and then have an even thinner layer to go through i.e. the one piece headlining- I’m afraid it will rip it. Is there a better technique to cut to a template?

The gap between the bulkhead and the inner lining is, from memory, surprisingly small at that point on the Sadler 32 - so you might struggle to cut one at a time. I think I might try first to make a hole just large enough to fit a small clamp through, then clamp ahead of the cut, sandwiching a piece of wood between the bulkhead and inner lining to keep it as rigid as possible, moving the clamped section as you go so you can cut both at the same time.

 

[jwilson]

I've done this once to GRP with a jigsaw, found it difficult to get a straight neat cut, though it was in an awkward access area. By the next time I needed to do similar square panel cutout on the boat I'd bought a multitool for another job at home, so used that. So much easier. Multitool definitely now one of those things I wish I'd bought a long time ago. For occasional use the cheap Screwfix ones seem fine, I've now used mine quite a lot.

 

[Fr J Hackett]

That just occurred to me as I was reading replies and has the advantage I already have one - any thoughts on which tool?

Padsaw was what I was originally thinking (just couldn't remember the name!)

If you have a dremel use one of the cutting discs.

 

[rogerthebodger]

If you have a dremel use one of the cutting discs.

This dermel attachment would also do the job.

 

[eddystone]

The gap between the bulkhead and the inner lining is, from memory, surprisingly small at that point on the Sadler 32 - so you might struggle to cut one at a time. I think I might try first to make a hole just large enough to fit a small clamp through, then clamp ahead of the cut, sandwiching a piece of wood between the bulkhead and inner lining to keep it as rigid as possible, moving the clamped section as you go so you can cut both at the same time.

Yes I think I remember that from replacing the compass on the opposite bulkhead - not just narrow gap but the inner layer, i.e. the headliner is effectively floating. I think I would have to cut them separately because the cut out in the inner layer would be smaller because of the shape of the rear of the plotter.

Need to sort out wiring before going ahead with this including procuring considerable length of thin cable suitable for routeing an NMEA 0183 input from the AIS receiver which I recall also needs to be earthed.

 

[salar]

I have done a lot of this with my fit-out. The neatest, strongest and safest method is to drill the corners with a diamond tile hole cutting saw. Then use the oscillating multi tool to cut between the holes. Job done.

 

[Daydream believer]

The cheapest & just as easy as all those suggested, is to buy a metal cutting blade (rather like a padsaw blade suggested earlier) for a Stanley knife.(£2-3) Do as suggested, drill 4 holes & gently cut along the lines. The fine teeth would be better than the coarser ones of most pad saws. You are less likely to do any damage taking your time.
It is a one off job & not worth spending money on expensive tools that would be "handy even if you never used them".

 

[langstonelayabout]

There is little more that puts me off buying a boat (other than wrong price & bad survey) than a load of instruments that have been inset into a GRP bulkhead and now have been superseded by others.

Certainly the instrument will look nice when first installed but what about in 5 years time when it has broken? You can't remove the thing as it leaves a gaping hole in the GRP. Patch the GRP and however good you are, you won't be able to colour match the gelcoat used for the repair.

Please arrange some other kind of carrier for your instrument! Use a spare washboard or bracket that hinges out into the companionway, but don't damage your perfectly good GRP. You'll regret it.

 

[Daydream believer]

There is little more that puts me off buying a boat (other than wrong price & bad survey) than a load of instruments that have been inset into a GRP bulkhead and now have been superseded by others.

Certainly the instrument will look nice when first installed but what about in 5 years time when it has broken? You can't remove the thing as it leaves a gaping hole in the GRP. Patch the GRP and however good you are, you won't be able to colour match the gelcoat used for the repair.

Please arrange some other kind of carrier for your instrument! Use a spare washboard or bracket that hinges out into the companionway, but don't damage your perfectly good GRP. You'll regret it.

An excellent point that has not, as far as I am aware, been mentioned before.
I would add that a touch screen plotter in a bulkhead might be a pain because as soon as a crew leaned on it, it could possibly change screens.
My plotter sits behind the tiller where I can use it whilst helming.
More importantly, I can see it, as I could not see, or reach it, if it was on the opposite tack on a bulkhead.