Cutting a 150mm 6 inch hole in 10mm marine ply?

[Ian_Edwards]

I need to cut a 150mm hole in 10mm marine ply, where the access is difficult.
I'd normally mark the circle and then use a drill to cut a series of holes just inside the marked circle, then use pad saw to joint the dots, finishing up with abrasive paper.
The location has very limited access from below, and constrained height above, so it's not possible to get normal drill in from above or below.
The hole is to allow me to fit a computer fan to extract hot air above a Victron 3kva inverter charger.
Any bright ideas?

 

[billcole]

Can you get at it with a multi-tool with the blade fixed a right angles to the body ?

 

[LoneHort]

or a dremel with a wood saw blade?

 

[NPMR]

A right-angled drill chuck?

 

[LittleSister]

A couple of potential tangential approaches to the problem -

1) In terms of space and appearance, could you cut a simpler (rectangular?) hole (or a series of smaller holes using a hole cutter) then fit a ply (or whatever) hood (possibly even angled) in which to mount the fan. You'd then be able to cut the large circular hole on the bench.

2) Another possibility is to use a different fan. There are smaller 12v fans - e.g 60mm (you might consider you need more than one, but quite possibly not required- the better quality ones will have a published spec indicating are volume shifted), and also fans that are moulded into a square body (with which you could cut an octagonal-ish hole, or other arrangement to accommodate the mounting screws with a square hole).

In fact I have, on the shelf next to me, a 12v 'NB BlackSilent PRO Ultra Silent Premium Fan' with 60mm dia fan in a moulded square body. This is far from the cheapest fan of this size available, though still not very expensive, but I was particularly looking for a very quiet one (I'm replacing the sometimes irritatingly noisy cooling fan in an instrument amplifier).

 

[Norman_E]

Remember the hole does not have to be round. I fitted a large computer fan to cool a fridge compressor compartment by making an octagonal hole using a multitool. Another point is that computer fans are usually designed for 12 volts with little tolerance for overvoltage, and can be burnt out by the 14.8 volts they are likely to get when batteries are being charged. The answer is to feed them from a small buck converter.

 

[Neeves]

Computer fans come in a whole host of sizes and I think they are all held in square housings, so no need for a round hole - simply cut a square hole slightly smaller then the fan. I have 2 x 150mm square but they come as small at 40cm square, maybe smaller. All the ones I know of are 12v. You can fit these fans on the 'inside' simply by glueing them in or screw them on the outside using the appropriate holes in the fan casing.

If you insist on a round hole - do as suggested - cut the round hole on a bench, using a hole saw and simply use what you 'make' as a facia on the existing board.

We use them for a variety of applications, cooling a fridge compressor and/or removing warm air from a fridge compressor being common - I have never heard of one burning out on a yacht (and they are standard units of Danfoss compressors).

Removing warm air is a good idea, from an invertor or fridge compressor and also replacing that warm air with cooler air is an even better idea . It was easy for us - we used ducting to drag, with a computer fan, air from our chain locker to our fridge and deep freeze compressors and further computer fans to remove the air made warm by the compressors.

Jonathan

 

[bluerm166]

Or cut a perfect hole in a small piece of ply on the bench and use this screwed , pinned or taped over the desired spot where the tools you can access may be hard to use precisely or upside down .Cut back to the pattern .Useful also where you need to enlarge an existing hole ( e.g. an existing thro hull ) .Finish back to the pattern with rasp or padsaw .Obviously taping is best if it will hold as no temporary holes to make good.

 

[Ian_Edwards]

Thanks for the replies, I've opted for a 90 degree drill, to add to my store of tools which only get used occasionally!
I have Ryobi one plus tools on board so I only have to buy the drill, I already have several battery packs and chargers, and go for the drill lots of hopes approach.

 

[Neeves]

Thanks for the replies, I've opted for a 90 degree drill, to add to my store of tools which only get used occasionally!
I have Ryobi one plus tools on board so I only have to buy the drill, I already have several battery packs and chargers, and go for the drill lots of hopes approach.

Your problem is not unique

Do us all a favour - when you have completed the task - post and tell us what was successful.

Good luck

Jonathan

 

[Neeves]

Or cut a perfect hole in a small piece of ply on the bench and use this screwed , pinned or taped over the desired spot where the tools you can access may be hard to use precisely or upside down .Cut back to the pattern .Useful also where you need to enlarge an existing hole ( e.g. an existing thro hull ) .Finish back to the pattern with rasp or padsaw .Obviously taping is best if it will hold as no temporary holes to make good.

Great minds think alike. I tried the very same, it looked awful - (maybe I lacked the patience). I bought hole saws. I had more space so put and flat piece of ply both sides (to secure the pilot hole) and used a hole saw

Jonathan

 

[Daydream believer]

Buy a cheap router/trimmer. Cut a pattern in a piece of ply & pin that over the hole. Use a 6mm router bit with a ball bearing follower & reach up & run that round the panel to be cut..
Router
Dirt cheap router
Both 8 inches high, Can you get it in the space?
Plus you need 240 V so must go on a pontoon with power for an hour

 

[colhel]

Can you get at it with a multi-tool with the blade fixed a right angles to the body ?

I borrowed one once to do a similar job to the OP. Something I keep meaning to add to my own toolkit.

 

[Ian_Edwards]

Update 7-2-22 in response to Jonathan's request.

Your problem is not unique

Do us all a favour - when you have completed the task - post and tell us what was successful.

Good luck

Jonathan

I bought a Ryobi right angle drill, main because I already have battery packs, and settled on a 110mm computer fan. I bought a pack of three, for the Victron Inverter charge, the Whisper Power's generator rectifier/inverter, and for the fridge. All of which are installed in tight spaces. I bought a 110mm hole saw, and 3, XH-W3001 12volt temperature controllers.
I've part installed the one for the generator power electronics.
The temperature controller is set to work in cooling mode. As a starting point, I've set them to turn on the fan at 30C and off at 25C, they are easy to adjust.
I had no real problems, except screwing the fan to the underside of the shelf, which required working upside down with my head in a cave locker.
The pictures below should be obvious.
Cheers
Ian