How to cut holes for speakers?

[yesnaby]

Hello,

This is for my freestanding car sat nav/speaker project.

I need to cut two holes in 12 mm thick plywood for the speakers, each hole 106 mm diameter. I suppose a hole saw of this size would be unavailable/too expensive/my drill would not be powerful enough to drive it? I do have a jigsaw so perhaps use that? Any help appreciated.

Michael

[paulsherwin]

A jigsaw is your best bet. You can use a hand coping saw but it's difficult not to make a messy cut. You can also use a routing bit in a power drill but again, it's difficult to make a neat job.

[emeritus]

I have used a power jigsaw for this task, but a holesaw will give a neater job and avoid the need for sanding down to remove the inevitable irregularities you get with a jigsaw, although this won't matter much if the hole is to be covered.

The closest holesaw to 106mm in the Axminster tools catalogue seems to be a 102mm Bosch at £14.24 (you would also need an arbour adaptor at £6.95), but it is shown as currently out of stock. Screwfix list an Erbauer 102mm holesaw and adaptor for about the same price.

The next size up from either supplier is is 114mm .

I would expect an electric drill to cope as long as you don't attempt excessive feed. It is easier to apply a gentle feed if you use a drill stand.

[pmmunro]

If you choose to use a holesaw of this size, you must use a side handle on the drill.

I knew that 6 years ago but forgot - I've just been for the fourth operation to try to restore some vision in the eye the drill handle hit when the saw jammed.

PMM

[Nickthedentist]

Blimey, PMM, that's news to me, I'll be careful.

I'd go with a jigsaw for this. Try on a piece of scrap first, and bear in mind that all blades are not the same, i.e. you can get various different teeth-per-inch etc.

[yesnaby]

Hello,

Thanks everyone, I think I'll try the jigsaw first - it sounds safer!

If I were to go for the hole saw I would probably use it in a drill stand (except I don't have one!).

Michael

[Herald1360]

How about this:

http://www.amazon.co.uk/Trixes-Adjus...=circle+cutter

[emeritus]

That's what I know as a Trammel cutter, really intended for cutting thin sheet metal. It should be OK for thin plywood, but you might have problems with using it on 12mm ply. It might work if you cut two concentric circles a few mm apart to allow waste to be removed as cutting progresses, otherwise the body of the cutting blade would not be able to penetrate far into the stock.

[yesnaby]

Hello,

Another problem is that I also have a rectangular hole to cut, about 7 inches by 4 inches, this should be OK with a jigsaw. And, I hope to cover the plywood case with Formica, so should I apply this first and cut the holes afterwards?

Michael

[Radio Wrangler]

Another method is to use a router.

Most of them come complete with a circle-cutting trammel. You use a small screw to pivot the guide at the centre of the hole-to-be and your router is fixed to cut a perfect circle. Plunge in and round you go. Don't cut all the way through the thickness, leave a bit to locate the tool. Unscrew the guide and cut the last bit out by hand.

Use the router again with a 'laminate trimmer' bit which has a ball race as a guide to allow it to cut the hand cut ring down flush.

For added marks, you can go round with a bearing-guided chamfer or founding bit to smooth the edge. This will give you a perfectly smooth hole. But you need a router or to be able to borrow one.

For even more marks, you can rout a rebate in the front face to take the speaker mounting ring, and the speaker is fitted from the front, finishing up flush. To do this for a B139 (about as awkward a driver as you could ever need to cut a hole for) I mounted a B139 to a spate lump of MDF and ran the router around the outside of it. This gave me an oversized B139 shaped hole. I wanted the big lump with the hole. A bit of calculation told me the size for a circular disc of MDF which I made with a hole in its centre. This screws to the router base and guides the router around inside the big hole template, so the router cuts a B139 sized hole. A second size of disc allows the same template to guide the rebate cut. The size of the disc depends on the diameter of the router's base and the diameter of the cutter used. Her's the result many years later. The Bi39 shows a few knocks, and the midrange was repaired many years ago but they still sound OK.

A few straight pieces of wood clamped in place will guide you for cutting a square hole, but you have to finish the corners by hand if you don't want them radius'd.

A cheapie router is OK, you just go slower and load it gently. Cheap Chinese bits don't last very long, but do last long enough. If you get serious, you can buy a cheap selection box and eventually replace the ones you wear out with high quality versions. Trend are a top make for bits, Bosch is good too. Freud is the brand name of Cassals who used to make stuff for trend but had a bit of a falling out.

Take care when using routers. You definitely need eye protection, and you need to keep a good grip with both hands all the time it is running.

David

[David G4EBT]

I'd endorse David's (Radio Wrangler) comments - a router is by far the best and easiest tool to use for cutting cicular holes.

If you use a trammel cutter for a hole of that size, you’ll need to use it in a hand brace unless you have a pillar drill with sufficient clearance to hold the workpiece on the worktable of the drill. You’ll have a devil of a job to use a trammel arm for cutting a large diameter hole in plywood using an electric drill – even a cordless one at low speed. It might make a neat hole in acrylic or soft plastic, but in thickish ply, I think you’d really struggle.

By far the easiest and neatest way to cut holes is with a circle cutter/trammel bar on a router, (which you can easily make from scrap). A cheap DIY store router with ¼” collet would be fine. Nowadays they’re invariably soft start, variable speed and from 1,000 Watts upwards. If you do use a router, you must make several ‘passes’ say 5mm deep - don’t try to cut the hole in one pass. Here are some links that might help:

How to make a Ron Fox Router Circle Cutter/Trammel Bar:

http://www.wealdentool.eu/rf_tips/rf_tips_04.html

How to cut holes with a router:

http://www.youtube.com/watch?v=lj8kcjx201A

http://www.videojug.com/film/how-to-...-with-a-router


If you don’t have a router but you do have a jigsaw, you should be able to cut neat circular holes with care. A ‘pendulum action' jigsaw with variable speed would make the job much easier. A pendulum action saw brings the blade away on the none cutting stroke so it doesn’t jam, and clears the dust. These links show how to cut holes with a jigsaw:

http://www.bing.com/videos/search?q=...86B42A3AD632A6

http://www.bing.com/videos/search?q=...B4CD7515E6D53B

As to cutting the square hole in the Formica you’ll need to glue it on first, then because laminates such as Formica are prone to chipping, carefully score a deep line with a craft knife (using a guide to make sure your knife can’t slip and damage the Formica). You’ll need to use a fine toothed jigsaw blade which cuts on the down stroke (most jigsaw blades cut on the upstroke which helps to keep the base of the jigsaw pulled onto the surface of the material being cut). You’ll need to hold the saw down onto the surface to prevent it ‘jumping’ and take it steady at a slow speed, cutting on the waste side of the line, letting the saw dictate the speed of travel rather than pushing it too hard.

Often when laminate is being cut with a jigsaw the finish of the edge doesn’t matter much because it’s things like holes in worktops which are covered by say a kitchen sink, but in your case, you only get one go and if you use an upstroke coarse blade, and don’t score the lines with a craft knife, that’s a certain guarantee of chipping the edges. But if you do chip the edges, unless the accuracy of the hole is critical, and I guess it isn’t, you can always uses a file or say 120G sandpaper to gently smooth the edges.

Hope that helps.

Best of luck with the project!

[terrybull]

I agree a router is best. Fine if you have one. If you do use a jigsaw then put strips of tape down firmly on both sides of the area you are going to cut. Masking tape pressed firmly down will take a pencil mark. It gives you a cleaner cut. Go slowly with a fine tooth blade.

[yesnaby]

Hello,

Many thanks for all your hints and advice. There is a lot to think about here!

No router, unfortunately, but maybe I will get one.

I tried a test circle on 12 mm MDF with a jigsaw and it came out pretty good. It was easy to smooth out to a neat circle using glasspaper and a round block. In view of this, I think I'll use MDF for the front of my cabinet, as it is easier to work, and plywood for the sides and top as they can be secured together more strongly.

I have a little time to think about it as the speakers I have ordered have not arrived yet.

PS Regarding the Formica-covered board, would it be possible to use a jigsaw from the 'other' side with an ordinary (upward-cutting) blade?

Michael

[David G4EBT]

Originally Posted by yesnaby

PS Regarding the Formica-covered board, would it be possible to use a jigsaw from the 'other' side with an ordinary (upward-cutting) blade?l

It isn't unknown for people to do that, but don't think it would be advisable as you won't be able to see the progress of the cut on the laminate side and whether or not you are doing any damage. Fine toothed down-stroke jigsaw blades especially for laminate are widely available. I guess it depends on whether the perimeter of the hole is going to be visible or not - obviously if it's to be shrouded by for example, the rim of a speaker mounting frame, it isn't really an issue.

This thread on down-stroke laminate jigsaw blades on the 'Woodweb' is relevant:

http://www.woodweb.com/knowledge_bas..._Laminate.html

Hope that helps a bit.

[k_yller]

check nearest lidl
2 weeks ago they have nice router

[yesnaby]

Hello,

The speaker holes will be hidden by grilles and the sat nav unit hidden by a plastic trim. It would be nice to have the holes looking reasonable though. Screwfix and Homebase seem to have the downcutting blades (as do B&Q for a price!). Probably best to do some practising first to get the hang of it.

Michael

[Radio Wrangler]

If working in MDF take care not to breathe the dust, however you cut it.

Routers are life-changing tools. You find all sorts of things you couldn't do before. I started with the speakers and wound up making a full kitchen... all the stile and rail doors included.

David

Originally Posted by pmmunro

If you choose to use a holesaw of this size, you must use a side handle on the drill.

Also known as a 'man whirler'.

[pmmunro]

It's easy to forget the torque a power drill produces - and the inertia at higher speeds. If they're used with large diameter bits, hole saws or other devices it's absolutely essential to have the secure grip that only a side handle can provide.

It took me about three seconds to realise what had happened and the cable was wound three times round the drill body - a broken wrist might have been the lesser evil.

Hole saws can be really useful, but do need care.

As David says, routers can increase the range and quality of projects but it's well worthwhile learning the best techniques, capacity of your machine and taking time over setting up - the last not negligeable.

PMM

[Bazz4CQJ]

You can get some specific blades which are less "deep" (i.e. about 4 mm rather than ~6mm) for use with jig saws on smaller radii; I think they are referred to as "finishing blades".