Woodwork questions.

[Doki]

I'm after a couple of bits of MDF to fit speakers to my car - 2 rings approx

6 inch OD and 5 1/4 inch ID, and if there's some easy way of doing it, and ideally the rings would be tapered, so that I can have the speakers pointing upwards out of the bottom of the doors, and a couple of bits that are straight on 3 sides and wavy on one of the sides, probably in around 9mm MDF.

For some idea of how the rings would look, here's an ebay listing for some in the US.

the almost rectangular bits would be fairly simple to cut with a coping saw, but I'm a bit stumped about how I'd get a taper with the rings. Are there any places that'll supply the wood and cut it? I very rarely do any kind of woodwork, so buying a lot of tools isn't going to happen, although there is a lathe in the shed that I could use, although I can't see any way of using a lathe to get a taper...

[Norman Billingham]

"

> Obviously the almost rectangular bits would be fairly simple to cut with a

Using a wood lathe it would be fairly simple. Make a false faceplate from a piece of MDF. Attach to one side of it a pice of wood which will lift one edge of the mounted work off the faceplate to the angle of taper you need.

Roughly cut the workpiece circular and mount it on the false plate via screws in the central waste, with one point on the faceplate and the other side resting on your previously attached scrap. The back face is now leaning at the required taper angle, as is the front, but you can now turn away wood from the front to bring it back parallel with the faceplate, thereby creating your taper.

Now turn the outside circular and finally part off the ring to the required diameter from the front.

The work will be a bit unbalnced so you'll need to run the lathe slowly to avoid vibration.

You can do the same thing perfectly easily on a metal lathe as long as it will swing the diameter.

[Doki]

>>> Obviously the almost rectangular bits would be fairly simple to cut with

Aha.

I've since had a second look and I've worked out that I'll need the baffle to be rectangular rather than round to allow everything to mount up properly. I presume my best bet would be to start with a circular bit of MDF, put the taper on, then cut the centre hole out with a coping saw and square the sides off? I assume it'd be a pain to be working on a big rectangular bit of MDF on the lathe.

Now all I need is a couple of scraps of MDF to meddle with.

[Dave Liquorice]

Does MDF turn?

[grumpyat]

FWIW

Tried it once and once only! Turns into a horrible dust, ended up using a full face mask with air supply!!

[Dave Liquorice]

I'm not surprised at that considering it's little more than dust in the first place. But did you mange to produce what you wanted or did it just fall apart or tear?

A proper mask should be used when ever machining or cutting MDF, the dust ends up very fine and gets deep into your lungs...

[Doki]

A bit more test fitting and so on suggests I won't be needing the lathe now, but thanks to everyone who gave advice. It all sounded complicated so I'm mildy relieved (a thousand other jobs to do on this car).

[Andy Dingley]

Yes, and tolerably well. You even get nice shavings from it. Surface is a bit poor though - needs something to fill it, such as car bodywork sprayable primer (under paint).

Valchromat (self-coloured MDF with extra resin content) works even better. This will sand and take a waxed finish.

As a way of making huge bowls and closed forms from glued-up stacked rings, it's well worth experimenting.

[The Natural Philosopher]

I've routed it and it routs well, so it must also turn fairly well.

Not the material I would use for turning though.

[Pete Verdon]

Yes. At school I made a plug for vacuum-forming by turning a block made of stacked layers of MDF. Worked quite well. Obviously I had to finish it with some sort of smooth sealant for release; I don't know if the surface would have been acceptable without it.

I don't remember using any sort of PPE except goggles though; this would have been the late nineties.

Pete