Utterly OT: accurately cutting wood panels to build speakers

[gridgway]

So, quite a long way off any car topic, in my other hobby, DIY hifi, I have got all the hardware and plans to make a pair of repro BBC monitors.

I'm kind of ok with wood in a DIY sort of way, but what do you need to accurately cut MDF for the speakers? The cuts need to be straight and square and the circles need to be good circles.

Do you need proper kit or can it be done by hand or with a jigsaw it similar?

Cheers
Graham

[BILLY BEAN]

Graham, What kind of joints are you going to use on the corners? Straight butt or a Lap joint (increases gluing area). Both of these with dowels or just screw and glue? Are the backs and fronts to be rebated or battened and ledged? The above choices would determine what tools are most appropriate. As far as I remember an efficient speaker enclosure has to be very rigid so the construction is important. The MDF also needs to be 25 mm thick or greater to ensure damping. MDF is a relatively benign material to cut but the dust when cutting may be a health hazard.
Cutting edges of tools must be sharp as the composition of MDF is pretty hard. The best option for cutting MDF for speed and accuracy is a table saw with a fine tooth tungsten tipped blade: not worth buying just for one project. However, unless you have already purchased the MDF a good DIY timber yard or B&Q will cut it to size for you. But check dimensions before leaving.

[8bit-ash]

I used to make speakers a few years ago, mainly PA stuff, folded horns etc but i've also made some home stuff. As an absolute basic you could get the panels cut at B&Q and do the rest with a jigsaw. A slightly better option would be to get hold of a router and a circular or rail saw.
It also depends on the finish of the cabinet. If you are painting it butt joints and glue/screws will be fine. 18mm MDF will also be fine as long as it is braced properly.
There are loads of great and simple plans out there using inexpensive drivers with great effect.

http://www.DIYaudio.com is a good source if inspiration.

[Ralph]

The easiest and cheapest way to make straight cuts in MDF is to use a hand held circular saw cutting up against a straight edge clamped to the board with speed clamps. A spirit level generally comes to hand to use as the straight edge.

Of course there are better ways to do this but as above is often good enough.

[AndrewSlater]

I bought a cheap router for £40 or so to build mine along with a circular saw.
The router can be used to cut straight edges, chamfer edges and to cut out perfect circles for the drivers.
The ones I build are shown here, with photos of the mdf parts.

http://www.troelsgravesen.dk/CNO-25_Andrew.htm

Andrew

[911GP]

I made a TV cabinet in a similar way. I would advise getting the pieces cut at a timber supplier. I used MFC instead of MDF. You can get various colours and finishes and even have the edges trimmed in the same material to get a professional result but if you do this remember to adjust your calculations for the thickness of the finishing. I have used Cutwrights in Feltham a couple of times and they were very good.

[gridgway]

Thanks all for the helpful tips. DDK never fails!!
Graham

[rhd racer]

Hi Graham

Agree with the above. In the last year I have made 5 built in wardrobes and two built in cupboards in a similar way. I made a plan and detailed all the cuts and put it on spreadsheet with a key. A local merchant here in Notts cut everything and delivered, each piece had a sticker on it showing the dimensions.

It was all MDF with oak veneer coating - I bought iron on edging strip online and edged every piece where needed (about 75m of edging ) on the probably 50 pieces. I put everything together using a dowel jig I bought online and normal hidden screw fixings. The results were good, sadly for me, as I have just also had to do a window seat and now shoe rack / seats for the hall have been ordered by my wife!!!

Cheers
Wayne

[gridgway]

Hi Wayne, that is very impressive! I've got a dowel jig which works well, but takes a lot of thinking to make it work ok!

I hadn't thought of getting the wood cut by the timber merchant, but that's an obvious thing to do now it's been mentioned.

I'll be getting the plans out at the weekend and doing some planning! I've got to get my amp finished as well which means re-engineering the case for bigger heat sinks as I made it too small. I guess I really ought to get one job done before starting another!

And there's the oil to change on the T!

Graham

[gridgway]

This is what I have...
https://meniscusaudio.com/product/conti ... -kit-pair/

[Hugh Jorgan]

I'm hopeless and can't bang a nail in straight.
But.
My cabinet maker mate (who is ocd with wood) is making us some fitted wardrobes in the house we're building.
He gets everything cut to size at a good local timber merchant with a decent panel saw. A lot of basic merchants are cutting all sorts of crap, then when you want them to cut to very tight tolerances the blade is blunt.
He will only use moisture resistant MDF (its green in colour) it's more stable than the normal stuff.
If he has to cut on site he has a festool track saw which is super accurate.

[gridgway]

Love the track saw!

[rhd racer]

MDF can be a buggar to cut (doing the hinge mounts for the massive doors I used with one of those drill bits that leaves a perfect indented circle) was a pain and made a mess. However, clean holes in a set position might be easier. Not sure what size those speakers are but you can get some pretty big hole saws. In my experience, they cut a few mm oversize, so if you don't have a router then this might work if the right size is available....you can do a few pilots to check it is the right tolerance. Just a thought,

Cheers
Wayne

[redrobin911]

The only proper way to do this is a CNC machine - but the cost of setting up the tooling paths to cut all the pieces is more than the MDF used. The only way to get your money back is to cut muliple sets to make many pairs of speakers in which case the unit cost per set then is very low. I have a CNC machine that would do the work but the setup cost could be £100 -£200, after that the CNC time would be very little. Just my 2p worth. If you have a mate with a CNC machine speak nicely to them - the finish on mitres and circular cuts is perfect and will reflect in sound quality.

[911MRP]

So, quite a long way off any car topic, in my other hobby, DIY hifi, I have got all the hardware and plans to make a pair of repro BBC monitors.

I'm kind of ok with wood in a DIY sort of way, but what do you need to accurately cut MDF for the speakers? The cuts need to be straight and square and the circles need to be good circles.

Do you need proper kit or can it be done by hand or with a jigsaw it similar?

Cheers
Graham

BBC speakers takes me back. When I left home to go to university my dad built me a set of Ls3/5a replicas.vague memory of bits coming from Wimslow Audio in NW? Still have them in a cupboard somewhere. His electronics were a bit better than his woodwork but certainly smart enough for a student. Very .nice sound. Not for loud student party bass but I never never blew them up but they could make a quack sound if overdoing it iirc

Good luck with project.

Steve

pS I came across a set of his old kef crossovers from when they used to do them for kit makers new old stock in factory box in my loft ought to construct them but my woodworking is average at best.