38mm MDF screw/pilot holes size recomendations pls

Hello chaps,

i am building a sturdy box to make an Infinite Baffle subwoofer out of 38mm MDF (four of them actually). all sides will be in the same 38mm MDF.

I have knocked up a sketchup for you to see here-

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size screws would you recommend to hold it all together? And will they need pilot holes, if so what size? How far apart for each screw? and finally what screws would you recommend? ie length, and gauge? (and brand if you want!)

Ta chaps

Steve

Reply to
Mr Sandman
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I would glue it - MDF glues very well and you would get an airtight box.

Reply to
Geoff Pearson

Where the 'kinell do you get 38mm MDF?

Are you going to glue it or just screw it? If you are gluing the screws are only necessary to pull the joints together while the glue sets. Most of the strength come from the glue.

General rule of thumb is twice the thickness as a minimum, so 70mm.

These do exactly what they say on the tin;

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And will they need pilot holes, if so what size?

No pilot, but clearance holes are a good idea.

4 or 5 should do it, especially if gluing.

As above

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Reply to
The Medway Handyman

Where the 'kinell do you get 38mm MDF?

Are you going to glue it or just screw it? If you are gluing the screws are only necessary to pull the joints together while the glue sets. Most of the strength come from the glue.

General rule of thumb is twice the thickness as a minimum, so 70mm.

These do exactly what they say on the tin;

formatting link
And will they need pilot holes, if so what size?

No pilot, but clearance holes are a good idea.

4 or 5 should do it, especially if gluing.

As above

>
Reply to
Mr Sandman

There's gonna be some weight in those, are you going in for demolition? ;)

Reply to
brass monkey

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>>> And will they need pilot holes, if so what size?

4 or 5 screws per side.
Reply to
The Medway Handyman

Build Center, although Jewson, who have taken them over, only seem to list up to 25mm in their on line catalogue. Same with flooring quality chipboard - Build Center did 38mm, but Jewson only show up to 22mm.

Colin Bignell

Reply to
Nightjar

pre drilled.

You're not doing it right. MDF has no grain, so it makes no difference where you screw into it.

But it's not just the clearance holes you have to drill, but a pilot as well.

Reply to
Dave Plowman (News)

e holes pre drilled.

Reply to
fred

that confirms my experience FWIW

Reply to
stuart noble

+1

However as this is for speaker boxes the OP can fit glue strips inside the corners and screw into them through the MDF giving a strong well sealed box without having to screw into the MDF at all.

I also note that the box is square which isn't a good idea with speakers and it may be better to slope the panels to reduce reflection effects inside the box.

Reply to
dennis

Try driving a screw without pilot hole into the face but close to the edge

- it will give problems in more or less the same way as into an edge.

Really? If you've only got basic drills, you drill the pilot first through both, then do the clearance one to the top part. Then countersink. There are bits around that do all three jobs in one go.

I've built lots of things using MDF with screws into the edge - but as has been said mainly to hold it while the glue sets. With the correct pilot, I've never had any problems. Just don't go mad tightening the screws.

I can understand this may not be suitable for machine assembly, though.

Reply to
Dave Plowman (News)

Reply to
Dave Plowman (News)

slightly.

It depends what you are doing. In some cases monitrs are used to get an exact balance of a mix as a reference: in other cases they are used to represent roughly what a plantpot with a 9x4 elliptical is going to hear in his car.

In neither case are sloping sides an advantage tho. box resonance is USED - suitably damped - to enhance bass performance. Or an internal labyrinth tuned pipe used.

Best results come from ES or horns anyway - but unless you are building a house around a sound system a 32 foot concrete bass horn is not the easiest of things to install.

Reply to
The Natural Philosopher

Horns are never used in decent speakers. Too many resonances. Fine for high powered PA systems - or low powered where high efficiency is needed, but not for general use.

Reply to
Dave Plowman (News)

Pilot holes AND clearance holes into mdf? You must still be using screws f= rom the 19th century. mdf screws have parallel shanks all they need is a cl= earance hole and then only if you wish to screw into the edge. Too much faf= fing around. I repeat, we tried all those methods and found none reliable. = Clearance holes could, and did, fail to alleviate the problem. The old adag= e holds true. An ounce of experience beats a pound of theory.=20

Reply to
fred

This is 38mm! It ain't gonna split!

Reply to
The Medway Handyman

fred wrote:

I'd use clearance holes so the pieces are pulled together tightly.

Never had a problem with TurboGolds.

Reply to
The Medway Handyman

Yes.

How can any screw grip with just a 'clearance' hole?

Right. The OP isn't making cheap furniture on a production line.

It sounds to me like you're repeating some story secondhand - rather than from your own experience. As I said, decent MDF (and there is plenty around which isn't) will take screws into the edge if you know what you're doing.

Reply to
Dave Plowman (News)

Well you use the right diameter clearance hole obviously (Match the core di= mension or smaller of the screw.)

I speak with 25 years experience of manufacturing office furniture. The ite= ms we would use mdf for are generally bespoke and as such contain a lot of = hand work and not production items. We've been down all the roads and metho= ds of joining items, dowels still in occasional use, biscuits ditto, pocket= holes, long before Kreg appeared on the scene, and anyway we found them un= suitable, brackets both plastic and steel, etc.etc. For production items we= use a multi spindle boring machine and kd fittings. We are not large manuf= acturers making items predominantly for our own retail outlet.=20

I don't now what experience you have of these things but I DO know what I a= m talking about and speak from many years experience.

You are well out on a limb here as your experience is diametrically opposed= to that of the vast majority of other users and as such I feel you may be = leading people astray

I'm not going to continue this discussion. We will just have to agree to di= ffer.

Reply to
fred

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