Screwing MDF

If its possible clamp 2 pieces of wood either side of the MDF where the screw/s are being inserted.

Either don't, find another way to do it, or use a tap (which you could make out of a screw), with clamping as suggested by "ben". I guess drill'n'fill'n'screw would be fiddly.

That's because you can't.

If you absolutely must, drill and glue hardwood plugs in there. Ideally drill the plugs through the face perpendicular and screw across them, like a wooden knock-down barrel nut.

Don't do anything to MDF that puts a tensile force across the laminations. It might not delaminate today, but it will do.

Heh! MDF does not have laminations, its compressed fibres.

If youre screwing with MDF youre screwed already. Use something decent

NT

Still delaminates, though. ;-)

It splits quite easily into thinner bits. Take, say, a 12"x1" bit of 1/2" MDF. Flex it severely, and see how it breaks. You know how your finger-nail sometimes flakes? Same thing.

Drill 2mm holes and use panel pins with a smear of glue on them.

Don't screw into the end grain - either use glue with proper cut joints or dowels, or metal plates or wooden battens with screws.

And those fibres are oriented in such a way that they effectively form layers which will easily split apart.

MDF is pressed in sheets, rather than rolled. The pressure is applied in one axis and so there are two strong tensile directions and one weak one. You can (pointlessly) argue the semantics of "laminated" and whether it means that such a material _must_ be formed by laminating flat sheets together, but the simple upshot is that MDF has inbuilt planes of weakness and disassembles into laminations, no matter how they were formed.

Thanks for the input chaps. No magic bullet then.......

Plan 'B'.

I'll try cutting a 6mm deep dado in the sides & screwing through from the outside - hopefully the tight fit of the shelf in the dado will stop the splitting.

I'll try that tonight & report back!

Dave

Slightly OT..

It's worth mentioning that it is now thought that dust from some types of MDF *could* be carcinogenic, due to the glue used to bond the fibres.

It's therefore very important to wear a face mask and cut it in a well ventillated area.

sponix

I've built mdf shelving with Scewfix Powerdrive carcass screws, straight into the end grain with no pilot hole. As long as you're dead centre, and at least 2" inches from the edge, you should get away without bulges. Boxed in 1000s, so not something you can try out easily. Maybe B&Q Warehouses would have something similar in smaller packs. I've never had much luck with "mdf screws".

Hi,

Have a look at the woodfit site, they have loads of fixings for this sort of thing, eg:

Also some good tips here:

If just a few holes I'd try giving the screws a good coat of molten wax then dropping them in oversized pilot holes filled with epoxy. After the epoxy has set the screw should home out (hopefully!) and allow the other bit to be fastened on securely. Would need trying on some scraps first though.

cheers, Pete.

Why not just glue it? I've made bookcases that way that held themselves together even without glue, which makes the gluing up pretty easy.

Try drilling and then screwing with 2 inch drywall screws from B &Q with a dab of pva glue. Done all cupboard door hinges this way and no bulging or splitting

It's really an assembly thing, difficult to glue up without screws in my somewhat cramped workshop.

Dave

Plan 'B' worked a treat! Applied glue to the dados (Titebond 11) and used

SPAX 'M' screws aren't cheap mind, £5:98 for 100 - but they do what they say on the tin.

Joints are as tight & strong as they could be - jobs a good un!

Dave