Max length screw to attach legs to 18mm mdf

[JP_]

I plan to fix table legs to a piece of 18mm mdf. The legs have a steel fixing plate. this one from screwfix

What is the max screw I should use? About 15mm?

 

[mrrusty]

If this is for a static support where the top is butted up to e.g. a wall it doesn't matter so much. If you are making a free standing table which people will lean against, move etc, then you are not going to get a good enough fixing with screws straight in to 18mm MDF - there is too much leverage from a 700mm leg and the joint will be very fragile and susceptible to the very short screws pulling out. You would be better making a simple frame out of e.g. 25mm thick timber, use a high strength adhesive to fix the frame to the underside of the table and then use e.g. 40mm screws through timber and into the top, which will give you a much stronger fixing.

 

[diy_fun_uk]

You should be fine with something around 15mm as the plate will essentially reduce the size by 2mm give or take. The only thing I'd add is to ensure the screws are suitable for MDF. Also, depending on the forces the MDF will be subject to, bear in mind screws can tear out of MDF easier than most real woods. So if for example there's any sideways movement (even just slight) it's possible/probable the MDF will fail.

 

[JP_]

thanks, sounds like I may as well stick some wood on the underside to be safe. It's going to be a desk, so I could fix it to the wall, but maybe better to just put more support on it and bigger screws.

 

[foxhole]

If desk is secured to wall then legs will be fine , though I would add 100mm square section of mdf to leg location so you can use 35mm screws .

 

[JP_]

Will look for a couple of strips of wood to run the length, or width, of the desk underneath for the legs - will make it more solid also.

 

[mrrusty]

Gluing the bracing is important - otherwise it is just a spacer!

 

[Notch7]

A square block of 18mm ply works fine.

Glue and screw it on.

Long length of timber only needed if table is free standing and you want to reduce tendency for racking.

 

[JP_]

Found some more bits of my son's bed I kept. Gluing now. Will screw in for added support, then put the legs on.