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screws in mdf

6/27/13       
Chewbacca

I've been asked to make some simple tables in MDF. Just a simple mdf top, with screw on legs, which attach via a metal plate. The plates are supplied with 5/8" pan head screws, however, I would like to find an alternative as I know a screw into mdf is not great. I was considering maybe using the plastic press-in dowels as supplied with many euro hinges. Any suggestions?

6/27/13       #2: screws in mdf ...
D Brown

You could glue a wood or plywood block to the underside of the mdf and fasten your legs to the block.

6/27/13       #3: screws in mdf ...
Chewbacca

D Brown,
I did consider using some slightly over-sized pieces of hardwood (maybe 1/4" thick), may be an option, but does add time and materials on 100+ tables.

6/27/13       #4: screws in mdf ...
D Brown

You could countersink through the top and use nuts under .

If any legs screwed to the mdf come out they may take material with them, seems like little integrity .
The time and cost to repair a table will take less then the blocks to apply prolly will .

6/27/13       #5: screws in mdf ...
Rich

Your answer of 100 tables implies a commercial job. Better make sure you liability insurance is up to snuff with that table design. Anyone bumping into them sideways is going to break off a table leg and dump whatever is on it right off. I assume you are talking about 3/4 MDF. That 5/8 screw is only going in 9/16, and the point doesn't hold much. You are looking at 1/2 or less of actual MDF and screw engagement. Mock it up, bet if doesn't take much to snap it off.

6/27/13       #6: screws in mdf ...
Chewbacca

Rich,
Those are valid points and I'm glad you pointed them out because I never would have had the forethought to consider it myself. Do you know where I might go to ask a knowledgeable group people for a solution to this potential problem? Like an internet forum or something......about wood......

6/27/13       #7: screws in mdf ...
mark

Cool it, Chewy. Not everything is durable. You seem to be describing a design that is not durable, regardless of which fastener you choose.
Drywall screws and PL Premium is about as good as it gets.

6/28/13       #8: screws in mdf ...
Chewbacca

Yeah, I'm not crazy about the design myself and really not excited about using mdf. I've not signed up to do the job and don't really want to if I can't feel good about it. However, I'd rather offer a cost effective alternative to the customer instead of turning it down all together. Hard to turn away any work these days.

6/28/13       #9: screws in mdf ...
scott

I really can't answer you question without some more info. Otherwise, I might tell you a 2" screw will hold better than a 5/8".
How thick is your material 3/4 or 1-1/8?
Is the bracket a thin, simple stamping or 1/4" plate?
Using a leg at each corner or a center pedestal?
What is the height of the top, 18" - 30" - 42" - big variance in leverage.

The answer really is this:
Use as long and as fat a screw that you can and if you are using 3/4 material add a 3/4" plate/batten on the bottom. Use a pan head sheet metal screw # 10 at least, preferably #12.

6/28/13       #10: screws in mdf ...
Chewbacca

3/4" MDF, stamped plate, 17" high, leg at each corner

6/28/13       #11: screws in mdf ...
scott

Eh,,, 17"H, a leg in each corner, 4 screws each I assume. I'd just use the 5/8 screws that come with it and go directly into the 3/4 & skip the extra plate.
Unless these are gonna get really abused or dragged around over uneven tile or whatever yer good to go. (Set the clutch on your drill to not spin out the 5/8 screws, MDF, it happens, especially when banging out 400 screws.)

6/28/13       #12: screws in mdf ...
scott

Oops 1,600 screws.

6/28/13       #13: screws in mdf ...
JeffD

First off I would want to do a mock up to see first-hand my options and how they'll work. Before I get that far though I'd throw out any idea of drywall screws or any normal wood screws or the screws supplied for that matter.....not going to work. Well, at least not going to work for long;>) Adhesives are not practical in this situation either.

The fastest and easiest is probably going to be drilling them for 5mm Euro screws. They'll hold significantly better than any other normal wood screw. The problem may be whether or not you can get the plates with the correct sized holes to work with Euro screws??? If you have to drill the plates it may not be practical. Plastic dowels could also work though will need extra time for drilling and insertion. Though they will work with whatever holes the plates are drilled for.

good luck,
JeffD

6/28/13       #14: screws in mdf ...
Chewbacca

A preliminary test:
Far Left:1/4" Maple glued to mdf, 5/8" screws (shown at 15lb)
Center: Nylon dowels in mdf (failed at 10lb)
Far Right:5/8" screws in mdf (held 15lbs)

Ok, so not at all scientific, but I was curious. Plates are angled not straight. Honestly, from the looks of it, the weak point seems to be where the dowel screw is in the leg. That's where it flexes under load.


View higher quality, full size image (3264 X 1836)

7/1/13       #15: screws in mdf ...
Mark B Member

If it were me Id be opting for the maple option with the substitution of a 3/4" or even a 1" screw as long as the 1" screw doesnt bulge the top surface. With that combo I would be comfortable that the entire corner will break off the table before the leg connection fails.

While the hanging weight is a good test the issue is of course as mentioned, sliding/scooting the tables around. That kind of stress on the leg over time is substantially more than a static dead load.

If they'll pay for the maple seems like youve found your solution.

7/1/13       #16: screws in mdf ...
Keith Newton

About 8 years ago, a customer brought some cheap pre-hung walkthrough doors to a job, and ask me to hang them in the opening. the styles were a very soft mdf, and no pilot hole had been drilled for the screws.

Needless to say, they fit nicely in the self-destruct category. However, I always keep the thin CA glue onhand, so I flooded that fluff for all it was worth. It really soaked it in, and turned the surrounding area into a solid plastic plug,

I had to drill a new pilot hole for the screws, to even get them back in. The doors are still holding, and I've used this trick a few more times since then.

7/1/13       #17: screws in mdf ...
mark

Score; good job, Keith!

7/9/13       #18: screws in mdf ...
Rich

Golly Chewy, nice reply to my advice. When you come onto a professional site and ask for help to screw legs to a piece of mdf, it appears that you need help with some very basic information.


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