Which type of screws for laminated MDF?

[Traveller]

Hi All.

I would like to ask if anyone can provide any advice on the type/length/size of screw required to attach a laminated MDF table top (25mm thick) to a table base and if possible, any tips that could be followed to achieve a good result.

Thanks.

 

[Burnerman]

Presumably you intend to fix the new top from below.....in which case, screws that are 6mm short from breaking through the new top would be fine - and using a slim pilot drill will help.
It depends if you are fixing with steel brackets or through the actual table frame which will determine the length of the screws you choose.
Its a good idea just to let the screws 'float' a little just to help with the expanding top - so a slightly larger clearance hole in the bracket or table frame wouldn't do any harm.
John

 

[Traveller]

Thanks for the advice, Burnerman. It's everything I needed to know!

 

[Traveller]

Well I thought that was everything I needed to know!

The table top is going to be attached to a single 'leg' in the middle, which is attached to a cast iron cross shaped bracket. The bracket has eight holes for the screws, four of the holes are 9mm in diameter and the other four holes are 7.5mm in diameter. The thickness of the bracket is also different for the holes. Four of the holes are 9mm deep and four of them are 8mm deep. Since I only need eight screws in all, I am thinking it would be a good idea to find screws that would be suitable for all the holes instead of having to buy two different packs of screws.

Based on the advice given, a suitable screw would be either 25mm or 30mm long and less than 6mm thick. It would need to have a head that is at least 10mm wide. The holes are also not counter-bored. So far, I haven't found any non-countersunk MDF screws. All the following are countersunk.

one

two

three

four

five

six

seven

Too long -

eight

I am assuming that in all the above links, the 3.9, 4.0, etc. is the thickness in mm and not the 'size' of the thickness. I'd have to find out their head sizes.

Any suitable flat head MDF screws available? If I do manage to find some and the heads are not wide enough, would there be any problem using a washer with the screw?

Thanks.

 

[Burnerman]

You don't need a kosher mdf designed screw really - all will hold but naturally enough as mdf is just compressed dust, the coarser the thread the better.
Always use a thin pilot drill to locate them.
Consider using self tapping screws - often stainless and always hard. They are available in round head, pan or csk and B&Q have a range.
The bracket holes are on the large side, so feel free to use a washer.
As before, use a screw thats as long as possible without any chance of break through.
At the end of the day, mdf is always going to be on the weak side, so your table wouldn't appreciate kids climbing on it, or being lifted up by the top.....you know the sort of thing.
John

 

[Traveller]

Thanks Burnerman. I have lots of screws which look like the self-tapping screws B&Q have. As I am not a screw expert, I have no idea if they are in fact self-tapping screws or what quality they are as they're probable from one of those cheap little fancy cases that you get full of different screws sold at cheap non-diy stores.

I haven't yet decided if I will use 25mm or 30mm because I have also read that this material tends to bulge as well if a screw is driven in too far, but on the other hand, your advice is to use a long as possible screw. If I need to use a washer, then 30mm would be more appropriate I think.

I am worried about the lifting the table problem, as I think the table will have to be lifted from time to time. The base is VERY heavy so I am thinking I'll have to stoop down and move the table by pushing the leg/pole.

Thanks for the advice. I think I might go for the self-tapping screws as you have suggested. I think I might also start off with a thinner screw, e.g. 4mm so that if they do become loose after a while, I can use the next size up to get a tight fix, etc.

 

[Burnerman]

There's always Plan B, Mr. T - and that is to fix a cross of softwood timber to the mdf......screwing it down with PVA adhesive and then fixing the steel framework to that.
This would allow you to use longer screws than those directly into the mdf as you are relying on the adhesive bond to keep things in place.
Screws will always take better into natural timber than mdf.
John

 

[Traveller]

Plan B sounds like a very good plan! Unfortunately, the table is a little on the high side already and there is also another layer to go on top of the table, which will make it even higher, so I really can't add even a few mm of extra height. Thanks for the good suggestion. I think I'll go for your previous suggestion and get them today!

 

[Traveller]

Hi Burnerman. Just an update. I opted for your suggestion of self-tapping screws and followed your advice regarding the method and it seems to have done the job fine. Thanks for your help.

 

[Burnerman]

You are most welcome - you can always go for a thicker gauge screw if they slacken at any time.
Wishing you well with your next project!
John

 

[Traveller]

you can always go for a thicker gauge screw if they slacken at any time

My thoughts exactly!

My last similar project was about five or six years ago, so I don't know when my next such project will be, but I know where to come. Thanks. (There is usually lots of other weird and wonderful little projects in between though.)