Screws for MDF

[MilDoc]

I've read that Confirmat screws are recommended for MDF, but was wondering if McFeely square drive, or Spax screws, would be as good or better?

And, on the subject of screws, some parts lists call for Fh or Rh woodscrews. What does the Fh & Rh stand for?

[LCHIEN]

quote:Originally posted by MilDoc

I've read that Confirmat screws are recommended for MDF, but was wondering if McFeely square drive, or Spax screws, would be as good or better?

And, on the subject of screws, some parts lists call for Fh or Rh woodscrews. What does the Fh & Rh stand for?

Flat head, round head

[crokett]

I've just always used coarse thread drywall screws with no problems.

[LarryG]

I too use CT drywall screws, but when fastening into the edges you have to make sure the pilot hole (drilled with a tapered bit) is the correct diameter and deep enough; otherwise, the potential for splitting is high.

[crokett]

Since all the MDF I've ever done is painted, I counterbore so I can fill holes later. A 3/8" bit is the perfect counterbore for drywall screws. I've never had MDF split. My brother was using a countersink last weekend on a project he is doing and the MDF was splitting. I told him to counterbore and his problem was solved. Of course I always glue as well.

[LarryG]

You lost me, David. The bit I use is the tapered kind, with an adjustable countersink/counterbore. But the splitting problem is not at the head of the screw, in the "top" piece. It's where the threads go into the "bottom" piece. And, again, note that I'm talking about fastening into the edge of a piece, not through its face.

[Woodnut]

There's a trick that professionals use to help.

Make a countersink on the inside edge of the "top" piece as well, this allows a bit of releif room for the "nubbies" that will be brought up as you drive in the screw.

The "inside" or "bottom" countersink does not need to be as dramatic as my diagram makes it out to be, just enough to help relieve the tension that the "nubbies" brought up by the screw going into the lower MDF.

[Jim-Iowa]

That is a good tip Woodnut. Another thing I found helped was to drive a few turns and back out. It seems like driveing full depth caused splitting and by driving a bit and backing out kind of threaded the hole?

[crokett]

Hmmm... Larry he is fastening into the edge of MDF and his problem was the splitting at the countersink - some of the holes were not countersunk perfectly straight. He switched to a counterbore and it worked. I've never had MDF split on me anywhere, so I guess there are mulitple places it can split.

[Andrew Benedetto]

I use the Kreg screws and pocket the corners. I think it is a better way b/c the kreg screws are self drilling and do not split wood,washer head,flat bottom not beveled also better, more grip due to angle of screw,one step drilling,very accurate,fast and repeatable. MDF drilled on end,90* is not that strong and can cause expansion internally. The con on the pocket is a larger hole to cover up but if painting MDF that is easy.
I just built a computer desk/printer station with melamine that way and Poly. glue. (all screws are hidden)I also made a shelf/backsplash for LOML to sit on top of the washer/dryer. The backsplash has little stress so I used caulk in the joint. You can also add biscuits too to keep the pieces lined up an add more strength. I think the kreg system is one of the best things I have ever bought.

[RodKirby]

When edge drilling MDF, I've found that the pilot hole needs to be only one size less than a clearance hole - ie barely enough to "grab". And I [u]always</u> countersink the back of the "top" piece.

This implies a good (Titebond?) glue is in use.

[Andrew Benedetto]

quote:Originally posted by RodKirby

When edge drilling MDF, I've found that the pilot hole needs to be only one size less than a clearance hole - ie barely enough to "grab". And I [u]always</u> countersink the back of the "top" piece.

This implies a good (Titebond?) glue is in use.

Is that metric or SAE?[^] How much 1/32" or 1/64"?

[RodKirby]

Andrew - 1/64".

This allows the thread to catch, without forcing. The length of the screw is enough to hold it - the best example of this is the confirmat screws

[Andrew Benedetto]

I will try it,I never have counter sunk the underside and that may be why the splitting.
Rod could you tell me your method of determining the pilot hole size,and do you use a specific screw type? I have found that drywall screws can break.

I have splitting on my wolcraft/sears folding stands where the top is screwed to the steel frame . I guess it is too close to the edge. I need to band them with hardwood or use carriage bolts.

[RodKirby]

I have a hole gauge - I drop the screw thru the smallest hole I can - say 11/64" for a #8 screw, then use 5/32" (-1/64") for the pilot hole.

I NEVER use woodscrews - always screws with the thread along the whole length, or with at least the shank the same dia the whole length.

IMHO If any screw breaks, the pilot hole is way too small.

If you need it, I'll take some pics tomorrow...