MDF - screws splitting the MDF

[studysession]

Hi -

What and how is everyone assembling their projects? I predrill and then screw. No matter what the MDF splits.

Please help. Thanks

[gtd107]

Using screws in MDF should be avoided unless you are screwing through the MDF into a solid wood base. Try using small bolts with properly sized washers. The washers will distribute the load into a greater area of the wood preventing tear out and splitting.

[94vette]

The machine that I'm currently building has many places were screws are going into MDF. But my method sounds different then your.

From what you said, you are drilling then turning a screw into the MDF. (like a wedge) The method that I'm using is one that I found here on CNC Zone and it works great.

1. drill pilot hole
2. tap hole
3. put super glue into the tapped hole (not to much, just even as possible)
4. re-tap hole after super glue is dry (I wait until the next day)

The super glue will seep into the MDF and cause it to expand a bit. This is why you need to re-tap. But the threads are nice and strong. And you don;t have to worry about the MDF splitting with the screw because there is room for the screw. Just like a nut.

Hope this helps.

[Jason Marsha]

When tapping into the side of mdf use a small 'C' clamp over the hole. This stops mdf from expanding. Do not try to tap the entire depth of the holl all at once, once pressure is experienced reverse the tap and clear the tap as well as the hole. The clap is important because on reversing the tap it tends to be a little hard and it will push outwards on the hole.

[Mike F]

My advice would be to use the proper screws, the ones developed especially for MDF. They have a very sharp, coarse thread that cuts into the 'end grain' rather than trying to push their way in. You also need to pre-drill the holes as they have a fairly large core. In the UK they are called confirmat screws and are designed specifically to go into the edge of MDF 15mm and upward.

I have used these extensively in my build and use them for student's work at school too and never has there been a case of the MDF splitting. Somewhere in my very long thread there is a picture of the screws along with some discussion. Just had a quick search and found it:
http://www.cnczone.com/forums/showpo...&postcount=150 The few posts after discuss the issue.

Hope this helps.

Mike

[aspenelm]

what about furniture bolts and dowels similar to
http://www.rockler.com/product.cfm?page=367 for right andle joints.

I have made my own nuts/dowels with 1/2" steel rod and drilled and tapped for 1/4x20 bolt. It is pretty easy to make and quite strong, and somewhat self aligning. I have also found the nuts/dowels at the speciality bins at the hardware stores.

[widgitmaster]

Try using T-nuts for wood!

[martinw]

Originally Posted by studysession Hi - What and how is everyone assembling their projects? I predrill and then screw. No matter what the MDF splits. Please help. Thanks

Dear studysession,

You say "the MDF splits". That probably means you are going into the EDGE of MDF, with either the wrong size of screw, or the wrong pilot hole diameter, too close a pilot hole to the edge, or any of the above. And more.

MDF really hates screws in its edge, and the diameter of pilot hole is really critical if it is not going to split. For example, a 3.5 mm diameter pilot will probably split the edge of 18mm MDF if you use a No.10 Pozidrive screw, even if the pilot hole is right on centre. A 4mm pilot will probably be too big to get a grip.

Add to this something else. If you put a pilot hole into the edge of MDF close to a corner, it will split far more easily than if it a long way from one. For No.10 pozidrive screws, I'd say at least 50mm from a corner.

Oh yes, if you over-tighten any of the above it may split.


Try different pilot holes, edge/corner spacings, screw sizes and MDF thicknesses. An hour spent getting a feel for it will save you thousands of hours later. I wish I had.

Really!!!

Best wishes

Martin

[Geof]

Originally Posted by martinw ....Try different pilot holes, edge/corner spacings, screw sizes and MDF thicknesses. An hour spent getting a feel for it will save you thousands of hours later...Martin

Also try a pilot hole with a clearance hole and use a long screw. Drill the clearance size, i.e. the diameter of the shank of the screw, 10 to 15mm deep and then pilot for the root diameter of the screw another 20mm past that. Use a screw long enough to enter around 30mm

[martinw]

Originally Posted by Geof Also try a pilot hole with a clearance hole and use a long screw. Drill the clearance size, i.e. the diameter of the shank of the screw, 10 to 15mm deep and then pilot for the root diameter of the screw another 20mm past that. Use a screw long enough to enter around 30mm

Dear Geoff,

Absolutely right about the clearance holes. I got hung up on the splitting, and forgot about the other workpiece. Thank-you

Best wishes

Martin

[vladdy]

I used common MDF screws, about 1/8" shank diameter..I pre-drilled the holes first, and then rubbed ordinary bar soap on the threads..
no splitting, and virtually no 'swelling' around the hole..except for the few that I did on the edges, no cracking though, just a small bit of swelling..

enjoy..

[studysession]

Thanks for the replies. Definately next time do it a bit different. Building a router for the first time is quite a learning experience.