Gluing MDF ?

[myxpykalix]

I'm trying to glue some mdf together to make it thick enough to turn round and make into spirals. I tried using titebond 2 and 3 and after being in the clamps overnite it still pulls apart. Has anyone glued mdf together and what did you use?

[harryball]

I glue MDF all the time... I use regular wood glue and apply a coat and let it soak in and dry for 30 minutes or so. Then I apply the next coat and clamp it being sure not to use too much pressure.

I don't remember where I picked up the method, but it seems to work.

Robert

[mthomas]

a couple of suggestions...

because the mdf is porous the 2-stage idea from Robert is a good one. the first coat kind of seals it so the second coat doesnt get absorbed too.

also, if the sections are of much surface area its hard to get really good uniform clamping force. for anything over 24" square i use a vacuum bag. leave it in for about 45 mins with a thin coat of glue on both faces. take them out of the bag and let them setup for another 2-3 hours. at that point they'll be laminated together. i do a lot of glue lamination of sheet goods so let me know if other problems.

mt

[myxpykalix]

This was only 1.5" x 22" (2 pieces of 3/4" mdf) so it was small. I went to drive a screw in the end to hold my mounting bracket on the end and the driving in of the screw was forcing them apart, so i figured it wasn't going to hold. I can predrill a small hole I was just concerned about the possibility of them coming apart at some point.

[fleinbach]

I glue MDF together all the time and I have used titebond 2 as well. I have had no problem with seperation. One thing I noticed was you said the part was only 1.5" wide. So after glueing your part was 1.5" X 1.5" X 22". Then you tried to put a screw in the end of the piece. This will never work. MDF end grain is extreamly weak. Putting screws anywhere in the end grain will split MDF. There are special screws made just for the purpose of screwing into end grain MDF. They are made by SPAX a german company. They are very thin with small heads and self taping. They work better then any others I've tried. But nothing will work, including them if you are within 2 inches of the edge. For this reason I always use solid wood for anything wider then 4" that will reguire screwing into end grain.

[beacon14]

As Frank says you have a very weak glue-up due to the nature of the MDF core. I'd be concerned about the workpiece shattering during turning, assuming you can get it mounted.

For screwing into MDF edges, always predrill using a tapered drill or a straight drill with the same diameter as the shaft of the screw (so only the threads cut into the MDF). You can also drill a 3/8 or 1/2" hole, glue a wood dowel into the hole, then predrill and screw into the dowel. For such a weak cross-section I would clamp the end of the workpiece to keep it from splitting while drilling.

The MDF is much more likely to split within one layer than the layers are likely to come apart if properly glued. Solid wood would be much more appropriate here I believe.

[fleinbach]

Correction.
I ment narrower then 4" not wider.

[paul_z]

http://www.mdf-info.org/ Look under "Using MDF", "Fixing" for some recommendations.

Paul Z

[patricktoomey]

I have had good luck gluing up MDF using hotmelt polyurethane glues but I haven't tried to carve the end result. I think it would work but the glue dries very hard and I don't know what it would do for bit life.

[fleinbach]

Here is a link to a company that carries Spax screws. http://www.ultimategarage.com/spax.html

They work very well in MDF. They also have self tapping screws that work in hardwood. They work just as well.

[myxpykalix]

Your suggestions have basically confirmed what i've experienced. The quickest fix might be to attach solid wood via a dowel. Probably it might be better to go back to a solid wood instead of trying to fool with mdf in this application. I'm glad i have my "mentors" just a mouse click away for all the help...thanks fellers!

[slayer]

If you don't need it 1 1/2 " perfect try to plane of one side of the mdf and try glueing it.