Question on using MDF

[Ed62]

I've never used it, but I have a small project I'm considering using it on. I know it's supposed to be very stable, so my question is, Does MDF need to become acclimated to the climate of the shop before cutting to size, like solid wood? Also, are there any widely available screws that will hold well in MDF? Rod??

Ed

[cabinetman]

MDF does not need to be acclimated. Some say "confirmat" screws work well. I have good luck with a pilot hole and a good drywall type screw, just bumped tight, not driven fast. Cordless drill on slow speed is how I drive them.

So, what's the project?
.

[jhart]

I've always heard that the pilot hole should be deeper than the screw, otherwise you'll get a small lump/bubble type area. A good course screw will work ok or you can get "special" MDF screws from the box stores or local hardware store. I'v had good sucess with drywall screws also, similat to C'man.

[Alex Franke]

I use drywall screws, too. I agree with jhart on drilling deeper than the screw is long especially if you're screwing into the ends.

Remember to paint/seal it and wear a mask when working it. Although you can get it without, MDF usually contains urea-formaldehyde.

[crokett]

YMMV but I've never used the special MDF screws. Plain coarse thread drywall screws and glue here. Some folks say countersink the hole on the back of the face piece you are running the screws through to avoid the bubble, I've never done that either and nary a problem. I just make sure the pilot hole is the right size and go slow.

[footprintsinconc]

exactly what cman says.

if you are using pockets for connections, then use just the coarse threads, but the most important thing is the when screwing it in, the drill has to be slow, and it should come to a stop once the head sets into the pockets.

[LarryG]

MDF doesn't have to be acclimated, per se, and it is very stable dimensionally; but if you store it incorrectly, it can still bow a little. This usually happens when one side is more exposed to the air, or a masonry wall or concrete slab, than the other. Also, the bow takes a lot longer to develop than with solid wood or veneer-core plywood, which as you know can and will banana on you overnight.

The two biggest problems with driving screws into MDF is that you can get some blow-out, in the form of little raised donuts around the drilled hole, between the pieces being joined. These can keep the joint from tightening up fully when you drive the screws. I always drill the holes, separate the pieces, pare off the donuts with a sharp chisel, then assemble.

It's also frustratingly easy to split the material when driving a screw into its edge. Carefully match the drill size to the screw shank, drill plenty deep as has been mentioned, and try to keep all fasteners at least a couple inches from the end of the piece, preferably more.

If you use drywall screws (which is what I've been using thus far, although I'm about ready to try Confirmats), use the coarse-thread type.

[cabinetman]

YMMV but I've never used the special MDF screws. Plain coarse thread drywall screws and glue here. Some folks say countersink the hole on the back of the face piece you are running the screws through to avoid the bubble, I've never done that either and nary a problem. I just make sure the pilot hole is the right size and go slow.

I don't agree with a deeper hole than the screw. My pilot holes are just short of the screw length so the first few threads are into full material. It is beneficial to countersink the backside of the primary piece, or mating pieces. For instance, if you are screwing two flat panels together, and the screw is driven through the first to the second, there is a tendency for MDF to crumble slightly. If that happens, there will be debris between the two sheets around the hole.
.

[drumpriest]

I'm with cabinetman on this one, I don't drill deeper than the screw. Occasionally I'll get a little bump, but I just plane it off with a hand scraper, doesn't take much work.

[poolhound]

I'm with Keith and CabMan. When drilling the pilots I always smooth off the backside with plane or sandpaper, even a sharp paint scraper works. Id find that if I am drilling directly through 2 pieces to be joined and they are clamped hard together it can prevent the raised edges on the backside and you can drill the pilots and then directly screw together.

[Ed62]

Nine replies already? That great!! Thanks very much for the tips. They're very much what I thought, but wanted to be sure about it.

Ed

[viking4949]

Hey Ed

Where are you from? I work in Griffith and live in Hobart, but grew up in Portage.

Brandon

[cabinetman]

Ed - What's the project?
.

[eccentrictinkerer]

I just finished a project for a customer that used MDF.

I read somewhere on the forum about countersinking the back of the panel that the screw is going through. This gives the blowout somewhere to go.

I did this and everything worked perfectly. Tight joints, no frustration!

[mclear6]

I read that in wood or shop notes

I just finished a project for a customer that used MDF.

I read somewhere on the forum about countersinking the back of the panel that the screw is going through. This gives the blowout somewhere to go.

I did this and everything worked perfectly. Tight joints, no frustration!

I recall that in either wood or shopnotes there was an article about mdf. They recommended drilling a pilot hole deeper that the screew, use only machine or dry wall screws that have a straight shank (a wood screw would split the mdf),and they said when joining two pieces, countersink the joining sides of both pieces so the "bubbling" won't occur leaving you a clean, flush joint.


I'll try to see which mag and which issue when I get home