MDF Layering with Glue?

[biomed_eng]

I would like to layer a few pieces of MDF togther to make 6" thick stock for routering.

My first try, I used Elmers wood glue, however, when cutting, the glue got gummed up and stuck in the router bit grooves and then caused the bit it to stall.

Can you recommend a more appropriate glue?

[ViperTX]

well all the alphiatic.....wonder what the correct spelling is....will do just that.....I would use a polyurethane glue.....you could also use any of the resin & catalyst glue.....like epoxy.....

[pminmo]

I've never had any issues like that. I always clamp tightly. Sounds like to much glue.

[keebler303]

i use tightbond wood glue. it works great. if its gumming up cut down on the amount of glue or let it dry longer.

Matt

[bigz1]

I agree with Keebler and his comments use Titebond. Its an alphatic PVA(Yellow in colour) which unlike the usual White PVA it tends to cut and sand easier.

I would not recomend polyurethane glue for MDF. PU glue is best used on timber as the moisture in the timber acts as a catalyst which speeds up the drying and improves the bond plus it messy. It also expands which may present a problem laminating large surfaces.

[drmosh]

I've done a fair amount of multiply gluing, and veneering, of large panels. I would advise on regular Titebond as already talked about here. However, a couple of points...

1) when gluing up panels, or even moderately sized parts, you'd be amazed how little glue you'll need. The skin on MDF isn't going to absorb the glue like a grained wood will, so you only need to apply a thin film. Get a foam roller used for paint to apply the glue - will make it a lot easier if the part(s) are large. You should rough up the skin of the MDF with 100 grit sandpaper to aid adhesion

2) if you're doing large panels, you won't get much clamping force unless you're using a vacuum press. you can try to do it with standard weights, but you won't be putting more than a few psi across the entire panel unless you have some really heavy (and large and flat) weights

[Harlow]

Thinning the TiteBond about 20% with water makes it spread and disperse a lot easier between the sheets. Still has plenty of strength. If you need a good sealer after then use TiteBond 50/50 w/water. Concrete blocks make good weights.

[sdantonio]

Recomended clamping pressures for most alaphatic glues are 70psi. If you go way over this you run the risk of squeezing to much glue out and having a starved joint. Much less than this and you run the risk of having to much in the joint and getting your gumming problem.

How big are these pieces you are laminating up? In violin making we do something called a rubbed joint. Put glue on the two mating surfaces and them rub the two surfaces together. This forces the glue deeper into the pores giving a stronger joint and also forces out much of the excess (and any air bubbles too. It is said that a good rubbed joint, with well matched and flat mating surfaces, you don't even need clamps. I'm not quite that trusting in my joints though and still use then anyway.

[drmosh]

I knew a guy who was trying to build some thick (over 2 inch) industrial table surfaces using plywood, mdf and phenolic tops. He was constructing them in 4x8 sheets prior to cutting them to spec. He showed me his method which included about 10 full sheets of plywood stacked on top of his glued sheets, along with a bunch (i don't know, maybe 15) concrete blocks stacked on top of that. It was very impressive and very heavy. Except when you took time to do the math...

The 10 sheets of plywood weighed about 750 pounds (roughly) and let's say the blocks added another 750 pounds. That's a total of 1500 pounds. Unfortunately, it was spread across 4600 square inches which resulted in about .33 psi. When I pointed that out to him it sounded pretty ridiculous.

Unless you're using a powered (hydraulic) press, it's very difficult to apply more uniform clamping force across large panels (24"x24" or greater) than a vacuum press. Atmospheric pressure at sea level is about 14.7 psi. For a full sheet of plywood, that equates to a 33 ton press.

The investment for vacuum pump, bag, platen, etc. may not be warranted for this kind of project, but it's absoutely the cheapest method for cold lamination of sheet stock with production quality and uniformity.

[Madclicker]

Dry wall screws every dozen or so inches will pull it tight enough. Just don't forget to remove them all between layer glue-ups.

You don't need a gozillion tons of pressure, just enough to pull the layers tight and screws will do it.

[drmosh]

Just be careful with the screws if any of the flat surfaces (the parts with the screws in them) are going to be used for horizontal surfaces (like a table top). No matter how carefully you drill holes, screws will bulge the substrate material. Not torqueing them down some crazy amount will minimize deflection on the surface, but the act of screwing them in will cause bulges in the interior layers. You cannot eliminate this - it's just how screws work. If you read other forums it's often discussed as a problem when using screws to hold multiple layers on a spoilboard.

It may sound like nitpicking, but things like that often account for that 1/32 inch inaccuracy that you can't explain.

[Madclicker]

You are right. I forgot to mention this. Around the edges you can visually see if the two layers are pulled together. If they aren't just back the screw out and drive it home a second time. In the middle (if 1/32 really matters) back all the screws out and drive a second time before going to the next one.

Can't imagine anyone would use MDF where 1/32 matters.