Problem with large inlays

Im doing a 20x20 inlay of my college’s official seal. the female (substrate) is white oak, and that carve went great. The male part was a panel glued up from .25" padauk I got from the hardwood dealer. I’ve run into 2 problems.

  1. How long does it take the glue to dry with a large panel like this? I gave it 48 hours and there was still a lot of wet glue when I surfaced it this morning.

  2. the panel buckled…possible from the wet glue and separated from the female. Is there aa way to prevent this? I had it clamped tight on the sides and a heavy chunk of granite in the middle. Would a much thicker piece be less likely to buckle on the glue seam?

Best I’ve seen is people using hydraulic presses to glue the two parts up…

1 Like

If the back is hidden from view, before you press them together, drill some holes to allow the glue to squeeze out and some air to get in to help with drying.

Also if you have too fine a finish on the mating pieces or you’ve burnished them by running the speed too slow during cutting, the glue cannot get into the grain. That mostly shows up with hardwoods due to the tighter grain.

Remember, a tree is just like a bundle of straws which it uses to move water up and down. When you’ve cut those straws cleanly, even at an angle, glue can get into them. BUT if you sand too fine or burnish the wood, you close off those straws and the glue cannot adhere.

If you want to prove this to yourself real fast, take a piece of corrugated (cardboard to you muggles), and cut it at an angle. Now take some sandpaper and sand that edge. You’ll see how the flutes fill up and close. Now imagine that on a microscopic level.

Here’s a pic of some corrugated I cut and of a piece of wood under a microscope to show what I mean.
Pony

2 Likes

You might be on to something. The padauk is extremely dense and oily. I was worried about glue adhesion anyway. I think I’ll just go with walnut on version 2.

2 Likes

I’ve been thinking about building some kind of press using a couple of car jacks and a 4x4 cage.

1 Like

Harbor freight 20 ton press, $250, 12 ton $180. Lower if on sale, plus a few other bits to properly distribute the force (a bunch of youtube vids on this concept). I don’t think it’s worth the time to try and make something with bottle repurposed bottle jacks - unless you have a bunch of steel kicking around and can weld really quickly and neatly. :slight_smile:

3 Likes

Given the size of what I do I’m thinking a couple of 30" sections of unistrut with a long bolt on each end would probably be sufficient. I can make 2 of those clamps for less than $50.

2 Likes

I wish I could still afford Unistrut locally. It’s at least $100 Canadian a piece around here which means it no longer makes sense to use it for anything unless a corporate gig is paying for it.

The brewery stand I built from that stuff for about $250 a few years ago would be over $1000 today.

1 Like

I would suggest a vacuum press and some sort of non water based adhesive like epoxy or polyurethane
so the material doesn’t swell from all the moisture in the glue.

2 Likes

For smaller inlays where you only do a portion of the work, has anyone just used the Z-gantry to exert some pressure on the glue up? Obviously you wouldn’t want to do too much, but you don’t need a lot of pressure for the glue up to be effective.

This is what I opted for, and it works well. Also works for panel clamping smaller pieces which I use on the CNC.

If I were gluing up in place on the bed of the machine I’d probably use cauls with my threaded inserts in the waste board for clamping pressure.

2 Likes

That is a terrific idea. I have beefy (M8) threaded inserts so it would work.

Oily woods don’t always glue well with PVA glue like tight bond three. I’ve never had a problem, but woodworking forums talk about failures with woods, like walnut due to this. Epoxy etc might work better for you.

I agree vacuum bag would be ideal. Cauls if you don’t have one, or don’t want one. There’s a company called roarrocket that sells a hand pump with a manual vacuum bag for reasonable prices. I have one and it works quite well. You’ll never achieve the clamping pressure that a vacuum bag can provide any other way.

I’d also make sure the wood that you have is properly dried. If the moisture content is not correct, it’s more likely to warp over time.

And finally might want to consider wood movement if you’re trying to glue down some thing that big. Over time it’s going to have a chance of separating from the female part regardless. Different woods shrink and contracted different different rates at different times of the year. Long-term there’s potential for you having some issues. Smaller inlays won’t have an issue with wood movement. As an example wood panels - not plywood - in furniture generally are left to float - not glued in - for the very reason. There’s plenty of online resources about wood movement to read up on. Just be careful. That’s a hell of a rabbit hole to go down.

I’m no pro just a hobbyist so take this all with a grain of salt. Just some thoughts to try to help.

2 Likes

Oh and I’d avoid polyurethane glue. They require water to activate and cure. Plus they foam up so you’d probably be left cleaning that up too.