Fix for sliding glue joints??

[ian maybury]

I've been laminating squares of 18mm ply together lately with the usual result - lots of fiddling about to overcome the tendency for the pieces to slide out of alignment as the clamps are tightened.

Does anybody have a proven and more or less universal solution for use with joints like these that doesn't involve fiddling about with locating blocks and the like? e.g. maybe a sprinkle of sand?

Thanks

ian

[Peter Quinn]

I've been laminating squares of 18mm ply together lately with the usual result - lots of fiddling about to overcome the tendency for the pieces to slide out of alignment as the clamps are tightened.

Does anybody have a proven and more or less universal solution for use with joints like these that doesn't involve fiddling about with locating blocks and the like? e.g. maybe a sprinkle of sand?

Thanks

ian

I keep a box of pumice handy in a little shaker can, like a baker might use for flour or icing sugar. It sure helps keep things put, but if you add lots of extra glue and out of parallel clamp pressure you can still cause things to slide around a bit. And I've certainly done both. But it gives you a fighting chance. A few brads shot in the right place can help too. When we skin plywood at work, usually in a stack of 4-10 piece traditionally pressed, we leave an extra 1/2" at each end, maybe 1/8" on each edge if its possible, and drive a brad or two into each end to keep things from sliding about. Later this gets cut off before any other machining.

[Kenneth Speed]

There's a lot that you aren't telling us so it's difficult to know what would work. If you're trying to build up a thick structure of plywood blocks laminated together I would recommend laminating two piece sandwiches and then laminating the sandwiches until you have the thickness you require. I'd also suggest hide glue might work if your project doesn't have to be waterproof. I frequently keep pieces that I'm going to laminate somewhat oversize and then trim them to size after they are glued up and dry.

Ken

[Robert LaPlaca]

how about a couple of short brads that you 'nipped off' with wire cutters
in the joint to keep the joint from sliding around

[Andrew Pitonyak]

I assume that you are not then trimming to size after the glue-up.

When it really matters that things do not move during a glue-up...

How about a jig? This is pretty common while gluing corners for things like picture frames. Take two legs and clamp them in position. I have also used squares that are clamped to the piece to hold it in position while things dry. When I had a bunch of pieces to glue, I placed a stop along the edges. The stops were made of wood and I placed some heavy duty packing tape on them (because glue does not stick to it). I then used clamps to hold the edges against the stops.

[Howard Acheson]

The two ways I used to teach were a brad or sand. I prefer the brad. Hammer the brad in a 1/4" or so then using a pair of wire cutter pliers cut off the brad at the level of the wood. This leaves a small sharp nib slightly above the surface of the wood. Put two in strategically placed to keep the boards from moving(sliding) in relation to each other. Apply the glue and clamp.

The other way is to sprinkle a very small amount of sand onto the glue. Then apply the mating board pressing down firmly. Then apply your clamps.

[ian maybury]

Sorry not to give more detail. I'm right now gluing up roughly 6in x 4in pieces of 18mm birch ply in pairs to make parts for a fixture for the table saw (a set of parallel bars for setting up angle cuts on the slider) - but it's the sort of job that comes up at intervals. It's no problem to go a little oversize in this case so that some movement isn't a problem - and it's possible to get quite good at positioning the clamps to minimise the movement. I definitely couldn't handle multiple pieces Kenneth.

It's even better though if there's no need for this - sometimes it's handy to have a good edge to put against a fence or whatever.

I've on occasion made fixtures and clamped blocks across the edges - wrapping the contact parts in cling film and laying everything out over a sheet of polythene works quite well to stop them sticking.

It's troublesome though, and there's times it handy (especially when the two pieces are not exactly the same size) just to spread some glue and clamp the pieces up. I'd seen mention of approaches like pins and sand, and wondered what the experience was.

Thanks for the input guys - think I'll try the flush cut pins first. Knowing my luck I'll put one right where a day later I'll want to cut. Pumice might be a bit more tool friendly. I've seem mention of using a sprinkle of saw dust as well....

ian

[Bill ThompsonNM]

Alittle pinch of grit from a parakeet (budgie you probably call them) works well. Usually it's sharp sand so doesn't interfere with the glue up but adds enough friction to prevent sliding. One box should last a lifetime.

[ian maybury]

Ta Bill. Will try that too. I'm guessing (a) it's the right grit size to work, and (b) placing it so that it's not going to have to be cut through afterwards is advisable...

ian

[Charles Lent]

What kind of glue are you using? I had these problems when using "Gorilla" glue. I went back to Titebond type II and my problems ended.

Charley

[Howard Acheson]

>>>> I'll put one right where a day later I'll want to cut.

Not to worry. A carbide blade will easily cut through a small brad without damaging the blade. Also, on the same subject, I meant to mention that sand (silica) is harder than the steel used for brads. Use only a few grains. They can damage sawblades in large amounts.

[Bill Petersen]

I haven't tried this myself, but have heard of someone using a little bit of sugar instead of sand. Supposedly it dissolves as the glue cures and is completely benign to tool blades. Plus, it would make a really "sweet" project.

Bill

[Bill ThompsonNM]

For those of you interested looking up the MOHs hardness scale:
Silicon Carbide: 9
steel shot: 8
Quartz. (silica sand) 7

I'm always afraid that if I use a brad I will slice through it and it will probably be exposed on some vital surface. You don't need more than a few grains of sand, and I've never found them while sawing, But of course i always seem to manage to find ill placed screws and nails more often then I would like. However, usually with no blade damage.

[ian maybury]

I've been using a liquid PU which is a bit more slippery than some.

Sounds like the real trick is possibly some sort of readily available and non toxic/harmless fine crystal material that won't damage blades, isn't water or solvent soluble and won't degrade the glue or the joint over time. Wonder if there's some sort of washing soda, resin or the like that would work? Any chemists about?

If it was insoluble enough you could mix a sprinkle into the bottle of glue...

ian

[John Coloccia]

Your clamps need to be straight. This problem comes up in guitar building all the time. You can make things oversized, you can use jigs, you can drive some brads/staples into a cutoff area, or you can make your clamps straight. In practice, I use all four techniques. Sometimes I'll drive some staples with my Bostitch staple gun through an area that I know will get routed away later (pickup location, for example) and set it high so I can pull it out later. For jigs, I drive brads with a brad gun somewhere in from the edge and anywhere else I plan on cutting later.

Making a jig probably makes no sense for you. The last technique takes a bit of feel, but what you do is align the clamps so that they don't pull it out of alignment. Now what helps here is don't use too much glue. The more glue you use, the more it acts like a lubricant. You just need to lightly coat the surface. A lot of squeeze out is not required. Bring the clamps down slowly, continually aligning them, and at some point it will grab. Then you can carefully crank it down. The clamps always want to align themselves square with the surface, so if you align them out of square to begin with, they will square up as you tighten down and drag pieces out of alignment.


For jigs, brad nail and then clamp is a slam dunk IMHO.