Need some glueing-up advice

[Knot Competent]

I’ve made some frames from 2½” x 1” (finished) pine 2’ 3” x 2’ 9” overall. The mortice and tenon joints are made on a Trend M & T jig, and as far as I can ensure, the joints are cut square.

The first two frames were glued up and cramped, but when the cramps came off they were decidedly twisted. I made two more frames, ensuring the tenons weren’t so tight. When these were uncramped the frames were still slightly twisted.

So, I need to go back to basics to find out where I’m going wrong. My worktable is pretty flat, the cramps are cheap aluminium 4’ jobbies, which may be distorting a touch if I’m overtightening. I’m using polyurethane rapid glue, particularly as I made the tenons a little looser (and, of course, because it’s much quicker than PVA).

Can anyone offer advice, guys and gals?

John

 

[SketchUp Guru]

Does the frame lay flat when dry assembled? If not, I would suspect either the tenons or the mortises aren't parallel to the faces. If it will lay flat, I would suspect your clamping method.

You might try a panel clamping jig like this and clamp the corners down to the jig. I have one of these for doing small panels and it works very well.

 

[Paul Chapman]

That's a great clamping jig, Dave - and what a simple idea (as the best ones always are :wink: )

I seem to learn something useful every day on this forum

Paul

 

[SketchUp Guru]

Thanks Paul, I can't take credit for the design. A friend of mine came up with it. The jig is very simple to make and you could make it any size you'd like.

You need to start with a square base. The pivots for the clamping arms are located 2 inches in from the nearset edges. Both need to be the same. The holes for the dowels are on 1" centers and need to be located symmetrically on the base. Finally, the holes in the arms need to be centered to get the arms to set up parallel.

 

[Knot Competent]

Ah, dry assembly! Now that's a stage I seem to have missed out on. Cut all the joints, try each one for fit separately, glue it up and Bob's your aunty! But I didn't assemble the whole thing to see how it sat. I was in a bit of a hurry, see? I'm so glad I ask questions here, there's always someone who knows where the errors creep in.

Could cramping too hard also cause problems?

But Dave's board seems a very good idea. How do I keep excess glue from sticking the frame to the cramping board? Be careful, I know, but with polyurethane there's always a bit that pops out somewhere. Would laying a sheet of polythene between the two work?

John

 

[Paul Chapman]

Thanks Dave, that's really helpful. I think I'll knock up a couple in different sizes.

Paul

 

[SketchUp Guru]

Paul, you're welcome.

John, yes, you could use plastic. I use waxed paper on mine because it is cheap and very thin. You could also wax the board or perhaps use a material to which the glue won't adhere.

You could also just plan to make the clamping jig part of the design and let the frame stick to it.


Edited to add that yes, your clamping method could be the prolem.

 

[JFC]

Do you mean your frames are out of wind ? if this is the problem then you could use a spirit level to level the frame out in the clamps also if you look down the work if the top edge isn't level with the bottom edge you can see your frame is out and adjust to suit .