Thread: Parallel clamps are moving as they tighten causing my glue ups to “slide”

Boards moving under clamping pressure isn't unusual and can be attributed to a number of factors
eg too much force, boards not square/parrallel, glue making things slippery etc

I'd say given that you've also brad nailed the boards you're gluing up and they are still moving its probably due to too much force being applied to the boards, realistically if you're brad nailing you don't need to clamp as well.

Thanks. Yeah this feels weird though. It’s like as I get everything “firm” but not tight it looks like this:
IMG_5833.jpeg

Then I start tightening, but very quickly it becomes like this (very exaggerated just to illustrate the point):
IMG_5834.jpeg

I thought the whole point of parallel clamps was to stay, well, parallel?

Do you have a pic of the items in your clamps?, you should not be getting that sort of movement, with those types of clamps

Are you sure your brad nail are long enough and going through into both boards.
re Clamps are they genuine or the lower quality Chinese copies.

Are these the clamps you are using?

Robin Lewis full review of Pony Jorgensen Clamps - I-Bar Sash Clamp, E-Z Hold Clamps - YouTube

I didn't take any pictures unfortunately. Can do it again and take some photos.

Brads definitely went all the way through.

I bought the clamps from Timbecon about 6 months ago (these "Cabinet Master" ones: https://www.timbecon.com.au/pony-jor...llel-bar-clamp)

The boards slipped about 2-3mm out of whack when I tightened it all up.

Originally Posted by lemerv

I didn't take any pictures unfortunately. Can do it again and take some photos.

Brads definitely went all the way through.

I bought the clamps from Timbecon about 6 months ago (these "Cabinet Master" ones: https://www.timbecon.com.au/pony-jor...llel-bar-clamp)

The boards slipped about 2-3mm out of whack when I tightened it all up.

Do you use salt with your glue up to help stop the timber moving?

Originally Posted by Camelot

Do you use salt with your glue up to help stop the timber moving?

Say what!?

Originally Posted by jack620

Say what!?

Found this video on using salt, it's been around for years, my tutor showed the class when I did my City & Guilds back in the late 70's/early 80's

https://www.youtube.com/watch?v=PWsy...nGuitarsExtras

Originally Posted by Camelot

Do you use salt with your glue up to help stop the timber moving?

I've heard of the salt thing but didn't think to try. Having said that, 8 brad nails should hold it pretty damn tight!

Given the clamps still forced it out of whack is why I'm wondering if I have a problem with the clamps

To get no movement at all, everything would have to be precisely parallel - the clamp jaws, and your joint line. I've never seen that happen in the best of all possible worlds

I just put in a domino (or biscuit if if you have a biscuit jointer) between the boards somewhere at each end of the assembly to maintain alignment and prevent movement under clamping.

The clamp jaws flexed? If that's the case and you tightened the crap out of them, your nails would not have been able prevent the movement.

You could try salt or sand next time, another set of clamps 90 degrees w/r to the others, not as much pressure, and/or lay your glued pieces at the bottom of the jaws opening.

Agree with what mr. brush said. I don't use cauls or anything to glue together panels and one of the things you have to get right is clamp application with parallel clamps.

the key in this case being that they want to pull parallel. that means if you're applying them anything but perpendicular to clamp surfaces in any way, they will attempt to pull themselves into parallel and move material while you're doing it.

Two tips - partially tighten the clamps when installing them so that they don't move the wood and jostle them just a bit to see if you find a direction that they're looser - if you do, they weren't parallel, and visually do what you can to get the same top and bottom part of the mouth on the item to be clamped. If the jaws are 3.5 inches deep and you have one end on 2 inches and the other side slips a little to 1 and you go to tighten, the clamp will pull on the materials trying to get itself flat on the mating surface.

when you partially tighten a couple of clamps and nothing moves, then you can go down the line and tighten everything. the clamps that are a little off shouldn't be able to move the others.

Embedded in this, too, is getting work to a tolerance tight enough that it doesn't need 1000 pounds of clamping force from end to end. Sometimes, you have a small gap to close and can't avoid it completely.

this sound tedious, but you sort of get the feel pretty quickly.

the last thing you want to have is partially dried glue shifted and sheared while clamping. I've seen exactly one glue joint failure in 15 years, and it came from trying to continue to adjust a joint that had been already glued for a few minutes. I fought it with a mallet and block and got it to move, and then on a whim put some pressure on it after it dried and it came apart without much trouble.

lastly, getting the right amount of glue on something that's a tight glue up is an art - too much and you're just greasing the joint. The bigger the layer of excess, the more the clamps will slide before the excess is wrung out.

Yes perhaps it is that the jaws are slanted inwards and then become parallel when put under pressure. There is definitely a bit of play in them so would not be surprised. I can actually easily test this (if they are parallel under pressure) so will report back.

I did definitely put on too much glue, so a contributing factor. But otherwise the boards were from a milled finger jointed board, so should have near-perfectly flat (or as flat as I could hope to achieve).