# Gluing: How do you know when the clamps are tight, but not too tight?



## dejones (Oct 15, 2010)

Hi,

I have finished a few projects at this point (a couple of bedside tables & a carving board) all of which required gluing. I have since heard about "glue starving"a joint when you tighten the clamps too much (and I, or course, really bore down on those guys...)

My question is how do you know when you have the clamps at the correct tightness? Is it a visual thing or a feeling? Is there some rule of thumb (like "watch until the glue stops squeezing out & then turn 1/4 more" for instance)?

Thanks,
Duncan


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## jack warner (Oct 15, 2010)

about 100-150- psi for soft woods and 175 - 250 for hard.
your on the right track. soft woods stop at the end of the ooozing. hard woods go that extra 1/4 turn


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## cabinetman (Jul 5, 2007)

I have failed to figure out how to incorporate PSI with clamps and actual clamping. I don't put any value on the tests done with PSI clamping pressure. Proper clamping is a per item subject. It would depend on the type of joint, wood species, temperature, humidity, and most importantly, just experience.

A well fitted joint shouldn't take much clamping pressure. Trying to bring warped or curved edges together with over clamping produces stresses in the wood that can work against the joint staying together. Too much pressure compresses the joint where glued, and when the glue cures and the wood relaxes, you have a joint that may have different properties of adhesion. 

A well fitted mating with a thin film of glue on both surfaces clamped up should produce some squeeze out. It's more of a matter of feel. I usually stop tightening when the squeeze out looks to be about it. On a project with multiple clamps, after all have been applied, I'll go back to the first one and give it a tweek, and check all the rest before going out to hunt for my dinner.












 









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## Rick Mathison (Jun 16, 2010)

You may have read about starving a glue joint by applying too much pressure but I have also read that it is basically impossible to apply too much pressure by hand. 

Rick


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## dejones (Oct 15, 2010)

Thanks for the good advice. I think that until I get more experience, I'm going to go with the "tighten until the oozing stops (+ 1/4 for hardwoods)" method, plus the "tweaking" of the first clamps if I use more than one.

I'm pretty sure that if it is possible to apply too much pressure on a joint then I did so on my carving board project. If it does not fall apart, perhaps that will be evidence that this could be more myth than fact (maybe "Myth-Busters" could do a bit on this)

Thanks again,
Duncan


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## rrbrown (Feb 15, 2009)

I'd agree with cabinetman especially about a well fitted joint needs little pressure when clamping. I would practice better joints and use only the clamping required to hold the joint together.


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## jack warner (Oct 15, 2010)

cabinetman said:


> I have failed to figure out how to incorporate PSI with clamps and actual clamping. I don't put any value on the tests done with PSI clamping pressure. Proper clamping is a per item subject. It would depend on the type of joint, wood species, temperature, humidity, and most importantly, just experience.
> 
> A well fitted joint shouldn't take much clamping pressure. Trying to bring warped or curved edges together with over clamping produces stresses in the wood that can work against the joint staying together. Too much pressure compresses the joint where glued, and when the glue cures and the wood relaxes, you have a joint that may have different properties of adhesion.
> 
> ...


golden advice there


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## Rick C. (Dec 17, 2008)

I'm with c'man:thumbsup:
Also if your shop's not heated, cold will cause joint failure. I'm not sure how cold, but mine was around 35-40 F. It was a step stool for my 80 yr old mother in law. Could have been a disaster, good thing I tested it first.


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## frankp (Oct 29, 2007)

I have yet to ever "starve a joint" despite trying my damnedest to do so. If you put a reasonable amount of glue on a joint, I don't care how hard you clamp it (unless you clamp it enough to move the joint out of alignment) you're not going to starve the joint with clamping pressure. I generally tighten my clamps as tight as I can, though it's probably way more pressure than necessary.

On the other end, I've done one or two joints with absolute minimal clamping pressure and they worked out also.


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## ACP (Jan 24, 2009)

+1 what C'man said. Apply it with a glue brush and get some even squeeze out and your good to go.


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## BWSmith (Aug 24, 2010)

Part of the equation is clamp size vs workpce.Using a smallish 12" sliding clamp on a cpl of 3/4 x 3/4 pcs of hdwd would be appropriate or easy to "feel" the tightness.Those same clamps on a 12/4 x 10" x 16' sections of Oak would not in alot of cases have the required,ummph to even out forces required for a good joint.And springy clamps are mighty handy within their range.

So the old sayin,"you can never have too many clamps" isn't soley predicated on the number of clamps........range of size also figures in.Its just part of the design process when clamping is on the menu.

I've always looked at clamps more for convenience and therefore will pick the right sz,best we can.....because of this.Don't feel like wrestlin with larger than necessary clamps.BW


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