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Clamp Time: How long is enough?

T

type C basses

Mar 2, 2011
229
0
Center of The Commonwealth
#1
There is definitely no absolute answer, although this questions shows up quite frequently on the web. This is an attempt to gather some good data from those of you pushing the limits of minimum clamp time.

Post:
-Brief description of joint*
-Materials being joined
-Type of adhesive (as well as brand)
-How many clamps used (or clamp spacing)*
-Time left in clamps
-Intended time before stressing joint (if applicable)
-any special notes (use of acetone, scratching of gluing surface, % of flush-ness if not 100%)

variables with a * are not necessary if a picture is provided.
Thanks to all who participate!
 
#7
I work almost exclusively with epoxy. I leave my stir-stick in the pot of leftover glue. When the pot's done, the joints are done...keeping in mind that an excess of leftover epoxy will cook off faster than a thin layer.
 
#8
I leave everything I do in clamps for 8-12 hours, so I'll probably be unable to use any of my own data for this project. So I may just test on scraps.

The more input data, the better. I will be inputting the data into excel and running matrices and regressions. In fact, without all of the variables being given a value, the data is flawed. I realize this seems kind of silly unless you're a statistics person, but complete data is very much appreciated.
 
#9
First and foremost, dry clamp it and look for any light coming through......

24 hours (clamped up) is my rule, period. If it ain't broken don't try to fix it (for me)....

That goes for any of my titebond glued pieces.

As many clamps that I can fit on the piece, or 1.5" apart

As soon as it's unclamped, I work with it at that point.

I only wipe with acetone on oily woods (like cocobolo for example)....... before glue up.
 
#10
Titebond says you can unclamp after 30 minutes. I tend to wait 2 hours or more depending on the pieces. Through necks and tops/backs I leave at least 12 hours. With epoxy I subscribe to the same general rule as barnaclebeau, when the leftover has set(but usually let it stand clamped a little longer).
As Jason said above, wiping down oily woods is always a good idea(cocobolo, bocote, Indian rosewood, etc.) Also agreeing with Jason, that you do what you know, and don't try to fix it because it works.
 
#11
Everything but CA goes overnight. The risk of delamination is far worse than the reward of being able to use some clamps sooner. If you don't have enough clamps, either get more, or arrange your schedule so the last thing you do for the day is glue up.
 
#12
I think this varies greatly depending on how much surface area you are clamping. When I worked as a commercial woodworker all of our pieces were on time schedules, not to mention limited clamp availability :scowl:, so you really didnt have the time to leave the parts clamped as long as you would like. To stay on schedule it was important to find out how much you could push the drying time without compromising the finished product.

For most joints, when using titebond 1 or a similar yellow glue, the best bet is 2 hours plus if you really want that warm and fuzzy comfortable feeling. If you feel a little adventurous I feel most joints can be unclamped after 45 minutes minimum. Anything less than 45 is just asking for trouble. At this point the glue should be dry but still will not reach its maximum strength for probably 8-24 hours but as long as you dont put undue pressure on the joint it will remain stable and will continue to cure without being in the clamps.

For large surface area glue ups like gluing a top or for bent/laminated glue ups that are under tension I think 4-5 hours is the absolute minimum time to stay in the clamps but 8-24 hours is best. When working on valuable and detailed pieces like instruments I suggest you err on the side of leaving the clamps on too long whenever possible.
 
#13
On my neck scarf joint test piece (which was red oak), I used Titebond and unclamped after 1.5 hours. There is now a small gap (about 0.5mm) between pieces that was not there before I unclamped it.

Luckily, it was a junk test piece and nothing I intended to actually work with. But I learned a valuable lesson from it, and that is to leave it clamped for the full 24-hour cure time. I'd rather take a little longer to build the thing than to get weak glue joints.
 
#16
after an hour i take my clamps off; if im still there; i try to do as much (planned) gluing before i leave for the night; the big question i usually ask myself is, how long before i stress the joint? the glue says 24 hr. and i relativly beleive that; but things like neck blanks will sit out of the clamps for days (weeks months, if possible!) before any kind of stock removal/shaping takes place;
i have a lot of faith in glue doing what it does; even a very moist atmosphere doesnt appear to change the 'skinning' of glue drops; a big issue could be said about the amount of glue and how long it takes to dry; but a good glue joint under tension will squeeze out any extra, so its a non issue. my $.02
 
#19
Hi.

jmorbita said:
Does anybody think leaving the clamps on for a long period of time might be counter-productive? how long is too much?
Click to expand...

I for one don't think it'd be counter-productive, but does not help any either. + You may need the clamps elsewhere.

Again, if the glue is a professional one, very precise information about the clamping time and the joint strenght developement time will be found on the tech sheet.

Regards
Sam
 
#20
jmorbita said:
Does anybody think leaving the clamps on for a long period of time might be counter-productive? how long is too much?
Click to expand...

I don't know for sure if its counter-productive, but I do know that these manufacturers pay their engineers and chemists a "butt-load" of money to figure out the best clamp times for their specific product. These figures are then recorded and made available via tech/spec sheets and sometimes even right on the container itself. However, container directions are usually generalities or averages. Tech sheets will typically have charts that factor in variables like temperature and humidity.
 

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