# Clamps: how tight?



## Smile_n_Nod (Jan 20, 2011)

When I use clamps to hold boards together while glue dries, should I snug up the clamps just enough to keep the boards from sliding around, or should I tighten the clamps until the skin on my palm rips off and the blood vessels in my forehead burst? (Hyperbole, obviously-but a serious question.)


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## Gregn (Mar 26, 2010)

I only tighten my clamps till I have a slight squeeze out of glue.


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## Knothead62 (Apr 17, 2010)

What Gregn said.


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## Sawkerf (Dec 31, 2009)

Just tight enough to close any gaps and get fairly even glue squeeze out. Squeeze out happens when the wood surfaces make contact and the glue has nowhere to go. When you see it, you're boards are where they need to be.

If you're having to "grind" the clamps to close gaps, you need to improve your edge joining methods.

Just for grins once, I took two pieces of scrap that went together with an almost invisible joint and glued them together with no clamps. I just squeezed them together with my fingers, laid them down and left them overnight. The next morning, they were as solid as a clamped joint.


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## Fuzzy (Jun 25, 2007)

I use Besseys' & Jorgies … I tighten them by hand, as much as possible … some will say that starves the joint of glue … others have PROVEN that to not be possible using only human hand strength. Most glue manufacturers (at least quietly) agree that more pressure is better, but they hesitate to make that recommendation, because some folks would just go nuts. Basically, with tools & clamps available in all but the most elaborate shops, it is not possible to over tighten your clamps, and the thinner the glue line, the better.


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## dkirtley (Mar 11, 2010)

Depends on the type of glue. Each will have it's own recommendations.


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## Loren (May 30, 2008)

How much pressure depends on the beam strength of the
boards you are gluing together. I have K-body clamps I
use and I crank them pretty hard. I bet most seasoned
woodworkers do as well.

Sometimes if the clamp is tightened real hard you won't
be able to loosen it with your hands and I've used pliers,
which scars up the handle. I have also drilled the handles
of some of my clamps to stick a screwdriver through it 
to apply pressure and/or loosen a tight clamp.


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## TCCcabinetmaker (Dec 14, 2011)

they call it tightening the clamps for a reason, tight, this will help make sure you have a solid board to board joint where the glue is in the wood, not a strange kind of glue weld where the glue fills the gap. Though you need not bust blood veins.


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## pintodeluxe (Sep 12, 2010)

I tighten them until the gaps are closed. With freshly jointed lumber and good pipe clamps, that is usually just good and snug. 
In other words stop after your fingers blanch slightly, but before a pre-frontal anuerism.


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## KenBry (Sep 13, 2011)

Tight enough to close all gaps but not so tight that the excess preassure creates new gaps. Allot does depend on the type clamp you are using as well. Use caution in clamping pressure too. You can over due it and destroy a clamp.


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## HoosierDude (Feb 22, 2010)

Here's information from Titebond's Product and Application Technical Guide:

Appropriate clamp pressure is essential for a successful bond. We recommend
the following guidelines:
For softwoods (pine, poplar): 100-150 psi
For medium density woods (cherry, soft maple): 150-200 psi
For hardwoods (oak, birch): 200-300 psi

I used to clamp the heck out of everything, just shy or bleeding hands and ruptured blood vessels. That was before I had a decent table saw and/or jointer.

Now that I understand the virtue of a joint that lines up without gaps before clamping, I tighten until I have uniform squeeze out. Either way, I've never had a joint fail.


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## BillWhite (Jul 23, 2007)

Not so tight that ya have blood explode from your eyes. ( I couldn't resist.)
Just get an even "squeeze-out" with PVA glues.
Bill


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## MonteCristo (May 29, 2012)

My understanding is that you can't make them too tight by hand. But I also agree that if you have to squeeze like crazy to close gaps, you need to re-joint.


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## Enoelf (Mar 15, 2012)

I agree with the suggestion of tightening to achieve a uniform squeeze out of glue. 
I remember watching a woodworking video where the presenter showed that with a properly jointed edge, you can actually create a strong bond between two boards with just water. If your edges are clean, crisp, and smooth, it shouldn't be necessary to burst any blood vessels or remove any skin.


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## Loren (May 30, 2008)

It is true that if you joint your boards perfectly the boards can
just be glued and rubbed together to spread the glue. This
is an old method used in Japan and I'm sure many other places.

The old glues may leave less of a glue line though and of course
good clamping makes the glue line quite thin and even less
noticeable.


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## dnick (Nov 17, 2011)

It's pretty much like everything else in woodworking, you just develope a feel for it. Over time you learn from trial & error, you develope a rythum, a feel for what works. You can learn volumns from others, as I have, but the best teacher is your own experiance. Pactice, practice, practice. The most difficult part of woodworking for me, was & is, patience. Learn from everything you do.


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## derosa (Aug 21, 2010)

Loren, that technique works fine in my limited experience. As I got into hand planes but still lacked a decent clamp I discovered it was very easy to joint two boards till no light could be seen between them. At which point I apply a thin bead of glue to one edge, lay the second edge on top and rub back and forth till there is a little noticeable resistance to movement, make sure the edge is fully lined up and walk away. Next morning there is a rock solid joint.


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## rance (Sep 30, 2009)

Once you get past having two properly flattened surfaces…

I crank em down pretty tight(by hand of course). Achieving 'even glue squeezeout' can be misleading. If you apply glue unevenly, then you will be guaranteed to have uneven glue squeezeout. But in that scenario, uneven squeezeout is not such a bad thing as long as you have at least some squeezeout all along the joint.

Apply clamping pressure. Glue will squeeze out and continue to squeeze out until the two boards touch. Once they touch, not much more pressure will be required.

*The 'rub joint' *described by others achieves this same situation. The rubbing squeezes out, and continues to squeeze out the overage of glue until the two pieces of wood begin touching and rubbing each other. This is about the perfect amount of remaining glue to keep most joints solid. For clarification, I believe most 'rubbed glue joints' are for segmented turnings and similar situations. It is not used for situations such as installing trim and other larger applications. One of the main factors that allows these to work so well is that there is no chance of the boards bending or sagging while the glue dries.

The enormous amount of clamping pressure required in some situations has to do with what it takes to force the overage of glue out of the joint. The viscosity of the glue and large square surface areas are mitigating factors.

*A glue starved joint *is not from clamping too tight(that is not possible IMO). A glue starved joint comes from not applying enough glue in the first place. Loosly spoken "The glue that makes a nice joint is the glue that squeezes out and lands on the floor.".

There are in fact situations where you might not want squeezeout. In those instances you'll have to weigh the risk of having a starved joint vs. knowing exactly how much glue you need to achieve proper adhesion.

Again, *ALL of the above assumes you have two flat, properly prepared surfaces*. If you rely on the clamps to make up for any lack of proper surface preparation(ie. flattening), then you should address those problems first. To boost your confidence, do some testing on some scraps with the blood-vessel scenario vs. the 'rub joint'. I think you'll be delighted with the equality.


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## HalDougherty (Jul 15, 2009)

According to information I found on the website for Tightbond III, the recommended clamping pressure for medium hardwood like walnut & cherry is 150 to 200 psi. For maple and oak hardwood the recommended clamping pressure is 200 to 250 psi. I make laminated blanks of walnut maple and/or cherry all the time using 55" long by 8" wide, and 3" thick laminates using 3, 5, or 7 boards. I make sure both surfaces are painted with a thin, but complete cover of glue, then I drill two holes, one on each end and insert a short dowel to keep the boards from sliding when clamping pressure is applied. The glue lubricates the boards so they slide like they are on ice till some clamping pressure is applied. If they do slip after pressure is applied and released. It takes a lot of force to move them back into position. The surface area I'm clamping is 440 sq. in. in size. Using the figure 250 psi times 440 sq/in, shows 110,000 lbs of clamping pressure spread evenly over the surface is needed. A press big enough to make my laminates is beyond what I can afford to buy, so I made my own. Making a frame that withstands that much force was tough because it had to be cheap to make and at the same time, strong enough to keep the hydraulic pressure from deforming the frame and making a curved blank.


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## richgreer (Dec 25, 2009)

The most important thing about gluing is to have the surfaces properly prepared. Then need to be flat, smooth clean and dry.

The second most important thing is even glue coverage. You need to brush it on so that there are no gaps in the coverage.

After these two points, clamping pressure becomes the third most important issue. No harm is done by extra clamping pressure, as long as it is hand generated. I usually tightened as much as I can do by hand without going crazy.

We can get into an argument about covering both surfaces or just one and/or the wait time from when you apply glue to when you clamp up. The answer to these questions is "it depends . . . "


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## BinghamtonEd (Nov 30, 2011)

If you buy the $1.99 black and orange clamps at Harbor Freight, it makes it easy to gauge. Clamp down until the plastic trigger pivot breaks. Then when the glue is dry, release them and toss them in the trash


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## ssnvet (Jan 10, 2012)

I don't lift weights any more…. so I use my clamps for an expression of all that pent up manly energy :^)


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## Adam_D (Mar 4, 2012)

@BinghamtonEd Actually laughed out loud at that one. Can't imagine who designed that and thought they'd be useful to someone.


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## JAAune (Jan 22, 2012)

I snug them until they stop turning easily. Usually if I want more pressure I'll just use more clamps.


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## MrRon (Jul 9, 2009)

If you have spread the glue well, leaving no holidays, squeeze-out will indicate the joint has the right amount of glue. clamping will also force out any trapped air. High clamping force is no substitute for a well fitting joint. If the wood surfaces are smooth, flat, clean and at the correct moisture level and using the right adhesive, clamping pressure will be minimal; as low as 100 PSI for low density woods and 250 PSI for high density woods.


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## shipwright (Sep 27, 2010)

I guess I shouldn't be surprised but in two current threads the term "glue" seems to be universally interpreted as "PVA glue". I realize that it is what most use but I am surprised that no mention is made of the many other equally good (or better) glues. ...... epoxies, urea formaldehydes, animal protien glues, etc. etc.

Not an argument, just an observation.


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## JackDuren (Oct 10, 2015)

Some jobs don't require much pressure and others require a lot. As far as a lot I'll crank a pipe clamp or I-beam till the wood can't squeeze anymore glue. But I still wont be satisfied till alternating clamps are tight as possible without a pipe wrench..


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## CajunWoodArtist (Oct 27, 2015)

> Here s information from Titebond s Product and Application Technical Guide:
> 
> Appropriate clamp pressure is essential for a successful bond. We recommend
> the following guidelines:
> ...


How does someone know the clamp pressure they are applying? A torque gauge for wood clamps is expensive…


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## DirtyMike (Dec 6, 2015)

I tested this tonight with smaller hardwoods that i use for making my cooking utensils. i always wondered if i was clamping too tight after reading about this topic. i concluded that with my bessey f style clamps and titebond 3 the best joint is made by tightening the clamps as hard as i can by hand. it leaves a lot of squeeze out but makes a nicer joint for me.


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## TheFridge (May 1, 2014)

Matthias Wandel of woodgears.ca did some tests on different glues and clamping pressure. Apparently it didn't really matter. I think the joints clamped only with a 10 lb weight did the best. Should check it out.


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## clin (Sep 3, 2015)

> Here s information from Titebond s Product and Application Technical Guide:
> 
> Appropriate clamp pressure is essential for a successful bond. We recommend
> the following guidelines:
> ...


Different types of clamps have different nominal forces they can apply. So based on this, you have the total force a given clamp can exert. For example, total lbs of force. To get the pressure you have to know how much surface area this force is acting over.

Because wood is not infinitely rigid (nothing is), you can't simple take the clamp force and divide by the surface area clamped. Rather you can calculate the effective area the clamp acts over. It turns out that the clamp pressure spreads out at a 45 degree angle. So if a board were 1" thick, the clamp pressure would extend 1" in ALL directions from this clamp.

If the board is too thin, for the force to spread out, you add a caul (block of wood or similar) between the clamp and wood. When you do these calculations, you'll understand why proper glue ups require a lot of clamps.

It's straight forward, but not easy to describe.

Here's a very good article on this:

"Get Serious About Clamping" 
Fine Woodworking 194
pp. 36 November 1, 2007 c

Here's a link to a page ABOUT the article. You need to be a member to actually get the article.

http://www.finewoodworking.com/how-to/article/get-serious-about-clamping.aspx

I found this link, which seems to be the same or similar article, with no special access needed:

http://www.wood-w.com/wood-materials/lessonsguides-get-serious-about-clamping.html


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## Timberwolf323 (Feb 3, 2016)

I turn the clamp handles until I get blood blisters on my palms. Took me weeks to figure out what those marks were lol


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