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View oldwood's profile

Glue up pressure and number of clamps?????

by oldwood
posted 01-18-2018 02:40 AM


36 replies so far

View TungOil's profile

TungOil

1210 posts in 858 days


#1 posted 01-18-2018 02:49 AM

I’d probably have 3 pipe clamps alternated up/down on that, just enough pressure to close the joint.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

View Gilley23's profile

Gilley23

489 posts in 745 days


#2 posted 01-18-2018 02:55 AM

I’d probably do the same, 4 alternating top/bottom clamps. You don’t need to kill it but yeah you want plenty of pressure. Remember, the glue is stronger than the wood.

View JohnMcClure's profile

JohnMcClure

618 posts in 1003 days


#3 posted 01-18-2018 02:55 AM

I crank down pretty tight, with F-style clamps I go to about 80% of the tightest I could possibly do with my bare hands, I’d say. With clamps with a pin or crank handle, which gives you a lever arm, I guess I go until the bar starts to flex.
But this seems like a great experiment since TungOil just closes the joint – I’d like to do 3 glue-ups on identically jointed boards and do a fracture test on all 3. Varying clamp pressure or number of clamps for each. Maybe someone else would like to try? To cold for gluing in my shop this week.

-- I'd rather be a hammer than a nail

View AlaskaGuy's profile (online now)

AlaskaGuy

5240 posts in 2672 days


#4 posted 01-18-2018 02:56 AM

There will be a lot of different answer on this one. I’m in this camp. Don’t over do it.

https://www.woodmagazine.com/woodworking-tips/techniques/skills/take-it-easy-with-clamping-pressure

-- Alaskan's for Global warming!

View Rich's profile

Rich

4419 posts in 952 days


#5 posted 01-18-2018 04:03 AM

The width of the boards matters too, not just the length. Since the pressure radiates outward from the clamp (I’ve seen diagrams that show 45º but that’s probably just an approximation), the wider the board, the fewer clamps you need for a given length. For example, picture gluing two 1/4 inch strips. You’ll need a clamp every inch or two, or, better yet, cauls to get even pressure along the joint.

And, I agree with AG, too much pressure will starve the joint. I learned to use just enough to bring the boards together firmly.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View clin's profile

clin

1027 posts in 1359 days


#6 posted 01-18-2018 04:54 AM

As an example, Titebond II clamping pressure, according to Titebond, is 100-150 PSI for softwoods, 125-175 PSI for medium woods, and 175-250 PSI for hardwoods.

While the clamping pressures, in the article listed by AlaskaGuy, may seem really large, the PSI generated can be much less if the area being glued is very large. So if you’re edge gluing boards that are 1” thick and 10” long, you have just 10 sq-in of area and still need a total of something like 1,500 lbs of pressure. Which you can get pretty easy with a handful of lighter duty clamps.

But if you were gluing up something, much larger, like laminating two boards together, something that may have 100 or more square inches, you probably need every clamp you can lay your hands on to begin to get close to what is recommended.


The width of the boards matters too, not just the length. Since the pressure radiates outward from the clamp (I ve seen diagrams that show 45º but that s probably just an approximation), the wider the board, the fewer clamps you need for a given length. For example, picture gluing two 1/4 inch strips. You ll need a clamp every inch or two, or, better yet, cauls to get even pressure along the joint.

And, I agree with AG, too much pressure will starve the joint. I learned to use just enough to bring the boards together firmly.

- Rich

I think the 45 degree thing is not just a rough approximation, I think it has something to do with the way materials react. Though I’m sure it does assume a uniform material. And you’re absolutely right on to bring up using cauls. I think most tend to use them as a way to not crush our projects where the clamp contacts it, but they’re important to spread the clamping force out across the joint. But because of the 45 degrees, you actually need the cauls + stock to be as thick as your spacing between clamps to get truly even pressure.

So if you were edge gluing 6” wide boards, you don’t need cauls if the clamps are less than 6” apart. But if you were gluing something just 1” thick, you probably need cauls.

-- Clin

View AlaskaGuy's profile (online now)

AlaskaGuy

5240 posts in 2672 days


#7 posted 01-18-2018 05:01 AM



As an example, Titebond II clamping pressure, according to Titebond, is 100-150 PSI for softwoods, 125-175 PSI for medium woods, and 175-250 PSI for hardwoods.

While the clamping pressures, in the article listed by AlaskaGuy, may seem really large, the PSI generated can be much less if the area being glued is very large. So if you re edge gluing boards that are 1” thick and 10” long, you have just 10 sq-in of area and still need a total of something like 1,500 lbs of pressure. Which you can get pretty easy with a handful of lighter duty clamps.

But if you were gluing up something, much larger, like laminating two boards together, something that may have 100 or more square inches, you probably need every clamp you can lay your hands on to begin to get close to what is recommended.

The width of the boards matters too, not just the length. Since the pressure radiates outward from the clamp (I ve seen diagrams that show 45º but that s probably just an approximation), the wider the board, the fewer clamps you need for a given length. For example, picture gluing two 1/4 inch strips. You ll need a clamp every inch or two, or, better yet, cauls to get even pressure along the joint.

And, I agree with AG, too much pressure will starve the joint. I learned to use just enough to bring the boards together firmly.

- Rich

I think the 45 degree thing is not just a rough approximation, I think it has something to do with the way materials react. Though I m sure it does assume a uniform material. And you re absolutely right on to bring up using cauls. I think most tend to use them as a way to not crush our projects where the clamp contacts it, but they re important to spread the clamping force out across the joint. But because of the 45 degrees, you actually need the cauls + stock to be as thick as your spacing between clamps to get truly even pressure.

So if you were edge gluing 6” wide boards, you don t need cauls if the clamps are less than 6” apart. But if you were gluing something just 1” thick, you probably need cauls.

- clin


And what sophisticated expensive equipment do I need to buy so I know how much pressure I’m applying?

-- Alaskan's for Global warming!

View Rich's profile

Rich

4419 posts in 952 days


#8 posted 01-18-2018 05:05 AM

And what sophisticated expensive equipment do I need to buy so I know how much pressure I m applying?

- AlaskaGuy

A simple gluepressureometer will do the trick. $8.95 at Harbor Freight (less if you have the 20% off coupon).

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View AlaskaGuy's profile (online now)

AlaskaGuy

5240 posts in 2672 days


#9 posted 01-18-2018 05:17 AM


And what sophisticated expensive equipment do I need to buy so I know how much pressure I m applying?

- AlaskaGuy

A simple gluepressureometer will do the trick. $8.95 at Harbor Freight (less if you have the 20% off coupon).

- Rich


Is that one of HF’s hidden jewels I keep hearing about?

-- Alaskan's for Global warming!

View unclearthur's profile

unclearthur

255 posts in 2151 days


#10 posted 01-18-2018 05:44 AM

In theory: For the OP’s cutting board, 18” long, say 1 1/2” thick, would make it 27 square inches of glue area. For an average pressure of 250 psi, you then need a total of 27*250 = 6,750 lbs clamping force. So about 12 F clamps (or 6 bar clamps).

Which would make it an F clamp every 1 1/2” ....... which seems over the top to me.

View Rich's profile

Rich

4419 posts in 952 days


#11 posted 01-18-2018 06:01 AM


In theory: For the OP s cutting board, 18” long, say 1 1/2” thick, would make it 27 square inches of glue area. For an average pressure of 250 psi, you then need a total of 27*250 = 6,750 lbs clamping force. So about 12 F clamps (or 6 bar clamps).

Which would make it an F clamp every 1 1/2” ....... which seems over the top to me.

- unclearthur

You are aptly named. I’m a degreed engineer, and I have never concerned myself with square inches, PSI or any of that when gluing up a panel. Besides, to complicate matters, what if you used psi clamps (Ψ)? That would throw the psi WAAAY off. It’s a slippery slope. Tread carefully.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View Andybb's profile

Andybb

1900 posts in 966 days


#12 posted 01-18-2018 06:27 AM

I know you guys are engineers but, is it just me or are you guys putting way to much thought into this? What ever happened to, “you can never have too many clamps”? I am an internet trained woodworker thanks in most part to lj’s and youtube and a few others. In the 10K woodworking videos I’ve watched and articles I’ve read I have never once heard this discussed or anybody saying, “This is what happens when something is clamped too tightly”. Clamp it good and tight (not over-tight)with as many clamps as seem appropriate then add a couple if there’s room. If there’s no squeeze out I know I haven’t put enough glue in the joint. If there’s a lot of squeeze out I know I put too much but I don’t take it apart like I might if I thought I put too little glue since, as someone already said, “the glue is stronger than the wood”. I might use a little extra glue with softer woods as they seem to absorb more than hardwoods.

Again, I have nowhere near the skills and experience you guys do but is clamping too tight really a thing?

To answer the OP’s question, IMO 4 should be good over 18”, using a long caul on each side and a clamp at the ends of the seam.

Rich, go ahead and have your way with me as I sure do respect your opinion.

-- Andy - Seattle USA

View TheFridge's profile

TheFridge

10858 posts in 1849 days


#13 posted 01-18-2018 06:27 AM

A lot. And a bunch.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View AlaskaGuy's profile (online now)

AlaskaGuy

5240 posts in 2672 days


#14 posted 01-18-2018 06:31 AM



A lot. And a bunch.

- TheFridge

But what kind?

-- Alaskan's for Global warming!

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TheFridge

10858 posts in 1849 days


#15 posted 01-18-2018 07:07 AM

The yellow kind and the long kind.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View AlaskaGuy's profile (online now)

AlaskaGuy

5240 posts in 2672 days


#16 posted 01-18-2018 07:12 AM



The yellow kind and the long kind.

- TheFridge

Got it!

-- Alaskan's for Global warming!

View RobbieB's profile

RobbieB

11 posts in 587 days


#17 posted 01-18-2018 08:44 AM

Fridge would use all da clamps.

View Rich's profile

Rich

4419 posts in 952 days


#18 posted 01-18-2018 09:42 AM


The yellow kind and the long kind.

- TheFridge

$8.95 at Harbor Freight. I believe the 20% coupon does not apply to these.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View clin's profile

clin

1027 posts in 1359 days


#19 posted 01-18-2018 05:38 PM


And what sophisticated expensive equipment do I need to buy so I know how much pressure I m applying?

- AlaskaGuy

Pencil and paper and the link you posted giving approximate pressure for different styles of clamps.

-- Clin

View AlaskaGuy's profile (online now)

AlaskaGuy

5240 posts in 2672 days


#20 posted 01-18-2018 06:10 PM


And what sophisticated expensive equipment do I need to buy so I know how much pressure I m applying?

- AlaskaGuy

Pencil and paper and the link you posted giving approximate pressure for different styles of clamps.

- clin


I much prefer the KISS System.

-- Alaskan's for Global warming!

View Rich's profile

Rich

4419 posts in 952 days


#21 posted 01-18-2018 06:28 PM

Beating a dead horse seems to be a common theme across threads on LJ lately. I wonder what’s causing it. Sun spots? Global warming? Gluten?

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View TheFridge's profile

TheFridge

10858 posts in 1849 days


#22 posted 01-18-2018 06:30 PM

Gluten and lack of alder.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Dustin's profile

Dustin

688 posts in 1103 days


#23 posted 01-18-2018 06:51 PM



Beating a dead horse seems to be a common theme across threads on LJ lately. I wonder what s causing it. Sun spots? Global warming? Gluten?

- Rich


Gluten and lack of alder.

- TheFridge

Fridge, Rich, both you guys just made my day.

-- "Ladies, if your husband says he'll get to it, he'll get to it. No need to remind him about it every 6 months."

View AlaskaGuy's profile (online now)

AlaskaGuy

5240 posts in 2672 days


#24 posted 01-18-2018 06:56 PM



Gluten and lack of alder.

- TheFridge

In case you didin’t know it, you can edge glue Alder with gluten.

-- Alaskan's for Global warming!

View Rich's profile

Rich

4419 posts in 952 days


#25 posted 01-18-2018 07:06 PM

Gluten and lack of alder.

- TheFridge
In case you didin t know it, you can edge glue Alder with gluten.

- AlaskaGuy

How many clamps at what pressure would you use for that, AG? And how would you measure it to be certain you were within spec?

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View AlaskaGuy's profile (online now)

AlaskaGuy

5240 posts in 2672 days


#26 posted 01-18-2018 07:22 PM

Gluten and lack of alder.

- TheFridgehttp://lumberjocks.com/topics/256905
In case you didin t know it, you can edge glue Alder with gluten.

- AlaskaGuy

How many clamps at what pressure would you use for that, AG? And how would you measure it to be certain you were within spec?

- Rich

Well I’d wing it. Id glue up a panel as usual . After 24 hours break it apart and see what thing looks like and adjust from there if need be.

-- Alaskan's for Global warming!

View Rich's profile

Rich

4419 posts in 952 days


#27 posted 01-18-2018 07:28 PM

...and the wheel goes around and around :)

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View Smitty_Cabinetshop's profile

Smitty_Cabinetshop

16109 posts in 2981 days


#28 posted 01-18-2018 07:34 PM

Gluten and lack of alder.

- TheFridgehttp://lumberjocks.com/topics/256905
In case you didin t know it, you can edge glue Alder with gluten.

- AlaskaGuy

How many clamps at what pressure would you use for that, AG? And how would you measure it to be certain you were within spec?

- Rich

Well I’d wing it. Id glue up a panel as usual . After 24 hours in the back of my pickup truck, I’d break it apart and see what thing looks like and adjust from there if need be.

- AlaskaGuy

There. Fixed it for you AK Guy.

-- Don't anthropomorphize your handplanes. They hate it when you do that. -- OldTools Archive --

View AESamuel's profile

AESamuel

93 posts in 1586 days


#29 posted 01-18-2018 07:36 PM

I think the obsession with clamping force is related to the obsession with lots of glue…more is always better, right?

Watching videos on YouTube of some people’s glue up, 90% or more of the glue loaded up ends up squeezed right out of the joint. Look at the glue line on an edge jointed board, it’s almost invisible because the glue isn’t a filler(generally) it’s a bonder.
Glue is the strongest part of a joint, especially if there is no mechanical strength at play so if you apply X psi with the clamps and squeeze all the glue out of it you are severely weakening the joint. Another thing to note is that if you use a ton of glue it is going to continue to seep out of the joint a while after you have clamped up so you’re going to have to come back in twenty minutes and re-tighten them again.

So it’s a balance, not too much, not too little. Think about some of the techniques people used to use for joining boards before metal clamps were readily available. Wooden cam clamps, timber dogs and even twisted string loops! I’d wager the majority of those joints are still together today…

In regards to your scenario, assuming the mating surfaces are fitting well then I would be more concerned with even clamping pressure rather than amount of pressure. Three clamps “hand tight” or maybe four if I was unsure about the mating surfaces and I would be more than happy!

View Woodknack's profile

Woodknack

12776 posts in 2743 days


#30 posted 01-18-2018 09:29 PM

Clamping, like bolt tightening, is a test of your manhood and you should use all your strength all the time. Alternately, you can use just enough.

-- Rick M, http://thewoodknack.blogspot.com/

View Steve's profile

Steve

1225 posts in 945 days


#31 posted 01-18-2018 09:40 PM

someone with a GI Joe kung fu grip would probably be able to clamp something pretty tight i bet

View jmos's profile

jmos

913 posts in 2733 days


#32 posted 01-19-2018 01:44 AM

I think the more relevant question is how strong does the joint need to be? I’ve also seen articles (FWW has one from 2007) basically saying use a s-ton of clamps (and that is impossible to over-clamp a joint with woodworking clamps, they’re not strong enough.) But I also see articles referring to a rub joint, where you don’t clamp at all.

I have no doubt on similarly prepared boards that the rub joint will fail before the one that is “properly” clamped, but does it matter? Do you need to maximum possible joint strength for a cutting board?

Personally, I tend to use fewer clamps, especially on panels. In the OP’s example, I would use two, and those wouldn’t be tight enough to bow the board. If my boards are well jointed, the glue line is still invisible, and the joint is plenty strong.

-- John

View TheFridge's profile

TheFridge

10858 posts in 1849 days


#33 posted 01-19-2018 03:11 AM

Rich. Alaska. You guys are my kinda people:) I’m still giggling like a girl.

Dustin, if I make one person laugh at the dead horse I’ve been beating then that makes it all worth it.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View oldwood's profile

oldwood

155 posts in 1607 days


#34 posted 01-19-2018 03:32 AM

Well class, that was fun now wasn’t it.

View Rich's profile

Rich

4419 posts in 952 days


#35 posted 01-19-2018 03:57 AM


Well class, that was fun now wasn t it.

- oldwood

Bueller… Bueller…?

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View Walker's profile

Walker

158 posts in 835 days


#36 posted 01-19-2018 04:26 AM

there is actually a very simple formula for number of clamps needed…

it’s almost always n+1, where n equals the number of clamps currently owned.

sometimes it’s n + cos x^2 where n is the number of clamps needed and x equals the number of clamps within reach.

-- ~Walker

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