# clamping pressure



## NotaJock (May 23, 2015)

How much clamping pressure is called for when clamping a glue-up?
Tight or barely enough to keep the pieces from moving until the glue sets?
Or somewhere in between?
Thanks


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## TimInIndiana (Jan 6, 2018)

I'm no expert - but these guys are: https://www.finewoodworking.com/2010/05/11/how-to-glue-up-joints-different-woods-need-different-clamping-pressure


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## BigMig (Mar 31, 2011)

"super tight" is too much; I know that for sure. Seeing even squeeze out without forcing teh clamp - that's about how I do it.
I have see Tommy Mac use a "spring joint" technique - and with one clamp can clamp decent sized boards.


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## John Smith_inFL (Dec 15, 2017)

in my early days, I have actually applied so much clamping pressure
that it squeezed all the glue out of the joint - and the boards fell apart
after the clamps were removed.
so YOU must find that "sweet spot" for each species of wood that you work with
and find what works best for you in your environment.
ensuring that your surfaces to be glued are true and straight and match precisely will be the key.
if you have to force a joint closed - you are asking for failure.
there is no "one way fits all" answer to your question.


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## pottz (Sep 15, 2015)

well im probably from the super tight club when i glue up boards,i like firm even pressure,less for soft woods and more for hard woods and ive never had a glue up fail yet.knock on wood-lol.


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## WoodenDreams (Aug 23, 2018)

It's easy to tighten down with too much pressure. You want a tight fit. Wrong. You want a snug fit with using the proper amount of glue. The key is straight and matched edges, and properly spaced clamps. BigMig and John Smith are telling you the way it is. www.finewoodworking.com or www.goa.com will show you a video how to example on their sites for free, or check out some youtube video clips.


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## rwe2156 (May 7, 2014)

IMO I think too much has been made about over little regarding this subject. In the real world, you can't measure clamping force, you just clamp until you get squeeze out, then a little bit more.

That said, I've used big time clamping pressure on table top glue ups with my pipe clamps. I've never, ever had a glue joint fail in 30 years of ww'ing.

As far as squeezing all the glue out of a joint, I'll believe it when I see it. You couldn't do that with a hydraulic press because there will be enough glue remaining in the grain of the wood to still create a bond.

That said, I respect what smarter people than me say, and I'll read that FWW article, but in the real world in my shop, I doubt it will change a thing.

Kings Fine Working on YouTube as some Titebond information about PSI in clamping.


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## Planeman40 (Nov 3, 2010)

Yep, what the guys above say - tight enough to squeeze out the excess glue then stop. I went deeply into this back in the early 1960s when I built a homebuilt airplane. Knowing your life is on the line with what you have made makes you sure to do it right. And if you don't know, educate yourself very well before building. The EAA (Experimental Aircraft Association) puts out handbooks on the various airplane building processes that are very informative. Back in the 1920s when so many airplanes we built of wood, the US government did a lot of study on gluing wood to insure the safety of the public. This information is still and excellent source of information.

And one more thing. Be sure to spread glue on BOTH sides of the wood to be joined and spread it evenly over the entire glued surface if you want maximum strength. Too may of us just run a bead of glue down one side of the joint and stick it together. To see how slap dash this method is, just do this and then pull the pieces apart. you will often see fairly large spots with no glue.


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## pottz (Sep 15, 2015)

> IMO I think too much has been made about over little regarding this subject. In the real world, you can t measure clamping force, you just clamp until you get squeeze out, then a little bit more.
> 
> That said, I ve used big time clamping pressure on table top glue ups with my pipe clamps. I ve never, ever had a glue joint fail in 30 years of ww ing.
> 
> ...


i totally agree,if my projects start falling apart then ill change my method.


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## CWWoodworking (Nov 28, 2017)

I think the glue on both pieces is kind a malarkey. Put a thick bead on one piece and smash it together and pull it apart. You will have plenty on both pieces. I will glue close to 1000 panels this year. No failures.

More important is a good joint and thick bead. Glue is cheap.


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## Planeman40 (Nov 3, 2010)

Could be malarkey. Try building a homebuilt airplane and betting your life on your method of gluing. If it works for you, go ahead. Glue tests by engineers say differently.


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## Tony_S (Dec 16, 2009)

Starting with cleanly, properly milled material, apply enough force that the joint closes tightly. If you're unsure, re-tighten slightly in 20/30 seconds. If you get any squeeze out on the second try, the first wasn't tight enough. It doesn't need to be anymore complicated than that.

You also don't need to apply glue to both surfaces on a simple edge or face glue up…and…it's absolutely impossible to squeeze all the glue out by over tightening. Not even to the point that the glue joint will suffer to any significant degree in relation to the strength of the wood you're working with.


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## Redoak49 (Dec 15, 2012)

How careful you need to be about glueing certainly depends on what you are doing. If you are doing an airplane, you need to be super careful. But if just two boards, anything goes.


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## 000 (Dec 9, 2015)

> Too may of us just run a bead of glue down one side of the joint and stick it together. To see how slap dash this method is, just do this and then pull the pieces apart. you will often see fairly large spots with no glue.
> 
> - Planeman40


Do it all the time. I guess you need to use a bigger bead.

100% agreement with Tony


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## Planeman40 (Nov 3, 2010)

You guys are probably right. I over do almost everything. But - I can honestly say that In the 60 odd years I have been woodworking I can honestly say I can't remember one of my glued joints failing over the years. But then I am an old man and there are a lot of things I can remember any more. ;-)


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## CWWoodworking (Nov 28, 2017)

> Could be malarkey. Try building a homebuilt airplane and betting your life on your method of gluing. If it works for you, go ahead. Glue tests by engineers say differently.
> 
> - Planeman40


Gladly. Based on true numbers, my failure rate is 0%. Even if I had 1 panel fail, that is .1%. That's better than almost any production part. Most mass produced part manufacturers (non life threatening) aim for less than 2%

I do this for a living so speed is key. This is an extremely low risk practice.

At the pace I glue panels together, there is a much higher chance I miss a season split or hair line crack, than a glue joint failure.

But hey, to each is own. Your probably not changing and I know I'm not.


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## lumbering_on (Jan 21, 2017)

> Could be malarkey. Try building a homebuilt airplane and betting your life on your method of gluing. If it works for you, go ahead. Glue tests by engineers say differently.
> 
> - Planeman40


As an engineer, I fully appreciate this information, but it really depends on what you are doing. As someone whose work involves aircraft, I can tell you the engineering specs are on a scale you just don't need for a table top. I have yet to see one woodworker use lockwire to secure a fastener, but that's what our techs have to do. However, I will definitely remember how to apply both sides if I'm going to make my own aircraft. 

You can just use tape to secure a glue-up, if you're just doing something like a small box, or trim. Of course, for major weight bearing joints in a table, chair, or bed, you'd want to make sure to get plenty of clamping pressure.


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## RichT (Oct 14, 2016)

> Gladly. Based on true numbers, my failure rate is 0%. Even if I had 1 panel fail, that is .1%. That's better than almost any production part. Most mass produced part manufacturers (non life threatening) aim for less than 2%
> 
> - CWWoodworking


It has nothing to do with glue pressure, but your 2% figure is a joke. I guess you've never heard of six-sigma. A six-sigma shop produces no more than 3.4 defects per million opportunities, or 0.00034%. No parts manufacturer, life threatening or not, could stay in business with a 2% defect rate.


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## 9x9 (Jan 2, 2015)

One thing I do is rough up the surface edges to be glued--use 60 grit sandpaper or scrach awl to rough surface--slap some glue on both edges and clamp--makes a very strong joint.


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## CWWoodworking (Nov 28, 2017)

Rich, I was referring to the "glue on both pieces rule". Didn't say a thing about pressure.

As for as 2%, I should re-phrase.

I purchased parts for a 300$ million dollar company. They bought a lot of parts. The parts I managed were about 30 million. One of my duties was to monitor scrap parts. Nobody cared a rats a$$ about 1%. At 2% it raised eye brows but little was done. Over 2%, we put the screws to parts manufacturer to make a change.

Now to be clear, scrap rate is a murky water. There a lot of factors that go into it.

Rich, think if it this way. If the percentage was as low as you say, people would never buy anything new cause it would last forever! Haha.

The company I was buying the $30m from controlled 85% of their respective market. And we used their higher end product.

This is all nonsense really. The fact is you can be sloppy with glue ups and be pretty successful.

I say aim for good joints and lots a glue.


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## RichT (Oct 14, 2016)

> Rich, think if it this way. If the percentage was as low as you say, people would never buy anything new cause it would last forever! Haha.
> 
> - CWWoodworking


Now you're confusing defects with durability, but it's time to move on and get back to the all-important issue of clamping pressure.

Does anyone else's clamping sometimes include foul language? Mine occasionally does. Like, say when I'm gluing up M&T joints, and the parts seize for whatever reason, and I'm banging and cranking the clamp but the sucker just doesn't want to move. Then I swear a lot. It's also why I keep a couple of bar clamps handy. Those wing handles are great for cranking. I've yet to find a joint that can resist them.


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## CWWoodworking (Nov 28, 2017)

And Rich, when major retailers start asking for discounts because they buy so much, probably the first thing they ask for is a 2% defect allowance. I also dealt with a nation wide sales team(unfortunately).


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## CWWoodworking (Nov 28, 2017)

Durability and defects go hand in hand because of warranty. Anything fails under warranty=defect.

I don't do M&T but I cuss a little.


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## shipwright (Sep 27, 2010)

Or you could use no clamps at all. 
http://lumberjocks.com/topics/289681


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## ArtMann (Mar 1, 2016)

It is entirely possible to over think this issue. I have been gluing up panels for over 40 years and i haven't had one fail yet. I have done a lot of destructive testing in the past and I never saw an assembly fail at the glue joint. I am certain it is possible to screw it up enough for that to happen but you would need to use some very bad technique.

It is easy enough to do your own destructive testing with scrap wood to confirm that what you are doing is good. I would strongly recommend you do that.

By the way, CNWoodworking was obviously not referring to the automotive industry when he said nobody cares about a 1% failure rate. The electronics plant I worked at did about a billion in sales every year and the products for which I was responsible amounted to about $100 million of that. A 0.1% failure rate would have been regarded as a colossal disaster and would have shut down production until the issue was resolved. Depending on the nature of the failure, it may have caused a DOT recall being issued. Way back in the 1990's we stopped measuring failures in percent and started measuring in parts million.


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## pottz (Sep 15, 2015)

> Or you could use no clamps at all.
> http://lumberjocks.com/topics/289681
> 
> - shipwright


animal glue and no clamps-i dont think so.i think ill just keep doing it the way i have for the last 40 years,i glue it clamp it nad it never fails,forget all the nonsense!


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## 000 (Dec 9, 2015)

> And one more thing. Be sure to spread glue on BOTH sides of the wood to be joined and spread it evenly over the entire glued surface if you want maximum strength. Too may of us just run a bead of glue down one side of the joint and stick it together. To see how slap dash this method is, just do this and then pull the pieces apart. you will often see fairly large spots with no glue.
> 
> - Planeman40


UNSCIENTIFIC TEST:
Comparing a smear glue joint to bead of glue joint. ( Titebond II )























































Looking at them, I couldn't pick one over the other for strength.
The glue bead wins for me, but only because of ease of application and time.

When it comes to smearing the glue, I do smear the glue on finicky joints where I let the glue soak into the wood for a few minutes then add the bead of glue before assembly. 
(end grains mostly, and when I need to control the squeeze out.)

These were done with very mild clamping pressure. Just a snug to pull them together.

When I'm clamping a glue up that consist of 3 or 4 boards I usually clamp everything pretty snug, then come back in about 5 minutes and crank them down another half a turn or so. 
In German it's called "Good-N-Tight"

PS, I would be interested to see the same test done with hide glue if anyone is set up with it. 
These pieces are 6×6 industrial PB for comparison.


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## shipwright (Sep 27, 2010)

> animal glue and no clamps-i dont think so.i think ill just keep doing it the way i have for the last 40 years,i glue it clamp it nad it never fails,forget all the nonsense!
> 
> - pottz


To each his own. Of course the choice is yours.
Just saying … it works. If the fit is good, the joint will last hundreds of years.


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## CWWoodworking (Nov 28, 2017)

> By the way, CNWoodworking was obviously not referring to the automotive industry when he said nobody cares about a 1% failure rate. The electronics plant I worked at did about a billion in sales every year and the products for which I was responsible amounted to about $100 million of that. A 0.1% failure rate would have been regarded as a colossal disaster and would have shut down production until the issue was resolved. Depending on the nature of the failure, it may have caused a DOT recall being issued. Way back in the 1990 s we stopped measuring failures in percent and started measuring in parts million.
> 
> - ArtMann


Actually, the automotive industry is a good example.

Me and 2 buddies all owned the same type of GM truck. All three of us had the exact same electrical issues(not a good yr for GM) What are the chances that we all were part of the .1%? But Im sure there was testing done in a lab that said it was a good part.

Ford has had a know issue with the radiator on the powerstrokes. Going by six-sigma, if there are a million of them under warrenty, they only replace 3 of them a year. My dad and brother both had theirs replaced. Fat chance that there is only one more out there.

Parts are not perfect. Add in the human element and things get effed up.

Jbay-nice test.


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## shipwright (Sep 27, 2010)

> PS, I would be interested to see the same test done with hide glue if anyone is set up with it.
> These pieces are 6×6 industrial PB for comparison.
> 
> - jbay


Hide glue is generally applied with a brush so it really doesn't come up.


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## RichT (Oct 14, 2016)

> Ford has had a know issue with the radiator on the powerstrokes. Going by six-sigma, if there are a million of them under warrenty, they only replace 3 of them a year.
> 
> - CWWoodworking


You have a propensity to talk about things you apparently know nothing about. Six-sigma is clearly one of them.


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## RichT (Oct 14, 2016)

> animal glue and no clamps-i dont think so.i think ill just keep doing it the way i have for the last 40 years,i glue it clamp it nad it never fails,forget all the nonsense!
> 
> - pottz


Hide glue and rub joints is an excellent method for adding glue blocks, assuming you use those. It'll allow you to position them in places where clamping would be difficult.


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## pottz (Sep 15, 2015)

> animal glue and no clamps-i dont think so.i think ill just keep doing it the way i have for the last 40 years,i glue it clamp it nad it never fails,forget all the nonsense!
> 
> - pottz
> 
> ...


i havnt but that would be a good use for it.


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## 000 (Dec 9, 2015)

> PS, I would be interested to see the same test done with hide glue if anyone is set up with it.
> These pieces are 6×6 industrial PB for comparison.
> 
> - jbay
> ...


I'm not sure what you mean by it doesn't come up? 
Comparison between smear joint or bead?

I would still like to compare the results of a brushed hide glue joint to the smeared/bead titebond joint.
If anybody that uses hide glue would like to do a quick test it would only take a few minutes.
I would even send you the 2 blocks of wood to keep the comparison the same.


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## RichT (Oct 14, 2016)

> I would still like to compare the results of a brushed hide glue joint to the smeared/bead titebond joint.
> If anybody that uses hide glue would like to do a quick test it would only take a few minutes.
> I would even send you the 2 blocks of wood to keep the comparison the same.
> 
> - jbay


I'll see about trying it later. I have some melamine lying around that's PB core. I'm not going to bother with LHG though, since that board would just drink it up.


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## wapakfred (Jul 29, 2011)

> How careful you need to be about glueing certainly depends on what you are doing. If you are doing an airplane, you need to be super careful. But if just two boards, anything goes.
> 
> - Redoak49


Reading through all these makes me think that 1) none of us have had a joint fail, and 2) we all do it a little (or a lot) differently. My conclusion is what Redoak said is the truth, anything goes. Me? I put as much force as I can on the clamps and let it dry (also have mostly never glued both sides) and like many here, have never had one fail.


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## rwe2156 (May 7, 2014)

> One thing I do is rough up the surface edges to be glued--use 60 grit sandpaper or scrach awl to rough surface--slap some glue on both edges and clamp--makes a very strong joint.
> 
> - 9×9


IIRC this has been debunked.

I've tried it myself with hand planed edges. No problems with glue adherence.


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## CWWoodworking (Nov 28, 2017)

> Ford has had a know issue with the radiator on the powerstrokes. Going by six-sigma, if there are a million of them under warrenty, they only replace 3 of them a year.
> 
> - CWWoodworking
> 
> ...


Your right, dont know much about it. I was using your numbers.

Really this is sillyness. Do some parts have a zero % failure? Sure. screws come to mind. But there are tons of things that fall into the 1-2% range for a lot of manufactures. I bought parts from an 8 billion dollar company. They flat out told me the same thing. If the cost of fixing the thing out weighs the 1-2%, they will keep doing it. Its simple as that.


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## shipwright (Sep 27, 2010)

Back to the topic, *Rich*, LHG is not recommended for rub joints. HHG works well because of the fast strong tack.
OBG does work because it is a gel at room temp but you won't be able to move it around right away like he does in the video.
LHG that is liquid at room temp would not be advisable.


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## Magnum (Feb 5, 2010)

> in my early days, I have actually applied so much clamping pressure
> that it squeezed all the glue out of the joint - and the boards fell apart
> after the clamps were removed.
> so YOU must find that "sweet spot" for each species of wood that you work with
> ...


I agree with John on this. I never Overtighten. I just use my Instinct and tighten it until it's Just Tight but NOT to much. If the Glue starts to Squeeze Out. That's Enough, maybe even to much!

As John said "there is no "one way fits all" answer to your question." It all depends on the situation at hand.

Rick S.


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## RichT (Oct 14, 2016)

> Back to the topic, *Rich*, LHG is not recommended for rub joints. HHG works well because of the fast strong tack.
> OBG does work because it is a gel at room temp but you won't be able to move it around right away like he does in the video.
> LHG that is liquid at room temp would not be advisable.
> 
> - shipwright


Right. I do use hot hide glue for that.


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## RichT (Oct 14, 2016)

.


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## Smitty_Cabinetshop (Mar 26, 2011)

Makes me want to revisit using only screws and clenched nails.


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## RichT (Oct 14, 2016)

> Makes me want to revisit using only screws and clenched nails.
> 
> - Smitty_Cabinetshop


Deader than a door nail.


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## NotaJock (May 23, 2015)

Thank you gentlemen for your input.
You've convinced me that I can be a lot less careful when making most glue joints.


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## waho6o9 (May 6, 2011)

How much clamping pressure is called for when clamping a glue-up?

When the glue squeezes out you're good to go.


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## lumbering_on (Jan 21, 2017)

> How much clamping pressure is called for when clamping a glue-up?
> 
> When the glue squeezes out you re good to go.
> 
> ...


The top left wasn't clamped enough.


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## waho6o9 (May 6, 2011)

Good call


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## CWWoodworking (Nov 28, 2017)

> How much clamping pressure is called for when clamping a glue-up?
> 
> When the glue squeezes out you re good to go.
> 
> ...


Is that considered a defect? Sorry. Couldn't resist.


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## waho6o9 (May 6, 2011)

Understandable

It all got sorted out after I clamped it up.


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## Tony_S (Dec 16, 2009)

> How much clamping pressure is called for when clamping a glue-up?
> 
> When the glue squeezes out you re good to go.
> 
> ...


Holy shat!!


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## 000 (Dec 9, 2015)

Titebond must have been on sale.


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## pottz (Sep 15, 2015)

> How much clamping pressure is called for when clamping a glue-up?
> 
> When the glue squeezes out you re good to go.
> 
> ...


yeah good example of too much glue and not enough clamp pressure!


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## waho6o9 (May 6, 2011)

Correct

You should have seen after I put the clamps on.


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## ArtMann (Mar 1, 2016)

Your point about vehicle failures is correct but irrelevant. The fact is if you use any complex device created by a human being, the eventual failure rate will be 100%. I doubt if the trucks you mentioned failed in the first week of usage. We are talking about initial failure rates here when we are talking about clamping pressure. As I already said, hide glue joints last a long time if they are done correctly in the first place. Heck, the video of the guy sticking two planks together might produce a reliable joint for all I know. My point was he didn't prove anything with that video because you can do the same thing with a $10 hot melt glue gun and a 25 cent stick of plastic glue. no test - no validity.

By the way, Rich is correct. You obviously don't have the slightest idea what "six sigma" is referring to.



> By the way, CNWoodworking was obviously not referring to the automotive industry when he said nobody cares about a 1% failure rate. The electronics plant I worked at did about a billion in sales every year and the products for which I was responsible amounted to about $100 million of that. A 0.1% failure rate would have been regarded as a colossal disaster and would have shut down production until the issue was resolved. Depending on the nature of the failure, it may have caused a DOT recall being issued. Way back in the 1990 s we stopped measuring failures in percent and started measuring in parts million.
> 
> - ArtMann
> 
> ...


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