Roubo lamination disaster

[Pat Barry]

Well, no one has any comments on the clamping advice from FWW and Titebond?

[Paul Incognito]

Pat,
Take the recommendations with a grain of salt.
Experience will teach you how many clamps you need and how tight they must be.
I've glued up hundreds of panels using all different types of clamps. The only failure I've had is similar to the OP's when gluing in the cold.
I read Fww's article when it was published and didn't think too much of it then, either. If you do a search, I think the topic has been discussed before.
Paul

[Tony Zaffuto]

One other comment is when doing a lot of gluing, such as laminations, use a glue with more open time, so the glue doesn't start to set before all pieces are in place. Titebond III is supposed to have more set time than II.

[Steve Baumgartner]

Pat,
Take the recommendations with a grain of salt.
Experience will teach you how many clamps you need and how tight they must be.
I've glued up hundreds of panels using all different types of clamps. The only failure I've had is similar to the OP's when gluing in the cold.
I read Fww's article when it was published and didn't think too much of it then, either. If you do a search, I think the topic has been discussed before.
Paul

And discussed to death! The article was highly controversial when it came out, with I think the majority of experienced woodworkers saying "Nonsense! I've never used so many clamps and I've never had a problem!". My conclusion at the time was that the professor's guidance was aimed at factory production in which a) the wood would be joined up straight off the jointer without careful adjustment for perfect fit (so the clamps have to take out both ripple and slight curves) and b) the goal was no visible glue lines at all, ever.

[Brett Bobo]

Well, no one has any comments on the clamping advice from FWW and Titebond?

Similar to Paul's suggestion, I view the FWW as merely a guideline or general reference as I personally think it misses some key info. Two important components are the surface area of the particular clamp to be used and the width of the caul and/or material thickness for the material joined. With those two things in mind, the effective surface area of each clamp can be increased at 45 degrees from the perimeter of the the clamp face. So, I'd work the other way and find the effective pressure of each clamp first and then compare to the required pressure of the glue joint to find the number of clamps required.

[Pat Barry]

Similar to Paul's suggestion, I view the FWW as merely a guideline or general reference as I personally think it misses some key info. Two important components are the surface area of the particular clamp to be used and the width of the caul and/or material thickness for the material joined. With those two things in mind, the effective surface area of each clamp can be increased at 45 degrees from the perimeter of the the clamp face. So, I'd work the other way and find the effective pressure of each clamp first and then compare to the required pressure of the glue joint to find the number of clamps required.

The clamping pressure guidelines were from Titebond, not FWW, so the issue reallly has to do wiith what Titbond is recommending for glue-ups. FWW might have built upon the Titebond recommendations, I don't know.

As it regards the clamps themselves however, a clamp applies a force and I don't think FWW estimation of the force applied by the clamp is unreasonable. Pounds are pounds so it doesn't matter the surface area of the clamp (as long as the clamp isn't dimpling the wood itself due to high pressure). Making the clamp pads bigger does not help apply more force at all - that is purely a function of the mechanical advantage of the clamp mechanism (ie: screw pitch), and how much torque you can apply to it.

The FWW formula is nothing special - its pure mechanics 101 - any engineer could tell you the same thing.

[Pat Barry]

And discussed to death! The article was highly controversial when it came out, with I think the majority of experienced woodworkers saying "Nonsense! I've never used so many clamps and I've never had a problem!". My conclusion at the time was that the professor's guidance was aimed at factory production in which a) the wood would be joined up straight off the jointer without careful adjustment for perfect fit (so the clamps have to take out both ripple and slight curves) and b) the goal was no visible glue lines at all, ever.

I would expect factory conditions to be optimum - it sounds as though you are saying that some careful fitting could reduce the clamping pressure? I didn't see anything in the Titebond literature stating that the clamping pressure guidance had anything to do with making allowances for improperly prepared surfaces and materials. Maybe I'm misunderstanding your point Steve.

[Daniel Rode]

I thought I should see how much pressure I can expect to get from my clamps. Here is what FWW had to say:

The graphic listing clamp pressure seems off to me. A parallel clamp is listed as less pressure than a quick clamp and significantly less than I-beam and pipe clamps?

My experience tells me that Bessy 'K' parallel jaw clamps are capable of exerting more force before bending or breaking than any of the others and the quick clamps are the weakest of all styles. FWIW F-Clamps are all over the place depending on the style size and brand.

The newer Bessy Revo parallel clamps are rated at 1500 lbs and my older style K clamps are rated at (IIRC) 1200 lbs. Maybe they divided the pressure by the area of the faces?

[Brett Bobo]

The FWW formula is nothing special - its pure mechanics 101 - any engineer could tell you the same thing.

I am an engineer as well--structural engineer

[Pat Barry]

The graphic listing clamp pressure seems off to me. A parallel clamp is listed as less pressure than a quick clamp and significantly less than I-beam and pipe clamps?

My experience tells me that Bessy 'K' parallel jaw clamps are capable of exerting more force before bending or breaking than any of the others and the quick clamps are the weakest of all styles. FWIW F-Clamps are all over the place depending on the style size and brand.

The newer Bessy Revo parallel clamps are rated at 1500 lbs and my older style K clamps are rated at (IIRC) 1200 lbs. Maybe they divided the pressure by the area of the faces?

So you are saying they were publishing PSI numbers instead of force numbers?? That could be. I'll try and find the article again tonight when I get home an see if this is the case because that could be a huge difference maker.

[Mel Fulks]

What is the point of giving force needed numbers for clamps? Was that article in the issue that had the double page color clamp ad with the two FREE computer disks on clamp use? That's where I saw the tip about using spring clamps on a sandwich to keep stuff from sliding out.

[Pat Barry]

Was that article in the issue that had the double page color clamp ad with the two FREE computer disks on clamp use? That's where I saw the tip about using spring clamps on a sandwich to keep stuff from sliding out.

LOL Mel - thats pretty funny stuff right there.


http://www.finewoodworking.com/item/...mber-of-clamps

What is the point of giving force needed numbers for clamps? .

The point is, you should know how much force various types of clamps can be expected to exert assuming you actually are trying to figure out how many clamps you need for a particular application in order to satisfy the glue manufacturers recommendations, that's all.

[harry strasil]

FWIW Dept: Gaps in Glue up, Were all the clamps the same kind, so that pressure was equal. Possibly there could have been built up stress in one of the boards that caused the gap. CAUTION, when sawing with table or band or skill or hand and chain saw, make sure you have wedges prepared to drive into the kerf so stress doesn't cause pinching of the blade.

[Steve Baumgartner]

I would expect factory conditions to be optimum - it sounds as though you are saying that some careful fitting could reduce the clamping pressure? I didn't see anything in the Titebond literature stating that the clamping pressure guidance had anything to do with making allowances for improperly prepared surfaces and materials. Maybe I'm misunderstanding your point Steve.

I didn't mean to steal this thread, sorry. There was so much misinformation and naive argument when this first came up that I regret mentioning it...we don't need to get that going again!

Steve