Clamping Pressure

[Cody Colston]

There was a thread a while back discussing how much clamping pressure was required on glue-ups. I believe the "just finger tight" crowd was the majority.

The Dec issue of FWW has an article that might change that method. It seems that most woodworkers use too little clamp pressure. The author puts some science into the equasion, recommending various clamping pressures for various wood species.

The most interesting thing to me was the illustration showing how the pressure radiates at a 45 degree angle from the clamp, thus dictating how many clamps are necessary on a given glue-up. I've always just kinda guessed at that...now I know.

[Gary Keedwell]

Ya, according to them, most of us are underclamping, and our fear of starving the joint is unfounded.
Gary

[Lance Norris]

And I guess all the things Ive made in the last thirty years are going to explode apart soon because I didnt use tons of clamp pressure. I hope Im not standing next to one when it happens.

[Rick Thom]

Most experienced wwkrs I know consider the FWW recommendations quite frankly out to lunch.

[Mike Cutler]

Cody
Did they break the adhesives dowm by type? Or was "yellow glue" the adhesive used for the article
Ya' know. It seems like one of the wood magazines was the catalyst for the last discussion on wood clamp pressure.
How many times can the magazine folks rewrite/reformat the same material? They have to know that they're making folks second guess themselves.

I'm going to keep using epoxies. I know the answer to that one.

Thanks for the headsup Cody. I'll try to find the mag' this weekend and check out the article.

[Rick Gifford]

So I wonder if they are going to create a tension device for our clamps that tells us when they are "just right"?

I don't know if my clamping is too strong or too soft, all I know is the stuff stay together when done. I just guestimate as I go.

[Gary Miller]

26 clamps on a 3' board!!! Come on.

[frank shic]

gary, don't you see the potential for bargaining with SWMBO? but honey, FWW says that i need at LEAST 26 clamps to make sure that this table top doesn't explode in the future, you wouldn't want that to happen now, would you?

[Cody Colston]

Cody
Did they break the adhesives dowm by type? Or was "yellow glue" the adhesive used for the article

Mike,

I believe all the clamping pressures recommended assumed PVA glue.

[Todd Jensen]

In laminated handrails, I've always used enough clamps to avoid gaps and enough pressure to eliminate/minimize glue lines, which can be SUPER tight. I get a ton of squeeze out but have never had a problem with de-lamination. With curved treads and cove molding blanks, I often get away with a lot less clamps or clamping pressure than I would think necessary when compared to the rails. I think ultimately this may be a 'situation dictates' thing, but if you use plenty of glue to begin with and 'size' your endgrain surfaces, I think it'd be really tough to over-clamp a joint. If your making 'nickel holders', i.e. crushing the wood with the clamps, you might want to ease off.

[Tom Henderson2]

Most experienced wwkrs I know consider the FWW recommendations quite frankly out to lunch.

In fairness to FWW, I believe they were testing per the glue manufacturers specs and recommendations.

Don't shoot the messanger....

[Eric Wong]

I think the take-away message for me was "don't worry about it". I've always been worried about putting too much pressure on and starving the joint. After reading the article, I said to myself, "self, just clamp 'em down hard. No need to worry about how much to tighten any more."

My wife worries when I start talking to myself like that.

[Todd Jensen]

Eric, I told myself, I like your style.

[Gary Keedwell]

In the February 2008 FWW #196 on page 10 there is a question from a Alan Schaffter ( Is that our Alan from the Creek?) about clamping pressure. Plus there is a big window block on the same page called Clamping Pressure: Reality Check. I highly recommend you check it out. I got my issue in the snail mail yesterday
Gary

[Lee Schierer]

I think the take-away message for me was "don't worry about it". I've always been worried about putting too much pressure on and starving the joint. After reading the article, I said to myself, "self, just clamp 'em down hard. No need to worry about how much to tighten any more."

My wife worries when I start talking to myself like that.

I agree. I've known for a long time that lots or pressure was needed and that getting too much was hard to do without crushing the wood. I've also known that the only way to starve a glue joint was by applying too little glue to start with. My HS shop teacher from years ago taught me how to glue up boards and how to place clamps. Clamps every 3-4" on opposite sides of the boards. Basically you have to leave enough room between clamps for the handles to swing. And there is no such thing as too many clamps.

Now about talking to yourself, sometimes that is the best way to have an intelligent conversation....