titebond clamping force for wasteblocks

[Dan Gaylin]

I will often use a wasteblock glued to a bowl blank to maximize the depth I can get out of a blank. I have had good success using Titebond II to attach the wasteblock to the bowl blank. For "clamping" I have always used a couple of square rubber coated 5 pound weights that stack, followed by a block of wood followed by some cinder bricks. Maybe 30-40 lbs of weight total. Never had any problems. Joints always seem really good, with nice glue squeeze out (I make sure that the surfaces are very flat). I know some people use double sided tape, paper joints, and hot glue...so I figured I was being pretty safe with this method.
,
I was reading the Titebond II information sheets recently and they recommend 150 psi??!! So with a 6" round waste block with an area of about 28 square inches, I would need 4200 pounds of clamping force?? Which would require several medium duty woodworking clamps at close to max force. I must be misunderstanding something here.

Would appreciate your thoughts including any perspectives on my clamping method. Just because I haven't had any problems doesn't mean it's safe.

Thanks,

-Dan

[Richard Coers]

Fine Woodworking did a test on those numbers a few years ago and confirmed high pressure was needed. PVA glue needs to get in the pores to reach the max strength.

[Edward Weber]

You do not need 4200lbs of pressure.
Your clamp provides pressure accross a wider area than just ONE square inch.
This may help you visualize
https://www.finewoodworking.com/2010...ing-the-clamps

[Mel Fulks]

Fine Woodworking is good at scary minutiae. Lots of work is done with just rub- glueing ….but that doesn’t clamp fear into anyone !

[Kevin Jenness]

"Enough (pressure) to bring joints tightly together" is what Titebond calls for. With well prepared joints and proper glue spread hundreds of psi are not needed to develop a bond stronger than the wood. Consider rub joints, mortise and tenon joints and vacuum pressed layups. I suspect the psi figures were developed for industrial use where the surfaces may be less than optimal and hydraulic presses are common.

If you want to test your procedure, let the glueline cure thoroughly, then try to split it apart with a chisel and mallet.

[Richard Coers]

Fine Woodworking is good at scary minutiae. Lots of work is done with just rub- glueing ….but that doesn’t clamp fear into anyone !

A well set up scientific test is not minutiae. Have you even seen the article? Are you suggesting we don't even have to use clamps at all in our work?

[Edward Weber]

A well set up scientific test is not minutiae. Have you even seen the article? Are you suggesting we don't even have to use clamps at all in our work?

You mentioned a test, can you post a link to it?

[Dan Gaylin]

Thanks for all the replies folks, which were very helpful. I searched a bit more and found some earlier threads on SMC and elsewhere on this topic more generally (not specific to turning). The consensus seems to be -- including information directly from Franklin (manufacturer of Titebond), that a modest (define how you will) amount of force/weight will produce a very strong joint. Using higher levels of force produces a thinner glue line, which is inherently stronger. So there may be science that tells us something in the referenced experiments, but for practical purposes, it appears that making a tight joint, with plenty of glue, and clamping it sufficiently that the parts are joined tightly together will be highly effective in most cases.

[Bill Howatt]

I think one of the keys is that you don't require the maximum holding force for your application to work satisfactorily. Also, they say the full holding is done after a couple days or so of curing - do you wait that long?
I do believe in the benefit of clamping regardless of the sticky being used and in my case, that is double-sided tape or hot glue almost always. I've cut way back on the amount of tape I use and it still sticks so well I usually end up turning the waste block off and I turn off the hot-glue blocks just as a matter of course.

[George Yetka]

I feel that Tightbond says 150# based on a 1" cube being glued to a 1" cube. A squeeze clamp can take care of that. but they would need a pretty elaborate scale to give you all clamping values for every possible glue up.

Ive lived buy firm pressure with parallel clamps using the triangle rule for spacing.

[Dan Gaylin]

I wait at least 24 and usually 48 hours. What kind of double sided tape and hot glue to you use. I have had trouble finding effective products, especially hot glue.

[Edward Weber]

Thanks for all the replies folks, which were very helpful. I searched a bit more and found some earlier threads on SMC and elsewhere on this topic more generally (not specific to turning). The consensus seems to be -- including information directly from Franklin (manufacturer of Titebond), that a modest (define how you will) amount of force/weight will produce a very strong joint. Using higher levels of force produces a thinner glue line, which is inherently stronger. So there may be science that tells us something in the referenced experiments, but for practical purposes, it appears that making a tight joint, with plenty of glue, and clamping it sufficiently that the parts are joined tightly together will be highly effective in most cases.

A well made, close fitting joint, whatever it may be, requires less glue and is more important than how much pressure is applied.
As it's been mentioned, many times I've used rub joints when making segmented turnings. So we're only talking my hand pressure, the glue lines that can be seen are almost imperceptible.
You will never make a glue line on a bad joint disappear or make a a weak joint stronger by adding more pressure.
example of rub joinery close up
IMG_2140 (600 x 400).jpg

There is no need to add excess pressure on joints, it does nothing.

[Bill Howatt]

I wait at least 24 and usually 48 hours. What kind of double sided tape and hot glue to you use. I have had trouble finding effective products, especially hot glue.

I have some double-sided tape that I got from Lee Valley years ago and it still works. I keep it in a fridge. I have also used Duck brand tape with good results.
This is LV's current offering which may or may not be identical to my old stuff which, BTW, is 1": https://www.leevalley.com/en-us/shop...d-turning-tape

For hot-glue it is just regular "heavy-duty" stuff that is a bit on the amber colored side - not the clear craft stuff. For the hot-glue in particular, I have a decent size flat ring area on the outside of the waste block and then I dish it downward in the center. The idea is that it gives interior excess glue somewhere to go when the pieces are pressed together. Nothing wrong with a little similar dishing on the bowl base if you wish.

[Dan Gaylin]

Thanks Bill!