Glue and Clamping Force

[Joe W.]

So here's a new one for me - 

 I came across an article on woodworking that stated when gluing wood pieces together to NOT overly tighten the clamps as it would squeeze out too much glue, resulting in a poor bond. 

So the questions are:  is that true and how much tightening with clamps is enough and how much is too much?

 

[TexasDIY]

I have wondered the same thing too.  Maybe someone can enlighten us with their knowledge. 

[preprius]

I have successfully glued 1/8" thick wood butted against each other. 

the boards were 2ft long, 6" wide and 1/8" thick.  End result is 18" x 24" x 1/8". 

Not many people thought it was going to work. 

I did this twice.  The first one I used bar clamps. to squeeze wood together. Of course the wood wanted to bow up. So I placed weights on the wood. The glue squeezed out some. The ends showed I starved the joint. Did not put on enough glue.  No glue squeezed out.

The second one i decided not to use bar clamps.  I just put weights on the wood so they would not separate. I also sanded them flat better than the first. I did push really hard before putting the weights on. I did not starve the joints.  But I also did not want much glue squeeze. 

Surprising both worked fine.  They are my hat brims. I do wear these hats to stores, restaurants. They get banged against car/truck doors and house doors.  The first one has not come unglued in 8 weeks.  2nd one is on week 2.

Titebond 3 is what everyone told me to use. A few weeks after, I watched a video that they tested glues.  Titebond3 was the best. The wood broke before the glue did. 

 

Overall, you want the glue to go into the wood grain. I think I read on titebond3 website that the joint should not be bigger than 0.005".  

 

Me. Mark Eason

 

[TAIrving]

I tend to adjust the clamping force depending on how well I was able to true up the surfaces to be glued.  If they line up well, then minimal clamping.  But if not, then clamp the little buggers!  I use Titebond 3 and have not yet had a glue joint fail.

As an aside, I am watching Barb's @barb.j.enders discussion on Safe-T-Planers.  I sometimes struggle with getting my work pieces trued up for gluing.  

Aside #2:  I sometimes get end pieces from a furniture maker friend, 1-3/4" thick hardwood.  Sometimes I resaw them into thin boards for scrolling.  But sometimes I like to glue them up into bowl blanks for lathing.  I have to clean the surface before gluing and can never get them quite true.  And it requires a LOT of clamping force to clamp 2 not-quite-true hardwood pieces, 6"x6"x1-3/4", to get them together for gluing.  Thank you Titebond!  

[Bill WIlson]

Here's one answer to that question.

 

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

[Millwab]

2 hours ago, Joe W. said:

So the questions are:  is that true and how much tightening with clamps is enough and how much is too much?

Joe, everything I’ve seen or read says that a small bit of squeeze out is all you need to make sure the glue has covered the joint properly.  The biggest thing is that the two surfaces are smooth and flat. Excessive pressure in most cases is trying to compensate for poor surface alignment.  I’ve often glued pieces up with no clamps, just using a "rub joint" and it was just as strong. 

[OCtoolguy]

2 hours ago, Millwab said:

Joe, everything I’ve seen or read says that a small bit of squeeze out is all you need to make sure the glue has covered the joint properly.  The biggest thing is that the two surfaces are smooth and flat. Excessive pressure in most cases is trying to compensate for poor surface alignment.  I’ve often glued pieces up with no clamps, just using a "rub joint" and it was just as strong. 

I've watched a ton of videos and many times I see the person that is in them, do what I call a "massage" of the two mating surfaces. Lightly squeezing them together while sort of moving them in a circular motion to spread the glue and also to squeeze out the excess glue. It pushes out any trapped air and takes away that "cushion" that the glue creates and brings the two pieces tightly together. At that point very little clamping pressure is needed.

[John B]

If you are using a PVA glue, clamping force is good as the glue is cross linked which means the molecules link into the timber. This makes the joint much stronger than the piece being glued. It is also, none gap filling. Other types such casein, animal, urea's, Polyurethanes and epoxies do not require such clamping force as the bond relies more upon the glue line. With a lot of these glues you can edge joint timbers successfully by just using a "Rub" joint and no clamps at all. It is possible with a PVA, but the joint may not be as strong as a clamped one.

 

[FrankEV]

Just to add my 2 cents, uniform pressure is as important,  or maybe more important,  than how tight you squeeze the joints.  

For joints (like for making a box) my rule is just a little tighter than what I considered "snug".  Which produces some but not excessive  squezze out.  Of course this is a function of how generous the glue application is.  Most apply much more than is really necessary, me included.  Spreading and getting a nice thin uniform layer of glue (talking Titebond or equal here) is critical to minimize squeeze out.  

I find a significantly tight clamping pressure is appropriate for Gel type CA glue, as CA tends to expand somewhat.  Altough I don't use it often, this is the same for "Hide" glues.  I also tighten the Sedy Clamp on my frames very tight to develope nice neat miter joints and then I rinforce the joint with "V" nails.

For panel glue ups (cut panel/backer), I found using clamps and weights was a PITA and very dificult to maintain alignment.  So I made myself a very rigid flat Panel Press (similar in design I saw for a vaneer Press) that applies uniform pressure to the entire panel with only 6 wing nut bolts.  The bolts and washers are epoxied in place.  This press can hold up to 14" x 24" panels.  Mine is good for up to 3/8" total Panel thickness.  Should have use longer bolts to allow for thicker panels. 

I apply Titebond Ultimate to the back side of the cut panel only using a small foam roller to get a nice uniform coverage without to much chance of squeeze out and being careful to not alloow to much glue to get into the cut-out's.  I then lay the cut panel on top of the (pre-painted or stained) backer being very careful to get good alignment, set the top half of the press.and tighten to a strong finger tight on each wing nut, sort of like tightening lug nuts on a car wheel.  I will  allow a minimum of 4 hours before releasing the press.

 

I'm very happy with how the press works.  

Hope this was helpful.

 

Edited May 6, 2022 by FrankEV

[Joe W.]

7 hours ago, FrankEV said:

uniform pressure is as important,  or maybe more important,  than how tight you squeeze the joints. . .  

  I will  allow a minimum of 4 hours before releasing the press.

I'm very happy with how the press works.  

Thanks Frank,
Another good technique I'll adopt.

[TAIrving]

On 5/6/2022 at 8:40 AM, FrankEV said:

I apply Titebond Ultimate to the back side of the cut panel only using a small foam roller to get a nice uniform coverage without to much chance of squeeze out and being careful to not alloow to much glue to get into the cut-out's.  I then lay the cut panel on top of the (pre-painted or stained) backer being very careful to get good alignment, set the top half of the press.and tighten to a strong finger tight on each wing nut, sort of like tightening lug nuts on a car wheel.  I will  allow a minimum of 4 hours before releasing the press.

 

Thanks Frank.  I think I need one of these.  

I like to use blue painter's tape to hold the pieces in alignment prior to clamping.  

[Blaughn]

 

For the word-art plaques I make, I edge glue my panels using a trammeling board.  I posted the particulars in this post in 2017. 

This has worked extremely well for me with stock as thin as 1/4".  (I haven't tried 1/8 inch but i have no doubt it would work.  I use Titebond III wood glue for all of my glue-ups.   Knock on wood, I have yet to experience a joint failure with this tool.

 

Bruce

[Joe W.]

5 hours ago, Blaughn said:

I edge glue my panels using a trammeling board. 

And yet, another new technique for me to explore.
Thanks!