If you like your Kerfmaster....

[Zz Yzx]

tool for tenons.

-Zz

[GarageWoodworks]

Doesn't seem to leave room for glue.

[-MIKE-]

>>> Similar tool for tenons.

I always thought a tight mortise a tenon, like dovetails, only needed glue to keep them from slipping apart. The strength is in the joint.

When gluing up panels, is there room for glue? Not really. You squeeze out what hasn't soaked into the wood.

I think the same can be said for M&T joints. You wipe on only enough glue to soak in. I've seen many a study that breaks the myth of the glue-staved joint.

[Leon]

> Similar tool for tenons.

Doesn't seem to leave room for glue.

As long as you apply glue to the entire contact area, even if some gets wiped off during insertion, it will be plenty of glue.

[Jim Weisgram]

>>> Similar tool for tenons.

I believe the fit is adjustable, FWIW.

[Leon]

>>>>> Similar tool for tenons.

Not directing this directly at you Jim.

I don't believe that making the joint looser is going to increase the strength of the joint. When you clamp two edges of wood together to form a wider board do you leave a gap or not tighten the clamp to insure that no glue gets squeezed out? The best glued joint is one that has glue on the entire surface before the union. After that the best glued joint is the one with the thinnest glue line/layer of glue.

To some it seems to be a common thought that it is OK to remove excess glue by squeezing the bejesus out of a panel glue up, which it is. But for some reason there is the belief of excess glue being removed from a joint by the sliding and scraping motion during assembly will starve the joint.

The common misconception of Glue Starvation is that in which excess glue is removed form mating surfaces during assembly. Glue Starvation happens when glue is not applied to the entire mating surface before the mating of the surfaces. Once there is a solid layer of glue on a mating surface it is either the correct amount or too much, never not enough. If a complete thin layer of glue dries out before assembly, that is another problem. Mating surfaces that do not fit tightly is another problem also.

[J. Clarke]

>>>

Read the specs on your glue--there's usually a specification for glue- line thickness. To the extent that you're able, go with the specification unless you have test results that show that you should do otherwise.

In the one case it's being forced into the grain, in the other it's being scraped off.

[-MIKE-]

Not correct. Leon is correct. You cannot force (carpenters) glue into the grain of wood. It goes in as far as it goes and that's it.

I remember reading and being amazed at how little glue is actually needed to bond wood together. I also remember in the same article that it mentioned if *any* glue was soaked into the grain, it was *enough* glue. Meaning, if you put a thin layer of glue on and it gets wiped off the surface, you're ok.

[J. Clarke]

Of course you can. There is porosity there, apply pressure and the glue goes into the pores.

I remember reading a lot of stuff. The fact that you read something doesn't make it true. Don't believe me, read "Mein Kampf".

[-MIKE-]

The path of least resistance in a panel glue-up is up, down, and out at the seems, not into the pores. It would take a lot more pressure than that for glue to go any further into wood pores than it would from passive wicking.

It's a moot point, however, as it is simply unnecessary.

It doesn't make it untrue, either.

[J. Clarke]

Fluid flow is not quite as simple as you make it out to be.

More pressure than what?

What is unnecessary?

No, but "I read somewhere" is not to be trusted.

[-MIKE-]

And gluing is not as complex as you're making it out to be.

More pressure than clamping up panels produces, when allowing the excess glue to push out.

Allowing "room for glue" in a M&T joint.

Well you know, I wish I could cite the source or point to a web site, but it was years ago in a respected trade mag. I also have my experience to go by and a quart of glue goes a long long way with me. And as little as I use, I still usually end up cleaning up 10x as much glue as remains in the joint. :-) No failures.

[J. Clarke]

Well, actually if you get down to the hydrodynamics of it, it is.

Nobody has suggested "more pressure than clamping up panels produces".

Please post your test results that demonstrate that joints that have less clearance that the recommended glue line thickness are just as strong as those that have the recommended glue line thickness.

What trade?

So how many structural joints that you have made depend entirely on the glue for their strength?

I'm sorry, but "I've been getting away with this for years" doesn't show that you are getting optimal bond quality, just that it's good enough for whatever you are doing. If you're working with 10:1 margins you can get away with quite a lot.

[Larry W]

Not really what you guys are talking about, but in a blind M&T, it is important to leave room for glue - at the bottom ot the mortise, by making it very slightly deeper than the tenon is long. Otherwise any glue that collects there as the tenon is assembled may keep the tenoned piece from fully seating.

[Leon]

That is correct, the glue that gets trapped inside the mortice will keep the tennon from going in all the way if the mortise is not deep enough to accomidate the glue also.

However, Originally I was responding to the "Doesen't seem to leave room for the glue" comment concerning the new BridgeCity Tennon maker. I does not have any thing to do witht he length of the tennon or the depth of the mortise. It works to size the tennon sides to fit the mortise sides. A close fit that would scrape off excess glue, "not leaving room for the glue" is how I read that comment. That would be a false assumption.

[Larry Jaques]

Small flats on the rounded length of the tenons can also prevent hydraulic lock like that. The glue seeps by the flat. Or take the clue from dowel makers. Run a nail down your tenons, raking a trough, so glue can escape.

-- Know how to listen, and you will profit even from those who talk badly. -- Plutarch

[Robatoy]

That also includes your argumentative posts.

Also, using words like hydrodynamic are beyond your skill-set. Know what they mean from an engineering stand-point before using. Hydrodynamic is not to be confused with hydraulic.

[-MIKE-]

Which is completely unnecessary for this debate.

That's my point.

Ok, I'll bite. What's the recommended glue line thickness? And tell me how it's maintained when clamping boards together to make panels.

What newsgroup are *you* reading? Is this being crossposted to some other trade's newsgroup?

"Structural" ...depends on your definition. Is a glued up panel structural? Tabletop? Neither of those allow for this "recommended glue line thickness" you mention.

To stay specifically on topic.... any "load bearing," if you will, strength in joints like M&T, dovetail, loose/dowel tenon, is in the wood and the glue pretty much keeps the two pieces from slipping apart. If you consider timber frame construction and look at a beam held to a post with a through tenon and a wedge. The wedge keeps the joint tight and does nothing to add to the load bearing capabilities of the joint. If the wedge fell out, nothing would happen. Yes, take all the wedges out and shake the house back and forth and things start to loosen up. That wedge is the glue in that joint.

Take any other joint where the glue is solely responsible for holding the two pieces together, butt, T&G, Dado, Miter, etc, and clamping results in glue squeeze-out that is surely tighter than any "recommended glue line thickness."

"I've been doing it this way for years, because I think it's necessary" doesn't show that it's necessary, either.