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View Full Version : Glue sizing end grain in dovetailed joints



Curt Putnam
06-25-2012, 7:45 PM
Does glue sizing the end grain make sense when dovetailing. I'm assuming one also then glues the end grain during glue up.

If it helps, does it help enough to be worth the trouble? Especially with tightly fit DTs.

If it makes sense, does that also hold true for stuff like Unibond 800 or Weldwood resorscinol, etc.?

Thanks, Curt

Jerry Thompson
06-25-2012, 8:40 PM
Is the glue sizing to lessen dye/stain pentration? I did it once using hide glue and the tails came out lighter but they looked better, to me, when they were darker.
My only concern in dovetail glue up is glue on the straight grain. Remember you also have the mechanical holding componet with dovetails.
I cannot comment on the glues you mentioned as I have never used them. I almost always use hide glue for glue ups.

Dave Beauchesne
06-26-2012, 12:43 PM
Curt:

My thoughts would be that the sizing is going to soak into the end grain, soak in and swell up the wood a little. It then dries out, some of the solids from the glue remain and your once snug fit is no longer able to be assembled. When one thinks about it, the fit ( gap ) on a snug, well fit dovetail is about three fifths of a gnat's eyelash, which isn't very much - at all!

An interesting thought though.

Dave Beauchesne

george wilson
06-26-2012, 1:16 PM
I'm a bit unsure which end grain you are talking about. If it is the endgrain on the dovetails that can be seen after the dovetails are assembled,there is no need to apply glue to those surfaces since they have no effect on the joint. Even the endgrain INSIDE the assembled joint has extremely little strength to add to the joint.

If you are making a guitar or violin,and gluing he top and back onto the sides,and the end grain of the neck and tail blocks,it is good practice to first have applied glue to the endgrain,let it dry,and scrape it smooth,since you must rely on those surfaces for strength. Violin makers have sealed those engrains for hundreds of years,because if they aren't sealed,the glue can just sink into the endgrain and starve the joint.

john davey
06-26-2012, 1:19 PM
Hey Dave, I am currently shopping for some new layout and measuring equipment. I would surly appreciate a link to the tool you used to measure a gnats eyelash. Sadly all of my equipment seem to measure a different part of the gnat and I would like to keep current.... Thanks, John...


Curt:

My thoughts would be that the sizing is going to soak into the end grain, soak in and swell up the wood a little. It then dries out, some of the solids from the glue remain and your once snug fit is no longer able to be assembled. When one thinks about it, the fit ( gap ) on a snug, well fit dovetail is about three fifths of a gnat's eyelash, which isn't very much - at all!

An interesting thought though.

Dave Beauchesne

Curt Putnam
06-26-2012, 10:12 PM
George, Thank you. I realize that the end grain inside the joint (end grain to face grain) has little strength. I am also told that glue sizing can dramatically increase the strength of an end to long grain joint. In the through DT situation of my blanket chests, the end grain to face grain is by far the largest amount of surface area. Just seems likely that even a little increase in strength might yield a large overall increase. What I was wondering is if this could be true in fact rather than just a conjecture on my part. Then, of course, if the strength addition is enough to be worth the worry about what sizing would do the fit. Then lastly, whether any of the conclusions change if the glue does.

Prashun Patel
06-26-2012, 10:50 PM
The only end grain joint is at the bottom of the tail socket,right? The marginal strength added here will pale in comparison to the glue on the sides of the tails I would think.

Curt Putnam
06-27-2012, 4:51 AM
That is the question. Does anybody know​ the answer?

Jim Belair
06-27-2012, 7:34 AM
I usually slightly undercut the end grain at the base of the tail socket so the end grain doesn't make good contact anyway.

If your approach is to cut this area square, I know there must be some added strength. "Some" times large area may be considerable overall. I don't recall seeing any quantitative comparison of joint strength but if you really want to know by how much, why not do some tests and see? Sized vs. not? Glue A vs. glue B?

Frank Drew
06-27-2012, 12:40 PM
That is the question. Does anybody know​ the answer?


Curt, there might be some marginal advantage to sizing the end grain portions of dovetail joints, since they then wouldn't soak up glue (that is, make it unavailable) during assembly, but I've never heard of the practice, never did it, and my dovetail joints have never loosened, as far as I know.

As Jerry notes, a dovetail is largely a mechanical joint, the glue serving to keep the parts together so that the mechanics can work. Most of the gluing advantage will be long grain to long grain (although at right angles), but if there's a way to increase the end grain to long grain glue face, go for it. Should be easy enough to test with some scrap woodl

Curt Putnam
06-27-2012, 12:40 PM
Why not do some tests? Good question. For me, there is no time, no instruments, no meaningful test plan, etc. Was just hoping that the subject had already been researched. Even anecdotal evidence would be useful. Just part of my attempt to question accepted practice. The old masters did things a certain way because that way worked and was efficient, but the reasoning behind it is often gone. Basically, I'm just curious.

Thanks, Curt