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Do you add any additional measurements when glueing objects together?

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Forum topic by Holbs posted 25 days ago 381 views 0 times favorited 8 replies Add to Favorites Watch
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Holbs

513 posts in 634 days


25 days ago

So I am in the process of building a clamp rack on wheels. Things are going great. Got to use my router mortise jig for the first time. I have a 3/4” plywood 4’x4’ and a mating dado in my base structure. I did all dry fittings and everything was dead-on and fitted perfectly. I toss glue in the dado and the plywood, clamp everything together… and I notice the top structure is slightly tippy by 1/16” or 1/8”. Confused, I peek around at the joints and dado, the plywood is not 100% seated into the dado like it was during the dry fit. Sure enough, there is my culprit. Too late to re-adjust everything as glue is dried with some additional screws slapped in. It’s not a disaster as this is just a utility car. But when it comes time for fine furniture work or high precision joinery… should I take into account the space glue takes up?


8 replies so far

View Redoak49's profile

Redoak49

271 posts in 593 days


#1 posted 25 days ago

No…you should not have that much glue in a joint.

You need to remember that wood will swell when it gets wet from the glue and you need to make certain all the joints are tight when you clamp it up. Also, you can get a small bit of sawdust in things while you are gluing it up.

View TiggerWood's profile

TiggerWood

192 posts in 211 days


#2 posted 25 days ago

I think glue can cause wood to swell slightly but I don’t think that is the case here. How did you clamp everything together. I’m thinking one of the boards got stuck on one of the plies.

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Holbs

513 posts in 634 days


#3 posted 25 days ago

lesson learned. I “should” have clamped the 4’x4’ plywood into the base 1st, but instead I glued up the supporting structure first (after dry fit where everything… 100% fit). Something in the support structure must of moved, or there was debris I did not catch in the dado. Dang it. I was curious about the glue thing because I did just run a bead in each of the dado corners without brushing it flat.

View Loren's profile

Loren

7274 posts in 2252 days


#4 posted 25 days ago

Well, how did you cut your dado? Did you measure it for
depth every few inches to make sure it was consistent.

In any case… I read about this in James Krenov book
where he wrote that people would say “that’s too tight,
where’s the glue going to go, man?” to which he
argued that the right amount of glue does not cause
problems and that many people use too much to compensate
for hasty joinery. If you cut a tenon too thin, dont
worry, just glue a thin piece like a piece of veneer or
an offcut to the cheek, let it dry and try again. It’s
better this way than to expect glue to fill your gaps.

An exception is foaming polyurethane glue. It does
fill gaps, though it’s easy to put in too much and it
comes foaming out all over the place.

If you put too much glue in the bottom of a dowel
hole or mortise, hydraulic pressure can do weird things,
so leave some extra room, like 1/8”, at the bottom for
excess glue to settle.

Wood movement itself is a far greater culprit in dimensional
movement of things like piston-fitted drawers than a
glue line would be I think. Wood even moves lengthwise
a little.

-- http://lawoodworking.com

View bondogaposis's profile

bondogaposis

2448 posts in 956 days


#5 posted 24 days ago

should I take into account the space glue takes up?

No, you should not allow extra room for the glue. You must have applied too much glue and or didn’t clamp it properly. Maybe the glue stated to grab before the glue up was complete. I like to use Titebond II Extend, for complicated glue ups, it gives me more time.

-- Bondo Gaposis

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Holbs

513 posts in 634 days


#6 posted 24 days ago

I did not clamp the 4’x4’ vertical plywood down into the dado as it “seemed” to fit 100% during dry fit, so didnt think anything would change during glue up. I took things for granted. I either put too much glue into the dado, there was debris, or one of the ply’s caught somewhere in the dado.
I’m learning as I go. This will not happen again :)

View Rick M.'s profile

Rick M.

3793 posts in 984 days


#7 posted 24 days ago

Glue is waterbase and will cause swelling. If the joinery is tight to start, yes it will swell and can make the joints impossible to fit correctly. So the answer is yes, you need to consider the glue. Anyone claiming different, even Krenov, are simply accounting for the glue subconsciously when they dry fit the joinery. To put it a different way … if Krenov can put water on dry wood and not have the wood absorb it, he’s beyond a master of woodworking—he’s using witchcraft.

-- |Statistics show that 100% of people bitten by a snake were close to it.|

View ChefHDAN's profile

ChefHDAN

279 posts in 1454 days


#8 posted 24 days ago

Work with sub assemblies, or use Norm’s old standby and “shoot some brads until the glue sets” lol

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