How much gap for glue for these joints....?

[bent]

I am curious how much gap to leave for these joints, which would entail possibly not gluing certain faces of the joints, and building for loose dry fit-ups. Sometimes I had control over gaps, some times not. I did not have any undersized, non-nominal tools. I was not prepared for the added space of the glue. I glued ALL applicable surfaces I wanted w/ a small paint brush. How much gap in thou, or 1/32" or whatever should be designed into this type of work? The finished pre-glue -up work would look like scrap to ME w/o knowledge of this. I am very picky about final dimensions.

some of the joints I have made recently which needed glue:

1)drawer lock joint w/ 3/4" face, 1/2" side birch (not Baltic) - (for drawer)

-TS and router table. 1/4" straight bit. Sanded quite a bit. Chamfered the corners w/ block. I dry fitted tightly. Thats what I wanted. Then came glue up. Worked out but I needed all my clamping power. Where did the glue go Phew.?

2)dado joint w/ 1/2" back, 1/2" side birch (not Baltic) - (for drawer)

-router table. 1/2" straight bit. There is like .025" or .030" between these two, so glue up was fine. When I made it I had serious reservations about using the joint! newbie

3)rabbet and dado (free-standing support pillars for sliding doors)

-router table. 1/4" straight bit. 1"x3" select pine. Dry fit was just right. Mallet time. No gap left anywhere (for glue)! Glued everything!. What a bummer. Amazed I didn't break anymore cast iron clamps! Had to sand to get the final thickness back.

4)butt (free-standing support pillar for door hinge side)

- no problems except run-out. Don't know what thickness it added. Seems like a lot. Disaster in another placement.

5)rabbet and dado (top door jambs) - actually the sides slide on screws and shimmed from behind, I can slide tops out w/ sides screwed in place, and they are jointed to be exactly 30" and 24", but I don't think I'll use any glue. Not much of any gap. More now. Nothing visible. Paintable. What do you think - expansion!?

BTW, I'm now curious about sliding dovetail front joint effect on strengthening box for future reference. How do these glue up as far as strength goes? So I could cover slides on sides. I guess false fronts for any face frame applications too.

[bent]

I used side-mounted bottom supporting slides for 8 drawers. They have 3 sets of slots and screw holes. Supposed to set-up in slot, then use o/ holes to secure. I found no other way than to lay out ALL holes first, before even finishing drawers. had the cabinet slide sides installed. Is it a pipe dream to even consider inset drawers into a face frame of a cabinet w/o also using face frames - in practice?

[bent]

because I knew it would be level

cabinet w/o also using

false fronts?

[Leon]

Make all of you joints to within .001-.005 of snug but not too snug. Then add glue.

[Leon]

Why are you laying out holes for drawer slides. Just screw the slides on when you are ready. You don't need to predrill for these short screws unless you are buying your screws at Home Depot and not using the ones that came with the slides.

Come again.

[Leon]

Are you new to this new fangled "inter net" thing????? You really do appear to always be having a conversation with only yourself and it always seems to be in some kind of code.

[Peter Huebner]

If you have to hammer or use clamps to pull the joint together, it's too tight. If you put it together dry and it wobbles around, it's too loose.

The wood and the shoulders should support the joint, and things should slide together snugly on dry assembly - that's all there is to it.

Consider that end grain does not really hold a joint - the important faces are where long grain meets long grain.

Don't be tempted to use epoxy as a 'gap filling glue'. A friend of mine did that in his (professional) joinery for a while and it all started falling apart within months. :-(

h.t.h. -P.

[Ba r r y]

That's actually surprising to me.

I've seen epoxy hold some amazingly poorly fitted structural joints on full-scale boats and large scale model aircraft with excellent results. Some of them were on very badly built 40-45 pound model airplanes that regularily pull 4-5 G's.

Did the glue itself fail, or the attachment of the glue to the wood?

[bent]

That would make sense , but I hope u realize I was talking before, and after glue, respectively. I have no doubt that no joint component could hold itself in position against gravity before being glued in all sides. (4 sides is too many...). the standard tooling vs. standard sized plywood I have closely avialable wouldn't hold the weight of a match. I am curious now what the point of undersized plywood router bits are. I saw a set where the 1/4", 1/2", and 3/4" where all 1/32" undersized. I can (now) see where you may want these for end gluing the joint (there would be no room side to side), but these are about tightm dry, and leave no room for glue. As I mentioned earlier, others Frued or Infinity, sell 1/16" under.

[bent]

are u the guy who called me out for posting out of succession too. U r the one man show here. I have not posted in spite of anyone. If u need to feel close I can tell u where u are needed. I hear Bin Laden is looking for a few good men.

[bent]

you have been sniffing glue

[bent]

its all relative

[bent]

I had control over how thick the slide-in thingy was, but not the groove (1/4" straight bit). I used a .001" dial caliper to set up. If it was within say .005" under, ok. Anyone who knows (how to answer) also knows how much of a drag it is to distinguish between this and the RIGHT set=up offset numbers I am looking for for the next time I have to set up the fence(s) for this situation.

[Leon]

Nope

[Peter Huebner]

I would say the adhesion of the glue to the wood failed. But it'd be hard to say without extensive testing under the microscope, maybe ?!?

The timber we're talking about here is gum - eucalyptus botryoides, ~fastigata, ~pilularis. I've several pieces here in my house, some offcuts of a benchtop he made for someone which I used to make trivets .. glue failed after 6-7 months. He also made a butcher's block as a wedding present for us and more than half the joints have failed on that; I kept having to re-joint it.

I myself tried epoxy on some gum 20 years ago (jarrah, don't know the species any better) for an end-vice for my woodworking bench and it failed within days. I never tried again ;-)

I have used all the above timbers successfully with aliphatic, resorcinol, aerolite 308 and premixed urethane glues and never had any failures so far. Go figure.

-P.

[Peter Huebner]

Oh my, this is getting awfully technical :-)

From the top of my head I would say that 1/32 is too much of a gap, way too much. Then again, most tools cut a little bit more off the wood than their nominal size, and now it's getting into territory where hardwood/softwood is going to be a telling difference, springyness of the timber, moisture content...

So, sorry, I don't go on figures myself; I mark out with a knife, I cut up to the knife mark, then I trim with a very very sharp chisel until the joint barely just slides home. Empirical. I don't use presized router bits, that's why I can't really be more helpful to you here. I've seen dovetail jigs, coveted them and never bought one :-) and I end up doing hidden joints, often do drawers with bisquits or I cut joints on the radial arm saw and clean up by hand.

-P.

[Ba r r y]

The joints I was referring to were mahogany, maple, bass, sitka spruce, oak, etc... Typical North American furniture, boat, and aircraft woods.

It's gotta be an thing with certain woods.

Barry

[bent]

its probly a Q for each type of joint and the number of faces which could/should get glue. I am thinking of yellow glue too. Each corner of drawer lock joint had 10 seperate faces to coat with glue. 52 9" long faces for each drawer before clamping in position. Thats 39 feet. Would you glue all the faces of a drawer joint first before assembly? Try that in a .250" x .250" seven foot long groove.

I think if you will coat both surfaces, that you should be able to count on the pressure from both sides being equal, so that though your initial measurement looks like you measured it with cabbage, it will look right after its dried. And I think you always need to leave a gap on the bottom of the joint, unless you aren't using glue there, b/c you would need enough pressure to either squeeze it into the wood, or out the ends.

Next time I do anything with glue I can tell you gravity won't be part of the equation. Thats not true. By magnitude of dimension it is true. But because everything warps, thats why its not true.

I've got no numbers, answers yet. Its like wax, how thick is wax, oh, a mile, a cm. try to apply it coat after coat and see. its science.

[bent]

I love math