Tightly fitting joints -- how tight is tight?

[space.dandy]

I watch a fair amount of woodworking YouTube videos. In the vast majority of these joints are fitted so that they go together tightly, requiring gentle persuasion from a mallet or clamping pressure. However, I've just watched a Rob Cosman video in which he says that the joint should go together snugly but easily; his claim is that if the joint is tight then the glue will be scraped to the bottom of the joint, resulting in a poor glue surface -- he was demonstrating a mortice and tenon joint at the time, so I'm not sure if he was making that claim generally or specifically for that joint.

I just wondered what other people's views are on that? True, true but irrelevant, or a load of old rubbish?

 

[bjm]

It's a trade off! You need some space for the glue to form a film between any mating surfaces but not so much that the glue becomes a gap-filler (which most wood glues aren't designed to be).

 

[Oddbod70]

Gentle persuasion for me but it does depend a little bit on what you are joining and the glue used.

I use a lot of PU, which foams and doesn't gap fill that well. The old favourite Cascamite (AKA Extramite or whatever it's called now) will gap fill a bit. And there is always epoxy if you really screw it up!

TBH I subscribe to the view that fitting a joint will only ever scrape off the surplus glue, not the glue that's doing the job and I'd rather have less (but enuf) glue and more wood any time. (I may be wrong of course, but it works for me)

 

[Sheffield Tony]

I was taught that in hardwood, it should be possible to assemble by hand alone, in softwood with gentle tap by mallet maybe. But this is to avoid splitting anything, not a glue consideration.I would have thought with water based glues at least, which soak into the wood somewhat, you would be pushed to make it too tight for the glue to work - think how tightly you would clamp boards when edge jointing to get an invisible glue line. I don't know about you, but I can't cut joints that fit that tightly all over the mating surfaces !

 

[sammy.se]

I do like what I sometimes see which is gently compressing the mating surfaces of a joint with a metal hammer (pin hammer or similar) so that it will assemble easily but will swell from the glue once assembled.

 

[thetyreman]

what he probably means is you've got to find a sweet spot between it being too tight and too loose, especially with mortise and tenons, I aim to make it as tight as possible without it splitting, finding the balance takes a lot of patience and very minor adjustments until you are happy with the fit, glues can make the wood expand slightly and then it is too tight, hide glue is better for this reason, but I prefer PVA. Different woods require different methods, oak can split easily, redwood pine compresses well without splitting, a wood like cherry will be different again.

 

[AndyT]

I've definitely had the problem of joints that fitted nicely when dry, but got tighter when the glue was on (but before it had set) - presumably by absorption of water into the wood. So I guess the answer is that it depends on the wood, the glue and how fast you work... not a very helpful answer really!

 

[Sheffield Tony]

Hah yes - my Smokers Bow chair only went together with a lot of persuasion and a big mallet because the Titebond 3 made the spindles swell. Nothing cracked fortunately, and however much glue got scraped off, it has not fallen apart yet ! Hide glue is much better for that sort of job, it seems slippery somehow so the joints slide together much more freely.

 

[Droogs]

When test fitting joints, I brush on a little blue chalk with a puffy make up brush. See where it has rubbed off and give it a little sand there and retest. then when I can fit it together by gentle taps with my palm or wood mallet but not take off most of the chalk, I consider the joint ready to glue. Brush off the tenon and glue up. If you need to swing the mallet more than a couple of inches to get movement then it's too tight

 

[AndyT]

@Droogs if you want to keep a puffy make-up brush in the workshop, please don't feel you need to justify it to all of us!

 

[Droogs]

@AndyT Well it has to earn its keep as I only really use it at weekends when you can call me droozila

 

[Max Power]

With glued joints a tap to assemble fit should be adequate or they risk being left with little to no glue

 

[space.dandy]

Thank you for the replies. I hadn’t actually considered that the type of wood might be a factor.

 

[Fitzroy]

Mr Matthias Wandel has some interesting experiments and videos.

https://woodgears.ca/joint_strength/glue_methods.html
I’m in the camp of goes together with a tap when dry, slides in easily if I apply glue and quickly assemble, needs a massive clamp when glue up goes wrong and the glue has sat for 5mins before I try to assemble the joint.

F.

 

[Ollie78]

Depends how complicated the glue up is, if its simple job tight enough to need a tap is ok.
If its complicated give yourslelf a chance by making them fit by hand otherwise panic and swearing will soon take over !

Ollie

 

[toolsntat]

Depends how complicated the glue up is, if its simple job tight enough to need a tap is ok.
If its complicated give yourslelf a chance by making them fit by hand otherwise panic and swearing will soon take over !

Ollie

"I don't know what you mean"

 

[johnnyb]

the leigh fmt allows adjustment in thous! but it soon becomes obvious to tight is the one to avoid. a few thou loose is fine. fine woodworking did an article on glues and covered various glues in snug, loose and tight formats. pu glue was worst in all. hide glue was strong in open grain(oak). not much difference between titebond 3 and 1 in strength. epoxy wasnt strongest in all woods but did gap fill a bit. look it up.
tight is usually strongest but not a thing to aim for.

 

[OldWood]

@Droogs if you want to keep a puffy make-up brush in the workshop, please don't feel you need to justify it to all of us!

Andy - it's a Scottish thing - we all have them up here!!!

 

[recipio]

I always feel it is the tenon which gives strength to a joint - the glue is to prevent movement with repeated use. Too many joints fail because they are a wobbly fit to begin with , hoping the glue will somehow compensate for the poor fit.
Ideally a groove should be cut on each face of the tenon to allow excess glue to ooze out. Its easier to do this on 'loose' tenons and I now use the 'Beadlock' tenon system available from Rockler in US. The tenon is naturally 'corrugated ' as the mortise is made with a series of overlapping holes. I made a set of dining chairs a few years ago and the joints are still snug as a bug. Its the same reason you see grooves on pre cut dowels and those 'V ' shaped grooves on Festool dominoes.

 

[Droogs]

Can't beat a draw bored M&T though