Glueing box joint

UKworkshop.co.uk

Help Support UKworkshop.co.uk:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

murphy

Established Member
UKW Supporter
Joined
7 Feb 2012
Messages
323
Reaction score
47
Location
London
What is the best way to glue up box joints, keeping it square is the main problem, the corners can not touch the clamps as they need to move, is a strap clamp better than bar clamps the box is about 7 inches tall
 
I sometimes use a strap clamp.
Are you sure you really need it clamping ?
A good snug fit and D4 glue usually do the biz for me
 
I've sometimes made boxes with dovetails or t&g corners and kept them square by stacking them, with weights on top. a.k.a. "gravity clamps".
 
Well fitting box joints are almost self clamping but you do need to ' nip ' them up to avoid hairline gaps. Rockler in the US sell sets of special clamps with 'fingers' to press on the 'fingers' of the joints and clamped up with a strap clamp. I find them a bit fiddly to use and they are only in imperial dimensions starting at 1/4". Now I use Japanese Hatagane clamps sold by www.fine-tools.de as they are the perfect balance between weight and clamping pressure.
Resist the temptation to grab an ROS sander to level the pins after assembly or you will probably remove a mm of wood in jig time. I use a router for that.
 
Thank you all, I have been looking on Youtube as well and a lot of people favour the strap clamp, as it takes a lot of bar clamps and bar clamps can also pull it out of square, recipio yes I mean to just nip them up, do you use a flush trimming router bit to trim the pins, I was thinking of trying something like this
 
If it's not too thin material and/or very tight boxjoints it can work to place the clamps inside the fingers.

If I need to place clamps directly over the fingers I make some "clamping cauls" for this at the same time as I cut the boxjoints. The cauls let me clamp directly over the fingers. The fingers on these cauls are cut off slightly in width on the bandsaw to leave some margin in the glue up. Technique presented at 25.02 in the video below the picture.

"Cauls" shown in pic below where they are tapet onto the workpieces. This is only for a bridle joint with few fingers but teqhnicue is the same for more fingers.
Screenshot_20230528_104200_YouTube.jpg

Screenshot_20230528_105348_YouTube.jpg


 
Thank you all, I have been looking on Youtube as well and a lot of people favour the strap clamp, as it takes a lot of bar clamps and bar clamps can also pull it out of square, recipio yes I mean to just nip them up, do you use a flush trimming router bit to trim the pins, I was thinking of trying something like this

I can see in the video that he doesn't bother about the individual fingers - he justs offsets the pressure point to allow the fingers to move a bit. Sounds good and I would probably round over the corner of the jig to prevent wear on the strap.
A snug fitting and dead square base will also help with squareness. Avoid a lot of glue as it is a pain to clean it all up .
As for trimming the fingers certainly a sharp plane will be fine. I happen to have a Festool MFK 700 router which has a virtual micrometer depth adjustment and makes life easier. Any bottom cutting bit will do as the router is cutting down on the joints. For flush trimming bits with a bearing a spiral bit would be advisable and clamp some scrap pieces on the box to avoid tearout.
 
Last edited:
What is the best way to glue up box joints, keeping it square is the main problem, the corners can not touch the clamps as they need to move, is a strap clamp better than bar clamps the box is about 7 inches tall
I use a block of wood with the corner cut off insode the corner of the box
 
What I usually end up doing is making some extra sets of fingers, narrower than the actual ones, as clamping blocks - these can then bear on the actual fingers to be clamped without fouling on the incoming fingers. It sounds a faff, but once set up for matching the box joints, it doesn’t take much extra time.

(I use a Matthias Wandel design screw advance jig on the table saw or the Woodrat for smaller things). The former by the way did take me a while to make, but has served well for some years.

In theory, another way is to make the fingers slightly shorter than the thickness of the sides leaving some planing or sanding of the sides - then you can clamp each end directly - but I usually end up with fingers longer. This approach is only good for solid wood boxes - I used to make a few boxes out of birch ply and hope this will be possible again some day.

Cheers
 
Birch ply makes lovely box joints but is terribly prone to tearout - it is a stack of veneers after all. Scrap supports at the ends of the joint are essential if routing them flush.
 
Back
Top