HELP!!! Gluing up advice needed

[Digizz]

Finished the top of my coffee table, all nice and square and ready for gluing up. Except I'm having a real mare trying to work out how to glue it up.

The top is a square frame as seen here:

I've got two biscuits per mitre. The table top is quite big - 1m x 1m. I only have a bench and/or table saw as makeshift 'gluing up tables', both are longer than 1m in one direction but short in the other.

I was planning on using sash cramps, one along the axis of each piece of timber, forming a 'box'. On dry assembly, I'm finding it a real problem juggling with wood and clamps! I'm also worried that when tightening up the clamps (unevenly), the timber pieces will slide apart easily.

Anyone got any advice for me? Should I maybe do this in two stages or is that asking for trouble with alignment when putting the two halves together?

What I really need is a huge, flat table!

Help!

 

[johnelliott]

This is really a perfect job for a pocket hole jig, if you had one. Then you could still use the biscuits, and the pocket screws, underneath of course, a couple in each mitre, would enable you to glue up one corner at a time.
Presumably you don't have one, so I'm going to have to say that I think you are right, this is going to be a very difficult glue-up.
Do you have any luggage straps, the ones with a ratchet? If you did you could make up four corner blocks and run the straps around them instead of the cramps. If I was facing this job, I would send off for a pocket hole jig (which I would practice with first)
John

 

[Digizz]

Thanks John - I'll have a look into it.

I could buy a strap/band cramp thingie I guess although this may still be as difficult to glue up?

 

[Chris Knight]

Digizz,

Big sash clamps will be difficult to handle on a frame like this and you run the risk of the pieces slipping or bending. Much better is to glue small 45 degree triangular clamping blocks - you will need eight of them - to the frame at the "side" of each corner and clamp across these with a small C clamp ("G cramp" if you are an Englishman!). Saw the clamping blocks off after the glue has dried and plane the edges of the frame smooth. If you have a hot glue gun, now is the time to dig it out!

A big band clamp would work fine too but maybe not get the pressure on the joint that you need to close it up.

 

[Digizz]

Ah, interesting - will hot glue give the strong kind of joint needed for this?

Should the blocks be fitted with a slight gap between them when closed up to make sure maximum pressure is applied to the joint?

I guess to be stable, you'd need to fit blocks both sides of the joint?

I'm not quite sure I exactly get what you mean?

 

[Chris Knight]

Digizz,
Like this (actually in this case the guy has shaped the clamping blocks and clamped them on - either method works)

Hot glue will be plenty strong.

 

[Shady]

Make 'external' corner blocks (nice thick lumps of soft wood) that go 'round' each corner (ie they are a single piece of wood for each corner, having thickness on the outside of the tip of the corner, so that they don't spread under load). Put a diagonal flat on the outside, to take clamp pads.. (so from above, they look like a symmetrical letter 'L' with a diagonal slice out of the outside of the corner).

Clamp diagonally across the table with your sash cramps: visual inspection will allow you to spot any 'creep'/'out of square', which you can correct with appropriate clamp pressure.

(edit: Chris's approach is the traditional answer, but be careful: you can 'burst apart' your hot melt joint to spectacular effect if you are over enthusiastic: I developed this technique to avoid this problem...) It works pretty well: if you feel the need, cut wedged slots to take c cramps on the corners as suggested, but you don't normally need them..

 

[Digizz]

Chris - like the idea of this - need to buy a load more clamps though!

Shady - this sounds good too.

What do you guys do for a flat surface when gluing up a large piece of work - I guess a flat surface is still pretty important?

Maybe I just use the kitchen floor (laminate flooring)!!!!

 

[Dewy]

Providing the mitres are accurate you could use a band clamp to hold it while the glue sets.
Before I bought a band clamp I used 4 pieces of L_ shaped molding for the corners and some garter elastic to impart equal pressure on all corners.
The equal pressure ensures that all 4 corners meet as they should.

 

[Chris Knight]

What do you guys do for a flat surface when gluing up a large piece of work - I guess a flat surface is still pretty important?

Yes it is. Depending on the size; for a metre square I would make up a flat surface (actually a simple pair of rails!) with sawhorses and 4x2's with shims to level the fourbys until my spirit levels and winding sticks told me that it was all flat. If you have lots of space, you can make dedicated flat surfaces with torsion boxes and a bunch of other things but I have no space to store this sort of thing when not in use.

 

[johnelliott]

What do you guys do for a flat surface when gluing up a large piece of work - I guess a flat surface is still pretty important?

Not if you are doing it with pocket screws, just do one corner at a time, as long as each corner is clamped flat as you join it, you will be OK
John

 

[Digizz]

Chris - if as in that picture you posted, the axis of the main clamp is off the centre line of the joint, wouldn't the lever arm component try to pull the joint apart very slightly at one end? (If you get what I mean?)

Does this a problem in reality though? I guess in theory, the clamps should be applied with the force acting through the centre of the joint?

John - I'll probably go for an external clamping solution as I think the pocket hole screws would interfere too much with my biscuit joints and intended fixing for the table's frame. Interesting thoughts though.

 

[Shady]

John: you got shares in Kreg or something mate??? :wink:

Digizz: yup to the flat - but as Chris says, it's a flat plane, not a flat surface, so a pair of levelled bars (sawhorses, 2 by 4's, etc) will do for this sort of thing.

As to pulling the joint apart in the photo - not if you 'snug them up' alternately, cos the one on the opposite diagnal will resisit that...

 

[Digizz]

Shady - By using only a pair of 2x4s, there is still the problem of supporting one set of the table top sections - how would you deal with that? (a couple of 2x4s at each end?)

I did experiment with using the flat cast Iron surface of my table saw (TS2500) and aligning the table top sections at 45deg to the edges (i.e. diamond shape) with the ends overhanging - kind of works but can be a bit precarious. The saw surface is nice and flat though.

 

[Shady]

Sorry, you're right, I was oversimplifying... I'd put a pair of 'sawhorse tops' down, level 'em with winding sticks/spirit levels, and bang a slab of mdf or chipboard on them and re-check: size it so that it doesn't interfere with your clamping strategy... (eg just smaller, or cut the corners off)

 

[Noel]

Dig,

Here's another option I use.

Although it's just a variation on items mentioned there's no glue, fasteners or cutting to do. If my mitres are dead on the two outer clamp cauls are not needed, but are handy.....With just the inner caul once the mitres are closed, generally without clamp pressure, they stay put until dry. Note the cut outs which leave space for glue squeeze out. These cauls are also handy when making cabinets etc.
Another option for an assembly area is to use your TS and a couple of identical, prepared batons, say 2" x 2", that are of sufficient lenght for your needs. Clamp these to the TS table using F or G clamps ensuring that the clamps do not interfere with the work. Some notches cut into the batons with the clamps secured upside down should do the trick.
Don't forget pictures of the finished piece.

Rgds

Noel

 

[Anonymous]

Blimey i may even print that and send it to the tait :lol:

 

[Noel]

That would be St Ives?

Rgds

Noel

 

[Anonymous]

or even the tate :lol:

 

[Digizz]

Not having worked much at all with MDF - how level do the larger sheets tend to be - is there on average much warp/twist etc?