Clamping distance

[Rick Akl]

I'm going to be clamping up 8/4 hard maple strips for a workbench top. I'll be using parallel clamps. how far apart should I space them? The bench will be 96" long and 4" thick.

Thanks

[Gary Breckenridge]

The more clamps the merrier. I think it would be impossible to glue the whole thing at once. Me, I'd clamp one piece on at a time and have a clamp about every 10" and crank those puppies down. A couple of hours later I'd clamp on another piece. Also consider the lbs. of clamping pressure and is the wood dead straight.:cool:

[Van Huskey]

I would prefer using cauls either shop made or something like the Bowclamp. Save that I would clamp every 6".

[Frank Drew]

The more clamps the merrier.

I pretty much agree with Gary; maybe a clamp every foot, alternating on top and below. In my experience, hard maple doesn't glue as well as many other woods (or, maybe better put, the glue lines sometimes open a bit after a while whereas they wouldn't have in another wood), so it's a wood than can use a little bit of extra attention when gluing.

[Tony Bilello]

I would glue the top up in probably 2 or 3 sections at first, depending on what you think you could handle. Then edge joint them the next day and glue the sections together. I wouldnt remove the clamps for at least 24 hours because these boards are under a lot of stress and if the glue is not completely cured, loosening them for a few minutes and reclamping again could break the glue bond.
As mentioned earlier, make sure the wood is dead straight - 8/4 hard maple dont like to bend.

Crank down with good pressure on the clamps but dont over crank them to death or you will end up with starved glue joints.

Clamps every 8" to 10" should be fine.

[Doug Shepard]

Ditto on the Bowclamps comment. Cheaper than buying all those additional clamps you'd need too.

[Prashun Patel]

I agree with Van. Use cambered cauls.

Consider using biscuits or dowels to help with alignment.

I've also used pocketscrews on the underside to assist with the clamping.

[Joe Jensen]

Are bowclamps really going to make a difference on 4" wide 8/4 boards? I'd glue 3 or 4 together at a time and leave to cure at least a few hours. Here is AZ PVA glues so I can't easily pull joints apart in 10 min so a couple hours would be plenty.

[Louie Ballis]

[QUOTE=
I've also used pocketscrews on the underside to assist with the clamping.[/QUOTE]


This works well +1

[Kent A Bathurst]

The pressure exerted from a clamp heads out from the clamp's surface at 45*.

"Enough" clamps from a technical basis would then be enough clamps so that the glue face is "covered" by these lines of force. The 8/4 helps in that the clamp faces are standing back off the glue line 2" nominal, versus 1" nom for 4/4. This is one benefit of cauls - the clamp surface stands back farther from the glue surface, allowing the pressure footprint to cover the glue face better.

Of course, the ability to put enough pressure comes into play as a consideration as well - as the glue face is farther away from the clamp face, then the clamp is spreading pressure over a larger glue surface, reducing the PSI at the joint.

So - now that technical explanation is done - my solution always is "how many you got, and how many can you cram in there?" I've got a lot, in different styles from ll to Jorgy F, to cabinet style, to bar clamps, and I freely intermix them to cram in as many as I can - paying particular attention to the ends of the ass'y.

Wait - wait - don't start - I realize that, at least in theory, it is possible to starve a glue joint with too much pressure. I am certain, in my experience at least, that it is impossible for a basement/garage shop operation like ours to get anywhere near that level.

Joe - Cambered cauls? I don't see the need in this application, personally. Got 'em, but I use them only on the surfaces to keep the boards aligned and minimize post-glue-up planing.
Tony - Starved joints? I don't see it happening. Sorry.
Gary - Agree entirely, other than I wouldn't wait a couple hours - I'd wait 60 min at most - as long as I was going to immediately glue and clamp the next board. When I was done, or at least done for the day, I'd turn out the lights and take off the clamps in the morning.

[Chip Lindley]

IF...8/4 hard maple is jointed straight and square, your slab will glue up easily. Clamps every 12", top and bottom, should be sufficient.

IF...the assembly is laid out on a flat level surface, there should be no racking (twisting) of the slab. A dedicated glue-up table is indespensible for accurate results. Any method which assures the bottom clamps are all fixed in the same plane aids in flat glue-ups.

Cauls could be useful if the slab to be glued, is suspended between it's ends. Cauls are an easy way to draw all boards into the same plane.

IMO, the use of pockethole screws are an unnecissisary step in a thick slab glue-up. An extra, involved step, when glue and clamps are plenty! If anything, threaded rods could be run through the slab, side-to-side, at intervals, bolted tightly, and holes filled with wood plugs.

[Rick Akl]

Thanks for the advice people. I'll be clamping every 8" on my torsion box, with cauls for flatness and I'll leave it on overnight for good measure.