Clamping and using cauls

[John Gregory]

We have some drawer fronts and raised panel doors to glue up soon. We have had a mixed history of getting our glue ups flat every time. I am open to suggestions from all of you. I have a flat maple workbench and I am thinking of getting some angle iron and clamping the doors and drawer fronts to the workbench using the angle iron as cauls. Do any of you have experience with this method? What size should the angle iron be? My workbench is 40" wide I would buy 48" iron angle.

What do you think?

John

[Mel Fulks]

I think we might need more info. Do you mean the stiles roll over and don't stay straight with the rails? The pipe clamps
sometimes get bent ,making it harder to keep stuff flat. If the clamps are straight tapping the work down to be flat on the
clamps helps.

[John Gregory]

The finished door will not close flat on the carcass.

[Mel Fulks]

I think you have to think in terms of flat and straight pieces. Not about how to make a flat door from from un flat pieces.
I'll keep reading and watch for more clues. I do not think angle iron is the remedy.

[Kevin Jenness]

I'm with Mel. If the stock is flat and the joints cut square and clamped up without distortion the result will be a flat panel. I glue up on top of parallel blocks on a flat bench rather than relying on clamps for registration.A straightedge is used to check for flat and clamping blocks between clamps and the work can be adjusted to get the assembly flat. The support blocks should be sized so that the clamp screws are centered in the stock thickness.

Cauls can be clamped across the assembly to force it flat but shouldn't be necessary.

This article by Ian Kirby may be helpful (paywall) https://www.finewoodworking.com/1981/12/01/gluing-up

[Al Launier]

To pick up on Kevin's comment I think a critical aspect of keeping glued panels flat is to be sure the glued edges are dead square. Although the glue itself may take up some of the gap variation if not square, I believe the panels will eventually, if not immediately, seek their original angular mating surfaces; even the smallest amount will cause out-of-flat panels. Wood glue is not the gap filler that epoxy is.
Setting up on risers to allow clamps to reach under the panels and under/over the cauls should provide you with flat panels. And, depending on the width of the panels, slightly tapered cauls would work well to provide more uniform clamping pressure to the center of the panels when gluing. I like to place wax paper between the cauls and the workpiece to prevent glue attachment to the cauls.

I wouldn't clamp directly to the work table.

[glenn bradley]

I'll chime in with Mel as well. When I learned how much influence well milled stock has on my eventual outcome I became a much happier guy. I also have a tendency to over over-tighten things if I am not cautious. Certainly well milled parts, over-torqued in the clamps could be distorted during glue up.

My take on an assembly table help me hold things in a lot of ways should they prove unruly. However, to the original point, forcing non-true parts to a flat plane will simply produce partially open joints here and there. I try to be sure my dry fits are valid without forcing anything into position. If they fit well dry, they will glue up the way I want them.

412785 . 412784

Modified HF f-style clamps.

412786 . 412788 . 412787

[John Gregory]

Wow Glenn. What a great system.

[Frank Drackman]

Not directly related to your questions but one of the things that had a huge positive impact on the quality of my work was understanding that if I had to really tighten the clamps to get the pieces together something was wrong. Time to unclamp and find the problem before moving on.

[Al Launier]

Not directly related to your questions but one of the things that had a huge positive impact on the quality of my work was understanding that if I had to really tighten the clamps to get the pieces together something was wrong. Time to unclamp and find the problem before moving on.

Excellent point!

[Robert Engel]

John,

You really don't need an elaborate setup for clamping, other than maybe an alignment jig to square up the door.

I don't like clamping down to a workbench because you can't clean up the down side of the joint and second, it ties up your workbench, therefore limiting the number of doors you can do!! Cauls are ok but I prefer to manage everything with clamp alignment.

he key is clamping - clamp alignment, and *don't overtighten*. Also the type of clamp and the how they are placed. I prefer parallel clamps for doors. I do not use pipe clamps unless forced to.

I believe keeping the door off the bar of the clamp is also important. This allows for flex you you can balance the clamp force.

After everything is intially clamped up and squared, I check for flatness and a clamp adjustment will correct it.

Needless to say, this assumes the stock is correctly prepared and acclimated.

[Prashun Patel]

I wouldn't rely on cauls to keep them flat. If your joints are not naturally square, the cauls will create visible seams on one side. DAMHIKT.

Beauty about drawer fronts and often doors is that they usually fit in a planer; I glue up when still thick then joint and thickness them after.

[Ron Citerone]

There are several things to do before the glue up stage and it starts before the milling.

1) Let the wood acclimate to your shop.

2) If you need to mill a lot of material, do it in several stages with a few days in between.

3) **** No jointer fence is exactly square to the table. The panel pieces should be set up for glueing so that the face that is against the fence on one piece is up on the first piece and the down on the next etc. Other wise the panel will create a cup when the clamps are applied. This is multiplied as more pieces are used on a panel. This single thing changed my glue ups forever and they are way better this way.

[Bradley Gray]

Lots of good advice about prep already. A few years ago I bought a Plano glue press and mounted it on my shop wall. the clamps are perfectly aligned, straight and flat, so well machined stock makes perfectly flat panels. Since the glue-up is vertical, gravity keeps the glue right where I want it. I use a glue spreader so application is controlled and get very little squeeze-out. Since the clamps are wall mounted, my bench is clear.

[John Gregory]

Thanks everyone. Advice from you guys never disappoints. I am convinced stock preparation is my issue. I need to make sure my stock is milled flat!!

Thanks again

John

[Malcolm McLeod]

Thanks everyone. Advice from you guys never disappoints. I am convinced stock preparation is my issue. I need to make sure my stock is milled flat!!

Thanks again

John

...Flat and SQUARE. Once flat, joint the 'glue' edge of a stile to exact 90deg. Rail ends have to be square, or I can call myself a Cooper (things are going to curve!). And my work got a lot better/easier, when I discovered the joy of checking my miter saw for dead-nut 90deg - both blade<>fence and blade<>table - on every setup. A 4" machinist's square is a wonderful thing.