good caul? GREAT caul!

[frank shic]

not really, i just arbitrarily did 1 1'2 inches but you could go out further as long as you don't blow out the hole near the edges of the caul.

[Doug Shepard]

Another satisfied customer. I've got some 3 and 2 footers and while they dont get used all the time, they're awfully nice to have when you get to bigger glue-us. I've got a pair of very deep reach (around 16" IIRC) clamps that I used to pull out for getting pressure in the middle of wide pieces. I dont think I've touched them since getting the bowclamps.

[Craig Feuerzeig]

I try to keep the rods as near to the ends as possible in order to maximize the usable surface of the Bowclamp. Murphy's law says you'll need just a little more.

[Peter Quinn]

I'm not trying to pick a fight here, but has anyone ever tried making there own bowed cauls? All scientifically calculated CNC cut curves aside, that is about $3.50 worth of maple and $20 worth of machining. Now if every piece of maple bent exactly the same as every other piece of maple I might buy into the scientifically calculated angle idea, buy one, and make my own from there as a pattern. Heck, with most maple all you need to do to make a bowed caul is joint it flat and wait a few days! But my experience has been that some maple bends a bit easier, some is a bit stiffer, and the ones I make on my jointer from the scrap pile in seconds work like hot cakes. Am I missing something here?

[Craig Feuerzeig]

Peter,

I've been asking for 3 years for someone (anyone) to share their experiences making they're own...

How well do they work?... what sorts of projects are you using them for?

Personally I never had much luck (before CNC). They always ended up being a taper instead of a curve... adding pressure to one spot near the middle, while leaving the rest of the surface un-touched. Handy for some situations...but you're not going to trust it to lay up a sheet of veneer, for example.

Here's a link to a really nice write-up from a guy (in Japan) who made his own. You can't tell what he's saying but this shot basically says it all.



but again, please share your experiences, good, bad, or otherwise.

[Fred Foss]

Frank -- those knobs are a great idea! thank you for pointing them out

craig, all this time i thought that the threaded rod/bowclamp combo was yet ANOTHER invention of dino's! if you read the original thread, dino hints " Wait 'till you see my Bowclamp" and then your post with the pictures follow. yet another example of ASSuming too much. BTW, i'm on my way to rockler's after work today to pick up some of those quick release five star knobs for 3/8" thread. i'll post pics after i'm done - hope it doesn't take my half an hour like last time!

-------------------------


Craig I have often wondered what kind of a curve they have, a straight radius, or a catenary or some other exotic curve????

I've been asking for 3 years for someone (anyone) to share their experiences making they're own...

How well do they work?... what sorts of projects are you using them for?

[Mike Henderson]

I'm not trying to pick a fight here, but has anyone ever tried making there own bowed cauls? All scientifically calculated CNC cut curves aside, that is about $3.50 worth of maple and $20 worth of machining. Now if every piece of maple bent exactly the same as every other piece of maple I might buy into the scientifically calculated angle idea, buy one, and make my own from there as a pattern. Heck, with most maple all you need to do to make a bowed caul is joint it flat and wait a few days! But my experience has been that some maple bends a bit easier, some is a bit stiffer, and the ones I make on my jointer from the scrap pile in seconds work like hot cakes. Am I missing something here?

People have been making clamping cauls for centuries, and taking a bit off the ends compared to the middle to accommodate the flex in wood. They teach that technique at the woodworking school I attend. I don't know anyone who ever had any problems with shop made cauls. I have a number of cauls I made by taking a few swipes towards the ends with a plane and I've never felt there was anything wrong with them - and never had any problems using them for clamping.

I'm very sure you can put a well defined curve on a caul with CNC equipment, but our ancestors did just fine with shop made cauls, as do many people today. Until I have problems with my shop made cauls, I probably won't see the need for cauls with CNC accurate curves.

Mike

[Edit: I use the cauls for a wide variety of clamping jobs. I've used them when doing a table top to get the boards to lay flat before I clamp them. I've used them to do veneer by putting a piece of 3/4" MDF on each side of the work and using cauls to get pressure in the middle (although now I have vacuum equipment). I make the cauls out of decent 2x4 material (regular construction 2x4s -select for straight grain). I let the 2x4s dry well (most are really wet) then joint them on a jointer. Then take a few swipes with a hand plane from the center to the ends, with more taken off the ends. Then put packing tape along the edges so the glue won't stick to the cauls. I have cauls in a variety of lengths, from short ones for small jobs to longer ones for bigger jobs.
When setting up to glue something like a table top, you put some spacers down, then lay the lower set of cauls on the spacers, then the work, then more cauls. Clamp the cauls first. I use a clamp on each end of the cauls to pull them together and create a flat surface on the table top. Then do your regular clamp up. The reason for the initial spacers is so you can get your clamps under the cauls. See the attached pix which shows these cauls in use clamping a panel.
I don't do things like kitchen cabinets so I can't comment on using them for applications like that. My use is all furniture.]

[Nissim Avrahami]

Some 10~12 years ago, when I was still in Japan, I made something like those cauls but not bowed...

I got the idea from Robert Wearing's book "Making Woodwork Aids & Devices" (Carcass cramping system - page 213).

The threaded rod is 1/2" x 39.5" and the drawing is showing that you can connect 2 rods to get longer length...

I use them for carcass gluing but I'm adding one or two clamps at the center on the caul itself.

I believe that Craig's couls are much, much better but...if I only lived in USA...

Regards
niki
01.jpg02.jpg03.jpg04.jpg

[Craig Feuerzeig]

People have been making clamping cauls for centuries, and taking a bit off the ends compared to the middle to accommodate the flex in wood. They teach that technique at the woodworking school I attend. I don't know anyone who ever had any problems with shop made cauls. I have a number of cauls I made by taking a few swipes towards the ends with a plane and I've never felt there was anything wrong with them - and never had any problems using them for clamping.

I'm very sure you can put a well defined curve on a caul with CNC equipment, but our ancestors did just fine with shop made cauls, as do many people today. Until I have problems with my shop made cauls, I probably won't see the need for cauls with CNC accurate curves.

Mike

[Edit: I use the cauls for a wide variety of clamping jobs. I've used them when doing a table top to get the boards to lay flat before I clamp them. I've used them to do veneer by putting a piece of 3/4" MDF on each side of the work and using cauls to get pressure in the middle (although now I have vacuum equipment). I make the cauls out of decent 2x4 material (regular construction 2x4s -select for straight grain). I let the 2x4s dry well (most are really wet) then joint them on a jointer. Then take a few swipes with a hand plane from the center to the ends, with more taken off the ends. Then put packing tape along the edges so the glue won't stick to the cauls. I have cauls in a variety of lengths, from short ones for small jobs to longer ones for bigger jobs.
When setting up to glue something like a table top, you put some spacers down, then lay the lower set of cauls on the spacers, then the work, then more cauls. Clamp the cauls first. I use a clamp on each end of the cauls to pull them together and create a flat surface on the table top. Then do your regular clamp up. The reason for the initial spacers is so you can get your clamps under the cauls.
I don't do things like kitchen cabinets so I can't comment on using them for applications like that. My use is all furniture.]

Mike,

With all due respect...less than two weeks ago, in response to a question about gluing 2 pieces of MDF together you recommended finding a flat spot on the garage floor and piling all of your heavy tools on top of it.

There's a tool for that.

Your shop made cauls you have are a taper not an arc. The difference is that they apply pressure to one spot in the middle, as opposed to everywhere along the length. That's why you needed to buy that vacuum set-up.

[Prashun Patel]

I'm not above purchasing these. But it's unclear why it's so hard to MAKE these yrself. Please enlighten.

[Mike Henderson]

Please see my comments in the quote:

Mike,

With all due respect...less than two weeks ago, in response to a question about gluing 2 pieces of MDF together you recommended finding a flat spot on the garage floor and piling all of your heavy tools on top of it.

That discussion was about getting a panel flat in two dimensions. Cauls are good for getting a panel flat in one direction but you'd need a torsion box to get two dimensions.

There's a tool for that.

If you have a tool that will replace a torsion box please elaborate.

Your shop made cauls you have are a taper not an arc. The difference is that they apply pressure to one spot in the middle, as opposed to everywhere along the length. That's why you needed to buy that vacuum set-up.

I didn't "need" a vacuum set up because of pressure problems. My veneer glue ups were fine. The reason I bought a vacuum set up is that handing large pieces of 3/4" MDF to press veneer is difficult and a pain. A vacuum bag is much easier to deal with.

My cauls are not cut to arcs - or maybe they're cut to very rough arcs - but they work. I never had any pressing problems using my shop made cauls. As I said earlier, the school I attend teaches how to make those cauls and hundreds of people have made cauls like that and have not reported problems with their use. Surely if there was some basic problem it would have been discovered by now.

I'm not knocking your product - I'm only reporting my experiences, and the experiences of other woodworkers I know who use shop made cauls. Your product seems to be addressing a problem I, and other woodworkers I know, don't have.

[I'll add the comment that cauls are good things - every woodworker should use them and have a variety of sizes - whether you purchase them or make them yourself.]

[Craig Feuerzeig]

Simply stated Mike, Bowclamps will absolutely replace your torsion box. Or do a great job of augmenting it. You'll thank me either way.

How do you get pressure out in the middle of the torsion box?

Bowclamps on top will reach far beyond your deep jaw clamps...across a 4 foot sheet of ply. But...

Bowclamps top and bottom, opposing one another, will do a much better job than the torsion box keeping things flat. You'll throw those things away.

[Matt Meiser]

I'm not saying don't purchase Craig's cauls, but its very simple to put a smooth arc on a piece of wood without a CNC:

1) Create a template from 1/2" MDF by using a spring stick to draw the curve. Then bandsaw and sand to the line.
2) Stick the template to your stock using double-stick tape.
3) Template route using a straight bit.

I'd bet you could crank out a complete set in an afternoon. Plus you'd have templates for future needs. Or you can buy Craig's and spend the afternoon doing glue-ups.

[Mike Henderson]

Simply stated Mike, Bowclamps will absolutely replace your torsion box. Or do a great job of augmenting it. You'll thank me either way.

How do you get pressure out in the middle of the torsion box?

Bowclamps on top will reach far beyond your deep jaw clamps...across a 4 foot sheet of ply. But...

Bowclamps top and bottom, opposing one another, will do a much better job than the torsion box keeping things flat. You'll throw those things away.

Thanks for the suggestions. I promise you, Craig, that as soon as I find a problem I can't solve with my shop made cauls, I'll order a set from you.

Mike

[This thread started me thinking more about how much bow to put in a caul. I'm not a mechanical engineer, but it seems that there's a bunch of things to consider.

The first is how the caul is clamped. For example, if you put the clamp pressure outside the work, as people do with threaded rod, you've created a lever arm and you'll need more bow because the caul will tend to bow upward and rise in the center. The amount of bow required will depend on the length of the lever arm and the length over the work. If you clamp the caul on the work (as shown in my picture in an earlier post), the center wouldn't rise but there would be a pressure gradient across the caul with less pressure in the center (if there was no bow in the caul). So for this second example, you only need enough bow to even out the pressure gradient.

Another factor is the stiffness of the caul material. If the caul was perfectly stiff, you wouldn't need any bow. But wood does flex and the amount of bow is dependent upon how much a particular piece flexes, and how the caul is used, as discussed in the previous paragraph.

The next question is what kind of curve would be required to provide "equal" pressure across the caul (once you take into account the other factors). My guess is that you'd need some kind of catenary curve, but the exact catenary curve would depend upon a number of factors, including those discussed above.

Finally, you don't need exactly equal pressure when clamping. All you need is sufficient pressure at the point of lowest pressure. So even if your caul is not curved exactly right, it applies sufficient pressure to get the job done. At least that's the experience I've had. Cauls have been shop made by woodworkers for centuries and they've done the job.]

[Rob Fisher]

Thanks for the suggestions. I promise you, Craig, that as soon as I find a problem I can't solve with my shop made cauls, I'll order a set from you.

Mike

[This thread started me thinking more about how much bow to put in a caul. I'm not a mechanical engineer, but it seems that there's a bunch of things to consider.

The first is how the caul is clamped. For example, if you put the clamp pressure outside the work, as people do with threaded rod, you've created a lever arm and you'll need more bow because the caul will tend to bow upward and rise in the center. The amount of bow required will depend on the length of the lever arm and the length over the work. If you clamp the caul on the work (as shown in my picture in an earlier post), the center wouldn't rise but there would be a pressure gradient across the caul with less pressure in the center (if there was no bow in the caul). So for this second example, you only need enough bow to even out the pressure gradient.

Another factor is the stiffness of the caul material. If the caul was perfectly stiff, you wouldn't need any bow. But wood does flex and the amount of bow is dependent upon how much a particular piece flexes, and how the caul is used, as discussed in the previous paragraph.

The next question is what kind of curve would be required to provide "equal" pressure across the caul (once you take into account the other factors). My guess is that you'd need some kind of catenary curve, but the exact catenary curve would depend upon a number of factors, including those discussed above.

Finally, you don't need exactly equal pressure when clamping. All you need is sufficient pressure at the point of lowest pressure. So even if your caul is not curved exactly right, it applies sufficient pressure to get the job done. At least that's the experience I've had. Cauls have been shop made by woodworkers for centuries and they've done the job.]

This is a great break down and discussion, thanks Mike! I am planning on making a few cauls of my own (buying them just doesn't seem to make sense when they are so simple to make) and I am wondering about your original question "how much bow"?

How much bow do you have in your existing framing lumber cauls? Could you measure?
I have some ash that I am planning on making my cauls with and I will probably start with about an 1/8" per foot. As for the curve I will use the previous suggestion of a spring stick. My intention is to clamp over the wood as you have shown in your pictures.

Thanks,
Rob