good caul? GREAT caul!

[frank shic]

i bought a full set of bowclamps from craig the other day but i was concerned that they might languish in the dust as so many other tools i've bought. up until this point i've built simple cabinets that required only a few clamps here and there or i've used confirmat and pocket screws to eliminate the need for clamping. today i had the chance to glue up a dresser that was inspired by pottery barn only to make the painful discovery that i simply did not have enough clamps until a brilliant thought occurred to me...

craig, this is an awesome product. i'll be buying three more pairs of the two footers from you on monday, BTW.

:D

http://www1.snapfish.com/slideshow/AlbumID=42072469/PictureID=1228318313/a=5878685_5878685/t_=5878685http://images1.snapfish.com/3469%3B%3A%3A%3C9%7Ffp339%3Enu%3D3237%3E%3A%3A%3A% 3E8%3B7%3EWSNRCG%3D32336%3B8%3A4%3B667nu0mrj

(file:///C:/Documents%20and%20Settings/Frank%20Shic/Desktop/bowclamp.bmp)

[Jim Becker]

Yea, they are on "my list" for acquisition before I start any cabinetry for our addition. Craig's product is super!

[Alan Tolchinsky]

I not aware of Craig or bow clamps. Could you elaborate? Is that a clamp on the table in the pic? Thanks Alan

[glenn bradley]

Do a web search on bowclamps. I hope I get this right; they are computer cut hard rock maple cauls that have a slight (but scientifically calculated (?)) bow to them. This along with a groove that accepts F clamp screw tips (or use Bessy's like in Frank's pic) distributes clamping pressure along the surface without the need for half a dozen clamps. I don't have any yet but everyone seems to rave about them and the price makes it hard to consider making your own. The convenience comes in when clamping those surfaces where you can't get a clamp in the middle of a panel.

[Frank Pellow]

I not aware of Craig or bow clamps. Could you elaborate? Is that a clamp on the table in the pic? Thanks Alan
Alan, look at the http://sawmillcreek.org/forumdisplay.php?f=27 Manufacturers forum.

I have a pair of the 48 inch bow clamps and I thinkt that they are going to come in vary handy. So far, I have only used them once and they worked as adv ertized.

[frank shic]

the bowclamps are fantastic when it comes to having to clamp MIDDLE sections in glue-ups. as you can see, they also come in handy in clamping the ends - i used only two clamps on the left side but four on the right because i ran out of bowclamps. i would highly recommend getting two or three pairs of the two footers (i wish that craig had some kind of a deal on these...). the besseys worked alright but they were a little tricky to fit in the beginning because obviously their large square jaws don't fit in the cauls. however, those jorgensen clamps are not too expensive... isn't it ironic that the point of these cauls is to eliminate the need for more clamps but i'm probably going to buy more to be able to utilize them to the best ability? i might try dino's low cost solution of running a threaded rod through two of them at a time and thus eliminate the need to buy more clamps altogether.

[Frank Pellow]

the bowclamps are fantastic when it comes to having to clamp MIDDLE sections in glue-ups. as you can see, they also come in handy in clamping the ends - i used only two clamps on the left side but four on the right because i ran out of bowclamps. i would highly recommend getting two or three pairs of the two footers (i wish that craig had some kind of a deal on these...). the besseys worked alright but they were a little tricky to fit in the beginning because obviously their large square jaws don't fit in the cauls. however, those jorgensen clamps are not too expensive... isn't it ironic that the point of these cauls is to eliminate the need for more clamps but i'm probably going to buy more to be able to utilize them to the best ability? i might try dino's low cost solution of running a threaded rod through two of them at a time and thus eliminate the need to buy more clamps altogether.
Threaded rod, what a great idea! Thanks Dino.

[Craig Feuerzeig]

Thanks guys...and Glenn I think you hit the nail on the head, very well said... might I just add that while I'm a huge fan of Dino's, I must give credit where credit is due...the threaded rod was the idea of a man named Bob Ross, a proud member of the Bowclamp family, who like many, I now consider a friend.

[frank shic]

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 Feuerzeig]

Oh Dino's got something up his sleeve, you can bank on that.:cool:

[Dino Makropoulos]

Oh Dino's got something up his sleeve, you can bank on that.:cool:
Craig.
The bow clamps are an invitation for imagination.
So far, I used ropes with a stick. (few turns of the stick)
Chains with 2 hooks and a lever. (one touch)
Shims for edge glue solid lumber.
similar to your picture here:
http://www.sawmillcreek.org/attachment.php?attachmentid=32354&d=1140450094

I used the bow clamps on clamping multiple pieces of wood to the table for multiple (gang routing) mortises, tenons , grooving and such.

The uses are unlimited and this simple thing allows me
to re-think my ways.;)
Thank you for that.

Next week I will post few pictures. :cool:
Feel free to stop over the ez forum and start a new thread about..
the ez bow clamp. :cool:

Thanks Craig.

[frank shic]

here's my latest modified version of the bowclamp with rockler-bought quick release five star knobs and a couple of assorted nuts and bolts and 3 feet 3/8" threaded rod from home depot. i got the idea from craig's picture and this month's popular woodworking tips. i'm planning on buying another three feet pair of bowclamps so that i'll be able to clamp up 24" cabinet sides.

http://images1.snapfish.com/346%3A77%3A%3A3%7Ffp344%3Enu%3D3237%3E%3A%3A%3A%3E 8%3B7%3EWSNRCG%3D3233739744%3C53nu0mrj
(http://images1.snapfish.com/346%3A77%3A%3A3%7Ffp344%3Enu%3D3237%3E%3A%3A%3A%3E 8%3B7%3EWSNRCG%3D3233739744%3C53nu0mrj)

[Craig Feuerzeig]

I LOVE it! :D

2 of those... boom... case clamp. Any cabinet, no clamps.

Even If I was using pocket screws, I would move the bar-clamp before screwing for each hole.

Man, I love watching you guys run with the ball.:cool:

[frank shic]

craig, that's exactly what i first thought when i saw the modified bowclamp in your forum section - manual case clamp! i've looked at the industrial versions but was slightly put off by the prices that averaged over $11,000. do you realize that you've made biscuits a much more viable and speedy solution? i have enjoyed using confirmat screws in the past because they eliminated the need for prolonged clamping afterwards, but now i think that i'll be using biscuits much more frequently. between your product and dino's eurekazone, i'm itching at the next opportunity to build some cabinets. maybe the garage could use some more...

:rolleyes:

[Bill Evans]

I hope it is okay to revive an old thread. But is there a preferred distance from the edge of the Bowclamp to drill the holes for the threaded rod as shown Frank's photo?

http://images1.snapfish.com/346%3A77%3A%3A3%7Ffp344%3Enu%3D3237%3E%3A%3A%3A%3E 8%3B7%3EWSNRCG%3D3233739744%3C53nu0mrj

Cheers and Thanks,

Bill

[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.:p

[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!:D 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 (http://www.geocities.jp/pongoo3/bowclamp.htm) 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.

http://i50.photobucket.com/albums/f339/cfeuerzeig/homemade.jpg

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!:D 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
128396128397128398128399

[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. :confused::eek:

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. :confused::eek:

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.:D

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.:D

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

[Mike Henderson]

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
I think 1/8" per foot is a bit too much but it depends on the stiffness of the wood and how you're going to use it. On my shorter cauls I probably have 1/16" to 1/8" total at the ends.

One way to test is to take two cauls with a small bow and put them face to face. Then put two clamps on the ends and see how much you have to clamp them to get them flat across the face. If it's too little pressure, increase the bow. I think you'll find it doesn't take a lot of bow.

When I use cauls, I don't clamp outside the work (generally) to avoid the lever arm issue. If you're going to use them with a lever arm, such as with threaded rod connecting them together, you'll probably have to compromise on some lever arm length. Again, trial and error testing is your friend.

Caveat: I'm not a caul expert nor a mechanical engineer.

Mike

[glenn bradley]

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

I made a template out of some scrap sheet goods and used a pattern bit on the router table. I used maple and they work quite well. They are not as trick or as refined as the real thing but, I had the maple. If I would have had to go buy the material I would've just bought the cauls; this would've saved time and helped support a fine independant business man too ;-)

[Peter Quinn]

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 (http://www.geocities.jp/pongoo3/bowclamp.htm) 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.

http://i50.photobucket.com/albums/f339/cfeuerzeig/homemade.jpg

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

Its a pretty simple affair for some pretty simple work. Take a stick of appropriate length, measure the center point, mark a line one inch in both direction from there, make a double ended taper on the jointer in a few light passes starting at the 1" marks, tune it up with a block plane to more closely resemble a curve, or a few passes with a compass plane to EXACTLY resemble a curve. Rocking it on a belt sander is another good option. A band saw with a big trammel for cutting radius table ends would be another quick way to do it, though not the way I use.

I've used them at work to glue up cabinets, force counter tops into alignment during glue up, anything the clamps wont reach. And if you come up with a light spot the cauls wont touch, a few strips of edge band tape or a wedge takes care of the rest. They work well.

For the little veneer work we do its flat cauls and heavy platens with LOTS of clamps. Annoying but effective. If we did a lot I guess we would have a veneer bag.

Now a question for you. I'm sure a CNC can cut a perfect curve, but is every stick of maple willing to bend exactly the same? I understand every species has an average modulus of elasticity, but in my experience every piece of wood is a bit different in reality. In the shop I put some clamps on a caul, see how it behaves and tune it accordingly. How does one curve provide the perfect arc on every bow clamp made?

[Rob Fisher]

Thanks! I will start light and increase as needed to account for the wood flex.

Rob


I think 1/8" per foot is a bit too much but it depends on the stiffness of the wood and how you're going to use it. On my shorter cauls I probably have 1/16" to 1/8" total at the ends.

One way to test is to take two cauls with a small bow and put them face to face. Then put two clamps on the ends and see how much you have to clamp them to get them flat across the face. If it's too little pressure, increase the bow. I think you'll find it doesn't take a lot of bow.

When I use cauls, I don't clamp outside the work (generally) to avoid the lever arm issue. If you're going to use them with a lever arm, such as with threaded rod connecting them together, you'll probably have to compromise on some lever arm length. Again, trial and error testing is your friend.

Caveat: I'm not a caul expert nor a mechanical engineer.

Mike

[Mike Henderson]

Thanks! I will start light and increase as needed to account for the wood flex.

Rob
And if you're going to use them to hold a panel flat, like I show in the picture, put packing tape on the working surfaces of the caul so you don't glue the caul to the panel (glue squeezes out from the joints).

Mike

[Edit: There's one more type of caul I make, and that's an engineered caul. That's a fancy name for an I-beam. I used 3/4" MDF for the flanges and 1/4" for the web. I don't put a bow into these but you could. I use them when I want to make something flat. I think this one is about 5 feet but you can make them whatever length you want (within reason). The deeper the web (the further apart the flanges) the stronger the beam.
The first picture shows the beam laying on it's side. The second picture shows the beam end-on.

Bigger versions of these are good to clamp things onto when you want to make sure they're straight - but they take too much storage room.]

[Craig Feuerzeig]

And if you come up with a light spot the cauls wont touch, a few strips of edge band tape or a wedge takes care of the rest. They work well.

For the little veneer work we do its flat cauls and heavy platens with LOTS of clamps. Annoying but effective. If we did a lot I guess we would have a veneer bag.

Now a question for you. I'm sure a CNC can cut a perfect curve, but is every stick of maple willing to bend exactly the same? I understand every species has an average modulus of elasticity, but in my experience every piece of wood is a bit different in reality. In the shop I put some clamps on a caul, see how it behaves and tune it accordingly. How does one curve provide the perfect arc on every bow clamp made?


That's the point exactly. Shim material to pick up the low spots. The problem is that as soon as you insert a shim, the pressure on either side of it is eliminated. If the pressure remained consistent they would be effective for a much greater variety of uses including but not limited to veneer work. You say you switch to LOTS of clamps, or a vacuum bag. That means that most woodworkers avoid veneer work... as if it were something other than wood sliced thin.:confused:

Vacuum bags are for curved work. For flat-work it's simply not necessary.

Mike, again with all due respect, I'm really in awe of your talent, but a quick browse through your portfolio... I can't find a single veneer project that couldn't have been clamped up with a set of Bowclamps and 6 cheap f-clamps. But you have your methods and that's great, whatever works, gett'er done.

However I really don't understand your answer about clamping the 2 pieces of MDF flat. Does up and down now count as 2 dimensions?:confused: And you say you use torsion boxes but you didn't fill me in on how you get clamping pressure out in the middle of your torsion boxes. Are you using home made curved cauls and I've just missed it, or are you piling heavy tools on top?


And Peter,

The CNC allows me to easily adjust the arc (Sorry Fred, yes it's an arc) as needed, then the Bowclamps are matched in pairs. And don't forget that LOTS of clamps means LOTS of money and LOTS of time... and hurry your glue is kickin'. :D

[Peter Kuhlman]

I have the set with 3 different lengths and use them frequently - as a hobbiest. I could have made my own, but would have taken quite a bit of time to duplicate. They are quality items with nice machining and have some type of finish that works well against glue. Probably need to add wax to mine now with all the usage. To make an identical item, getting the nice curve, adding the slot for the F-clamp pad, would take time that I did not want to spend. To me, for the price, these were a very worthwhile purchase versus the time it would take to make. The slot is really worthwhile as it allows the clamp/caul assembly to stay together while I am trying to get everything in position. I have a wall full of clamps but this sure makes my glue-ups far easier.

It is like everything, I could have made my own positioner and fence for the router table, made a tenoning jig for the table saw, etc. This item was just worth the price - to me.

[Mike Henderson]

And you say you use torsion boxes but you didn't fill me in on how you get clamping pressure out in the middle of your torsion boxes.
A torsion box is an engineered structure which is somewhat equivalent to I-beams in two dimensions. The goal is to design a box that is very stiff so that when used for clamping, pressure is carried across the box. That is, the pressure is essentially equal across the box. Of course, all structures have some flex so the pressure in the center is slightly less than around the edges but it is sufficient to press veneer or other large gluing projects.

Here's a picture of a torsion box under construction (note that two are required - the work is placed between them and they are clamped together). The webs are 1/4" tempered hardboard and the skin is 1/2" Baltic birch plywood in this box - other thickness materials can be used. The webs are glued to the skin - that's very important for strength and stiffness. The structure is effectively I-beams in two dimensions. As with I-beams, the deeper you make the webs, the stiffer the box.

[Just a comment: the completed torsion box will have a top skin applied. The picture shows the box under construction. I don't have any pictures of the completed boxes and no longer have the boxes so I can't take more pictures of them.]

The disadvantage of torsion boxes for clamping is the weight (handling them - these really took two people to set down properly, although I have done it by myself) and storage when not in use. I had discussed these boxes earlier in the forum and someone asked me what they weighed. If I recall correctly, they were under 50 pounds each. I used these for veneer work for a while but sold them when I got my vacuum pressing setup. So I went from sheets of MDF with cauls, to torsion boxes, to vacuum bags. The vacuum bags are much better for veneer work.

Mike

[After poking around on my computer, I did find some pictures of the completed torsion boxes. One picture shows how they'd be used - the veneer is placed between the boxes with a sheet of plastic on both sides (to keep the boxes from getting glued to the veneer). I'd use a lot more clamps when actually doing a clamp-up. I took these pictures to show how torsion boxes are used so I only put a few clamps on (lazy, I guess). The third picture just shows the hand holds I put on the ends of the boxes to make them easier to handle.

I also made a set of smaller torsion boxes (last pix) that I used to use for smaller veneer jobs. I still have those boxes and occasionally still use them.]

[Vince Shriver]

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


I have made up some clamps of similar design: I plane off some thickness from the ends of a 2x2, leaving the middle full size, and sandwich them together with a couple of carriage bolts, fender washers and wing nuts through both ends. Although I'm sure the "real deal" is probably more user friendly, you are right - you can cobble up a clone with very little trouble. And they work great.

[Craig Feuerzeig]

My question is... they work great for what?

Are you using them purely for keeping boards aligned during glue-ups, or as deep jaw clamps to get pressure out in the middle? And if so how far do you realistically go?

If you had a 4 foot hardwood edge or a cabinet face frame... how close are you spacing your clamps? Are you really going 4 feet? Longer maybe?

Not saying it isn't being done... but I am saying I haven't seen any evidence at all that that is the case. And it certainly isn't being taught in schools (that I know of) unless they are using mine.;)

And Mike... what am I missing?? :confused::confused: I know what a torsion box is. I get it... It's a flat surface to clamp to. My question, again, is what are you using to clamp to it? To reach out into the middle to press down?

[Mike Henderson]

And Mike... what am I missing?? :confused::confused: I know what a torsion box is. I get it... It's a flat surface to clamp to. My question, again, is what are you using to clamp to it? To reach out into the middle to press down?
Please check my previous posting. I added some pictures of the completed torsion boxes and show how they're clamped. Also please read the text which discusses how they work. The reason for using torsion boxes is so that you don't have to clamp in the middle. If you had to clamp in the middle, there would be no advantage to the torsion box - you'd just as well use a sheet of MDF.

Mike

[From your question, I think you're making the assumption that only one torsion box is used and things are clamped to it. In actuality, two torsion boxes are used and things (especially veneer work) are placed between the two boxes. Since both boxes are stiff, you can clamp along the outside of the boxes and get fairly even pressure across the work.]

[Mike Henderson]

If you had a 4 foot hardwood edge or a cabinet face frame... how close are you spacing your clamps? Are you really going 4 feet? Longer maybe?

I had a cabinet that I wanted to clamp on the sides (to make sure the sides were straight) and that's why I build those I-beam cauls. The cabinet is about 55 inches high and the cauls are about 5 feet. I used one caul on each side of the cabinet. The back is a piece of 1/4" MDF with veneer on both sides. It is set into a rabbet around the sides, and is glued to the sides to provide support to the sides and to keep them from bowing. So while they were gluing, I wanted the side to be straight - therefore the caul. In this case, I didn't want more pressure at the center of the caul because it might have bowed the side inward - I just wanted straight.

I could have used more than two clamps on the I-beams but I felt that two was enough.

The bottom was screwed on (and glued). A very slow setting epoxy was used to give me time to get everything together. It was a really hot day when I did this clamp up and the epoxy set a lot faster than I expected. I was really glad I used very slow epoxy (West Systems with the slow setting hardener.)

Mike

[Dino Makropoulos]

Some input from a user of the bowclamps in many demanding applications
where nothing else worked to my satisfaction.
I made my own before I tried G's bowclamps.
I used plastics with memory, softwoods, maple and even spring bars with
adjustable ( controlled) tension.

I was surprise to see the results of Greg's Bowclamps.
Anything can do the job but not better than the Bowclamps.

Here is a nice trick to save you some money. ( sorry Greg ):rolleyes:
You can rip the bowclamp and make few out of one if you need a low profile Bowclamp for unique applications.
I'm testing the Bowclamps for over two years now for a project
that nothing else worked right.

It's something about the right arch ( CNC ) the NJ air and the type of wood (Maple)

[Craig Feuerzeig]

Mike, thank you for clearing that up. 2 torsion boxes. All the difference in the world.

Thank you for also clearing up the fact that I really don't think you understand what we're talking about.

You have posted 2 examples of straight cauls. Used for the purpose of keeping things straight.

Curved cauls go a step further and apply clamping pressure downward. In your example clamping pressure tapers off as it moves at approx. a 45 degree angle from the clamp. In my example... it doesn't.

I keep hearing how they are so easy to make.

You went through a tremendous amount of time and effort and expense to make those torsion boxes. They are bulky. They require the use of 2 foot long clamps to clamp a 3/4" thick work-piece (typically... the longer the clamp, the fewer I own).

I'm sorry but it begs the question...

Why didn't you just take a few swipes with a block plane to a 2 bye?:confused:

Please don't take this personally... I'm not just speaking to you. I'm asking all of the "it's easy, I do it all the time" crowd.

And I'm really hoping it is done all the time and we can actually talk about it. But until I see some proof...:(

I would love to see... how'd you do it. How effective are they really?

And an important overlooked piece of added advice to those who are making they're own... pay close attention to grain direction. Bowclamps are quartersawn. Wood is much more ridgid when the grain direction runs perpendicular the the curved face. Also keeps seasonal movement from affecting the "money side"... as movement will be across the width.

Just trying to help.;)

[Craig Feuerzeig]

In that cabinet glue-up Mike,

The cabinet is what, about 14' deep? You have 3 clamps across the width. What if the cabinet was 24" deep? How many clamps would be required? At least one more, right? And the pressure is still spotty. If you had Bowclamps it wouldn't matter. 2 clamps, equal pressure across the whole width.

Is there a face frame going on that cabinet? A lot of guys would nail it.:eek:

Or perhaps a veneer edge? That expensive vacuum bag isn't going to be much help there.:rolleyes:

How would you do it?

[Mike Henderson]

In that cabinet glue-up Mike,

The cabinet is what, about 14' deep? You have 3 clamps across the width. What if the cabinet was 24" deep? How many clamps would be required? At least one more, right? And the pressure is still spotty. If you had Bowclamps it wouldn't matter. 2 clamps, equal pressure across the whole width.

Is there a face frame going on that cabinet? A lot of guys would nail it.:eek:

Or perhaps a veneer edge? That expensive vacuum bag isn't going to be much help there.:rolleyes:

How would you do it?
That cabinet is a display cabinet and will have doors on it. I'm building to a client's design - so I'm just contributing the woodworking skill. You can follow my progress on that cabinet here (http://www.mikes-woodwork.com/Cabinets.htm) - it's in reverse order, like a blog. I document my progress so the client can see that I'm making progress and haven't run away with their money (I get 50% down).

I'm retired but have other demands on my time so my progress is slow (but steady:))

If you look back in this thread, you asked people to respond with how they used shop made cauls. That's what I did. I'm not in any way knocking your product. I've had good success with my shop made cauls. When I encounter a clamping problem, I can fabricate something to meet my needs - or at least so far, that's been the situation.

Mike

[I don't think we're making any real progress here. If you want to continue the discussion, let's take it to PMs.]

[Craig Feuerzeig]

Well to demonstrate your knowledge and experience with curved cauls you posted 2 projects of cauls that were not curved.:confused::confused:

Yes I did ask for examples of people using shop made cauls. Still am.

Thank you for your contribution. I know it must seem as though I'm singling you out... But you're the resident expert here. This is a woodworking forum. People come here to gain knowledge about woodworking. What you say carries some pretty heavy weight.

I'm trying to have a hypothectical conversation. You say you can fabricate something when the need arises.

Veneer edge.

Happens ever day in a woodshop.

Simple question. Not just for you Mike. For everyone.



Never mind. I already know the answer.

Actually there are always more than one way to skin a cat.

There are whole industries built around trying to solve this problem.

Contact cement. And

Hot melt glue.

Or

You can spend $30,000 on an edge-bander if you are doing production, which again uses hot melt glue.

Both work-arounds because you can't effectively glue it and clamp it...like you would like to do.

But now you can. And a couple of swipes across a two-bye isn't going to cut it.

I just want people to understand what it is we are talking about here.

[Craig Feuerzeig]

Here's an example. This is a job I built... well the date is stamped right on it.

http://i50.photobucket.com/albums/f339/cfeuerzeig/hartman1.jpg

The desk is black laminate with a maple edge. The unit on the right (also duplicated on the left... the room is symmetrical) and the unit behind the desk are all plywood tops with hardwood edges. If it weren't for the ogee edge I could have pocket screwed it (love my Kreg jig, but sometimes you gotta just glue and clamp). The bookshelves are plywood with a built-up veneer covered edge, as is the bottom edge also covered in veneer (again duplicated on the left side).

I'd been cranking out stuff like this for 20 years. Nuthing special.

Before Bowclamps I did this.

http://i50.photobucket.com/albums/f339/cfeuerzeig/8ft1.jpg



now I do this


http://i50.photobucket.com/albums/f339/cfeuerzeig/8ft2.jpg

and instead of torsion boxes for veneer I do this

http://i50.photobucket.com/albums/f339/cfeuerzeig/012_12.jpg

Now, I'm sure there are lot's of home-made versions out there and I'd love to see them. I'll be the first to say great job, thanks for sharing.:)

[William Nimmo]

I bought the bow clamps after reading this thread. Put them under my mft and thought , stupid impulse buy, probably never use them..
well, used them on a cabinet made of solid pine boards that were edge glued before I got the cauls. After 5 minutes of figuring out how I was going to hold the clamp, the caul and the work piece. Got it. I must say I am pretty impressed. Solid pine panels do not lay as flat as ply, so pulling in the center was easy as pie with these. I honestly think I will use these on every assembly.

[Craig Feuerzeig]

I honestly think I will use these on every assembly.


Thank you William. That's about the highest compliment a tool-maker can hear. And if you have an MFT you'll dig this set-up, sent to me by another proud member of the Bowclamp family.

http://i50.photobucket.com/albums/f339/cfeuerzeig/rogermft.jpg

[Bill Evans]

Craig,

Thanks for the quick shipping on the Master Set. I have been playing around and get used to them. And also thanks for the photos using the Festool MFT. That will be my prime use as well.

I am a very novice woodworker so I am on the steep end of a bunch of learning curves but I used the whole set today to make a simple glue up panel.

http://lh6.ggpht.com/_rqLNS-z1IIU/SsU1ehrG9UI/AAAAAAAAM80/ymfBF5c3oa8/s800/Bowclamp%20Cauls%20-%201.jpg

http://lh6.ggpht.com/_rqLNS-z1IIU/SsU2bkuqgPI/AAAAAAAAM88/beVHojGLU74/s800/Bowclamp%20Cauls%20-%204.jpg

About as soon as I had everything in place, I started thinking of better ways.

Ah, the beauty of being on the steep end of the curve.

Thanks, Bill

[Craig Feuerzeig]

That is simply outstanding Bill. Thank you so much for sharing.