Tutorial: Shop Made Cauls

[Mike Henderson]

I recently did a tutorial (http://www.mikes-woodwork.com/Cauls.htm)on making cauls. I'm sure many of you already know how to make cauls but new woodworkers often do not.

For those of you experienced, I'd appreciate comments and suggestions - especially on better ways to make cauls.

Mike

[Jim Rimmer]

Mike:

Thanks for the tutorial. I'm not a newbie exactly but not real advanced either. That's some good info I can use.

[Dan Forman]

Mike---Thanks for this, I need to make some. Don't you run into trouble though with planing against the grain on one half of the caul, when starting in the middle?

Dan

[Kent A Bathurst]

Mike - looks good - straightforward instructions. I got so aggravated years ago at scrambling around trying to find stuff to use for cauls that I bit the bullet and made a set - I think I have like 20 of them, all exactly identical.

Mine have a lot in common with yours, but there are some differences:
1. I used 10/4 hard maple, ending at about 2-1/4" square. Yeah - maybe overkill, but I wanted do do it once. That was 10 yrs ago.
2. I wrapped two lines around the centere of the caul, 2" apart (1" offset from the center line). On the face to be toward the glue joint, I put an X in the middle of that box. These lines tell me where the center of the caul is, looking from any direction, and the X tells me which side goes against the glue-up.
3. Mine are 32" long. I taped a stacked pair of dimes to one end, then set the dime end well past the running jointer head, and plunged the caul down, and moved if forward. Repeated until the jointer cut came to my line. Then, pulled those dimes, taped 4 dimes to the cut end, and repeated for the second end. No better than a handplane, just faster, and both bevels are identical. Clear packing tape, of course.

Accessories: I used scrap plywood to make pairs of U-shaped brackets (the U opening sized to receive the caul), attached to a piece of plywood as a base, with the pair offset by about 12". This gives me a flat, stable base to keep the cauls up off the bench. The height was designed to let me get a C-Clamp under the caul. The entire setup runs up to 1"+ panel with 6" C-clapms, over that takes 8" clamps.

Last, I used a bunch of 3" square pieces of plywood to make a bunch of short stacks. On top of each stack I screwed a piece of 1" PVC that has a slice of about 40% cut away. The height of the stack is correct to allow a 3/4" pipe-clamp to be snapped into a pair, and hit the correct glue-up height, as already determined by the U brackets and cauls. Someday, I'm going to make a set with grooves to receive and hold parallel clamps, but with this setup and the cauls, I have no trouble at all with the pipe clamps - the fixtures to hold the clamps lets me easily alternate above-below, without fumbling around.

As I am in the glue-up, the lines around the cauls tell me where the "flat spot" is to center over the joint.

Since I started using these, I have never again needed to run a glue-up through the surface planer. I use a card scraper or a scraping plane for the very minor offset I get, if any.

[Bill Huber]

Good info.... I will have to say I am lazy and can't use a plan for anything yet so I have an MDF template that I use with a trim bit to make mine.

[Mike Henderson]

Mike---Thanks for this, I need to make some. Don't you run into trouble though with planing against the grain on one half of the caul, when starting in the middle?

Dan
Softwood, like fir used in construction 2 by 4's, is pretty forgiving. I never had any serious problem hand planing it.

Kent - how about some pictures of your setup. It would help to understand what you've done.

Mike

[Peter Quinn]

Nice tutorial Mike. I use a jointer to do mine at work. A few light passes in each direction from a center line and maybe a bit of tune up on a big horizontal belt sander. A few seconds to make a set from the scrap bin for any given project. I usually use soft maple when its available, though I have used sappy WO, sappy black walnut, MC ash, whatever 8/4 material was left over from the last job and usable for other work. I think we use the same brand of tape!

I understand the bow clamps are nearly perfect renditions of this concept, and though I have never used them, I am amused that wood workers would pay so much for something they can make very effectively and cheaply to suit most purposes.

[Mike Henderson]

Craig Feuerzeig was kind enough to send me a PM and suggest a way of testing the contact along the cauls. He suggested putting pieces of paper along the joint and see if you can pull the paper out.

So I went out to the shop and did that test. I found one spot that was not tight but was able to adjust it easily. See the pictures.

And thanks to Craig for this excellent test technique.

Mike

[Wes Grass]

I clamped a pair together with spacers at the end, warping them until the centers touched, and then jointed the outside edges straight. Generates a proper catenary curve.

The trick is in clamping them together. I bored 1/2" holes across the center, and made a couple of steel bars with 1/4-20 threads in one and a clearance hole in the other, bolts on each side to pull them together. Putting the holes across the center line has little or no effect on the stiffness. Might be able to do this with dowel and wood screws too. Or if you make the hole big enough, you could hook a small f clamp through one at a time.

Since they hung out the sides I had to use the jointer. Or maybe use a long wood screw, *well* countersunk, and straighten them out on a table saw.

[Prashun Patel]

Thanks Mike. This was very useful to me.

[Mike Henderson]

I clamped a pair together with spacers at the end, warping them until the centers touched, and then jointed the outside edges straight. Generates a proper catenary curve.

The trick is in clamping them together. I bored 1/2" holes across the center, and made a couple of steel bars with 1/4-20 threads in one and a clearance hole in the other, bolts on each side to pull them together. Putting the holes across the center line has little or no effect on the stiffness. Might be able to do this with dowel and wood screws too. Or if you make the hole big enough, you could hook a small f clamp through one at a time.

Since they hung out the sides I had to use the jointer. Or maybe use a long wood screw, *well* countersunk, and straighten them out on a table saw.
Great idea, Wes. You're right - that will produce the proper curve, accounting for the flexibility of the wood, which is variable sample to sample. No calculations, no muss, no fuss.

I'm going to try that.

Mike

[Dan Forman]

This thread just made it into my woodworking folder. Thanks everyone.

Dan

[Garth Keel]

I appreciate the time you took to put this together and the pictures.

[Myk Rian]

Thanks for the writeup. Great info.
Definitely sticky material.

[Paul Saffold]

Thanks Mike. This is a definite keeper. Paul

[harry strasil]

FWIW, I use Saran Wrap on my Cauls, and my clamps to keep glue from sticking to them.

[Mike Griffin]

Thanks for the info.

Looked at your works and was awed. Great craftsmanship.

[Craig Feuerzeig]

Thank you Mike for a great write-up.

I know I need to be respectful about advertising policy... but a few thoughts.

Mike, when asked about tear-out you specify that soft-wood is forgiving...when trying to get pressure, these are 2 factors I typically don't want in the equation...soft and forgiving. But more importantly I think is this...

The more accurately you can make them the more use-full they become.

I would like to talk about the types of jobs you are using them for. I think most people when they think of cauls are refering to keeping boards aligned during glue-ups, but rarely beyond that.

For example... would you trust yours to do this? Not saying it can't be done...but I've certainly never seen it. I'm pretty sure you're just buying more clamps. Expensive parallel jaw ones at that...:confused:

http://i50.photobucket.com/albums/f339/cfeuerzeig/000_0012-1.jpg

http://i50.photobucket.com/albums/f339/cfeuerzeig/000_0002_2.jpg

[Matt Meiser]

Why don't you two just exchange a set of your respective cauls and each do side by side tests to prove each other wrong? The Great Caul-Off of 2010...East Coast v West Coast....Lets get ready to claaaaaaaaaaaammmmmmmmpppppp! :rolleyes:

Actually, I'm pretty serious.

[Kent A Bathurst]

Kent - how about some pictures of your setup. It would help to understand what you've done.

Mike - here you go - sorry for the delay - camera was on vacation in Philly for a few days, but it eventually followed SWMBO back home.

Simulated glue-up. Real thing has pipe clamps alternating over/under. Also, some type of screw clamp on the glue joint at the ends to pull the joint tight there. The "X" is flat - cauls taper from the "X" to the ends. I center the glue line on the "X" on the bottom cauls, and then use the wrap-around lines to align the top cauls - so the 2" flat spots are centered on the glue line. C-clamp and crank the ponies. Cello packing tape on the "X" caul surfaces. All I need is a card scraper or scraping plane to smooth the joint.

Photo 001 shows the "U" fixtures nested - they stack real nice that way :). The first version - I failed to allow enough room for the C-clamps to slip under the bottom caul - lesson learned - raised the "U" and pipe bracket height.

FWIW - a section of wall has those PVC clips screwed in vertically-aligned pairs between studs - the pipe clamps snap into place and stay where I put 'em. Also - you'll see PVC clips that slide on the pipe - keeps pipe out of the glue.

I need to do the "clamp on paper strips" trick noted in an earlier response. Mine seem to work great, but I could never think of how to check the curvature of the earth under clamp pressure - that is the way.

[Mike Henderson]

Why don't you two just exchange a set of your respective cauls and each do side by side tests to prove each other wrong? The Great Caul-Off of 2010...East Coast v West Coast....Lets get ready to claaaaaaaaaaaammmmmmmmpppppp! :rolleyes:

Actually, I'm pretty serious.
I want to make it very clear that I don't have anything at all against Craig's products. Neither do I assert that the particular shop made cauls I describe in my tutorial can do everything on the face of this earth, including changing the baby when needed.

I was simply passing along a technique I was taught to make cauls, plus a few things I learned along the way. For what I do, my shop made cauls satisfy my needs - your mileage may differ.

I will not be drawn into any type of contest between what I described and Craig's products. If you like Craig's products, buy 'em. If you want to make your own, my tutorial is one way to do it (and there may be better ways).

Mike

[Craig Feuerzeig]

Please understand that the last thing I want is a competition either. I am the first to applaud Mike's effort...but as someone said earlier..."why would someone spend good money...?"

I think it's fair to address that question. I also think it's fair to ask..

What sort of jobs are you using your home-made versions for? And am I mistaken about their capabilities? And if so, how much time and money and effort did you put in, in order to get there? etc.

Mike is completely right about this being the way our ancestors did it. But I bet they wished they had a CNC. :rolleyes:

Other small point of note... that flat spot in the middle... will bow backwards when you clamp the ends down, leaving a void. ;)

[dan sherman]

Now that we have covered several methods of how to make cauls, can we discuss their design? for example is their a rule of thumb to determine how much bow they should have base on length or the like?

I wan't to make some of these, but being the physics geek that I am, my mind keeps saying figure out how much bow the should have. Thus lets say I have some nice SYP all milled up that's 26" long by 3" tall, by 1-1/4" wide, how much bow Do I have to give the cauls?

[Kent A Bathurst]

Other small point of note... that flat spot in the middle... will bow backwards when you clamp the ends down, leaving a void. ;)

Ummm.......if you notice the photo, you will see that I put the C-Clamps close to the edge of the panel, not way out on the end of the cauls (unless that's where the panel ends).

And those "voids" you mention must be working pretty doggone good, since with this setup, for nearly 10 years, I have only had to use a card scraper to smooth the glue joint - never the thickness planer. Brings to mind Lincoln's reply when told Grant drank heavily - "In that case, find out what he's drinking, and send a case to each of my generals."

You can certainly tell me you prefer a different design, but I don't understand how you can assert that mine doesn't work. :)

My "project quality" has included dead-nuts repro pieces of Stickley/Ellis, with #1 bookmatched old-growth QSWO - pushing $18/BF from Talarico. I'm not building some paint-grade toy chest for a niece (I did that one without any cauls).

I am so very happy you have a CNC, but I'm not inclined to apologize for my setup. I wasn't entering some kind of contest or argument, Craig - I was responding to Mike's request for photos. In the way-back-when, I would have jumped on Mike's tutorial, but I had to muddle my way through.

And no - I'm not advertising anything because I'm not selling anything. Not my furniture. Not my cauls.

Yeeeesh.

[Mike Henderson]

[This is in answer to Dan Sherman's question above]

I don't think there's an easy answer to that question. Let me go into some discussion.

The ideal curve is a cantenary (http://en.wikipedia.org/wiki/Catenary). If all else if perfect, a cantenary curve will cause the caul to put the same pressure all along the surface. But there are some variables that affect your selection of the cantenary.

For example, if your cantenary is too curved, you won't be able to pull the ends down. All of your pressure will be in the center and none on the ends. If your cantenary is not curved enough, you will not get even pressure along the surface - there will be a gradient of force along the surface with more on the ends and less in the center.

So which cantenary should you choose. Well, that depends on the stiffness of your material, and with wood, that will vary from sample to sample.

But all is not lost. For most caul applications just getting pressure along the caul surface is sufficient.

A very good technique to get a cantenary curve is the one described by Wes Grass earlier in this thread.

I don't worry about all the mathematics. I do a trial fit pulling the two cauls together face-to-face and see how much pressure I have to use on the clamps to get the cauls down. When I feel it's enough pressure, I then check the fit of the surface of the cauls to make sure the two faces are touching all along. If they are, I'm good to go. If not, I adjust the surface until they are, using Craig's paper test. I may or may not get perfectly even pressure along the faces, but it works for me.

Mike

[Let me add a bit about the cantenary curve. If your curve is too shallow, you can clamp them with equal force along the cauls, but you may not be satisfied with the force. That is, you'll have to put very light force on the ends to get even force along the cauls. If you make the cantenary too curved, but within the bending limits of the wood, you'll have to put a lot of force on the ends to get even force along the caul. So a perfect curve is only perfect for one amount of force on the ends.]

[Ben Martin]

Mike,

What size are the Bessy clamps that you are using in the last set of pictures that you posted, are those 12"?

[dan sherman]

Mike, I have an idea, but i will have to ponder it a little longer over lunch, I think we might be able to use the sagulator to calculate the bow.

[Mike Henderson]

Mike,

What size are the Bessy clamps that you are using in the last set of pictures that you posted, are those 12"?
Yep, those are the 12" and I find that I use them quite a bit. When I first got them I thought they would be "special purpose" clamps but they're more like "general purpose" clamps for my use.

Mike

[Oops, I hope we're both referring to the same picture. Most of the pictures show the 12" and I think that's what you were referring to.]

[Prashun Patel]

Please don't let's debate the benefits of shopmade cauls vs cnc ones. That's been covered in other threads. Let's keep this one to a 'how to'.

[Craig Feuerzeig]

Ummm.......if you notice the photo, you will see that I put the C-Clamps close to the edge of the panel, not way out on the end of the cauls (unless that's where the panel ends).

And those "voids" you mention must be working pretty doggone good, since with this setup, for nearly 10 years, I have only had to use a card scraper to smooth the glue joint - never the thickness planer. Brings to mind Lincoln's reply when told Grant drank heavily - "In that case, find out what he's drinking, and send a case to each of my generals."

You can certainly tell me you prefer a different design, but I don't understand how you can assert that mine doesn't work. :)

My "project quality" has included dead-nuts repro pieces of Stickley/Ellis, with #1 bookmatched old-growth QSWO - pushing $18/BF from Talarico. I'm not building some paint-grade toy chest for a niece (I did that one without any cauls).

I am so very happy you have a CNC, but I'm not inclined to apologize for my setup. I wasn't entering some kind of contest or argument, Craig - I was responding to Mike's request for photos. In the way-back-when, I would have jumped on Mike's tutorial, but I had to muddle my way through.

And no - I'm not advertising anything because I'm not selling anything. Not my furniture. Not my cauls.

Yeeeesh.


Kent I wasn't repying to your post or referencing it in any way. I'm sorry if you think I was. I happen to think it's a nice set-up. I was simply referring to the method of starting to plane 3-4" inches from the center... leaving a flat spot. I was just trying to give a pointer based on experience.

And the whole point I'm trying to make is that of course it works for you, for the purpose intended. My question to nobody in particular is simply... Do you use them for other jobs around the shop? Do you use yours for veneer work? If you can get rid of those flat spots... maybe you can.

[Matt Day]

I need to make some too - thanks so much for the step by step!

However, I think I'll make one using a hand plane but to make copies of it I'll probably use the router with a pattern bit so I can knock out mutiples. What do you think?

[Kent A Bathurst]

.... to make copies of it I'll probably use the router with a pattern bit so I can knock out mutiples. What do you think?

Matt - I think that's a great idea - then they will all be the same, and will all act the same way, regardless of which one you grab. Tee it up.

[Mike Henderson]

I need to make some too - thanks so much for the step by step!

However, I think I'll make one using a hand plane but to make copies of it I'll probably use the router with a pattern bit so I can knock out mutiples. What do you think?
That should work. Bill Huber (above) says that he has a template. Contact him and maybe he can send you a copy. He only needs to send you one side, then you can duplicate it.

But you can knock these out with a hand plane pretty quick. It's not something you're going to do every day and you don't take a whole lot of wood off so my recommendation is to use the plane and enjoy the feeling of some hand work.

Mike

[dan sherman]

Mike, how does this jive with your real world cauls?

my assumptions:
1. over a 24" span I would use 4 clamps
2. each clamp applies 75% of maximum clamping pressure
3. cauls are SYP

thus:
1) 0.75 * 1000 = 750lbs. (force excreted by each clamp)
2) 750 lbs * 4 = 3000lbs. (4 clamps)
3) 3000lbs. / 2 = 1500lbs. (divide by 2, because cauls are used as sets)

running this through the sagulator, says the center of the cauls should be roughly 3/64" of an inch thicker then the ends.


http://www.sawmillcreek.org/attachment.php?attachmentid=134646&stc=1&d=1260307029

[Ben Martin]

Yep, those are the 12" and I find that I use them quite a bit. When I first got them I thought they would be "special purpose" clamps but they're more like "general purpose" clamps for my use.

Mike

[Oops, I hope we're both referring to the same picture. Most of the pictures show the 12" and I think that's what you were referring to.]

Yep, that's the one! I got a steal on some 24" Jorgy's, I think that I will be modifying them a bit down to 12".

[Mike Henderson]

[This is in response to Dan Sherman's post above]

What I did was go out to my shop and measure the gap on one of my 48" cauls - see pixs.

With the end and the middle clamped, the opening on the other end is about 5/16". Another set would probably have more or less of a gap since I decide the gap by feel (pressure on the clamp). Also, remember that I'm using fir.

I can't really analyze that for you except to say that it works for me. A bigger gap would give more force in the middle of the cauls.

Mike

[Scott T Smith]

Great info here - thanks Mike, Wes and others. This thread has been printed out for my shop notebook.

Scott

[Wes Grass]

Hmm. Mine are Poplar, 36" long, 2" thick, and I think about 3" tall. I'd have to double check to be sure.

I arched one side 1/8" and the other 1/4". According to the Sagulator, 900lbs in the center should straighten the 1/8" side. That sounds like quite a bit, but when I actually tried them it seemed like not nearly enough force to keep the panel straight, so I flipped them to the 1/4" side. That didn't seem like a lot either, actually. But getting 4 or 500 lbs thrust from a screw doesn't take a lot of torque.

[Brent Ring]

Just one other suggestion - I frequently check the scrap bins at the orange borg, and recently found some 4', very straight (and straight-grained), reasonably knot-free, KD cutoffs - while not free, they were only .51 a piece. I bought 6 boards, and have enough to get started making my cauls now. Every orange borg that I have been to in Utah puts their cutoffs in a scrap bin. You have to pick thru, but you can find some gems once and awhile. I even built a router table a few years ago and the bulk of the carcass only cost me about $15.00. Someone left some awesome 3/4" melamine coated mdf and top grain plywood.

Just an idea for the cost cutters out there :D

[Michael Schwartz]

I recently did a tutorial (http://www.mikes-woodwork.com/Cauls.htm)on making cauls. I'm sure many of you already know how to make cauls but new woodworkers often do not.

For those of you experienced, I'd appreciate comments and suggestions - especially on better ways to make cauls.

Mike

nice cauls, I made a very sturdy set out of 8/4 ash a few weeks ago but regardless of the material they have endless uses.

My next shop project is a flat MDF torsion box to be used in combination with cauls.

[Cody Colston]

Great tutorial, Mike. I personally don't believe that caul design is rocket science but your method is an easy way to keep them consistent between pairs. I'll be making a few when I get home.

Thanks again for taking the time to document the process.

[Salem Ganzhorn]

Thanks Mike! I made some using your method a couple days ago and used them for a glue up. Really nice! My only additional comment is to use a setup like Kent's to elevate them to make room for the clamps. That worked great!
Salem

[Karl Brogger]

I'm not sure I understand what these are for.

Using a stick to spread out clamp pressure is pretty much SOP, but I don't understand how using two clamps is better than say 5 with a straight piece.

[Stephen Edwards]

I'm not sure I understand what these are for.

Using a stick to spread out clamp pressure is pretty much SOP, but I don't understand how using two clamps is better than say 5 with a straight piece.

I've only worked with cauls a few times. I'm not certain that it is better. But, the few times that I've used them they worked just as well as the traditional method of using a straight stick and a bunch of clamps.

To me the advantages are twofold.

You don't need as many clamps for a particular glue up. If you have a lot of glue ups going at once, not having enough clamps isn't a problem.

On some glue ups that I used them for, using two clamps was the only practical way of performing the operation, one clamp on each end of the caul.

[Mike Henderson]

I'm not sure I understand what these are for.

Using a stick to spread out clamp pressure is pretty much SOP, but I don't understand how using two clamps is better than say 5 with a straight piece.
Cauls are generally used where you can't get a clamp. Suppose you had a cabinet with a shelf set into a dado and you wanted to apply pressure along the outside panel where the shelf is to make sure the shelf was fully seated during glue-up. If you had some clamps with very long reach jaws, you wouldn't need cauls. With cauls, you can put a caul along the outside of the cabinet, in line with the shelf and get pressure all along the panel. You might only use two clamps, one on each end of the caul.

Another common use is for flattening a panel during glue-up. You can use cauls without any curvature, but you won't get a lot of pressure in the middle of the panel because the caul will flex. By using a curved caul, you can apply pressure all along the caul, which will help align the boards of the panel, and will keep the panel flat while the glue sets.

There's a whole lot of situations where cauls can be used, and Craig Feuerzeig of Bowclamps has described many here on the forum and on his web site.

Mike

[Karl Brogger]

Suppose you had a cabinet with a shelf set into a dado and you wanted to apply pressure along the outside panel where the shelf is to make sure the shelf was fully seated during glue-up.

I can see that. Can't say its something I've ever actually checked. Just seems like a bizare use/tool. I don't use clamps for much of anything but finished ends, and the occasional face frame that won't sit down nicely. Its not something that would really work for me with faceframes as I rarely run short on clamps, and for me finished ends, (not panelled), the backs are rabbet'd in, leaving just 3/8"x1/8" worth of material to clamp to. So I'm putting all the pressure on two clamps, and crushing that 3/8" tounge sticking out.

[Robin Jepson]

Wes, I just tried the spacer method on cauls made from maple and poplar scraps and it worked great! I drill a 1/2" hole with a forstner bit to conceal the head of a 1/4" carriage bolt at the center, then placed a small 1/4" hardboard spacer at each end. I used an adjustable taper jig on the table saw to cut the curved edge straight. After removing the carriage bolt I have a perfect camber on the one edge. I used a piece of paper to test the tightness as the cauls were clamped together and they worked flawlessly. I had tried different methods to create this camber, but none worked quite the way I wanted. This works perfect, thanks for the idea!

[John Zappulla]

Mike,

I realize that this thread is a couple of years old, but I wanted to thank you for an excellent tutorial on making cauls. I just finished making up 3 sets of 24" cauls and they work great! Thanks for sharing.
I had to take a peek at your work. The lines on your rockers just flow so perfectly and truly enhance the entire project. Your attention to detail is remarkable on your trays.
You are in every sense of the word a "craftsman".

[Carl Hill]

Some great information here. Now I wish someone would post on making culls. :)

[Jerome Hanby]

Just do a search for any of my posts <g>


Some great information here. Now I wish someone would post on making culls. :)

[Bobby O'Neal]

Thank you for this, Mike.

[Mike Henderson]

Thank you for your kind words. When I realize that something I'm doing may be of interest to someone else, I try to take pictures and post how I did it.

Someone recently contacted me about how to install quadrant hinges on a jewelry box - and they're difficult to do - so next time I'm doing some, I'll try to post pictures of it.

Suggestions for other things????

Mike

[Don Jarvie]

Nice tutorial Mike. Just added that to the library.

[Steve Kinnaird]

Glad this was shared today..... by Paul Cahill