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An old idea tweaked by the computer revolution
Text, photos and video by Tom Hintz
Posted - 2-25-2010
Clamping cauls have been around at least since someone thought of clamps. Since then the argument on how to make the "perfect" clamping caul has raged on. The advent of the computer did two things for that argument. The Internet gave those "discussions" more range than ever before. The good side is when someone applied the digital precision of the computer to machining centers and that gave Bowclamp™ creator Craig Feuerzeig an idea. By the way, that idea is patented.
It's the arc stupid!
The arc has long been appreciated as a strong, predictable way of dispersing or focusing energy. Woodworkers have tried creating an arc in their shop-made clamping cauls for a long time but the problem has always been consistency. If the arc is not perfectly consistent, it delivers energy unevenly and pretty much negates its usefulness.
Bowclamps™ are made using CNC (computer numerically controlled) machining to cut the arc with far more precision than we can do with sticks, strings and hand tools. The computer also allowed Feuerzeig to tweak the arcs on each of the different sized Bowclamps™ so that they all apply force evenly over their length.
That CNC consistency of those arcs is important because it means that with a clamp at either end, pressure is applied consistently across the full width of the Bowclamp™. You don't need a clamp at the center - or every few inches - depending on the situation. If you made your own arc some of those clamps are likely to be pressing your caul down where the arc is not right and that further disrupts the application of clamping force.
Bowclamps™ are made from clear hard maple and shaped using CNC equipment to be certain that the arc is precise and consistent over its full length. The arc is different and specifically designed for each of the three sizes available, 2ft, 3 ft and 4ft.
All Bowclamps™ are 1-3/4"-wide which gives them a wide footprint that resists crushing or marking the wood like the smaller jaw surfaces on conventional clamps might. The straight surface of the Bowclamps™ have a 1-1/8"-wide T-shaped groove (the smaller portion of the groove is 9/16"-wide) running its full length. That groove is designed to accept both ends of some F-style clamps. The T-slot also helps retain the clamps while you position the wood, in many cases making the process much easier than with other clamp styles. K-body parallel jaw clamps can also be used on the bottom surface of the Bowclamps™ though using a flat piece of scrap wood between the clamp and Bowclamp™ is advised.
Each Bowclamp™ has a hole drilled in one end that comes with a leather lace installed for hanging-type storage. The Bowclamp™ literature touts this as a "space saving" feature and while that might be pushing it a bit, the leather lace does give you lots of options for hanging these tools in shops that are always light on storage space.
In the Shop
After using the Bowclamps™ for a few days in my shop I can say that they do what they advertise. Though I fully expected at least one of the Bowclamps™ to blow up during the clamping process, they did not. It is odd though watching the bowed side become flat and the flat side become bowed but they do.
As far as I can tell the pressure is very evenly distributed over their full width. I tried several glue ups and was careful to apply glue evenly on the wood. In all cases the squeeze out was always uniform over the length of the joint. I suppose we could try it with a bunch of high-buck pressure sensors to confirm this but I don't have that kind of budget and doubt it would show anything different anyway.
The only issues I had was when I discovered that the heavy-duty F-style clamps from Bessey and JET are too big for the T-slot in the Bowclamps™. However, the regular-duty (cheaper) versions seemed to fit fine and with so many people buying on price first, this should present no big problem. Even if you do have to spring for a couple clamps, it is just a couple because you do not need clamps in the middle of the Bowclamps™.
The Bowclamps™ represent a nifty idea that applies to most hobbyist woodworking shops. Being able to apply uniform pressure over the length of many common project types with only two clamps certainly could be a money saver. Prices range from (2-24-2010) $44.95 (pair) for the 2ft models, $64.99 (pair) for the 3ft Bowclamps™ and $84.99 (pair) for the 4ft versions (single Bowclamps™ are also available) and $179.99 for their Master Set that includes a pair of the 2ft, 3ft and 4ft Bowclamps™. Those price tags mean spending the time to try and make a perfect arc (several times no less) in your shop is not looking as smart as it once sounded.
If you are looking for a way to reduce the number of clamps needed in your shop or just need this kind of reach, the Bowclamps™ should get a hard look.
See the Bowclamp™ site for more info or to order your Bowclamps™. - Click Here
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