August 27, 2011
"You can never have too many clamps" - so true. Often, we only need two or three at a time, but occasionally there is that big glue-up that requires at least four more than you have. Good news is that you can get some pretty decent clamps at a good price - great if you are buying one or two. Unfortunately, even reasonably priced clamps can still be a hefty financial burden, if you need a large number of them. For this reason, I decided to make some of my own.
I already have quite a few clamps: pipe clamps, c-clamps, spring clamps and six (at last count) bar clamps. Of these four types, the ones that get the most use are the bar clamps. Bar clamps are fast and don't give up much clamping pressure (in comparison to c-clamps) in exchange for their ease of adjustability.
So, when I decided to make clamps, I chose the use the bar clamp as the model.
My first version used a notched bar:
These work very well, as demonstrated in this video:
One thing that makes them less convenient to use is that there is a lot of space between the notches, making for a lot of cranking of the handle to close the jaws together. My reason for making the notches this far apart was to try and prevent this wood from breaking off under clamping pressure - by reducing the distance to half, I would be making the clamp more fragile.
Another 'problem' is that when clamping wide pieces, the bar would bend under the load. Of course all bar clamps bend while in use, but these can bend quite a significant amount, making it seem that they may break. The bar is made from maple, 1/2" thick and 1-1/2" wide - so not really undersized, but the notches effectively reduce this width by a full 1/4". Making the bar wider would help but also make the whole assembly more bulky and necessitate the use of stock that was not deemed as 'scraps'. Using up scraps counter balances the time spent building them, making for a really economical project.
So, I gave it some thought (well, a lot of thought actually) and came up with a better method, one that addresses both of the issues touched on above:
This one is basically the same as the first ones with one key difference: there is 1/4" threaded rod on the front of the bar. The threaded rod mates with another short piece of threaded rod that is glued into the moving jaw and locks the moving jaw in place. The threaded rod replaces the notches that were cut in the bar in the previous version, allowing for much finer adjustment before tightening.
Also, the threaded rod was pre-stressed (tightened, via the nut at the end of the bar) after it was put in. This pre-stress counters the compressive force of clamping, preventing the bar from bending back. Although I knew this would be somewhat effective, I was pleasantly surprised to see just how well it works - under quite a lot of clamping force, the bar deflection was minimal:
The piece of wood being clamped is 17" long, and I've put more force on it than I'd normally use during a glue up. There is so much force, the clamp is actually twisting slightly, as seen in the picture above.
This success more than makes up for the extra cost of the threaded rod. As for build complexity, this version and the earlier one are about the same.
Once it was complete, I did a video going over some of the details and showing it in action:
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