Friday, August 27, 2010

Perfecting the Twin Screw Vise

About a month ago I put up a couple posts here on my building of a detachable twin screw vise based on Chris Schwarz's take off on the vise pictured in 17th century period woodworking books. To read up on the back ground and the previous parts of the build you can go to this link HERE.

Here's a pic of what I had called a job well done.

It works great, holds work tight and solidly connected to the workbench thanks to a pair of "F" clamps. Well I guess I had a problem with using the "F" clamps. Don't get me wrong, the work and work well, but they are like two spikes sticking up on either side of the vise, Their silvery bars hanging out in my peripheral sight and leering over my shoulder while I work, like they're trying to steal my sawdust secrets. (OK maybe I have my paaroid moments)

No matter what it was I just wasn't a huge fan of the clamps. Chris mentioned in his blog about the work that he could use either the clamps or a pair of long hold fasts. I liked the idea of hold fasts but I didn't have any that were anywhere near the foot long behemoths they would have to be. First I looked for some bigger ones, but quickly gave up on that. I had to come up with a way to use the shorter hold fasts I own.

I thought if I could add or create a ledge on the backside of the vise that I could hold down from my front row of dog holes, then that might be the ticket. I then spent a few weeks thinking about the joinery, there would be a lot of natural rocking type stress put on the joint between the boards and I wasn't 100% sure how to handle those forces. The joint screamed for a dovetails but the grain of the two boards would be weaker with the bottom cuts running along the grain.

I decided that I should really just go for it and stop over thinking it, I could make decisions and fix things on the fly or I could hold off and paralytically contemplate the issue forever. Action is always better. So I found a nice red oak 1x4 (I built the rest of the vise from hickory but I had run out) to serve for the ledge board and I started to cut the tails into the back board of the vise.
I then marked and cut the pins in the side grain of the red oak, I pared them to a good fit, (doing this is where I slipped with the chisel and the vise and I became blood brothers from here on out, you can read about that experience HERE)

Now here's the problem, I usually only dry fit my dovetail joints about halfway because I don't want to leaver them too much during the process, If the first half fits well then I can usually get the joint all the way together for glue up. The side grain is a different animal and I guess I knew that but routines are what they are sometimes. during glue up the joints wedged at halfway and wouldn't go farther. . . I decided to go for broke and go caveman. Mallet in hand I banged on the oak, trying to merge it with the hickory, and the oak split, right at the bottom of the pin cuts.

In retrospect, I wasn't really surprised and I'm glad it happened at glue up and not a week into using the vise. It gave me a chance to sit back and think about how I could fix my side to side grain problem.

The answer I decided on was to take what was to take what remained of the 1x4 and cut it into sections 3 1/2" long. Then I could turn the pieces and edge glue them back together. There was nothing I could do about the side grain of the vise, but this gave me the same size, and length board but with grain running the better way for dovetails. It was a funny glue up though, it took some weight to keep the pieces from bowing under the clamp pressure.
That glue up done I recut the pins in to the new board, pared and shaped them, and went into glue up mode again, (This time without the obligatory trauma, to my fingers or the 1x4)
A little plane work to clean up the joint and I had just what I had pictured. But now would it work?
I put the vise together and set it in place with the hold fasts . . . moment of truth time and I found I could move the weight of the whole bench around using the vise as the handle. Now if that's not solid enough for dovetailing and other cutting then I give up. This was every bit as strong as the "F" clamps solution, a little more elegant, (imho) and a little more versatile for use on different benches like my joinery bench which has a front apron on it that would require me to go bar clamp at least to hold the vise otherwise.
Finally I was done with the vise and happy with the design and the function. I sealed her up with a couple quick coats of Danish Oil. Let that dry and rubbed some wax into the threads of the wooden screws.
Then I took it for another test drive. Just some sloppy dovetails cut freehand to give it a go. I have always wanted on of these vises but I could never abide by the space it would have taken up on the bench. I always thought they looked kind of . . . in the way I guess. Now this one is there when I want it and out of the way when I don't. Once again I want to thank Chris Schwarz for bringing this idea out and into the light.
I start the next project for the shop today, a saw till, and I'm setting a challenge for myself to see if I can build it in one day. You gotta keep challenging yourself, or everything starts to look the same, like you're headed down a strange tunnel. . . .
Cheers

Oldwolf

4 comments:

  1. I would put triangle bracket braces between the clamping shelf and the back vise jaw. Maybe one on each end and one in the middle. It might be fine with just the joined edge but I am kind of a belt and suspenders kind of guy myself.

    I would also drill a hole in the screw knob so you could possibly put a bar in for tightening. You have the hand strength to clamp it in hard enough but those little shop helpers won't be able to.

    ReplyDelete
  2. Why not a simple glue joint? It's long grain to long grain, similar to gluing up a panel.

    ReplyDelete
  3. BTW, I forgot to say -- It looks great.

    I like the idea of the clamping edge on the back instead of holdfasts on top. Having all that clear real estate on top is a real asset.

    Have you tried edge planing on it as well? Do the holdfasts get enough grip horizontally? How far out of square can you set the jaws for irregular pieces? Do you think that it will be better to fit into dog holes? Maybe tapped holes in the bench top?

    I can see a bunch of other possible uses for it. I keep trying to think how it could be fitted to the saw benches as well.

    ReplyDelete
  4. I guess I have had simple glue joints fail in the past, poor technique on my part, ya probably, I felt like the intermingling of the woods through the dovtails would be the strongest construct I could manufacture, besides I just really, really enjoy cutting dovetails.

    Thanks for the ideas David, I have been thinking about adding a cross bar to the handle, but making it easier for my daughters is the best reason I can think of. I drilled the holes to a pretty tight tolerance so I can get maybe 2 inches of deflection, I could loosen it more if and when I need to. No garters so it's slightly sloppy.

    I haven't planed with it yet, probably a little high but for smoothing work, ya that could work, but fitting it to the saw benches, now that's something I hadn't thought of at all. that could be cool for the right reasons. . .

    I love how you always come out with some extra takes or ideas. Love the help my friend, Thanks

    Oldwolf

    ReplyDelete