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Dovetail Tales #2: The Left-handed Moxon or A Study in Bad Design Decisions

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Blog entry by GeBeWubya posted 09-13-2013 10:24 PM 1096 reads 0 times favorited 4 comments Add to Favorites Watch
« Part 1: A Bandsaw Jig For Pins and Tails Part 2 of Dovetail Tales series no next part

I saw a description of a double screw Moxon vise made from a pair of handscrew clamps in a recent issue of Popular Woodworking and thought it would be a useful addition to my shop. I had some seldom used handscrew clamps and a 4’ Oak 3/4” x 5 1/2”, so off I went.

My first bad decision came when I considered how to remove one of the handscrews from the clamps. The clamps are designed so that the handles on the screws stop the opening of the clamp before the screws come out of either jaw. I decided the easiest way was to hacksaw one of the screws between the jaws. A better choice would have been to drill out the rivets that held the handles on the screws.

The next bad decision was which screw to cut. In case you’ve never looked closely at a handscrew clamp, each screw has left handed threads on one end of each of the screws and right handed threads on the other end. On all the clamps I’ve examined, the threads on one (the outer screw) meet half way between the jaws, and on the other (the inner screw) there is a 3/4” unthreaded gap between the left and right handed threads. That gap just looked like such a nice place to cut, and removing the inner screws would leave a wider opening between the remaining screws, so I cut the inner screws. The consequences of that decision didn’t become clear until I finished assembling the vise.

With one screw gone, the clamp could be disassembled. After marking and drilling holes in the pair of 2’ oak pieces I got from the 4’ board, I glued the jaws of the clamps onto the oak vise chops. That was the third and fourth bad decisions. I should have countersunk screws to attach the chops to the clamp jaws, and I should have used thicker stock, at least 5/4.

I attached a scrap of 1 X 4 to the back chop to clamp the vice to the bench. When everything was assembled and clamped to the bench, I realized that the screws I had left were left-handed. The loosen clockwise and tighten counterclockwise! Moreover, the handles and screws do not move toward the workbench when the chops close, but actually extend an additional half the distance between the chops. Clamping a board in the vise to plane the edge, I have to dodge around the screws to move past the vise.

The finished vise does grip boards up to 18” wide for dovetailing well and has a full 7” travel, but it would have been in the projects section instead of hidden here in the blog if I’d thought through the design and execution better.

-- (- |: \,/



4 comments so far

View Tim's profile

Tim

1394 posts in 715 days


#1 posted 09-14-2013 12:34 AM

Thanks for sharing. Everybody makes mistakes, but it helps if we can learn from someone else’s instead of making them too. You can still laminate some more boards onto the inside of your vice faces to get the extra thickness you’re looking for. Good news is you already have the clamp. And hey at least it works, it wasn’t a total loss.

View GeBeWubya's profile

GeBeWubya

47 posts in 789 days


#2 posted 09-14-2013 03:08 AM

Tim, Thanks. I don’t mind sharing my mistakes to try to help others avoid repeating them.

I think I may laminate a soft wood piece inside and claim the oak is for strength and the pine is to protect the workpiece.

-- (- |: \,/

View stefang's profile

stefang

13633 posts in 2088 days


#3 posted 09-14-2013 08:19 AM

Tims idea is good. You could also probably make inner jaws with just long slots to slide over the screws instead of laminating them. That way you could also have inner jaws of varying thickness if you wanted. Just a thought.

-- Mike, an American living in Norway.

View Tim's profile

Tim

1394 posts in 715 days


#4 posted 09-14-2013 05:38 PM

That would work too, Mike. I was just thinking laminating because it adds a lot of strength. A laminated board of a given thickness is generally stronger than an unlaminated one with the fibers going in slightly different directions, different weak points and whatnot.

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