Thursday, July 10, 2008
Bench #3 -- The Tail Vise
To install the tail vise I first have to fit the front laminate to the end cap by means of a double dovetail. Dovetailing the end of an 8' long, 1-1/2" thick Ash board is not my cup of tea. It's not like I can clamp in a vise and start sawing vertically. So after careful layout with a knife I got close with a jigsaw (yes, a regular old hand-held jigsaw, but a good quality Bosch saw with a nice blade) then pared to the layout lines. If anyone knows a better way to do this, I'm all ears. The tails did turn out pretty good, all things considered. I've never been much of a dovetailer.
I mark out the half-blind pins on the end cap with my Czech Edge marking knife.
I got rid of most the waste with a router. Gee, I won't be able to do this with the new bench's tail vise. That's why I'm keeping bench #2!
I pared to the scribe lines.
They fit, and they are solid. I had to glue in a couple cosmetic "shims" here and there. Good 'enuf for this bench.
I drilled through the end cap for the screw and bolts.
The tail vise hardware. In this entry I posted drawings from Landis' book for David Powell's tail vise design. A fellow woodworker got me in touch with a retired machinist who has a complete machine shop in his garage. He was able to manufacture the parts to my specifications for the vise. The screw and nut I purchased from Woodcraft. The guide rails, plate and angle I had fabricated. As I mentioned in the previous entry, I did away with Powell's crossbar. It's not necessary.
The guide railes are mortised into the underside of the bench. I scribed lines for the mortises.
I cut the mortises with a router equipped with a guide fence.
In this vise, the screw remains stationary as the nut traverses the screw. Contrary to a typical tail vise arrangement where the clamping force is applied against the screw's attachment flange, in Powell's arrangement the clamping force wants to push the screw out of the end cap rather than pulling it in towards the bench (the vise is tightened by turning the screw counterclockwise). Landis doesn't mention this in his book, so judging by the small screws holding the screw flange to the end cap in Landis' drawing, I believe this may have been an overlooked element in Landis' analysis of this vise. In order to counteract these forces, I completely eliminated the screwed flange and decided it would be prudent to bolt the flange to the end cap. This way the clamping forces would be working against the threads of the two 5/16" bolts, instead of the rather weak holding properties of a typical wood screw.
The 5/16" nuts on the inside of the end cap.
The dog block mounts to the angle component of the tail vise. It's rabbeted to cover as much of the iron as possible without interfering with the capacity of the vise.
There is a square hole milled into the angle and plate to allow the dog to pass through.
The view from the top of the bench. This is the slot where the dog block goes. To the right is the first dog hole in the bench top.
The dog block in position, bottom view.
The dog block in place, top view.
The screw alongside the dog block, top view. As the screw turns, the block advances or retracts.
The complete vise from the bottom.
A short video of the tail vise's action.