Why do vice jaws need to be so thick?

[John Ziebron]

I am in the beginning stages of building my first real woodworking bench. The base is done and I'm starting on the top which is going to be 2 inch wide hard maple pieces, 2 1/4 inches thick. My front vice (already have the hardware) is a standard single screw, twin dowel quick release type. I do have a copy of the workbench book and have read many articles on building these benches. They all seem to make the movable jaw of the front vice very thick, like 3 inches or so. This is not an issue for me, but really a curiosity question. If one were using a hard wood, like hard maple in my case, wouldn't 1 1/2 or 2 inches thick for the jaw be sufficient?

[Jim Koepke]

The vise jaw needs to be stronger than what it will be holding. If you will be using the vise to hold wood while you are sawing, planing or just about any other method of working wood, the jaw has to be strong to be effective.

If the vise's jaw will be holding something on just one side it may be helpful to have an anti-racking device:

http://www.sawmillcreek.org/showthread.php?183743-Anti-Rack-Spacer-Stack

Different vises may need different spacer shapes and dimensions.

jtk

[Stanley Covington]

The thicker the jaw, the stronger and stiffer it will be, and the more resistant to flexing and cracking. Mine is 7" thick, and the extra width comes in handy in more ways than just strength.

Stan

[Rich Riddle]

Wood flexes more than you think, even a 1" or 1.5" piece of Maple. Watch a maple tree in the winds and how easily it flexes. This is a case where bigger is better.

[Simon MacGowen]

If one were using a hard wood, like hard maple in my case, wouldn't 1 1/2 or 2 inches thick for the jaw be sufficient?

It is a trade-off between rigidity of the jaw and the max. opening. I've seen thick jaws like 5" and if I used that in my vise, the max opening would be cut to 8" or less instead of 11" that I am getting, which I can use to hold small drawers. With hard maple, a 2" to 2-1/2" thick jaw is more than enough for a single screw QR vise.

Vise racking is a different story and I would not put in a 4" thick jaw to deal with that problem as there are many other good solutions to handle vise racking.

Simon

[Rob Luter]

The soft maple chop on my twin screw is pretty thick. About 4 1/4" as I recall. It opens up about 12". There is no perceptible flex when clamping something up tight. The chop is lined with adhesive backed sheet cork. The apron is plain soft maple.

https://c1.staticflickr.com/3/2674/4104026708_bf9aa479f9_b.jpg

[Jim Koepke]

The soft maple chop on my twin screw is pretty thick. About 4 1/4" as I recall. It opens up about 12". There is no perceptible flex when clamping something up tight. The chop is lined with adhesive backed sheet cork. The apron is plain soft maple.


What is involved with keeping such a large vise jaw from saging?

jtk

[Pat Barry]

... Mine is 7" thick, and the extra width comes in handy in more ways than just strength.Stan
Wow, now that's a vise!

[Rob Luter]

What is involved with keeping such a large vise jaw from saging?

jtk

Keeping it closed when not in use. When closed there's really not much cantilevered load. It's over eight years old and doesn't sag a bit. I hit the screws with a little lithium grease every couple years and that keeps things working smooth.

[Frank Drew]

Vise jaws don't need to be so thick; on my Scandinavian style bench with a front shoulder vise the moving portion of the vise is maybe 1-1/4" thick and it has never once noticeably flexed under load, let alone split or broke. More important than thickness, IMO, is lining the vise faces with something grippy, like rough-out leather which can significantly lessen the clamping pressure needed to securely hold your work.

[John Ziebron]

Thank you all for the advice and experienced comments. I probably should have mentioned that I plan on making my vice jaw about 15 inches wide. That said, I can certainly understand that the thickness of the jaw has some correlation to it's width, i.e. a wider jaw would have more of a tendency to bow than a narrower one of the same thickness.

I do like Frank's idea about using something like leather to increase friction. Would the leather be glued on? And, I assume, on both faces.

[Phil Mueller]

John, check out the recent thread "leather on vise jaws" (started by Trevor Goodwin 8/28)...a number of good opinions offered.

[Stewie Simpson]

With such a long wooden vice jaw, the design of the twin screw vice makes it impractical to plane edge grain.

[Stewie Simpson]

If your wanting a sensible approach to work bench design, this is a far better option.

https://www.youtube.com/watch?v=yvhn-PAfEW4

[Rob Luter]

With such a long wooden vice jaw, the design of the twin screw vice makes it impractical to plane edge grain.

I don't seem to have any problems with that.

[Frank Drew]

I do like Frank's idea about using something like leather to increase friction. Would the leather be glued on? And, I assume, on both faces.

John, yes, line both faces of your vise. The lining can both cushion your work and add some friction to the vise's pressure. Some like to use cork pads, others try rubber sheets, some of us like leather --I tried both smooth side out and rough side out and much prefer the latter, for the increased grip. I applied it with a spray adhesive (3M 77, maybe?)

An important point to remember is that no matter how big and strong you make your vise, the interface with your work should be softer than the workpiece; if you crank the bejesus out of your unlined hard maple vise jaws onto, say, a mahogany table leg, you stand a good chance of denting the mahogany.