front vise advice needed

Re: front vise advice (long)

Wiley Horne--Glendora CA

>Hi Jerry,

I think you'll like the twin-screw. I have one for a front vise, and one for an end vise and am happy.

Now on the design, there's a problem with anchoring to a block which is attached to the underside. The problem you mentioned--clamping pressure at the top--will not be an issue, because you take out the slack by tapering the front jaw face. LV recommends 3/32" taper in their generalized design, but since you're going to have about 5" of clamping capacity above the screws, you might think about a full 1/8".

But here's the problem with anchoring to a block under the benchtop. If you clamp a board in the top 4" of the vise--which is a very typical thing when you're edge jointing a bunch of short pieces--then the vise action is trying with all its might to rip that block off the bottom of the benchtop. The entire clamping load, magnified by the lever arm of the jaw depth, is being absorbed by the connection under the benchtop. I expect it would fail, or get loose.

The LV design (see their instructions), involves lagging a rear jaw onto the bench front. In this design, the clamping load is being absorbed by the nut, which is let into the rear jaw, and is well buttressed. Now you may be thinking, 'yeah, but I want to clamp flush with the bench front, and not have a rear jaw standing off the bench front'. You can do that if you run a thick apron (2"+) along the front of the bench, with depth sufficient to satisfy the jaw requirements. In your case, the apron depth would need to be 8-1/8" to meet requirements (in the LV cross-section drawing, your A=4", B=1-1/2", C=2-5/8", add em up and it's 8-1/8").

I don't know if your design will accommodate this deep apron, so will not take it further here. But I made an 8" apron all across the front, and wrapped around one end of the bench, dovetailing it on itself at the corner. Am very happy with the setup.

But in any event, you will need a true rear jaw, with depth of 8-1/8" minimum. This jaw will either stand off the bench front for the width of the vise, or else you can turn it into a full apron.

Hope this helps. Wiley

Re: front vise advice (long)

jerry schram

>Wiley what you wrote about the blocking wanting to pull off makes perfect sense! I'm now thinking about cutting a notch for the screw and mounting the top 2 screws ( the nuts have a flange with 4 screw holes) in the back of the front 2 pieces, then there will be 5 3/4" of blocking to support the bottom of the nut.Thank you very much! Jerry