Cross Slide Vise for Benchtop Mortiser

Bench top Mortiser Cross-Slide Vise

Here is a new addition to my woodshop.
I’ve had the Powermatic bench top mortiser for a few years and have cut many a mortise on it. It’s a great tool, but I have been envious of the full-size mortisers with the sliding table. Even though my mortises are crisp with the machine, set-up, alignment, and moving the work piece to cut the mortises has been time consuming. Getting the perfect alignment has always taken too much time, especially when boring only a couple of mortises for a project.
I’ve been thinking of installing a cross-slide vise on the mortiser for a couple of years and finally got around to it. I found a great article on popularwoodworking.com with a great solution for adding the vise.
Popular Woodworking - 3-D Mortising Upgrade

The problem with using a cross-slide vise on bench top mortisers is that the clearance below the chisel is usually 4-5 inches and these vises can range from 5 to 7 inches tall. They also are configured to clamp the work piece perpendicular to the mortiser table.
The solution is two-step:
1. Either add riser blocks to the mortiser (if available) to gain proper clearance from the chisel, or build a riser table and mount the vise.
2. Modify the cross-slide vise to orient the clamp parallel to the table.
Both of these solutions are outlined in this article (see link above).

I started by modifying the vise (Grizzly G0164, 4” vise for $45.95) so that the clamp and Y-axis threaded rods are on the same side of the vise, pointing toward the operator. The article shows you how to do this, by removing the Y-axis rod and tapping new mounting plate holes on the opposite side. It took all of about 30 minutes to do this. I also removed the original screw handles for the X/Y-axis movement and replaced them with a couple of 5/16-18 star knobs I had sitting around. The threads on the vise handles is 8 mm, slightly larger than 5/16”. Since the knobs have a threaded brass insert, I just cross-threaded them on to the rod posts and the fit is tight.

To build the riser table, I used scraps of plywood and MDF for all the components. It’s a very simple table to build; a few dados and glue the whole thing together. I modified the construction from the article a little. For the interior supports to bolt the mortiser to the table, I doubled each support using two pieces of ¾” plywood. I dadoed out 11/32” wide by 11/64” deep channels in the four pieces (opposite sides of two pieces for each support), in-line with the mounting holes on the base of the mortiser column, glued two matching pieces together. This gave me through bolt holes in the supports to attach the mortiser to the riser table. You could used long hex cap bolts to through bolt all the way to the bottom of the table, but I used some 5/16-18 cross dowel nuts and 3-1/2” long socket head cap screws. I think that either of these modifications from the original article will give much better holding power when securing the heavy mortiser to the table. I wouldn’t trust four lag screws set into the edge of ¾” plywood to hold it in place.

After assembly, I rounded over the edges, a little sanding, and painted the table to match (close enough) the Powermatic mustard gold color. The whole system is bolted to my rolling stand.

I’ve already cut a few mortises with the new rig. It took me about a quarter of the time to mount the piece, square up the chisel, set the depth and plough out the mortise. And fine-tuning is miles ahead of the old table hold-downs, which required tapping and checking each piece. Now with a slight twist of the X/Y knobs, I can line up the mortise in a couple of seconds.

I think I’ll add some outfeed supports on the table for stabilizing larger pieces.

If you do a lot of mortising and only have a bench top mortiser, I’m sure you’ll find this upgrade well worth it. And even if it’s only a few mortises every now and then, this project is a great addition to your tool arsenal. The vise cost me $55 (including shipping) and the bolts and nuts $5. It’s a pretty cheap upgrade that has made my woodworking life a little bit easier.