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Cross Slide Vise for Benchtop Mortiser

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Bench top Mortiser Cross-Slide Vise

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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 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.
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Cross slide vise for mortiser

Thanks for the kind words. The mortiser table is working great for me. Ploughing out the mortises is soooo much easier.

As for the squaring of the vise to the chisel, I made sure that when I cut the stock, that everything was exactly square and similar components were cut on the table saw at the same time. After assembly, I double checked the flatness and parallel of the vise table and the mortiser head mount platform and both were dead-on. And finally when the vise and mortiser head were assembled, I put a 1/2" chisel in the chuck, clamped a flat piece of maple in the vise and used my machinist square to check for squareness. Everything was perfect.
Of course you can always shim the mortise head or probably the vise, if it isn't right, but with careful cuts of the table pieces, including the dadoes, you shouldn't have any issues.
Post some pics when you get yours done. It's great to see everyone's designs and modifications.

Well, after looking at my Jet, it should be a cinch to build a table for it, as you did.

My only other question has to deal with squaring the vise in the vertical and horizontal to the bit.

Is yours adjustable or not?

If not, did you just shim it or was your table perfect and did not require any further adjustment?:D

If is is adjustable, how did you accomplish this?

Oh, by the way, I just ordered the vise from Amazon.

I am giving my wife your email address!:haha:
Cross slide vise for mortiser

I cut them on the table saw and finished the inside corner on the band saw. I think this is the best way to keep the two table surfaces parallel to eachother. I tuned my TS fence and TS miter gauge just before making the cuts, to be sure.

Thanks for the feedback.

One last question. Cutting the L shaped boards seem to be the most critical.
Did you cut them on the table saw and finish them on the bandsaw or did you do them entirely on the band saw?

I am talking about the top edges. I assume the bottom and back edges were done on the table saw.
Cross slide vise

You're on your way to easier mortises! Definitely post pics when you get the base done and all assembled.

The photo of the Grizzly vise is taken after the vise has been turned one eighty and the rod rethreaded. Just need to get a drill bit and a tap.

The other photos are of the Jet Mortiser already disassembled. Took some measurements of the Jet positioned in reference to the vise. Should be able to do some fairly wide boards.

Hope to have it up and running by the weekend. It is supposed to get cooler!!!
Cross Slide Vise for Mortiser

Looks good so far.
A couple of suggestions you might want to consider:
1. Swap the X-axis screw to the left side of the vise, if you have your mortiser plunge handle on the right side. This way you can move the workpiece in the vise and keep your right hand on the mortiser plunge handle. For me, it makes for quicker and more efficient work.
2. Can't tell from the photos, but you should have the mortiser column bolt through the supports and not just to the riser table top. My concern would be that the weight of the mortiser and the torque when mortising might pull the mounts or even the riser table out of square. You can always through bolt all the way to the base plate of the riser table with long hex bolts and T-nuts counterbored into the base plate.
3. I offset the vise relative to the centerline of the mortiser chisel, so that the X-axis movement travels less than an inch to the left and the majority of the travel is to the right. Since I start my mortises from one side (in this case being the left), I have maximum travel going to the right for larger mortises. At the end, I just reset the travel to the left and start again on th next mortise.
4. I did the same for the Y-axis travel, screwing the vise inwards until it was almost extended, and measured down from the chisel. This way, if I have thick mortises, I can just back the Y-axis screw outwards for the next row of mortising cuts.

Can't wait to see it all mounted and finished. Let us know how you like it after your first mortises.

Well, I am not finished but I got most of the MDF cut to size. I mocked up the design so you could see my changes.

I doubled up the MDF like Michael did but I just made three supports. I made the first one sit right down the center line (probably the best place for maximum support for the vise and the mortiser). The outside supports were positioned to clear the x axis vise handle on the right and 1/2" of support on the left. The

I did not cut the bottom yet since it will be oversized for clamping to a mobile tool station. It will be daddoed like the tops were.

Just need some clamps, glue, paint, and some hardware.
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Cross Slide Vise Mortiser Table


Great job! That's a nice looking mortiser table. I'm sure that you'll like it as much as I like mine. Shop life is just a little easier with it.
Let us know how you like using it and any ideas/modifications you find that might make it even better.
As I said in a previous post, I plan to add left/right side supports for larger workpieces. When I get something put together, I'll post some pics.
Once again, excellent work.
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