LittleRat Mortise Rail

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Mortise Rail

The Mortise Rail
A Mortise Rail (MR) is a term coined by WoodRat to describe a particular jig that can be used on either the LittleRat or WoodRat to hold stock. In many instances stock can be held to the Rat using the supplied clamp(s) attached to the sliding carriage but these only work best with vertical stock or pieces of certain limited dimensions. The mortise rail allows long horizontal stock to be attached to the carriage. This particular jig in concept is really nothing more than a platform that allows small shop clamps to be used in conjunction with the Rat.

Dimensions for a mortise rail jig are provided in the Rat manuals. That design is for a jig that can be clamped to the Rat using the standard clamps and then used as desired. There is a problem with the implementation of this. The main problem is that the Rat clamps are fairly weak by clamp standards and attaching a somewhat heavy jig to them leads to some problems keeping the jig properly in place relative to the cutter.

After a bit of thought I came up with a mortise rail design of my own. A few differences between this design and the one shown in the manuals are:

1. Doesn't use the Rat clamps to attach.

2. Is smaller in cross section to reduce weight, and provide as more area for the cutter.

3. Uses embedded T-track for the attachment of additional accessories.

While the original clamps supplied with the Rat do work, there is room for improvement in their operation. You may ask what does this have to do with the mortise rail - good question. After some careful thought I decided that I was going to replace the original clamps with something better and no longer needed the little saw-tooth device inside the sliding carriage - so I removed it. The groove in the sliding carriage is basically a giant T-slot; I am taking advantage of this T-slot to attach the mortise rail and in the future will do the same for any other jig developed for the Rat.  Removing the sawtooth device gave me the critical clearance I needed in the T-slot.

On the back of my rail is a long metal plate with three threaded holes. To attach the jig I simply slip it into the sliding carriage and tighten down the three -20 Phillips head bolts. This provides for quick, simple, and worry-free installation.

There are all sorts of good reasons for adding T-track to the mortise rail; it is cheap, easy, and provides all kind of operating flexibility, even things yet un-thought of.  If I were building this jig again I would use the Incra track with the scale exclusively.

The vertical tracks are used to attach other accessories or clamps. The track in the top of the jig can be used for similar things but would be used mostly for stops and indexers. Of note is that this particular track has built along side it a moveable tape measure. This allows for all sorts of position indicating possibilities.

This particular design would be useful enough if all one ever did was clamp work pieces to it as described in the Rat manuals. However, the embedded T-tracks open up a whole new arena of jigs.  The image below shows just a few of the jigs or attachments that could be used with the mortise rail, I tried to put as many on as possible for this photo.   Note that the router base has been removed for clarity.

Lots Of Jigs

This is a view showing the left end of the MR, the rail is made primarily of 1/2" plywood and a few scraps.  The rail is basically the same cross section as described in the manuals but a little thinner.  The vertical members are also wider to accommodate more surface for whatever may be affixed to the rail.

Having the top track extend beyond the jig is no accident, it allows attachments such as the stops to be installed and still allow the full face of the rail to be under the router base section.

Front Detail

Back Detail

This view is of the back or the MR, note the 1/8" thick hardboard used as a spacer to hold the MR away from the chassis.  The rig must be spaced away from the chassis otherwise when it is clamped down it would be immobile, this is because the sliding carriage is slightly below the plane of the chassis.

The whole rig is affixed to the Rat by using a large T-nut that runs in the slot of the sliding carriage.  Here I'm using 1/8" thick steel flat stock which I have cut to size and installed three 1/4-20 threaded inserts.

At right is a cross sectional view of the mortise rail; the section is taken at a point between the vertical track stations where one of the three attachment bolts are used.

It may not be intuitively obvious but this whole assembly needs to be aligned once installed.   The sliding carriage on the Rat has a little bit of slop in it that is magnified when you install (or clamp) things to it.  I've made provision to align out any induced angle by making a 10-32 threaded hole above and below each 1/4" bolt hole.   This allows any error in angle to be corrected using set screws (which push against the carriage); only one setscrew at each bolt location would be required.

Cross Section

My thanks to Incra for providing the T-track used in this project.

Drawings   Click the printer icon to download a set of dimensioned drawings for a jig made similar to the one shown above.

Mortise Rail Accessories

The following are a collection of accessories I have made to use with the LittleRat and the Mortise Rail shown in the article above.

Vise A holder for a small vise.  This allows the vse to be held either flat to the Mortise Rail or perpendicular to its face. 90 Clamp A small block attachment that allows stock to be clamped 90 degrees to the to the Mortise Rail.
Beam Clamp A long beam that can be used as a clamp for large stock. Other Clamps A view of a couple other clamps that can be used with the Mortise Rail.
Stops Two kinds of stops that can be used with the Mortise Rail. Cursor A removable cursor that allows the tape in the Incra track to be read.
Stock Lifts Two styles of lifts that allow stock to be held into position while it is being clamped. Indexer An X-axis indexing device that can be used with the Mortise Rail.