From: clewis@ferret.ocunix.on.ca (Chris Lewis)
Newsgroups: rec.woodworking
Subject: Re: Morten Mortise and Tenon Jig
Date: 3 Sep 92 04:26:59 GMT
Distribution: na
Organization: Elegant Communications Inc., Ottawa, Canada

In article <1992Aug31.180100.2246@adobe.com> bennett@adobe.com writes:
>Nobody's yet described how the thing works, so here goes:

I have one of these too.

>Bascially, the jig consists of a right angle plate, a template plate, and a 
>5/16" diameter straight bit (1/4" shank) with a bearing above the cutting 
>edges.

The wooden fence and stop guide is included too.

>You clamp the workpiece to one face of the right angle plate (or to a 
>wood fence attached to the plate), 

It has to be attached to the wooden fence in order to get the mortice/tenon
centred on the edge (or end) of a 3/4" board.  You can adjust the joint
by using different thickness fences.  I made another fence to move the centre
of the mortice 1/8" farther back - ideal for the mortices on table legs
when you want the rails recessed a bit.

>positioning it such that the center of the 
>mortise of tenon is aligned with a scribe mark on the template plate. You 
>plunge the bit through the template into the work, with the bearing riding 
>against the template plate. Reportedly, this is somewhat tricky without a 
>plunge router.

Yes, the instructions do say that.  I've done a lot of joints, including
doubles and triples, with an ordinary router without any trouble.  My trick
was to place my elbows on the table supporting the jig (I usually clamp
it on the edge of my table saw) and carefully lower the router straight
down into the jig.

>For mortises, the template plate has a hole with rounded ends. For tenons, you 
>have to cut in two passes, cutting 1/2 the tenon and flipping the plate to cut 
>the other half. Since you can enter the tenon cut from the side of the piece in 
>most cases, it's less tricky than the mortise cut. Essentially, this is 
>template routing. 

Precisely.

>Nobody's really pointed out that the Morten jig only makes M&T joints of a 
>single size (I believe it's 3/8" wide by about an inch or so long). I suppose 
>you can vary the length of the tenon by not placing the workpiece up so close
>to the template plate.

You can make the tenons only slightly longer than 3/4" - the bearing will
run into the wood.  You can make them as short as you want by sawing them off.
But, directly, without a spacer, the shortest you can get is probably around
5/8, without running the risk of having the bearing go over the template
and grounding the blade into the template.

Yes, they're are 3/8" thick.

You can make them *wider* than the one inch or so, by sliding the template
along the wood, but there aren't stops or gauges to help you.  I did this
once.  Somewhat tricky, but it worked out well.

It's a wonderful tool for making face frames, screen doors, and the frames you
use in cabinetry or tables to support drawers.  It will do thru tenons (sort of)
in wood < 3/4".  You can make ganged joints for lumber thicker than 3/4",
but I haven't tried that yet.  But it's not a general purpose tool.  And you
can't make mortices in the middle of a piece of lumber.  It has to be on or
near the edge.

You can do joints amazingly fast.  With spring clamps holding things
together, I can do about 8 joints (8 tenons and 8 mortices) in about half
an hour without rushing.

>For the $45 it costs (mail order) you can buy the bit (< $20) and make your own 
>template plates to cut any size mortise/tenon you want, however, you will have 
>to do some fiddling with the template to get the tenons and mortises to match 
>so well (important if the joint is exposed).

The jig will make amazingly tight joints.  There are some minor problems with
sawdust jamming up against the template and throwing the cut off by enough
to make the joint too tight.  So I've gotten into the practise of running
the router around once, blowing the dust and running a flat screwdriver
around the template to scrape the dust off the template edges, then running
the router around again.

The bit that comes with it is a ordinary HSS bit.  Mine seems to have become
slightly smaller in diameter (through wear), so the joints are becoming too
tight.  So I will probably switch to a carbide bit (Lee Valley carries a
carbide replacement) soon.  Sharpening it is only going to make the problem
worse.

One further warning about the bit.  The real shank is much smaller than 1/4".
A split sleeve is slipped over the real shank to hold the bearing in place
against the cutters.  If the router collet isn't cranked down good and tight
the sleeve will start rotating on the real shank, and overheat everything
*very* fast.  And mak the depth of cut vary.  My bit is slightly burnt from
this.

>The Morten Jig would be more useful and a better value, IMHO, if PC made the 
>plate larger, with a number of differently sized joints on it.

My main beef is that there's no way to solidly mount the thing on the edge
of a table - I end up having the clamps hold both the wood to the
jig, and the jig to the table saw table.
-- 
Chris Lewis; clewis@ferret.ocunix.on.ca; Phone: Canada 613 832-0541
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