Charlieb,

You could just re-orient the part in the FMT or whatever tool to cut a
mirror mortise, but then you would be referencing the position of the
mortises from opposite sides of the part, which is a basic no-no of
woodworking. To get accuracy I always pick a face side and then mark one
edge and one end on that face side with chalk. The face side and the marked
edges are where I derive all measurements from to machine that part. Working
from opposite edges or opposite faces will induce board thickness and
measurement errors and result in a poorly machined part that will require
all kinds of sanding and manual fitting adjustments. This will be true no
matter what kind of tool that you use to machine your parts, even a table
saw. I prefer to make my parts without these accumulating errors so that my
joints fit with little or no sanding, and that's why I always mark and
reference from the face side only. Many steps can be eliminated if you don't
follow this rule, but quality will suffer.

--
Charley


"charlieb" wrote in message
...
Before I get to Charley's great response - note that in my earlier
attachment,
#8 has an error, The "back view" is wrong. The mortises should be
shown
at the front left corner of the part in that view.

Charley wrote:

snip

it isn't necessary to mark the placement of the second
mortice (on the bottom) if it is going to be placed in the center of the
part. The FMT has a guide that you can lock in place to position parts
at
the same XY location and the second mortice will come out in the correct
position without marking for it. If you wanted to place mortices off
center
or mirror imaged from each other on each end it's a bit more involved
but
you can avoid marking the follow on pieces if you use the FMT's top
table
positioning capability to locate each of the 2 mortices.

Ah - and there's "the rub" - the Devil in The Details. While
perfectly
centered mortises make using jigs a LOT easier, you don't need to
keep
track of parts orientation in the jig since things are symetric on
both X & Y, there are times when you need an "offset" mortise.
THAT's where things get a bit trickier - requiring that you mark the
mortise center on BOTH ends, another jig set up (which on the FMT
is quick and easy but you still have to do it) AND the need to pay
very close attention to parts orientation. I hate when I spend the
time to get the show face grain working together then blow an
orientation when doing the mortises on one part resulting in the
non show face showing. Despite the odds, when that happens,
the non show face has an ugly pitch pocket or the like right in
the middle of it

snip

Once the FMT has been set up it's easier to make mortices and then make
the
matching tenons to fit them than it is to make just mortices and then
make
floating tenons separately.

With traditional mortise and tenon joints, it's those damned tenons
that
complicate thing. You have to account for the length of the two
tenons.
And god forbid you don't cut all the tenons for all the parts that
are
supposed to be the same length BEFORE you change the depth of cut
on the router. I never seem to be able to reproduce a set up I
changed,
even 10 minutes ago.

The only time that I make floating tenon joints
now is when I want to make M&T joints at a significant angle to the
grain,
such as when joining 45 degree mitered pieces. Since the tenons made on
the
part would end up with significant cross grain and would not be very
strong
I would make mortices in each piece and then cut a floating tenon from
straight grained stock to go between them.

I found angle tenons a bit tricky when using the TREND M&T JIG. The
layout
requires more time since the center of the mortise at the top of the
tenon
is not centered on the part - the bottom, at the shoulders, is.

It's really quite simple but a bit difficult to describe. Watching their
Demo DVD explains everything.

Will request the DVD - thanks for the info.

charlie b