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charlieb charlieb is offline
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Default Need Leigh FMT Jig User To Review of Procedure

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