Linear Mag. Brake + encoder stylus ?

[jethro]

Hello all, I am looking to build an analog wood duplicator. It will be a 2 axis
track and for z it will have an analog feedback/servo between the pickup
stylus and the cutter. I am want to make x axis make passes the long way
and Y advance it over 1 bit width at the end of each path. I want to put
an electric activated device on the y axit so I can "Lock" it down to the track
while X is moving. I was immagining some type of magnetic brake which might
grab a steel bar paralell to the track. Something like a smaller version of an
electromagnetic milling machine chuck. Does anyone make something like this
or have yall canabalised something for this purpose ?
Also I will have (proposed anyway) a verticle moving stylus to encode the
height of the model to be duplicated. The flaw is that my model will have
some 90 degree steps (about 1/4 inch tall) that I can't see how the stylus
could get over without hanging. Is there a better way to encode the height
than a linear bearinged stylus moving onyl in Z axis ? Seens like there must
be other ways? ( my feedback circuit would have a resistance pot on the
encoder and another on the cutter with a difference amp set to drive the
cutter to keep the difference to be zero - - and I would be driving the cutter
in X axix at a constant but very slow speed (1 mm/ 5 sec perhaps) )

Any thoughts ???????
Tim