The escapement is the part of a mechanical clock that keeps the pendulum swinging despite friction losses by imparting it with the potential energy of a weight, or spring, while transforming the regular swings of the pendulum into regular increments of rotation of the escapement wheel, which can then drive a gear train to show seconds, minutes, hours, etc...
A Graham escapement is also known as a dead-beat escapement because it does not force the wheel to move anti-clockwise during the parts of the cycle when no impulse is being given to the pendulum, i.e. it produces no recoil.
This Openscad design should allow you to create a variety of Graham escapements, with different numbers of teeth for the wheel, different escapement gaps, etc... It is fully parameterized and commented.
I created it as an exercise in understanding escapements, and Openscad, and plan to eventually build up to a full clock. I'm amazed by how far, how fast I got with Openscad, BTW, it rocks! :-)
I tried to comment as much as possible in the Openscad design, and used a lot of parameters, so read up a little on escapements, and play around with the file.
The values I used give a pretty standard 30-tooth/7.5 tooth gap escapement which would give sixty ticks per revolution and work well with a pendulum with a 2 second period.
This is more of a proof of concept / engineering doodle and I would not expect it to work as is... besides having to add the pendulum, this is an ideal Graham escapement and some drop and some lock would need to be added to both the entry and exit impulse faces. :-)
(EDIT: I designed a little test jig powered by a rubber band for this thing, here: http://www.thingiverse.com/thing:7801 )