Sine plates are normally used with gage blocks or spacer blocks. They
would mostly be used with a surface grinder or for very light cuts on a
mill. Depending on the model, some are held down just by the weight of
the plate and the arced clamps while others also have clamps on the
pivots. see the url below for some more instructions.

http://www.auto-met.com/subtool/stcat/st_136.html

Jon Elson wrote:
wrote:

Just starting out, I have a sine plate with one end as a hinge. It has
a small locking bracket but it could not take any pressure, Is the
upper angle part supposed to go in the vise to hold it securley.

Generally you put a stack of spacer blocks under the upper round bar
to set the angle. Spacer blocks are lower-precision gauge blocks, often
with a threaded hole so they can be stacked up on a setscrew.

Jon