Terry wrote:
My 13" SB metal lathe has been retrofitted with a PM DC motor. It's
not a treadmill motor, it's continuous duty according to the tag and
can handle up to 180 V. I assembled a speed control from a
treadmill-type board. Unfortunately it doesn't appear that the
controller provides enough oomph.

What I'd like to try instead is a 120v 20amp variable transformer,
output to a bridge rectifier, then filter the DC and send it to the
motor. By happy coincidence I have all the parts, total cost will be
simply a bit of time.

The rectifier I have is a GBPC1210W; data sheet says 12 amp, 1000 v.
It is rectangular with a hole through the center. It looks like it
ought to be mounted to a heat sink, but the data sheet I saw doesn't
say anything about doing so.

The question is: should a bridge rectifier be heat-sunk (sinked?) in
such an application? If so, how big (roughly) should the heat sink
be? Would it be sufficient to bolt the rectifier to the 4" square
metal enclosure? Thanks for your input.

I don't know how much current you're dealing with, but figure about 1-2
volts drop across such a module X how many amps you're pulling = how many
watts it will dissipate.

since it's rated 12 amps, you're probably going to need larger than 4x4 of
heatsink to keep it happy.

quite honestly though, it's going to be easier to just mount the thing and
do the touch test than to try to calculate all sorts of stuff with
guestimated values.

If it gets too hot, use a larger heat sink. big deal.