My US Burke Millrite model MVI vertical mill (resembles a Bridgeport,
but 2/3 the size) came with a X-Axis power feed, an Asong AS-250. This
unit never really worked correctly, and kept on blowing speed control
pots out, as discussed in the thread "Repair of an Asong AS-250 X-axis
power feed" in January 2010. This is a general problem with Asong.

I eventually replaced the original tenth-watt carbon-film pots with a
five-watt wirewound pot, which worked for a while, and then it too blew
out. At which point I gave up: if a wirewound pot won't work, what
will?

The circuit diagram that comes with the unit is an artists impression,
and is neither a correct circuit diagram nor matches what I have in the
slightest, so fixing the circuitry was likely to be a chore.

So, after some research, I bought a Servo "Dymano" model D-1000X-0200
unit. Servo is the traditional US maker of power feeds, and Dymano is
their Taiwan-made answer to Asong et al.

The bolt patterns didn't quite match, so I made a new adapter plate to
go between the cast-iron right-hand end bracket on the mill and the
power drive unit.

The leadscrew is too short, and so I reused the extension shaft from the
original Asong installation, and machined the brass hub (with helical
gear track that engages the drive pinion) to accept the large end of the
extension. The large end is a sleeve, and is pinned to the original
leadscrew with a bit of 0.125" brass rod that is trapped by the hub.

The hub also had to be machined to fit properly into the engraved drum
scale, so the scale graduations would be close to the indicator line.

All machining of the hub was carried out on a lathe, and a lathe is
essential. (If there is a Dymano kit that's better for mounting on a
MVI, I didn't find it, but this was all sight unseen.)

Anyway, it all works, although some spacer shims will be added to set
gear clearances et al.

What is not mounted is the switch that stops motion if the table moves
too far in either direction. The switch is designed to fit on a
Bridgeport, and is far too large for the MVI, and wrongly-shaped to
boot. The Asong switch had the same problem, and was never mounted
either. The theory is that the 0.125" brass pin will shear and save the
day. I will eventually make a custom switch for the MVI.

Joe Gwinn