The Millrite gets a new X-Axis power feed

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
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[snip]
All true. The problem is the limited space, especially with the DRO scale. And limited time.
There is a 1/4" T-slot in the front of the table, and the moveable stops use this T-slot. The is a fixed stop in the center. I would replace this fixed stop with the switch housing. Within the housing would be a pair of microswitches. I just have not gotten around to designing and fabricating it.
Joe Gwinn
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In article

[snip]
Thanks.
I'd be interested in the HSM article as well.
The most time consuming part of the effort was precisely measuring the locations of the four large flat-head hex-socket machine screws that hold the adapter plate to the cast iron end bracket. I think the original was done by clamping plate to bracket and drilling through both, so the parts matched exactly, but were on no precise pattern. Anyway, I did measure them well enough, and the new plate screws to the bracket perfectly.
I reused a few parts from the Asong installation, but it would not have been that hard to make those parts, if they didn't come in the kit.
Actually, while I didn't do this, I should have called Servo and asked them which kits are best for mills not directly supported. I used their standard kit for such mills, but for instance the Asong came with a suitable extension shaft, while the Servo did not.
By the way, the MVI will work just fine with the right hand table bracket missing and the end of the leadscrew flopping in the breeze, so you would have no problem milling the key slots in the adapter using some small endmills. (X-axis motion is controlled by the left hand table bracket assembly.) The trick is black sulfur oil and blow the chips out of the slot from time to time, so chip re-cutting doesn't widen the slot.
Again, one can remove the entire X-axis leadscrew and use the same MVI to drill the 0.125" diameter cross-hole leadscrew and extension shaft together for the brass rod, using the Y-axis to position and center.
Joe Gwinn
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Joe Is your Millrite a beautiful RED machine? And if so I need some help. Thank you Nelson Collar nel2lar (AT) yahoo (DOT) com
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