Ulma Doctor

Infinitely Curious
Feb 2, 2013
I did a VFD and 3 phase 3 hp motor upgrade to my Shenwai 900B lathe, because i had a problem with the anemic single phase 1 hp single phase motor the lathe came with.
the issue was really evident when parting stainless. so much as to make me want to do the upgrade.
i wanted to use the original apron switch to operate the start and stop functions
i also set out to do it as inexpensively as possible as an added challenge ;)
i chose the Huanyang 2.2KW inverter, $150

VFD 2.jpg

i chose a used salvage/surplus 3hp, 3 phase Dayton 56HZ frame 230/460 dual voltage 1740 rpm motor for the powerplant- i replaced the bearings in the motor with SKF bearings $80 total cost ($40 per bearing)

VFD 3.jpg

the problem was that the original motor was a metric frame motor with a 19mm shaft
the motor i intended to use had a 7/8" shaft.
56 frame motors usually have a 5/8" shaft.
the best recourse i could imagine was to bore and broach the pulley to fit the upgrade motor.

VFD 7.jpg

luckily i had a second lathe, a Hercus ARH 9" lathe to help out during the process.

i needed to bore the pulley but didnt want much deflection in a boring bar.
the stiffest bar i had was for a larger lathe, but i made some modifications to get over that hurdle...
i had to turn down a larger lantern toolpost to install into the Hercus compound rest
VFD 19.jpg

after that i could use the larger boring rig
vfd boring bar.jpg

VFD 8.jpg
VFD 9.jpg

i drilled to 25/32", then bored the pulley to 13/16" and used a .7845" straight chucking reamer under backgear power to ream the bore to finished size

VFD 11.jpg

VFD 13.jpg

i held the 5/8" reamer shank in an indispensable, antique, Double Grip drill chuck in the tailstock

VFD 12.jpg
live action shot of the reaming operation,
VFD 15.jpg

here is the finished bore
VFD 16.jpg
next is the broaching of the 3/16" keyway, and a test fit
VFD Pulley Broaching 1.jpg
VFD 17.jpg
i installed the key and locked down the transverse lock screw too
VFD Pulley Broaching 2.jpg
VFD 18.jpg

i then installed the motor into its nook
VFD 21.jpg
VFD 20.jpg

i replaced the belt with a B32 drive belt after the conversion, the belts were in poor shape.
i also added a salvage disconnect

VFD 4.jpg
VFD 6.jpg
i wired the disconnect to the VFD, and from the VFD to the motor, then the VFD to the Apron Control Circuit

the project worked out like this...
150 inverter
80 bearings
10 miscellaneous hardware
85 miscellaneous electrical cord, connections and twist lock plug
20 belts
total estimated cost $350

i set the vfd up and wired it in and changed the VFD operational parameters to suit my needs.
i was able to wire in the original apron switch to operate the VFD's directional control.
i chose to use the operator potentiometer to set and adjust the frequency
i'm operating in the 0- 70 Hz frequency range and will use the pulleys to manually change between speeds outside that envelope.

for those interested, i made a video of the set up as well as my parameter selection for my motor.

if you have nothing better to do for the next 9:44, have a look :)

also for the interested is the parameters i set for the 3hp, 3 phase, 1740 rpm motor, as follows
PD005=70 (you can safely set up to 90)
PD008=240V (set you inverter to your tested supply voltage reading)

DCM is the supply voltage for the inverters multi input
i used the DCM power through my original apron switches to operate the VFD
the forward apron switch was connected to the FWD terminal of the inverter
the reverse apron switch was connected to the REV terminal of the inverter
vfd big.jpg
as always thanks for looking, reading, and watching!
Last edited:


May 14, 2021
Nice I'm in the process of fitting one to. Just started out today to figuring out where to put the tachometer. Didn't find any place inside so I think I'll do it like this. It's on the inside of the chuck and I'll fit the magnet in one of the chuck bolts on the backside. Don't have any other chuck so that's no problem...
Where did you put your? inbound3161004496958696470.jpg


H-M Supporter - Gold Member
H-M Supporter Gold Member
Jan 2, 2019
I have my VFD setup but haven’t installed the tachometer yet. The only thing I don’t like about the above setup is a rotating tab like just seems like it would b a hazard. Much better to get it onto the other end of the spindle if possible.



H-M Supporter - Silver Member
H-M Supporter - Silver Member
Nov 25, 2015
that Hercus looks like a SB clone or wanna be.
Damn you didn't clean that motor up before mounting it... it's in need of a bath :)

nice, haven't watched the vid yet, you going to put a rotary switch for speed? maybe I should watch the vid. but watching the tampa bay, philly game.


May 14, 2021
Yeah my plan was to fit it inside but there just weren't any room. I'll take a look at the rear. But at least this won't let go. Welded some stainless and gonna get a magnet with a hole that I can bolt in.


May 14, 2021
20220117_202451.jpg So I did a flat spot at the rear end instead and mounted it there. The hole magnet didn't fit but I think it will work. Nice not to have anything in the front
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