Alternate title is "What to do when the tiny mini lathe motor burns out".
That is what happened while turning a rather large (2.5" diameter) part for my Grinding Fixture.
Selection of the motor and VFD was easy. Checked eBay but I found a very good pair at Amazon.
Shipping was free ( I have prime) so my total cost was about $300 for motor and VFD.
Price of the tiny replacement motor from LMS was $350.00....Really? for a 500 watt motor? Oh Well.
The controller was another $273.00 and that is just the circuit board without any controls.
I wanted to replace that motor last year but never got around to it. So I took some measurements,
pulled some bearings out of my stock (15mm inner diameter) and thought about it for a minute or two.
What I needed was a jack shaft. Used a piece of 3/4 inch drill rod. Turned both ends to fit the 15mm id
of the bearings. The main drive pulley for the mini lathe had a 15mm shaft so all that was necessary on that end
was a 15mm section with flats to match the pulley. (two types of pulleys are available from LMS for the Mini Lathe).
Other end has a 16mm section for the driven 48 tooth pulley and a 15mm section for the bearing. Flats as required for
the pulleys. The new motor pulley was to be 24 teeth but the hub was so small that it could not be bored to 5/8"
for the 1HP 3 Phase motor so I ordered another one with 28 teeth and bored it to fit the 5/8 motor shaft.
The jack shaft was mounted using the original motor mount and adding two 1/2" aluminum plates to house the bearings.
Bearings are a -.001 fit and pressed in easily after freezing the bearings in the fridge. New holes were drilled in the lathe bed
for the new bearing mount.
Found a $100.00 enclosure that was 6x6x8 inches on the bay for $30.00. Used a hole saw for the large fan hole and
greenlee chassis punches for the fuse,pushbutton, and lamp holes. After wiring it all up I went over the manual to pickout
the custom settings I wanted for my system and that was it. Used an old wall plug in power supply for DC power for the lamp power.
I removed the circuit board from the plastic enclosure with the dremel.
Motor current is easily read out while operating the lathe. All controls are external and just to my left side when running the lathe.
I prefer the new location for the controls as it frees up space on the headstock and keeps the controls from being bumped.
Total pulley reduction with the 3450 rpm motor gives just about the right amount of speed. I generally turn on the slower end and
the increase in torque is very welcome.
Prior to installing this new motor and VFD I had nothing but trouble with carbide insert tools. Now it is a breeze and I was cutting
twenty thousands deep (.040 off the part) on a 1.3" diameter part. Very smooth.
I should have done this mod last year when I could have kept the motor as a spare for my mini mill. The little motor is perfect for the mill
but I think it is a bit small for the lathe unless all you are turning is plastic and aluminum. Just sayin!
Thanks Nelson, so far it is very positive. Not that I am using more than 1/2 HP at present but the lathe just performs better.
I think it has a lot to do with the extra mass of the rotor in the new motor. I still have the original lathe pulley and belt system
and I am sure I would pull all the teeth from the belt if I even tried to pull 3/4 HP from it.
Nice thing about the vfd is the various parameters you can read out. I leave it on amps and control my HP by limiting the amp draw.
Should have done it two years ago...
Nice build and setup JR! The jack shaft is an interesting approach and gives opportunity to change pulley's if desired, although the VFD will minimize that. Nice find on the Hoffman NEMA 4 box for $30, I assume it's old stock or lightly used. Would you be so kind and provide a link to the motor and VFD from Amazon.
Thanks for sharing this build with us!
Nice thing about the VFD is that it converts 120vac single phase to 230 3 phase..
Not that I would ever use the full 1 HP from this setup but I bought what was available.
A real 1/2 HP 3 phase motor would be fine but I did not find one that would take up less space than my monster motor.
The motor is 3450 rpm which is less than the 5000 rpm original motor. I have also added an almost 2 to 1 reduction.
I think the speed is about right. I never ran the lathe past half speed with the old motor anyway. Now I have
a lot of torque that I was missing from the original setup.
Back in the day a motor was rated in real horse power not "peak horse power".
I am pretty sure that the 1/2 hp motor that was on my lathe was 1/2 peak hp.
Of course you can never get 1/2 hp from such a motor. Well I guess you can
but it only happens just as all the smoke leaves the motor......LOL.
That's a very nice set up you have. I put a 1 1/2 hp 220 single phase on my lathe where it replaced a 3/4 hp. The additional power is very nice and at low speeds it cut superb. Yours being 3 phase you can raise the 60 htz to 70 htz and go the other direction down to 50 htz. I have a 2 hp 3 phase on my mill and the VFD make it nice to change speed up or down.
Nice job o your lathe.
Thanks JR. Nice little VFD for a descent price well matched for the motor. I put them on my want list. I find it interesting about HP ratings also, but noticed your has a service factor of 1.15, not that it would likely be used but does help with high frequencies of the drive with the F rated insulation (150C°). Very few actually give PF ratings anymore either. A far cry from the 550lbs 1 foot in 1 second of yesteryear's...but the modern for electrical specs takes all kinds of thing into consideration, that they typically don't tell you but sell you on their goods with Smoke and mirrors.
Thanks guys, I really find the new motor setup with VFD puts new life in my little lathe.
The extra torque is very welcome. One of my next projects for the lathe is to make a new
set of pulleys for the drive system. Planning on using 3L section kevlar V-belts. I would think
they will perform much better than the timing belts in use now.
Nice work Jr
I have a smaller lathe similar to yours that I would love to do something like that to as well, I'm sure you'll enjoy the fine RPM adjustments, my 6913 Clausing Lathe has a variable speed drive, hydraulic adjustable sheaves, it's really nice to fine tune the RPM's for your work.
Again Great Job
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