[whiteriver]

I am building my second cnc lathe and this one has a 6 speed belt and
pully setup. Its a real pain to be pulling the belt of one pully and
placing it on another all the time.
Questions are. What is the best setup for having a variable speed?
VFD and 3 phase motor? I would like to run 110V ac to the machine.
Trying to avoid 220 and 3 phase is not a option.
DC motor with DC speed Control? Can Mach contol a DC speed control? I
think it can do some VFD's?
Or since I would like to add a "C" axis to this lathe would it be
better to add a 1700 oz nema 34 stepper or some size of servo with a
encoder. The current size motor is a 3/4 hp AC cap start. So I need to
find a setup with comapariable power and a speed range from 60 to 2000
rpm.
Whatever I put on must be avalible for replacement. Can't rely on ebay
or surplus center for this. Commercial product and all.

Donny

[Karl_T]

The best option is VFD and three phase motor. You'll need 220 single phase to run this. You'll have to increase your motor size considerably to have the same torque at low RPMs as you do today. A VFD motor run at 1/2 speed has half the horse power, torque is constant and horsepower is RPM * torque. If you try to run all speeds with no belt changes, you could try running a two pole (1800 RPM) motor at 3600 to get 2000 RPM. The motor would then run 108 RPM at a spindle speed of 60. You'd have about 6% of name plate horse power at that speed or a 10 horse motor to get back to what you have today. That's why CNC machines have such huge motors. If you have a backgear(2 speed gearbox) for low speeds, you could cut your motor size considerably.

Karl

[Al_The_Man]

If you want to avoid 240v then, I would consider DC or AC PM motor & drive, from the likes of Baldor etc, It wont be the cheapest way however.
I believe there some VFD's that are 120 1ph in, but you may have problems getting a 3ph 120v motor.
Personally I would get a high grade flux vector VFD 240v 1ph in with a 3ph 4 pole motor and encoder input, they can be obtained with torque capability down to zero speed, The only thing is, if you want C axis control from it and it is not direct drive to the chuck or at least zero backlash from motor to chuck, you will have to put the encoder on the final chuck shaft, and scale it accordingly.
You will also need a motor cooling fan for low speed operation.
Al.

[whiteriver]

Looking at VFD's from Automation Direct they have a GS2 that takes 120v 1phase power and produces 3 phase 230vac. The GS2 is not Vector control. The GS3 is but its only takes 230 3 phase input. If I have to I will go with 240 1 phase input.
AL your saying if I can find a good (flux vector?) VFD with encoder input I can use that for my C spindle? I notice they have breaking. Will it hold enough and index accuretly enough to rotate my spindle to a set point and use live tooling on it from the cross slide? This would act like a servo drive I would think. All new to me. I'm a stepper man.
So with the right VFD and a 1hp 4 pole motor 3 phase motor it would be equal to the 3/4 hp on the lathe now? I would not need a 10 hp motor? Plus I could interface with Mach3 and control the speed and position? Am I following along on this or did I go down the wrong channel in the river without my oars?

Donny

[Al_The_Man]

There are VFD's out there that can closely compare to DC servo's, you have to buy the proper unit. I don't know why Auto.Dir limit their vector unit to 3ph as the motor is not that large.
There are many out there that go up to around 2hp and above for 1ph input.
I have seen units used on Gantry crane hoists, that will hold a stationary load, that was previously done by a brake on the AC motor.
Mitsubishi is one of the better makes of VFD's.
I don't know wether Mach3 has the ability to feed the analogue signal required I believe someone has a convertor to interface the two.
Al.

[gotis]

There are VFD's out there that can closely compare to DC servo's, you have to buy the proper unit. I don't know why Auto.Dir limit their vector unit to 3ph as the motor is not that large.
There are many out there that go up to around 2hp and above for 1ph input.
I have seen units used on Gantry crane hoists, that will hold a stationary load, that was previously done by a brake on the AC motor.
Mitsubishi is one of the better makes of VFD's.
I don't know wether Mach3 has the ability to feed the analogue signal required I believe someone has a convertor to interface the two.
Al.

Is´nt that the pixiedrive?

[RotarySMP]

You do not use an encoder with the VFD. Flux Vector VFD are looking at the motor windings directly and working out whats needed.

[whiteriver]

Why do the Flux Vector units offer a encoder input option if they don't need it? The option is almost as much as the Vfd base price. So I got the answer above about holding power. What about posiontal accuracy? Will they be a accurate as a servo with an encoder? I seen where AL says they will closly compare. How close? Would not want to invest $1200 and find out it won't do the job.
Why not get a rutex or pushing it a gecko servo drive and get a large 90vdc pm motor add a encoder and be ahead of the game on price? Do servos not have the holding torque? Seems like other than brushes that would be the cheaper way to go. Am I way off on this one? How many hours of run time could one get before he needed to change brushes? This will be a commerical machine in a small job shop or school envoirment.

Donny

[Al_The_Man]

Flux vector use feedback electronically, the drive takes an electronic picture of the drive, usually be running through self tuning and this enables the processor to calculate where the rotor is at any time, the problem is that when the rpm drops, it has a harder time of controlling the motor. The alternative is to fit an encoder so the processor know where the rotor is at any given time.
Although I have not used one for C axis, I have used Mitsubishi for mill applications for rigid tapping etc, but there the Z axis syncs to the spindle encoder.
It is a slightly different application than C axis for a lathe, but Mitsubishi claim max torque down to zero rpm.
What is done in some commercial lathe applications, is a servo is used in tandem with the main spindle motor to position when used as a C axis.
Within your motor size, it might pay to get one of the larger DC servo's to use as a spindle and then only use one encoder on the final drive shaft, this you will need for CSF as well as threading, in any case.
Al.

[vladdy]

Not sure how fancy you want, but a PWM Dc treadmill motor of around 2 hp are available fairly inexpensively.. I recall on the Gemini site that qty 5 was just over $100 each with controller.. should give approximately same or slightly better performance than your 3/4 hp ac motor that you have now..
An add-on tach circuit [less than $10] would give output to Mach3 easily, these controls use pot to vary speed, not sure how easy that would be to integrate, never looked at that part of mach3..
just a 'cheapy' idea...
enjoy.

[whiteriver]

The VFD idea is nice but out of my price range. Now i'm looking at the DC side of things.
I believe you can take a dcpm motor like a treadmill for instance . Say 180Vdc. and add a encoder and drive it with a rutex drive and you have a servo. Am I thinking right??
Now one needs to come up with a 180 Vdc power supply. Why cant you take a cheap dc speed control that works with 180vdc motors and use its output as the power for the rutex drive? Since the rutex is a relay does it matter where the 180 vdc comes from? Or can you build a 180 vdc powersupply for less than $70? Would you need to put some large caps between the dc speed control(powersupply) and the dc motor with encoder(servo) to get a nice smooth constant voltage? If so what size?

Donny

[vladdy]

I had picked up a couple of treadmill motors and controllers at the local scrap yard, one was rated 90vdc and the other was 130vdc...both were labeled as 2hp units , but I believe this may be just a bit optomistic...
When I looked at the specs for the controllers both seemed useable up to maybe 10 amp output, after that they both recommended forced air cooling and / or additional heat sinks, neither of the treadmills had these installed ..
Both of the controllers were rather simple, just had adjustments for torque compensation, and adjustment for high speed limit, i assume that was just a voltage limit as neither had feedback visible, just the pair of power wires [and ground]
The larger of the two will wind up [hopefully] on my old south bend lathe, it' more than sufficient..

enjoy..

[Al_The_Man]

I doubt if you wil get C axis positioning with a DC treadmill motor, the majority I have seen have low pole count which does not allow them to position easily around zero rpm.
Al.

[whiteriver]

Still looking for the answer for this question "Now one needs to come up with a 180 Vdc power supply. Why cant you take a cheap dc speed control that works with 180vdc motors and use its output as the power for the rutex drive? Since the rutex is a relay does it matter where the 180 vdc comes from? Or can you build a 180 vdc powersupply for less than $70? Would you need to put some large caps between the dc speed control(powersupply) and the dc motor with encoder(servo) to get a nice smooth constant voltage? If so what size?"

How do you tell how many poles a pwmm motor has? And how many poles do you need for good positioning?

Also I never got a answer to "How many hours of run time could one get before he needed to change brushes?"

Donny

[Al_The_Man]

I think what you are asking is how can I take a cheap DC motor (treadmill) and a cheap controller and have top grade servo performance!
Unfortunately it doesn't usually work out that way, if you want top performance, especially according to your first post you did not want to go with surplus or eBay, then generally you have to pay for it (unless you are willing to go the ebay route).
The use of PWM is usually used to describe the drive, not the motor, which can be a PWM driven AC or DC servo motor.
If you are looking at DC servo's/motors, one tell-tale sign of general purpose type, is if they only have one pair of brushes, as opposed to two or more pairs.
Treadmill motors come in all flavours, some are true DC motors, some are Universal (AC/DC) motors, I have purchased several types over the years and even the ones supplied by Baldor as DC servo/treadmill duty are lower grade than their regular DC servo's.
The brush life in a DC motor depends on alot of factors, including brush composition, current/arcing, etc, I have seen older high quality Gettys motors that have been in constant daily use for 8 to 10 years before requiring replacement.
The bottom line is that if you are buying off the shelf, bells and whistles cost money.
Al.

[whiteriver]

Al, Thanks for the explantion. I just exlporing all the avenues. I know pacsci sells treadmill style motors for aroud $300 just trying to figure out if a 1 or 2 hp motor like that will work. Short answer maybe. Long answer probably not. Information is power they say and when I came into this option I knew nothing. Now I know a little more than that. Like most people i'm trying to do this on a budget and do it right at the same time. Hard thing to do on a small budget. Ok C axis out for now. Will have to be a expensive addon. unless someone can tell me where to get good quality 1 to 2 hp DC servo motors for under $300 besides ebay.
Thanks for helping on this Al I really appreaciate it.

Donny

[dkowalcz]

Mcmaster will sell you 1 and 2hp DC for a little over $300, a local motor shop should be able to set you up as well - if you need to build a one-off cheap but need a brand name they may have a rebuilt or returned motor. They are Leeson brand, respected, but not quite top notch (I consider Baldor in that category).

I've used them in servo positioning apps and they work well; live C will be fine on a lathe but you need a brake if you want to do live tooling ops like cross-drilling and milling.

Brush life - I've been running the surplus 2hp treadmill motor on my lathe quite hard for about 2 months now and it's been fine. I blew a relay right off when I changed spindle motors, after that I've been OK. Just ship spares to your customer.

180VDC you can get easily. Hook a diode bridge up to your 120VAC line, no caps needed. Most of the 90/180V DC speed controllers work this way. Be sure to fuse it.

[rokag3]

i am also thinking to replace my 550 w ac by a 2hp dc 180v using uhu driver
max speed 4000rpm gear ratio 2.4 with air fan for low speed
have you done it
is it working (my lathe is much smaller than yours 400mm max)
where is the trap?

[vger]

Not sure how fancy you want, but a PWM Dc treadmill motor of around 2 hp are available fairly inexpensively....... these controls use pot to vary speed, not sure how easy that would be to integrate, never looked at that part of mach3..
just a 'cheapy' idea...
enjoy.

One option to control the pot would be to just couple the pot to a small stepper with limit switches to keep from damaging the pot.
By the way, those treadmill motors work great as a drill press drive motor.
Steve

[rokag3]

hello,
the motor i have turn fairly smooth with a 1.2v 1400mAh nicd batterie and has 42 contact stripes on the collector H42Y
he was produced for tunturi (very expensive sport equip.) by a chinese firm omega and labelled Y8F5D -C50012
the axes is mounted on 2 very good quality bearing
i bought 2 of them for 40 euros (that's while i bought 2 despite my back problems) in a greek fleemarket
and now i am thinking about installing the encoder on the lathe or the motor
for the power suply i founf every thing i need
but the question is
Is it going to work at low speed with a good torque
considering that i have a very small lathe
where should i but the encoder
and 1650 rpm (2.4 from 4000rpm) is it enough for a small lathe (i believe yes since i am a hobbyst )
if i use the encoder on the lathe and not in the motor could i avoid a cranted pulley and belt ?
thank you lucine