Sieg lathe motor conversion

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Nikhil Bhale

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Joined
Nov 15, 2019
Messages
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Location
Vidharba, India
Hello,

I have a Sieg C4B lathe. It is similar in size to Sieg SC4 lathe but it has a AC reversible motor and belt and pulley system for speed control.
For slow speeds/ back gear the lathe uses a toothed belt of 1.5mm pitch. This belt is "delicate" and gets damaged easily and is very difficult to source locally.
I am thinking of changing the drive to a DC motor drive.
I have seen people on YouTube and elsewhere using a treadmill motor for this conversion.

After searching on the internet I have two motor options.
1. Treadmill motor DC 180V, 1-1.5kW

treadmill.jpg


2. Ebike motor DC 48V, 1kW
ebike.jpg


I want to ask which motor will be more suitable?
Both motors cost nearly the same and the controllers for the motor are also in the same price range.
Do we need a separate cooling arrangement for the motors as they may run at less than optimal speed for a long time?
The low voltage ebike motor will draw more current than the treadmill motor. Will this affect anything?

I will add that my "workshop" is not air conditioned and the temperature at my place goes to 47-48C during summer. I generally avoid working in this high temperature but I try to work if temperature is 40-42C.

Regards
Nikhil
 
Most of the industrial electronics that I have seen is rated at 40°C. Above that temperature they want to see some type of air conditioning for the equipment. It doesn't mean it won't work above that temperature, but it does mean that you are shortening the useful life of the equipment. Where I work in Iowa, we've got an "845"Hp motor on a large air compressor. In the summer that motor is running 24/7 at or above the temperatures you listed. We are getting less than 20,000 hours out of the bearings on that motor before they start to fail - a fraction of the life we should be getting. Those failures are due to the way the manufacturer treated that poor motor during the design - just to get the desired performance at a lower rated Hp. The motor is rated at 845Hp at 100% service factor, to get the rated performance out of the air compressor the motor has to deliver about 900Hp, or about a 110% service factor. You do that to a motor and sooner or later something is going to give.

Forced air cooling for the motor, you betcha! The original Sieg motor was probably rated at 600-700W if you're lucky. Even at 1KW the new motor will see a greatly reduced load than it was designed for, but extra cooling won't hurt it - especially if you plan on running the motor at a greatly reduced speed. We've got a number of 600Hp extruder motors that are designed to run 24/7 from 0-1750 RPM at 100% torque throughout the range, they've also got 5Hp cooling fans on them. Those extruder motors have been in place for about 20 years and haven't failed yet. A cooling fan on the electronics wouldn't be a bad idea either. I'd use a computer "muffin" style blower on the electronics, and a squirrel cage blower with a shroud for the lathe motor.

Given my 'druthers, I'd go with the Ebike motor, it's smaller and they're designed to live in a nastier environment than the treadmill motor is designed for. But obviously, the choice is yours.

Don
 
The motor is only half the battle. You mention the controllers are roughly the same price, but I think you may find out that they can be the differentiator between the motors. I'm not familiar with either the treadmill controller or the the e-bike but speed/load regulation is a concern - if you set the lathe for a speed and then apply a cutting load, how does it handle that? Do some research on that front before deciding. There have been some really bad motor controllers that couldn't handle that situation (hopefully all in the past).
Lastly - does the "controller" make the DC voltage (more likely for treadmill) or just regulate it (likely in the e-bike case - think battery supply) - it may be that's another item to get (DC power supply) changing the cost equation.
 
Thanks Don and ninefinger for your replies.

I am watching a lot of youtube videos and browsing the internet to get information about the conversion.
I came upon this site DazeCars, Upgrading shop tools for variable speed which uses a cheaper option for motor control.
But this needs some electronics knowledge which I lack. There is a guy in my neighborhood who is good in electronics, I will get his advice if this is doable.

Nikhil
 
Hello,

I have a Sieg C4B lathe. It is similar in size to Sieg SC4 lathe but it has a AC reversible motor and belt and pulley system for speed control.
For slow speeds/ back gear the lathe uses a toothed belt of 1.5mm pitch. This belt is "delicate" and gets damaged easily and is very difficult to source locally.
I am thinking of changing the drive to a DC motor drive.
I have seen people on YouTube and elsewhere using a treadmill motor for this conversion.

After searching on the internet I have two motor options.
1. Treadmill motor DC 180V, 1-1.5kW

View attachment 145300

2. Ebike motor DC 48V, 1kW
View attachment 145301

I want to ask which motor will be more suitable?
Both motors cost nearly the same and the controllers for the motor are also in the same price range.
Do we need a separate cooling arrangement for the motors as they may run at less than optimal speed for a long time?
The low voltage ebike motor will draw more current than the treadmill motor. Will this affect anything?

I will add that my "workshop" is not air conditioned and the temperature at my place goes to 47-48C during summer. I generally avoid working in this high temperature but I try to work if temperature is 40-42C.

Regards
Nikhil
Nikhil,

Have you considered obtaining the necessary parts from Sieg (or one of their dealers) in order to convert your C4 Lathe to an SC4. I have owned an SC4 for about six years, and have found the brushless DC motor and controller to be very good.

Positive notes regarding the SC4 include; 1) The motor controller is designed to handle changing loads, and easily maintains a constant speed when starting cuts, and during interrupted cuts. 2) The motor controller has a very good overload cutout circuit that cuts the motor very quickly, preventing motor damage. 3) The motor controller has motor brake circuitry, which stops the spindle near instantly when you hit the stop button.

There was only one problem with the factory standard SC4, and that is that at the minimum spindle speed (ex Factory) for the SC4 is approx 100 RPM. I found that at 100 RPM the lathe lacked torque as the motor RPM was too slow. At spindle RPMs greater than approximately 150 RPM, there was no lack of torque. The problem was first observed when single point threading at 100 to 120 RPM. It was too easy to stall the motor. Threading at 150 RPM, where the lathe does not stall, was a bit too fast for my liking's. The lack of torque at low speeds was also very noticeable when turning diameters at the lathes maximum limit. For turning large diameters, I changed from HSS cutters, to Carbide cutters, and turned the spindle speed up a bit.

I cured the lack of low spindle speed torque by modifying my lathe to add a 'back gear'. That was simply achieved by adding an extra toothed belt pulley on the motor shaft, and larger second toothed belt on the driven shaft. Changing from high gear to low gear is a simple and quick process of sliding the toothed belt from one set of toothed belts to the other.

I hope that information is useful.

Regards,

RoyG
 
RoyG thanks for the suggestion.
I will check with the firm from whom I bought the machine.
One of the reason I wanted to do this conversion is that I want to try out single point threading.
My lathe lowest speed is also in the same 150-200 range and I am afraid to do threading at this speed.

Nikhil
 
RoyG thanks for the suggestion.
I will check with the firm from whom I bought the machine.
One of the reason I wanted to do this conversion is that I want to try out single point threading.
My lathe lowest speed is also in the same 150-200 range and I am afraid to do threading at this speed.

Nikhil
A work around for threading at that speed is to uses an internal threading bar on the backside of the material and run the lathe in reverse. This will allow you to start near the headstock and thread away from it for right hand threads.

Another workaround is to make a crank that wedges in the spindle bore (to the rear) and turn the lathe by hand as you do the threading. You control the speed and can turn the lathe quite slowly.
 
I have a similar low speed problem. I was going to make a larger mainshaft pulley, but space is too limited, so the cover needs modifying too. But I use a spanner on the jaw of the chuck to crank the shaft 1/3rd rotation at a time... I like the idea of fitting a handle in the back-end of the mainshaft! May even see if I can arrange a different motor drive there as well...? - with a simple disconnect for when I don't need it?
K2
 
While not the cheapest option but probably not priced terrible by the time you chase everything down, www.servomotorkit.com has complete motor kits or just parts to do the conversion with the ubiquitous sewing machine motors that are available online.
I bought my motor and controller off eBay, but I needed timing belt pulleys, my lathe was tore apart so I couldn't make any. I discovered the website and ordered pullies from him. I'm still in the middle of my project so I can't comment on the motor. I decided to beef up the bed under the headstock on mine, instead of having the motor right there. Which has added a fair amount of complication over just a motor and controller swap.
 
Steamchick.. Steve Jordan put one {crank} on his Myford lathe
 
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Hi,
Finally I decided to go with 3 phase motor and VFD.
I got a cheap new old Delta M VFD drive for around $70.
Motor was hard to find as in India I could only get 3 phase motor in 440v. Dual voltage motor are available on custom order and delivery time is long. I converted a 1.1 kW 3 phase 440v star connected motor to 220v delta connected motor. I have no idea how much I derated the motor.
I used a EMI filter on VFD input and and have output wires wound around ferrite core.
I am getting lathe rpm upto 1000 with current setup. I have ordered some new belts and pulleys and will try to get more rpm out of them. I also ordered a new enclosure box for the VFD.
Some of the pics
IMG_20230606_180151.jpg

Delta VFD drive

IMG_20230606_180217.jpg

3 phase motor

IMG_20230606_180123.jpg

EMI filter

IMG_20230606_180146.jpg

Wire wound around ferrite core

IMG_20230606_180044.jpg

Remote start stop, fwd reverse, rpm control and rpm indicator


Regards
Nikhil
 
The new motor has a different frame as compared to factory fitted motor. 80 vs 71. I had to modify the motor mount so that it can fit the lathe.
From my experience I can say that it was not a straight swap job for conversion. If you want to go down this path do your homework first. Get as much information as you can get before starting the job. And don't start removing anything from the lathe until you have all the parts on hand. My conversion was unplanned and had to order parts as I required them. I spent about 2 months in sourcing and fitting the parts.

Regards
Nikhil
 
Well done on achieving a result!
Just take care, as the difference between a gear driven speed variation (means the torque available changes with gears according to the gear ratio) compared to a variable speed motor system (where the torque may be a constant (around higher speeds or even fall-off dramatically as speed is reduced).
This may mean that when you need torque (for low speeds, large diameters or threading where a large cut is made at minimum speed) you have very little, when compared to a geared system where the motor is at a relatively high speed and the torque is magnified by the gear ratio. I am used to "almost no torque" with my DC Permanent magnet motor, the torque at 100 rpm won't take a 0.010" cut on cast iron when machining a large diameter flywheel or something. - I can stall it when tapping at 60rpm if using a 1/2" Whitworth taper tap on mild steel! But at high speed it does all I want. (My motor runs about 3 x Spindle speed - it really needs to be >10 times for the low speed torque to suit me, but the lathe will probably twist out-of-accuracy at that higher torque...).
A friend's gear driven lathe (same size as mine) with gear box on a single phase constant speed synchronous AC motor (same power & torque as mine) never has any problems of "low torque at low speeds".
K2
 
This may mean that when you need torque (for low speeds, large diameters or threading where a large cut is made at minimum speed) you have very little, when compared to a geared system where the motor is at a relatively high speed and the torque is magnified by the gear ratio.
Yes. You are right. A geared system will give a greater torque range compared to belt system with fixed pulleys and variable speed motor.
But I checked the lathe after your message. I can get a 1mm doc cut on a 25mm piece of aluminium at 60 rpm. At higher doc the belt starts to slip. So I think the torque will be sufficient for my threading needs.
Anyways I have a 6 speed pulley system on the lathe and I can change the belt to a higher ratio pair for more torque.

Regards
Nikhil
 
I am in the process of upgrading my Clarke CL300 mini lathe (Sieg) to 3 phase. The new, bigger motor is mounted to the rear of the lathe with an intermediate spindle mounted in the original motor housing. This simplified the drive arrangement. A new control box was built containing a NVR switch for the mains supply for the inverter (which is mounted on the wall, behind the lathe). The inverter is controlled by a seperate control box, with "Start", "Stop" and speed control functions.
inverter.jpg
modified_box.jpg
new_drive.jpg
new kit1.JPG
 
Nikhil, FYI: recently I was cutting threads on some brass and bronze fittings - really easy to machine, but reached the limit for the lathe.
Cutting 1/4in x 40 tpi threads with taps and dies was no problem, with variable speed on lowest speed - showing 50 rpm.
But it struggled with 5/16in x 40 and 32 tpi threads - I had to "help it a bit by hand - applying torque to the chuck just gripping the outer diameter.
Yet as soon as I tried cutting 1/8in BSP threads (3/8in OD) it said "What? You want torque at this low speed? Ha! Ha! Ha!" and stalled as the cut developed. The taper tap made about 3 threads - just enough to start alignment - before stalling - and I had to apply the spanner to chuck jaws to hand wind the main shaft with power off. A clue: The limiting torque is less than the torque that holds the tap shank in the 3 law drill chuck in the tailstock - the tap slips when it bottoms in a blind hole. (My bit of "safety"). It is about as much torque as I can apply if I grip the 1/2in drill chuck and rotate it by hand.
Although it is a "1kW" motor, it is probably less than the torque of a 100W motor with 12:1 gearing!..... My controller limits the motor current to 10 Amps, so that defines the motor torque limit - all the way through the speed range. But my cheap lathe doesn't have the strength for "more torque" anyway. You can see it flex with "too heavy" cuts on steel, or whatever.

76 Dave: Great installation of the new motor and drive. Is the yellow plate holding the new motor in place a substantial chunk of steel? Looks like some 2in x 2in box steel section. Just a word of caution... The lathe bed will have been designed to not twist "too much" when the full torque of the original motor was applied at full cut size and feed rate on the chosen metal and diameter ("max torque" is usually when the speed controller cannot maintain the speed). You won't remove metal any faster with the new motor without distorting the bed and losing dimensional control, unless the bed of the lathe is precisely secured to a strong and stiff base... such as a 6 in x 6 in H-section, or better still 6 x 6 box section or something torsionally stiff. I cannot see from the pictures what base frame you have beneath the lathe. Mine is 2 in angle steel and 1/2 in of wood... but cannot restrain the lathe bed from twisting under heavy cuts with the standard motor. But a 0.020" max cut on Brass suits me as a limit.... I can spend the time with many light cuts. The lathe bed, saddle, cross slide and mounting is the limiting factor for heavy cuts, not the motor torque, for me. (I REALLY should make a strong and stiff frame for it! Planning for 4 in x 2 in box-section steel rectangle- but must do some sums for stiffness first.). I didn't see a reason "Why?" you have invested in the new motor and controller: Was the old motor "goosed"? If it was to increase the metal removal rate you may not achieve all you hoped for... But I hope your new motor set-up works for you...? Have you compared torque ratings of the new motor versus the old one? - WORTH CHECKING.
Another observation.... I would have ensured the controls were in front of the lathe, so you can reach them without reaching over the rotating bits of the lathe. The pictures don't show where on the wall you have mounted the inverter, and controller.
But now is the time to Enjoy your uprated toy!
K2
 
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