# What size pulley should I use with DC treadmill motor?



## jdsantiagojr (Feb 16, 2022)

Hello! I would like to make a poly v-belt pulley for DC treadmill motor, but unsure how big the pulley would need to be . I have searched YouTube but a lot of the videos on the subject are in a different language.

Hoping someone would be able to point me in the correct direction. Setting this up on a 1924 11” south bend. Mounting  motor about one or two feet behind headstock.


Thank you!


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## Hawkeye (Feb 16, 2022)

You need to start with the RPM of the new motor. Next comes the RPM that you need to put into the lathe. If the original lathe motor was rated at 3450 RPM and the treadmill motor is 6000 RPM, that gives you a ratio of 1.74:1. If the pulley on the new motor is, say, 1.5", the new pulley on the lathe would be 2.6" in diameter. 

An original RPM of 1725 and a new RPM of 7000 would give a ratio of about 4:1, so the new lathe pulley would be 4 times the diameter of the treadmill motor pulley. Easy enough to work out what you need.


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## jdsantiagojr (Feb 17, 2022)

Hawkeye said:


> You need to start with the RPM of the new motor. Next comes the RPM that you need to put into the lathe. If the original lathe motor was rated at 3450 RPM and the treadmill motor is 6000 RPM, that gives you a ratio of 1.74:1. If the pulley on the new motor is, say, 1.5", the new pulley on the lathe would be 2.6" in diameter.
> 
> An original RPM of 1725 and a new RPM of 7000 would give a ratio of about 4:1, so the new lathe pulley would be 4 times the diameter of the treadmill motor pulley. Easy enough to work out what you need.


Would this be the same if I wanted to go directly from the motor pulley to the cone pulley on the lathe ? The original setup looked like the attached .

I removed everything that was mounted behind the machine. The original pulley on the AC motor was 3" and the others on the back measured about 8".


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## Bi11Hudson (Feb 17, 2022)

The likely spec for the OEM motor on the lathe is probably 1800(~1740), a 4 pole motor. What will be needed is the rated "base speed" of the DC motor. It most likely has a 'permanant magnet' field. . . Then you must figure in the installation of a speed controller, either on install or some(possibly remote) time into the future. With a 'PerMag' field, you cannot easily overspeed the motor. I don't know your particular machining circumstances, as a rule I would try for a ~2400 or so RPM at base speed. 

The reduction arrangement of multiple belts/pulleys may well serve several functions. Direct drive from the motor to the spindle is not recommended. Motor torque will fall off dramatically at speeds below 40-50% base. You will need to keep the motor speed up to some nominal speed and use the belts for reduction. Older machines were basically designed to be run from a line shaft, the speed of that source would have been much lower than an electric motor. Even then, there was a small reduction between the drive and the spindle.

The desired pulley sizes will be a ratio rather than absolute sizes. Figure the size of the OEM pulley. Then, knowing the base speed of the DC motor, find a pulley, either larger or smaller, to give a similar speed on the first stage of the countershaft. Making the allowance for above base speed as desired. That should get you started, it may be necessary to adjust the drive pulley up or down from there.

.


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## jdsantiagojr (Feb 17, 2022)

Bi11Hudson said:


> The likely spec for the OEM motor on the lathe is probably 1800(~1740), a 4 pole motor. What will be needed is the rated "base speed" of the DC motor. It most likely has a 'permanant magnet' field. . . Then you must figure in the installation of a speed controller, either on install or some(possibly remote) time into the future. With a 'PerMag' field, you cannot easily overspeed the motor. I don't know your particular machining circumstances, as a rule I would try for a ~2400 or so RPM at base speed.
> 
> The reduction arrangement of multiple belts/pulleys may well serve several functions. Direct drive from the motor to the spindle is not recommended. Motor torque will fall off dramatically at speeds below 40-50% base. You will need to keep the motor speed up to some nominal speed and use the belts for reduction. Older machines were basically designed to be run from a line shaft, the speed of that source would have been much lower than an electric motor. Even then, there was a small reduction between the drive and the spindle.
> 
> ...


Thank you. I am just getting started in hobby machining .. off and on for two years. This is my first old lathe and was not sure how to proceed with conversion to dc motor. Some of the video I have watched do direct to cone pulley,but I was unsure with this approach. Really appreciate the information. Going to think about it and start sketching something out.

should I just look at also reusing original setup with only motor and motor pulley replaced ? Only problem I have is space with the original setup


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## Hawkeye (Feb 17, 2022)

The first mistake we all make with machining is in not getting the cutting speed (RPM) right. Different materials can stand different cutting speeds - stated in Surface Feet per Minute. Different cutter materials (HSS or carbide) can stand different speeds. Exceeding those speeds by much of a margin will ruin the cutting edge.
As already mentioned, treadmill motors run at a much higher speed than your original motor. If the manufacturer needed a jackshaft with extra pulleys, your new installation definitely will. Your easiest installation will be to turn the jackshaft at the same speed as before. This will involve using the right size pulley feeding into the jackshaft. Simple math as outlined above to design that diameter.


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## Grendel (Feb 18, 2022)

I may be wrong, but I think the south bend literature for that era quotes the countershaft speed (I seem to recall thats what I worked to, so I then use that speed, in the end my slowest non backgeared speed was about 600rpm at the spindle,


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## RJSakowski (Feb 18, 2022)

I converted my G0602 lathe to run on a dc treadmill motor last year.  Rather than use the OEM poly v pulley, I adapted it to with the lathe's OEM motor.  The old motor was  1725 rpm 1 hp motor @ 120 volts rms while the new motor was rated at 4090 rpm, 2.5hp at 130 volts.  Calculating torque, the OEM motor developed 3.02 lb-ft. and the new motor developed 3.21 lb-ft.  My controller runs directly off the line voltage, rectifying via a full wave bridge and has an output of 176 volts with no load.  

I retained my OEM pulley configuration and designed my own controller.  The controller uses pulse width modulation with feedback to set operating speed.  Operating on the medium-low belt position, I can generate useful torque from 20 rpm to almost 950 rpm at the spindle.  While the motor would normally lose torque at lower speeds, the feedback circuitry senses a decrease in speed under increased load and adjusts the control pulse width to maintain the set speed.  This effectively maintains torque at low speed.

Using the OEM pulley configuration, the range of spindle speeds are from 10 rpm to 7500 rpm (an insane speed , btw.  I wouldn't try using that speed under any circumstance.  The OEM spindle speed in the highest belt configuration is 2400 and the bearings are rated at 5600 rpm.)  So far, all my lathe work has been on the medium low belt configuration and  between 20 and 700 rpm at the spindle)

This will all be published in gory detail on a dedicated future thread.  As of now, I am working on a Prony brake to measure spindle torque.  The plan is to measure torque vs. motor speed at various controller settings. This will be used to optimize the controller feedback. and determine actual performance vs. the theoretical.


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## jdsantiagojr (Feb 18, 2022)

Really appreciate everyones response. I do have another probably dumb question, but I was curious if someone could explain to me the setup in the attached picture highlighted by the purple rectangle. I noticed the pulleys are two different sizes (4", 8") driven by same size pulleys (3", 3") below. What is the purpose of this ?


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## Bi11Hudson (Feb 18, 2022)

I can't see the entire gear train in the photo, but the general area appears to be for a "back gearing" mechanism. If so, there will be a shaft with a gear at either end and a latch mechanism to allow the cone pulley to rotate individually from the shaft. Please note that *back gearing and the latch must never be engaged at the same time*. 

My machine is ~25-30 years newer and of different manufacture, so I am just guessing about most of what I'm saying. The only thing I am sure of is that back gearing and the spindle latch should no be used at the same time. As with most things, there will be exceptions. But for a novice, *NEVER* is a good rule until you have some idea about what you're doing.

.


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## mattthemuppet2 (Feb 18, 2022)

I'd strongly recommend against running the treadmill motor direct to the spindle, they are waaaaay too fast. You'll be running the motor really slowly and have next to no power. I have a 1:4.5 reduction from motor to countershaft and haven't yet made the countershaft step pulley, so I'm using a single poly V pulley that gets me around a 1:1.5 reduction on the middle pulley. That's still too fast as the top speed is around 2000rpm, which is a bit much for a 1929 lathe  When I get round to making the step pulley I'll aim for a top speed on the largest spindle pulley of around 1500rpm. Not that I intended using it for long at that speed, but for short spells it'll be fine.


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## jdsantiagojr (Feb 18, 2022)

Bi11Hudson said:


> I can't see the entire gear train in the photo, but the general area appears to be for a "back gearing" mechanism. If so, there will be a shaft with a gear at either end and a latch mechanism to allow the cone pulley to rotate individually from the shaft. Please note that *back gearing and the latch must never be engaged at the same time*.
> 
> My machine is ~25-30 years newer and of different manufacture, so I am just guessing about most of what I'm saying. The only thing I am sure of is that back gearing and the spindle latch should no be used at the same time. As with most things, there will be exceptions. But for a novice, *NEVER* is a good rule until you have some idea about what you're doing.
> 
> .


I was actually curious about the red and 


Bi11Hudson said:


> I can't see the entire gear train in the photo, but the general area appears to be for a "back gearing" mechanism. If so, there will be a shaft with a gear at either end and a latch mechanism to allow the cone pulley to rotate individually from the shaft. Please note that *back gearing and the latch must never be engaged at the same time*.
> 
> My machine is ~25-30 years newer and of different manufacture, so I am just guessing about most of what I'm saying. The only thing I am sure of is that back gearing and the spindle latch should no be used at the same time. As with most things, there will be exceptions. But for a novice, *NEVER* is a good rule until you have some idea about what you're doing.
> 
> .


the image was bad . I was actually curious about the two different pulley sizes on the counter shaft (purple). Both have belts to the 3” pulleys below. The ratios are different and was curious what the setup is called and why they’re setup like that .


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## jdsantiagojr (Feb 20, 2022)

Grendel said:


> I may be wrong, but I think the south bend literature for that era quotes the countershaft speed (I seem to recall thats what I worked to, so I then use that speed, in the end my slowest non backgeared speed was about 600rpm at the spindle,


You're correct. Just checked and it mentions the speed in one of the lathe catalogs.


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## Grendel (Feb 20, 2022)

thaanks, I just rechecked my speed and I am turning the countershaft way too fast (whoops) so I too need to recalculate and redo my latge pulley on the countershaft.


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## Grendel (Mar 18, 2022)

further to mu comment above, I have calculated my countershaft is running about 900 rpm (whoops) so I have obtained a billet of aluminium to make a 12" driven v pulley on the countershaft to replace the 6" one I currently have, fortunately I found the necessary aluminium local to myself, on ebay, and managed to get 11 pieces 300mm dia and 30mm thick for just £100- thats less than scrap value


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## Grendel (Mar 18, 2022)

this is it, its the bit cut out when they build roulette wheels = 12" diameter 1 1/4" thick


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## aliva (Mar 18, 2022)

This may give you some insight





						Pulley Calculator. RPM, Belt Length, Speed, Animated Diagrams - Inch
					






					www.blocklayer.com


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## Grendel (Mar 20, 2022)

well i didnt have a big enough chuck to hold the pulley blank, so using the two holes already in the plate, I bolted it to a 10"faceplate.
then I turned down that side to thickness, all except for the area of the bolts, drilled some new holes that would pass into the previously turned area and faced off the remainder, if you have a working lathe, you can make replacement parts, and new pulleys comes under that heading.
now I have the boss I can hold in the chuck to true up the other side, but first i think I may leave this on the faceplate to drill the hole and  shape the v groove, and yes, there was a huge amount of aluminium swarf to clean up


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## jdsantiagojr (Mar 21, 2022)

@Grendel, @Bi11Hudson
I ended up keeping the pulley arrangement the same and machined a small v-pulley for the motor. Welded some brackets, added new pillow blocks and swapped the belts. I also wired up the SCR motion controller to dial the motor speed to 2400 RPM /  220 RPM @ counter shaft. Still not at the 290 mark but a little worried about how hot the motor got after running continuously for 15min to 20min.

With this original arrangement I can always go back to AC motor that was originally used. If for some reason the DC motor fails or catches on fire. . . lmao.

@Grendel I did have question about the motor heating up. I noticed after running it for about >15min it did get hot to touch. Does your motor get hot ? How are you keeping it cool?


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## Grendel (Mar 21, 2022)

once i complete this mod it will bring my countershaft speed down from 900 rpm to a more reasonable 450, not the 275 mine should be but better than over 3 times the speed, that should in turn raise the torque available.
I was originally planning to machine the V groove on the original setup, however my engine mount stops me getting a tool to the material in the correct orientation to do this, so I had to dismount it, turn it around and hold it by the boss, this of course allows the whole plate to sing to me while machining, slowing down to my current slowest speed using back gears does reduce this, but I am still getting chatter, never mind - its just a vee for a pulley, it doesnt have to be pretty too.


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## jdsantiagojr (Mar 21, 2022)

Grendel said:


> once i complete this mod it will bring my countershaft speed down from 900 rpm to a more reasonable 450, not the 275 mine should be but better than over 3 times the speed, that should in turn raise the torque available.
> I was originally planning to machine the V groove on the original setup, however my engine mount stops me getting a tool to the material in the correct orientation to do this, so I had to dismount it, turn it around and hold it by the boss, this of course allows the whole plate to sing to me while machining, slowing down to my current slowest speed using back gears does reduce this, but I am still getting chatter, never mind - its just a vee for a pulley, it doesnt have to be pretty too.





Grendel said:


> once i complete this mod it will bring my countershaft speed down from 900 rpm to a more reasonable 450, not the 275 mine should be but better than over 3 times the speed, that should in turn raise the torque available.
> I was originally planning to machine the V groove on the original setup, however my engine mount stops me getting a tool to the material in the correct orientation to do this, so I had to dismount it, turn it around and hold it by the boss, this of course allows the whole plate to sing to me while machining, slowing down to my current slowest speed using back gears does reduce this, but I am still getting chatter, never mind - its just a vee for a pulley, it doesnt have to be pretty too.


I did have question about the motor heating up. I noticed after running it for about >15min it did get hot to touch. Does your motor get hot ? How are you keeping it cool? Should I be concerned at all or am I worrying for nothing. . ?


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## Grendel (Mar 21, 2022)

mine does occasionally get warm to the touch when running for extended periods under load (ie when doing heavy cuts), but I am running a 3/4 hp single phase ac motor that has a speed of 1400 rpm at UK standard voltage (230V). mine does have a built in fan inside the motor shroud, that i suppose is for cooling.


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## woodchucker (Mar 21, 2022)

jdsantiagojr said:


> I did have question about the motor heating up. I noticed after running it for about >15min it did get hot to touch. Does your motor get hot ? How are you keeping it cool? Should I be concerned at all or am I worrying for nothing. . ?


add a fan. It can't hurt. If you can add a fan to the motor shaft. If not add a small computer pancake fan.. AC high cfm fan..


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## jdsantiagojr (Mar 24, 2022)

@woodchucker I may need to add a fan . I ran it last night and it failed after an hour. It did do a decent job, I may go back to using the AC motor. With the setup I have I should be able to swap it back with no issue.

@Glendaler @Bi11Hudson @mattthemuppet2 I attached photo of setup. I am using serpentine belt from a truck as drive belt. Will this be okay our should I look at using the Replacement Drive Belt for South Bend 9 & 10 lathes.?


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## Jim F (Mar 24, 2022)

I just installed a serp belt when I did the felts on my 1947 C.


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## jdsantiagojr (Mar 24, 2022)

Jim F said:


> I just installed a serp belt when I did the felts on my 1947 C.


Is it better than a serpentine belt ? Serpentine is working but sometimes it slips.


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## mattthemuppet2 (Mar 24, 2022)

that's a pretty darn cool set up - are those gas struts to tension the spindle belt? I don't have any problems with a serpentine belt (poly-v) on my SB wide 9 with the v's against the pulley.

when you say your motor failed, what happened? did it just stop working or did it slow down over time? Was the casing hot to the touch when it stopped?


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## jdsantiagojr (Mar 25, 2022)

mattthemuppet2 said:


> that's a pretty darn cool set up - are those gas struts to tension the spindle belt? I don't have any problems with a serpentine belt (poly-v) on my SB wide 9 with the v's against the pulley.
> 
> when you say your motor failed, what happened? did it just stop working or did it slow down over time? Was the casing hot to the touch when it stopped?


@mattthemuppet2 Yeah. I used gassed struts. I was not sure they would work but so far so good. Will look at other options in the future.

the motor started sparking after about an hour of running  and turning on and off. It was really hot. I tried letting it cool down for about 15 to 20 min it would continue to spark and shutdown.


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## Saguaro Slim (Mar 25, 2022)

aliva said:


> This may give you some insight
> 
> 
> 
> ...


Great Link! The chain / gear calculator just solved a big problem for me on another project.


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## mattthemuppet2 (Mar 25, 2022)

jdsantiagojr said:


> @mattthemuppet2 Yeah. I used gassed struts. I was not sure they would work but so far so good. Will look at other options in the future.
> 
> the motor started sparking after about an hour of running  and turning on and off. It was really hot. I tried letting it cool down for about 15 to 20 min it would continue to spark and shutdown.


how are you powering the motor? I had a friend who toasted a treadmill motor on his 2x72 belt sander - he managed to blow through over half the brushes before it finally conked out. How about belt tension from motor to countershaft? Don't want that too high either.


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## jdsantiagojr (Apr 3, 2022)

I ended up swapping the DC for AC motor. Posted some images of new setup.


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