Lathe speeds

[Kram]

Id like my lathe to be useful at lower speeds - under 500rpm there is no torque, and the motor spins to slow for the cooling fan to do its job.

Its V belt drive, dc variable speed motor. As is, the top speeds are 1000 and 2000 rpm - although some electronics is broken, I can turn it 50% faster, but can hear motor is not happy, so I dont.

There is no space for a bigger driven pully, the drive pully could be smaller it would probably slip.

I am thinking add a gear reduction and move the drive pulley or a second belt - but tensioning might be a pain.

Would steel mod1 gears be adequate for a 1kw motor?
How would you do it? I may have asked this before but cant find the thread..
Pic is not mine, its a warco wm-240. They did make a belt drive model withoutvariable speed, I will ask them if I can buy the drive parts..

 

[MattF]

A photo or two of your current setup may help.

 

[God mode restorations]

What lathe do you have

 

[eLuSiVeMiTe]

Warco wm240
Edited above.

Assuming your using the outter pulley for slower speeds.

 

[Bill Edwards]

It might be a case of adding a pair of pulleys on a shaft, i.e the motor has a small pulley which turns a large pulley coupled to another small one, which then goes to the large one on the lathe. Like a compound gear train.

 

[Hopefuldave]

HI Kram,
As Bill says, a compound belt setup with a double pulley may be the best way, you could pick up the two cover-mounting bolts and put a plate across to hold the pulley shaft (would need tensioners, e.g. as fitted on car cambelts), or make up a Banjo that rotates on one of the cover studs with a slot to move the shaft to tension one belt, swing the neck of the banjo to tension the other (would be best if the pivot lined up with one of the original pulley axes, otherwise it's like juggling cats trying to get both tensioned correctly).

About motor cooling, the Warco etc. Chinese lathes/mills are all built down to a price and equipped with lowest-cost motors (I've seen inside 'em...) that don't last long at all if used at low revs and high(ish) loads, a PC type cooling fan on the end of the motor's a Very Good Idea and may preserve it a bit longer (when they do finally give out, it's common for the motor speed control board to go with it...). I run a huge, ancient and irreplaceable 3-phase 3-speed motor on my lathe from a VFD and use an external sock-blower for cooling at low revs/stationary.

Dave H. (the other one)

 

[God mode restorations]

Warco wm240
Edited above.

Assuming your using the outter pulley for slower speeds.

Arh yer. Blonde moment

 

[Kram]

Id prefer not to touch the spindle bearing adjusters, which will prevent me swapping the spindle pulley, but if I did and modified the guard I guess it could go a bit larger.

Would like to add 500 and 200rpm speeds, and keep the existing options tho I rarely use 2000. A double pulley should be easy to turn up. Put bearing in the pulley center so it can rotate on a shaft.

Any good way to calculate belt length. I assume pulley size I want a 2:1 and a 5:1 but unsure if the ratio to existing pulleys is relevant?

 

[knighty]

how easy is the motor to swap? - swapping to a 3 phase motor and using a vfd would give you the most speed options and should be very robust

if you go for belt drive, swap the motor pulley to a twin one - then you could add a shaft and a couple of pulleys right above the motor...

if you make the mounted pulley adjustable, up/down and left/right then it'll be easy to tension both belts from that pulley pair

I'd build it and them measure and buy belts to suit... better than trying to build it to suit the belts you pick

 

[optima21]

yeah its not so difficult to do, you need a couple of pulleys, the one on the motor needs a third step to drive a second pulley that will allow speed reduction and to drive the pulley on the spindle.

if you have a look at the picture of a standard hobbymat drive arrangment, which has 4 speed, 250, 500, 1000 and 2000 rpm.

you could get a slow speed kit, which added a slow speeds of 76 and 156 rpm. the pulley on the left is a new motor pulley.

and how its fitted, the new motor pulley is top left and the new reduction pulley is bottom left

and viewed from above, the motor pulley is on top, the belt on that is driving the reduction pulley (on the original pulley this drive grove doesnt exist.)

hopefully it doesnt confuse you

 

[Kram]

Unsure what type of V belt I need. I can only find standards of Z, A, B, C which are too wide. I measure my belt profile as 7mm wide and 5mm deep.

 

[optima21]

Optimat VB belts are available in 5, 6 and 8mm widths

https://www.optibelt.com/en/products/v-belts/optibelt-vb-sc-plus/

which are available from simply bearings

https://simplybearings.co.uk/shop/B...-Belts-5-/-6-/-8mm/c4601_4790_5053/index.html

my lathe uses 6 and 8mm wide belts

 

[addjunkie]

There are websites that tell you how to calculate belt length.

Id also suggest you want a really low speed if your going to screw cut.

One example
https://bepltd.com/pages/how-to-calculate-belt-length

 

[roofman]

surely if you want it to run faster you use a bigger motor pulley..ok a tad bit of slow torque would be lost but this would be got back by a higher speed..

 

[Kram]

Vb-8 looks close, thanks. Will a large reduction work with a small belt, at low speed? "intended for fractional hp at high speed". 1kw motor on this.

Toothed v belts? I have not seen toothed V pulleys so assume it has some advantage?

 

[rtbcomp]

What you do have to be careful of with a large difference in pulley sizes is that the belt wraps round the smaller pulley sufficiently to get a good grip, so space the pulleys as far apart as possible.

 

[Gwil]

HI Kram,
As Bill says, a compound belt setup with a double pulley may be the best way, you could pick up the two cover-mounting bolts and put a plate across to hold the pulley shaft (would need tensioners, e.g. as fitted on car cambelts), or make up a Banjo that rotates on one of the cover studs with a slot to move the shaft to tension one belt, swing the neck of the banjo to tension the other (would be best if the pivot lined up with one of the original pulley axes, otherwise it's like juggling cats trying to get both tensioned correctly).

About motor cooling, the Warco etc. Chinese lathes/mills are all built down to a price and equipped with lowest-cost motors (I've seen inside 'em...) that don't last long at all if used at low revs and high(ish) loads, a PC type cooling fan on the end of the motor's a Very Good Idea and may preserve it a bit longer (when they do finally give out, it's common for the motor speed control board to go with it...). I run a huge, ancient and irreplaceable 3-phase 3-speed motor on my lathe from a VFD and use an external sock-blower for cooling at low revs/stationary.

Dave H. (the other one)

A sock blower? Well I never. So it inflates your socks ready for fitment? The modern world eh? Full of stuff I never even thought of.....

 

[Hopefuldave]

A sock blower? Well I never. So it inflates your socks ready for fitment? The modern world eh? Full of stuff I never even thought of.....

Big EBM Paper machine cooling fan, ideal for tidying teenagers' rooms - switch on and all the dirty socks and pants form a heap in the corner...

Dave H (the other one)

 

[Bill Edwards]

Vb-8 looks close, thanks. Will a large reduction work with a small belt, at low speed? "intended for fractional hp at high speed". 1kw motor on this.

Toothed v belts? I have not seen toothed V pulleys so assume it has some advantage?

There’s no such thing as toothed pulleys for V belts.
The teeth on the belt are to allow it to go round smaller pulleys (give more flexibility).