have 4:1 from 3000rpm dropping down to 750 rpm what gears to get 600rpm

It's a lathe not a record player. The correct speeds for an old Drummond are Fastish, Slowish, and Something inbetween. Have a look at typical lathe pictures and you see the small motor pulley drives a big pulley on the countershaft. The biggest you commonly see on ebay is 6 or 7 inches so get that but as your motor is twice as fast as usual you might want to find the biggest you can. (mine is 8in)

Then on the countershaft put a step pulley similar to the one on the spindle, or smaller. You can make this out of wood to experiment. (mine goes 1&1/2 to 3&1/2).

Meanwhile look for a 1425 rpm motor.

Jockey pulleys don't always help - the linear distance of belt contact around the pulley is the important aspect. The actual contact area can only transmit so much power without slipping. This effectively means that for some power level there is a minimum pulleys size what ever type of belt it is, some types being more capable than others.

John

-

Edited By Ajohnw on 03/07/2016 11:17:34

You don't say which motor type you are going to use, but if it is a single phase two pole induction motor, it's theoretic speed is 3000rpm, it's actual speed will be about 2850rpm, at that speed the ratio you require is 4.75:1 to give the 600rpm you want. Ian S

Edited By Ian S C on 03/07/2016 12:34:49

double post

Edited By Ian S C on 03/07/2016 12:37:41

Gentlemen,

I may be wrong [it has been known]; but I think it's reasonable to assume that Martin is working with the Kity motor that was the subject of this earlier thread, and the happy ending of  this one ... If so, then suggestions of substituting a 3 phase motor and inverter might be considered inappropriate.

MichaelG.

Edited By Michael Gilligan on 03/07/2016 13:05:11

One point no-one's picked up on so far - if you're looking to get the lathe top speed at 600 rpm then you should be doing so with the SMALLEST diameter pulley of the three (?) on the lathe spindle not the largest - that's for the slow speed.

Gave up and bought a laser RPM gauge as someone above said cant rely on online tables so will see if they are acurate when it arrives. thanks for all the help

Cheers

M

Edited By Martin Newbold on 03/07/2016 13:35:30

Looking back I think you had it right early on in the thread Martin.

1 on the motor and 5 on the counter-shaft would reduce 3000 to 600 rpm. Then to get from the counter-shaft to the 4 on the lathe, you need a 1:1 ratio, which would be provided by another 4.

So 3000 x 1/5 = 600

and

600 x 4/4 = 600

I think anything between 350 and 650 rpm would do for most general purpose work. Ideally you would have three of four speeds available between 100 and 1000 rpm. The extra speeds make it easier to do a wider range of jobs.

Cheers,

Dave

Hi Dave

Yes have been working on this two measuring all the pulleys This is the information I have gathered ( the data is without the benefit o the rpm gauge i have ordered )

Lathe

Largest : outside 114mm(4.5 ” ) inside 100 mm(4”  ).

Middle: outside 90mm(3.5“ ) inside 80mm(3“ ).

Small end:  outside 64.5mm(2.5“ ) inside 55mm(2“ ).

Motor

Small End: inside 25mm(1” )

Middle: inside 50mm(2“ ).

Largest:inside 75.5mm(3“ ).

Floating Pulley

52mm 1”.

Therefore using Pulley Calculator

1:4.5 = 658rpm, starting with 3000rpm.

1:4 = 750rpm, starting with 3000rpm.

1:3.5 = 833rpm, starting with 3000rpm.

1:3 = 1000rpm, starting with 300rpm.

1:2.5 = 1179rpm, starting with 3000rpm.

1:2 = 1500rpm, starting with 3000rpm.

1:3 = 500rpm , starting with 1500rpm.

2:3 = 1000rpm, starting with 1500rpm

2:4 =750rpm, starting with 1500rpm.

2:5 =600rpm, starting with 1500rpm.

If this is correct would just need a 5" pulley next to my 2" driven from the motor, On a question with your sized pulleys Dave would the bigger pulleys give better torque than the 2" to 1"

The trouble wth a 1 to 5 giving 600rpm i would nee a 3.5,4.5 or 2.5 pulley to match the lathe not so easy to find i think. This is why I have been looiking for other options

Cheers Martin

Edited cause of Damn smileys

Edited By Martin Newbold on 03/07/2016 19:16:35

Hi Martin,

Good timing - you got rid of the smileys whilst I was away logging in.

Re: 'On a question with your sized pulleys Dave would the bigger pulleys give better torque than the 2" to 1"

Well, in theory no. The torque conversion simply follows the same ratio as the speed conversion, only the other way round. (So a 2:1 ratio would halve the speed and double the torque whereas a 1:2 ratio would double the speed and halve the torque.)

It's not that easy though. Theory is fine and dandy but in the real world belts slip. And they are much more likely to slip on a small pulley than a big one. Slip costs both torque and speed, wears the belt and might overheat. Therefore for a given load and speed it's unwise to go below a certain minimum pulley size, which is why some of the other posts questioned your 1" pulley.

I'd give it a try and see what happens. If you get slip that you can't control with a jockey wheel or other way of adjusting belt tension, try bigger pulleys.

Trouble is, if you double the size of the driver, you have to double the size of the next one too.

It's a bit of a balancing act.

Cheers,

Dave

tah ,Dave am going to wait till i get a tachometer reading to see if my figures are correct , with the 4.5 opposed to 4 of the lathes pulley, as this will have a bearing on my extra pulleys and if its compatible with 4". If it is then this will be eaiser. My motor is on a wedge pulling the tension by its own weght so no problems there . The second stack of gears will need a tensioner havent thought about how to work this yet .

Cheers

Martin

ok according to laser guage have 150rpm on back gears and 420rpm on main drive.

Cheers

Martin

Well don't worry about buying one of these its not accurate cant understand why anyone would make one that doesnt give continuous readings

**LINK**

Aha found out why it didnt work had the tape on the outside didnt work has to be on on the diameter poking over edge got top speed 1013 r.p,m and 113r.p.m low back gear . This is why its been heating up the bearings needs to reduce to 600 rpm. so 5" and 4" pulleys here we come me thinks

Yep you were right the Pulley calculator isnt accurate on the online pages my motor is running at 2939 r.p.m and cannot get any combination of the pulleys on the site to get speed to 1013 r.p.m so think you are correct it does not work

Cheers Martin

Edited By Martin Newbold on 11/07/2016 21:57:48

Ahh, I see, bodge. Thread started on the wrong track. The real issue was substitution of an inappropriate drive? Too powerful, too fast (for a plain bearing spindle?) and likely excessive radial loads, beyond the bearing limits and possibly in the wrong direction? Nowt better than proper design, rather than trying to beat the mechanical constraints of the installation.

Yes thats about the long and short of it, ( been there, seen it and done it, on same model lathe. ) plus there are three threads running all to do with same model lathe . Martin Cleeve did some excellent articles on lathes and drives in the ME years ago, one in particular comes mind to do with an EW lathe, gave much information on the ratio of speed increments as one moves the belt across pairs on cone pulleys,

Have spent much time on drives on my own lathes, and run a double counter shaft on the main use 4 inch lathe , which came about because i wanted the motor under the lathe ( bit different from your usual myford ) so this gives two highs and lows using two steps ( counter shafts and motor pulleys are doubles ) plus the usual four on the mandrel cone = 16 speeds plus 16 more with the back gear engaged, low low with back gear in is about 12 rpm, high high direct is around 1000-ish, motor pulleys a poly v belt and motor pulleys are easy and quick to make so could go faster if need be......................b ................powered by 1/2 HP 1428 motor !............b

yes plain split p/bron bearing .............(. so is my 4 inch lathe ) ...................sorry for all the edits had refer to notes to check speeds..................b

Edited By bodge on 12/07/2016 06:35:07

Edited By bodge on 12/07/2016 06:40:59

Edited By bodge on 12/07/2016 06:52:57

Edited By bodge on 12/07/2016 07:10:40

Cant believe the gearing charts online are such rubbish . Its going to make it hard to work out which pulleys to use to get close to 600rpm any ideas. Will be putting in a second set of pulleys but need to work out what sizes to use as the website data i was using is completely wrong

Well am getting 113rpm on back gears and 1013 rpm from a 1" to 4.5" drive on a 2939rpm as powered from motor . Am clueless as to figure out lay shaft if these block pulley charts are all rubsh which it seems they are .

How did you work out your pulley sizes bodge ?

Cheers

M

Edited By Martin Newbold on 16/07/2016 12:32:15