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

Hi am wondering what intermediate pulley size to use in above to get to 600rpm please with three pulleys or four one extra of 1"

My pulleys are 4" 1" and 1" what would other pulley be to deliver as near to 600 rpm from 3000 I can get please?

Cheers

Martin

Hello

Ah I see from the 750 rpm I need a driven 5" pulley driving a 4" on the final from my 1" on motor driving 4" So would need a 5" and a 4", on single intermediate shaft.

Cheers

Martin

A 1" pullely driving a 4" pulley will give a 4 to 1 reduction. If they are V belt pulleys then you need to know the effective diameter. You do net get the correct ratio measuring the outer diameter or the diameter of the bottom of the groove. I have never seen a V belt pulley as small as 1"

Les.

You will probably find the info you need in a belt drive manufacturers catalogue. Some make belts and pulleys.

John

-

Martin,

1 in pulley on motor driving 4 inch on lay shaft with a 1 inch driving a 1.25 inch on the driven shaft.

So, 1"->4"/1"->1.25"

You will need a small section belt, 1 inch is a bit small even for a z section belt I think. If you need accurate speed reduction, positive drive is required - belts "always" slip and change ratio as they wear.....

Mark

I'm somewhat confused by your query. In the title you say you want to know gearing to achieve the reduction, then in the body of the text, you mention pulleys. You simply want a combination which will give you a reduction ratio of 5:1. Using one intermediate gear in a gear train will not affect the overall ratio at all. Without knowing the application, it's difficult to recommend a suitable combination, but if one pulley is only 1" diameter, I suspect that you're probably going to have to go to a toothed belt/pulley set-up. A quick look on the Beltingonline web site indicates mega-money for a 12 tooth/60 tooth combo to accept a 25mm wide belt. Depends how much power you need to transmit, too. You could possibly make do with a narrower belt if, as I suspect, the power transmission is fairly low. For example, I get away with a 10mm wide belt on my toolpost spindle, but that is powered by a 90W sewing machine motor.

Others may have a different interpretation.

John

Sorry to confuse you jon . It would not let me edit the title to change it to a pulley I am measuring the inside of my pulleys in the narrowest section is this wrong?

If you use poly-v you can use a 3/4" on the motor and a 3 1/4" pulley on the drive.

Neil

I'd come at this problem from another direction, that is how to get useful speeds from the ratios provided by a standard step pulley set. The advantage of using a step pulley pair is that only one belt is needed to change speed, with the drive-shafts arranged so that the belt is also a standard size.

For example a pair of these with 2", 3" , 4" and 5" diameters would give you:

3000 rpm x 2" / 5" = 1200 rpm

3000 x 3" / 4" = 2250

3000 x 4" / 3" = 4000

3000 x 5" / 2" = 7500

As these ratios driven direct from a 3000 rpm motor are far too fast, the motor should be geared down first with a fixed ratio pulley or gear pair. Of these:

2:1 in front of the step pulleys would give you 600, 1125, 2000 and 3750 rpm

3:1 would give you 400, 750, 1333 and 2500

4:1 would give you 300, 562, 1000 and 1875 rpm - this starts to feel reasonable for your Drummond

5:1 might be better with: 240, 450, 800 and 1500 rpm.

6:1 gives 200, 375, 666 and 1250

Hope I got the maths right and that this makes sense!

Cheers,

Dave

Martin - have a look at the following web-page - http://www.gizmology.net/pulleysbelts.htm - on that you'll see that for a V belt the pitch line is fairly close to - but not the same as the outside of the belt. Have a look at the Gates belt website as well. There are belt calculators on there that you can run on-line and when you put in the information about your drive it will tell you what belts are suitable as well as working out centre distance, ratio etc.

It looks as though your lathe only has a single pulley on the spindle - if so that will limit what you can do as you need to alter the spindle rpm to suit the job in hand. The speed that you're trying to get is pretty much the maximum that your lathe will stand. The lathe when Drummond built it would have had 3 different diameter pulleys on it, driven from 3 pulleys on the treadle. Drummond's recommended speed for the counter-shaft for a A type (round bed) is 250 rpm with the cone pulleys on that and the lathe spindle giving spindle speeds of 125, 250 and 500 rpm. If you are now looking at installing a counter-shaft then see if you can get a speed change facility through that as without it you'll be limiting yourself to the work that the lathe can cope with.

Oh dear this is getting confusing . I have 3 pulleys on my Drummond 3b not a round bed am using the top one which i thought to be a 4" inside and 4.5" outside. The belt runs on the brim of this as its a round profile.

The motor has also there pulleys I am in smallest with 1" inside and 2" outside this runs well in the v shape

I have a 3000rpm motor and used which is a really good site .

This said it should be running 750 . So if i use two indermediate gears with 5" as drive to 4" on lathe and 4" to my motor will this not give me 600? I understand this is the correct rpm

Using this again to derive the final speed from 750rpm

Edited By Martin Newbold on 02/07/2016 19:37:45

Edited By Martin Newbold on 02/07/2016 19:44:51

Hi Martin,

Yes if you mean this way

Edit

Whoops I got the diagram wrong.  Will try again in a minute!

Dave

Edited By SillyOldDuffer on 02/07/2016 20:46:17

Hi Martin,

Second attempt to get the diagram right!

Cheers,

Dave

No Dave , your diagrams not right middle should be 4 and 5 and bottom 4. is what i thought from my pages and post above.

So 1 to 4 sharing spindle  5 to 5

Cheers

Martin

Edited By Martin Newbold on 02/07/2016 21:48:05

Actually i think you are right Dave but this is not going to work for me as have 4 on lathe and 1 on motor

Just get a motor speed controller? Fit a RPM indicator (a fiver, or so, from epay). Then choose any speed you fancy.

Questions might be ' Why 600rpm?' 'What tolerance?' 'What type of prime mover?' 'AC or DC, if electric, and brushed or brushless?' 'What space restrictions?' Etc.

As mentioned, V belts do not drive on the bottom of the groove. Only flat belts do that! Washing machine motors, working with multi v belts, can have a huge speed reduction in one go.

Yes, it may be easier , and possibly cheaper, to control the motor speed....

Edited By not done it yet on 02/07/2016 23:36:44

Hi Notdoneityet

I had a feeling I rang some kind person who had a website about Drummond's an I think Tony said mine should run at 600rpm i think. But this was a while ago and much has happened . Speed controller from ebay do you have a link please

Cheers

Martin

Edited By Martin Newbold on 03/07/2016 09:14:45

Your web calculator is only approximate. To be exact it would need to know what the belt profile was. There are several of these.

It's generally not a good idea to use a pulley as small as 1" dia to transmit power so just how feasible that is depended on the power of the motor you have and the belt profile you are using.

In order to use a speed controller the motor would need to be a brushed type or 3 phase driven from an inverter.

Tony probably said 600 rpm as the whole area is a little to difficult to go into over the phone. For a one speed lathe it's not a bad choice but a range of say 250, 500 and 1000 along the lines of what Dave suggested would be a lot better. Your Drummond very probably did use a speed reduction from the motor to a counter shaft and then pulleys on that and the spindle to set the speed. Some use a pair of pulleys on the motor to counter shaft drive to obtain more speed.

If you want to do the speed reduction in one step Neil's poly V suggestion will probably work out with a small pulley in the size you are contemplating on the motor up to circa 1/3 hp / 250w output motor but the belt will need to be pretty tight and 5 to 1 via a 1" pulley is still a bit extreme for these as there wont be much belt lap round the small pulley. If it was a 1400rpm motor which is what is usually used on belt drive lathes this would be lot less of a problem.

John

-

I may be reading this all wrong-but. If you want to gear down a motor to run a lathe the exact speed is not important, measuring V pullies on the outside will be near enough, it is a ratio so both errors will be similar. Small dias. not good, but if you must then use a jockey pulley to give more wrap on the small pulley. Multi-vee belts are the way to go for small pullies.