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

Hi Martin,

Due to the way you have your lathe set up, you can only really use the largest pulley on the lathe mandrel, trying to use the two smaller sizes will at the least cause a loss of grip due to less contact area, (also may cause clearance problems, the bigger the pulley the better the grip.) So the final drive ie last driven pulley in the drive train will be one to one ( 4 inch pulley driving the 4 inch lathe mandrel pulley ) I would also suggest you use a polyurethane type belting on this section of the drive train as it will grip better due to being a better fit and give a smoother drive. I would also suggest you obtain 1428 / 1500 rpm motor, 1/2 hp will be enough.

To work out the speeds/pulley sizes, using my one pic as example= Motor pulley 11/4 inch dia`at 1500 rpm - Driving - 61/4 inch = div 6.250 x 1.25 = 5 --- 1500 rpm divide by 5 = 300 rpm, So driving speed is now 300 rpm.

The cone on the driven shaft is the is the same as the cone on the mandrel ie --4--3--2- now

driving --2--3--4-- so 4 driving 2 (is = to 1 to 2) will be 600 --3 driving 3 ( is = to 1 to 1) will be 300 -- 2 driving 4 (is = to 2 to 1 will 150 rpm

The above is example only and no allowances made has been made for motor slip, the above gives fastest possible ----(but its near enough)

The problem as i see is you will need to rig a pair of cones and shafts under the lathe, might not be to pleasant to use, ........................b

To use 3000 rpm motor , you would need 1 inch motor pulley driving 91/2 pulley.........

Edited By bodge on 16/07/2016 22:34:26

HI bodge

Hmm am in need of som emore info as am not driving up to a 91/2 pulley as its huge

With my 4.5 on my lathe and 1 " on my motot at 3,000 and looking at two pulleys under side by side as a lay shaft. its hard to find a 4.5" puley so not sure i can use one to 9 1/2 am in need of a differant solution of pulleys.

cheers

Martin

Coming in late on this, it seems that your solution has already been given.

Make up a Countershaft. Drive from the 1" motor to a 5" on the Countershaft, and then from a 4" to the 4" on the lathe mandrel. Then you should have your required 600 rpm. The Countershaft/Mandrel belt tension is set first, and then you set the tension on the Motor/Countershaft belt.

Being me, I would try to arrange things so that there were at least three sizes of pulley on the motor shaft and on the Countershaft, with little or no change in belt tension as you change speeds Although cannot see ANY need to run the mandrel faster than the motor on an elderly plain bearing machine)

Possibly the best way is to have a 1" pulley on the motor with three sheaves, driving to three pulleys of increasing diameter on the Countershaft. The motor will need to be moveable to set the tension, but If you want to increase the wrap around on the pulleys, use a longer belt and run a jockey pulley on the outside of the primary belt (motor to Countershaft). The jockey pulley can adjust the tension by various methods, 1) a lever with a weight on the end of an arm, to given more or less constant tension, 2) a screwed rod to adjust the position of the jockey wheel, or 3) a spring to hold the jockey in contact with the back of the belt..

Also, with a large enough range of movement on the Jockey Wheel, that can be used to set the tension, as well as increasing the angle of wrap.

With regard to tension, Vee belts tend to increase tension when at speed, because of the centrifugal forces acting on the belt. And, if you over tension the belt, you increase the load, needlessly, on the bearings. You only need enough to prevent slippage, just about 1/2" of movement, with a little force applied midway between the pulleys, assuming a centre distance of about 10".

The Countershaft could run on a pair of plummer block bearings set on a pivoting  frame.  The Countershaft possibly could be sited behind the lathe, driven by the motor below.

H T H

Howard

Edited By Howard Lewis on 23/07/2016 13:35:42

Yes Howard, yes i know its been said but the final drive pulley on lathe is 4.5 not 4

The only size lathe I would(do) run from a 1" pulley on the motor is something the size of a "Super Adept", with a 100W or so of power and driven through a 5 mm heat fused belt. Unless you are using a Poly V belt, 1" does not have enough surface area to prevent belt slip, and for an ordinary V belt it is too tight a bend.

Ian S C

.

Martin,

Please heed this ^^^

MichaelG.

Martin,

Please correct me if I have chosen the wrong pictures but; for the benefit of any late-comers to this thread, I think it worth linking a couple of your photos.

1. Early configuration: **LINK** http://www.model-engineer.co.uk/sites/7/images/member_albums/152239/660217.jpg
2. Replacement motor, currently in use: **LINK** http://www.model-engineer.co.uk/sites/7/images/member_albums/152239/681115.jpg

May I suggest that you set up a countershaft with a primary reduction on poly-vee, and a secondary reduction on the existing vee-belt arrangement ... I'm sure this would make things much easier.

MichaelG.

Martin,

Yes, it's me again ... I just had another look at the first picture that I linked in the previous post.

You appear to have the cone pulley on the motor the wrong way round ... Usual practice is to have the motor pulley the pointing the opposite way to the lathe pulley.

MichaelG.

Yes that is why i refer to my one & only pic, poly v primary drive, round belt finale drive, 200 watt 1428 rpm motor. ( As can see in the pic, still need to cut second step on large pulley & make two step motor pulley ) always think it best to sort out lowest direct speed first & aim for around 100 rpm, as this has direct effect on what speeds you get with the back gear engaged.

Martin

The counter shaft cone ( the cone hidden behind the big pulley ) is exactly the same as the mandrel cone, it may well be 41/2 in, on the biggest pulley of the cone, i didnt check it, but what ever it is the two cones are the same, so the ratio will also remain the same.........................b

Interesting but firstly Tony said to use this type of belt he should know. Secondly Pulley maybe wrong way round but its easier to change belt this way round without taking out whole motor or pulley off.

Havent sorted out pulleys as have been two busy writting reports to get in workshop

Cheers

Martin

Edited By Martin Newbold on 02/08/2016 22:33:43

.

Please let us know how you finally sort this out, Martin.

MichaelG.

It mght be easier to re-instate the 4 Pole 0.37kW Motor and ABB ACS150 Inverter Drive you have, with a 4:1 belt ratio. This would give full power delivery to the Lathe from 342RPM to 685RPM for 50Hz to 100Hz and good torque performance from 100RPM to 342RPM.