Lathe Pulley Sizes

[PMD6]

Hi all

Im seeking some advice on lathe pulley sizes.

I have an old Grayson 3.5" it came with flat belt pullies, these are not original to the lathe and are extremely heavy. As such I have decided to convert to V pullies.

I have small pulley to fit to the motor. This has a diameter of 2".

The motor is 1425 rpm.

For the large one I have a 5.5 inch pulley - is this too small? If yes which is my fear what size should I be looking for?

Thanks in advance

 

[larry_g]

http://gadi.agric.za/software/renting/pulley_calc.php

Did a quick search on PULLEY SIZE CALCULATOR and came up with the above, as well as a few others. What is critical on a lathe is surface speed of the material being cut. So you have to size your pulleys to give the surface speed you need for the material and the diameter of stock being cut. You can also find calculators for selecting rotational speed to give a surface speed in ft/minute. http://www.calctool.org/CALC/eng/mechanics/linear_angular

So we cannot give you an answer with the information given.

lg
no neat sig line

 

[Guster]

Like this Grayson?
http://www.lathes.co.uk/grayson/index.html

Looks like the rebadged version of it, called Granville was fitted with v-belt pulleys:
http://www.lathes.co.uk/granville/index.html
Looks very much like a Myford too. Might be some ideas in those photos for you.

Personally if I was to change it to v-belt pulleys I would figure out what the 3-4 most popular speeds that I would want to change the 1425rpm drive to for general machining. Ie. pick 3-4 speeds and match the pulley ratios to that and go from there.

 

[PMD6]

Yeap - just like that

 

[PMD6]

I found this page.

http://www.lathes.co.uk/latheparts/page3.html

I think Ill go for a 7" pulley as they are readily available at a resonable price.

This will give me speeds of 200 / 400 / 800 rpm which should be sufficient to get me started. Im only tickering around at the moment

 

[Guster]

The flat belt pulley in the headstock appears to be original and the weight is not a bad thing even for a lathe this small. I'd be also be considering any limitations of the headstock bearings and would caution not loosing the integration of the bullgear and the much needed torque it provides with the additional 3x lower speeds.

If you are talking about the drive pulley only ie. the big one on the back mounted drive I would still consider maintaining the speed ranges you want for general machining. That is match the pulleys to achieve a similar ratio. Downgrading that big one to 2" may loose you a lot of the higher speed ranges which may be critical to achieve the needed surface speed when machining small diameter objects.

 

[PMD6]

By big pulley I mean the large 12" one top left.

In the set up shown in the pic the pulley on the motor was 2.5" giving speeds of

148 / 296 / 592

Im not looking to do anything to technical at the moment - just make some crash bobbins for a motorcycle out of aluminium

 

[onewaydave]

One other consideration is spindle speed. It probably has babbit or brass spindle bearings. I wouldn't exceed the original design.

Personally, I like the extra weight/mass. It provides momentum for a small lathe, as well as mass for vibration dampening.

Dave.

 

[Guster]

Phosphor bronze if it is original which is better than babbit in some ways but still limited compared to a decent roller/ball bearing if I recall.

Seeing as you are staying in similar speed ranges I would say go for it. Being close to a Myford in design you might even be able to upgrade to a decent bearing if you would like to achieve higher speed. Given the age and volume of use, might be time for new spindle bearings anyway.

 

[PMD6]

Cheers Guster - where are the bearings to which you refer - in the head stock either side of 3 step cone pulley?

 

[Guster]

Yes, the headstock bearings are stated to originally be phosphor bronze:
http://www.lathes.co.uk/grayson/index.html
"Following contemporary light-lathe practice, the headstock had split phosphor-bronze bearings closed down by clamp bolts at the front"

You may find that since the drive belt pressure and tool pressure is roughly in the same direction your bearing closest to the chuck will develop some wear in that direction over time. If worn you can easily machine new ones or do a little more measure and research to see if they are exchangeable with another like the Myford lathes it closely resembles. Another alternative is to research replacing them with ball or roller bearings as many Myford owners have done. Though the latter may require some machining using either mill or other lathe to line bore the headstock. Something you will want to do with some precision given the nature of the machine.