# Need Help With Lathe Pulley



## COPE 19 (Jan 21, 2016)

Hope someone can help, I have an old Enco 12 36 lathe model 92030 DOM 1983 and it looks as if someone has changed the motor and has put a single pulley on it. It came with a 2 step and I have no clue what size to shop for. I have checked with Enco and they cannot help. Everything else on the lathe works great so I would like to put the correct pulley on it. Does anyone have one that they can measure or a manual that will help or better yet some experienced knowledge. The best I can find is a part number for a similar lathe pulley , part # 3G-17 but no clue what size the pulleys are. Any help will be greatly appreciated.


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## brino (Jan 21, 2016)

Hi COPE,

Welcome to the site!

If you know the motor speed(from its plate), the size of the driven pulley, and have some indication of what your spindle speeds should be it's not too complicated to work out the missing pulley speed.

If you are missing some of the above and you get no direct measurement from someone else then my advice would be to find out what i) fits within the size constraints, and ii) if there's a choice in sizes get the one that gives a lower final spindle speed. I find I usually use the slowest pulley arrangement I can get on a lathe, with or without the back-gear engaged.

-brino


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## Bob Korves (Jan 21, 2016)

A lot of times there is very little movement of the motor available for tensioning the belt.  Make or buy a step pulley that has the same change in pulley sizes as the lathe end, but the opposite diameter steps, so the motor will be in the same place after tensioning it.  Something different might work as well, but you will then need a different length belt for the other groove set, and the mounting may be a problem due to interference somewhere.  Make sure also that the belt grooves are the same width and that the belts will end up with the same spacing from each other and in the same plane with each other.  Basically, you need a mirror image pulley in terms of diameter difference.

+1 on what Brino said about figuring out the original ratios by the stated speeds.

+1 on WELCOME to the site!


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## COPE 19 (Jan 21, 2016)

Thanks, That mirror image is what I was hoping would work on the lathe end there is I think a 3" and 5" the I need to find a 5 and 3 for the drive end. Will I get the same results if I get a 4 and 2 just as long as the belt keeps the same tension when switched or should I stay with the same sizes that are up top.  The speeds are posted on the plate but I am not sure that the motor RPM's are the same as what came on the machine new. Since I am new to all of this it probably doesn't matter as I am working on the slower side of the pulley and than have the back gears.  I just really like having things the way they were built as close as possible and it seems that whoever changed it did not care. Thanks for all the help, I need all I can get so any recommendations help.


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## Bob Korves (Jan 21, 2016)

Don't be in too big of a hurry to move toward lower speeds.  With time and practice you can do threading at higher speeds.  If you use carbide tooling on small stock you will soon be wishing for more RPM's.  My 13x40 has speeds from 70 to 2000 rpm and I have wanted both more and less than what it gives me at times.  Use brino's idea and determine the gearing from the lathe pulley to the spindle.  Then factor the ratio of pulley sizes and motor rpm into the equation.  PM me if you need help.
Edit:  A couple photos might help as well.


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## Bob Korves (Jan 21, 2016)

A four and a two would keep the same belt length as a three and five when changing speeds because it is the same diameter change.  It is the change in diameter that matters.  Pi is constant in both so it can be ignored.


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## brino (Jan 21, 2016)

I found a cheap digital laser tach is useful to have around the shop.

like any of these:
http://www.ebay.ca/itm/Digital-Lase...626354?hash=item4d15a52572:g:gDIAAOSw1S9WeNNC
http://www.ebay.ca/itm/Digital-Lase...792868?hash=item35f6ace5e4:g:kKUAAOSwNphWXwYb
http://www.ebay.ca/itm/Digital-Lase...958813?hash=item43e1ac105d:g:nAUAAOSwBahVaJVf

Note I am not recommending any particular suppler.
I got mine locally for about 4x those prices(doh!) at my local tractor supply place.

-brino


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## CluelessNewB (Jan 21, 2016)

You could use a belt length calculator in reverse.    You know the pulley center to center distance and the pulley sizes at one end.  Plug in different values for the other pulley 
and try to get the same belt length for both pulley combinations.   I would think your original motor would have been approximately 1725 RPM motor rather than something like  3450 RPM.  If your "new" motor is 3450 that would be suspect.         

Here is one online belt calculator:  

http://www.calculatoredge.com/mech/vbelt length.htm


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## epanzella (Jan 21, 2016)

COPE 19 said:


> Thanks, That mirror image is what I was hoping would work on the lathe end there is I think a 3" and 5" the I need to find a 5 and 3 for the drive end. Will I get the same results if I get a 4 and 2 just as long as the belt keeps the same tension when switched or should I stay with the same sizes that are up top.  The speeds are posted on the plate but I am not sure that the motor RPM's are the same as what came on the machine new. Since I am new to all of this it probably doesn't matter as I am working on the slower side of the pulley and than have the back gears.  I just really like having things the way they were built as close as possible and it seems that whoever changed it did not care. Thanks for all the help, I need all I can get so any recommendations help.



A 4 & 2 will both have the same belt length when reversed but they both will lower the spindle speed over their 5 & 3 counterparts  if used on the motor end.


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## COPE 19 (Jan 26, 2016)

Thanks to all, I am having trouble finding a pulley that is correct. I guess I need to get someone with more experience than me to make one. Anyone know the approx. cost of such?  My actual sizes on the top drive end is 4 5/8 and 5 5/8  with a 5/8 bore.


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