# What are the actual spindle speeds



## David Pollard (Nov 3, 2013)

Hello Again,
Sorry for all the questions, I hope they are constructive and that others will also read and benefit from my newbeness.
I'm trying to figure out what the actual spindle speeds are for each of the pulley and gear positions.
The machine is an Atlas V42 and I have figured out that it is a 10F.

Firstly the motor has 1435 RPM Stamped on it.
I also notice that the motor and the next pulley both have two positions however both pulleys are larger than the ones currently in use so it would seem I need a different sized belt to use them. (See attached)
Is this standard or an add on feature?

I have been looking through a manual I found online "Manual of Lathe Operation and Machinist Tables" and can't find anything about what rpm each of the pulley positions actually produce.

With the 4 major pulley positions and the back gears, this would produce 8 speeds.
With the second pulley on the motor this would bring the number of different speeds to 16.

I'd like to be able to calculate a rough surface speed based on the type of tools I'm using and the diameter I'm turning.

Has anyone got a clue where I can start to figure out all the possible speeds?

Thanks
David


PS I made my first test cut today after 30 Years out of the trade.  Bit of a mile stone really 
(Nothing exploded)


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## Dranreb (Nov 3, 2013)

Hi David, the on line manual may vary from mine but the info you need should be on page 47 in the chapter headed 'Part 4, The Machining of Various Materials'

Bernard


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## pdentrem (Nov 3, 2013)

The belts are simply moved from one position to the other. You release the tension on the countershaft and slip the belt over. The motor is only suspended on a pivot thus you have to lift it a bit and this will give you the slack to move the motor belt to the other range.

This is based upon regular North American motor speeds running 60 cycle electrical supply. Motors here are 1750 rpm. Your speed will be only 82% of these RPMs listed.
No. of Spindle Speeds: 16 (8 Direct, 8 Backgeared ) 
8 Direct spindle speeds RPM: 164, 266, 418, 500, 685, 805, 1270, 2072 
8 Backgeared* spindle speeds RPM:* 28, 45, 70, 83, 112, 134, 211, 345 

More info on Atlas/Craftsman lathes can also be found on the yahoo groups and the lathes.co.uk site.

Here http://www.lathes.co.uk/atlas/

Pierre


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## Terrywerm (Nov 3, 2013)

It appears to me that the motor pulley is installed backwards on the shaft. Normally the smallest motor pulley will belt up to the largest countershaft pulley, and the largest motor pulley will belt up to the smaller countershaft pulley. In this way you retain the use of the same belt for both positions. 

In its current configuration, moving the belt to the larger two pulleys will probably result in a countershaft speed that is very near to the speed that it runs with the belt in its current position, but requiring a longer belt.

You can also determine your own shaft speeds as follows by first calculating the drive ratio, then using the drive ratio to calculate the speed of the driven shaft:  

Drive Ratio = Drive pulley diameter / driven pulley diameter        
Driven shaft speed = Drive pulley speed x drive ratio 

These formulae work whether your speed is increasing or decreasing. Using the outer pulley diameter will not give you a perfect result (pitch diameter should be used) but using the OD will get you so close that you will never know the difference. These formulae also work with chains and sprockets and with gears. If using the formulae for sprockets or gears, you can substitute the tooth count from each sprocket or gear instead of using the measured diameter or the pitch diameter.

Once you have the countershaft speeds calculated, you can repeat the process to determine your available spindle speeds using the same formulae.

To determine the SFM (Surface Feet per Minute) of the item you are turning, use this formula:
SFM = RPM x (Diameter of workpiece in inches x 3.14) / 12

For metric measure, the surface speed in Meters per minute is calculated similarly (if I remember correctly the correct measurement is Surface Meters per Minute):
Surface Meters per Minute = RPM x (Diameter of workpiece in mm x 3.14) / 1000


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## pdentrem (Nov 3, 2013)

You are right ! It is backwards on the motor. The 2 1/2" is to the motor side and the 4" is the outside.
Pierre


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## Privateer (Nov 3, 2013)

Here's a handy image of the spindle speeds for a 1750 rpm motor.  




I printed one out for myself on a sheet of paper, and leave it on the bench for reference. One day I might even hang it on a wall. 

Terry


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## pineyfolks (Nov 3, 2013)

http://www3.telus.net/findNchoose/pulley_calculator.html    This may help get the speeds you're after or figure out what you have.


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## David Pollard (Nov 4, 2013)

That's great information,  I thought the first two pulley sizes looked silly, I never thought one might be around the wrong way.

I should be able to just calculate the speeds as a percentage based on my motor RPM.

I'll just draw up a chart basses on the one pictured.

Damn I saw a wheel puller at a garage sale the other day and I didn't buy it.
I liked it but thought "what would I need that for"
This was before I bought the lathe 

I'll post the end result.
David


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## Terrywerm (Nov 4, 2013)

I noticed that the motor pulley is held on with a tapered key, or what some folks call a gib head key. Once you get the key pulled out, the pulley should just slide right off the shaft. Removing tapered keys can be a trying experience, but usually they aren't too bad. Pry bars, vice grips, wedges, hammers; they all come in handy to get those keys out!


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## schor (Nov 4, 2013)

I have an rpm gauge and use that to find out my exact spindle speeds.


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## caveBob (Nov 4, 2013)

pollardd said:


> ...snip
> 
> I should be able to just calculate the speeds as a percentage based on my motor RPM.
> 
> ...snip



Get yourself one of these, ~$15 shipped from Amazon:

Digital Photo Laser Tachometer Non Contact Tach
http://www.amazon.com/CyberTech-Digital-Tachometer-Contact-bundle/dp/B001N4QY66

You could use "digital tachometer" for a search term there at Amazon or Google for others. Point is... they are actually pretty darn accurate, just apply a small strip of the supplied reflector tape to the edge of the spindle pulley. Lotsa other uses too...


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## David Pollard (Nov 5, 2013)

I couldn't believe it I pulled the key out with my fingers took the pulley off and turned it around and taped th key back in aga in about 20 seconds.  I need to take my time to adjust the belt tension again.  I'm not even sure if the same belt will still fit.  This may be the reason the pulley was put on backwards in the first place.  (to make a belt that was lying around fit)

While we are on the subject (or off subject) the large pulley on the counter shaft seems to have about 10 degrees of free play which I guess means the key is damaged.  The grease cap comes off easily.  Any special instructions to remove this pulley and access the shaft and key?


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## Dranreb (Nov 5, 2013)

Are you meaning the stepped pulley? If so be aware that the keyway can wear sideways in the pulley and trap the key in the recess, pulling it off may not work and cunning needs to be applied. 

Bernard


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## David Pollard (Nov 5, 2013)

I figured out the pulley free play problem.
The problem is with the large pulley on the counter shaft (the two step pulley and not the one on the motor shaft)
It is the one closest in the attached picutre above.  After I took a carefull look at it I can see it is held on by a grub screw.
I removed the grub screw and then removed the pulley.  There is no damage to the shaft.

All reassembeled no problem and the free play is now gone.
I adjusted the motor to tension the belt and it now fits correctly in both positions.

So all in all a happy ending!

BTW I think I'll invest the $10 on one of those laser RPM devices.


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## David Pollard (Nov 7, 2013)

I thought I had better post the answer.
here are the calculated speeds (based on 82% motor speed)


Back Gear In
      1.     2.    3.      4 
A.   23    37    57     92
B.   68    110  173   283

Back Gear Out
      1.     2.    3.      4 
A.   134  218  342   560
B.   410  660  1041 1700

David


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