# Atlas MF motor belt



## intrepid (Jul 25, 2022)

Trying to locate the correct motor drive belt for a Atlas MF.  The manual calls for a L3-125.  This is a 1/2" x 34" belt.  The old broken belt measures 3/8" x 31".  The pulley groves on the machine and motor measure only 3/8" wide.  The counter shaft 2 step pulley appears to be the factory correct with marking M6-427.  The hole shaft is 5/8" with a 1/2" bushing.  The spindle belt is a 1/2" belt.  Several other topics elsewhere all state the motor drive belt to be 1/2".  Did Atlas use different width drive belts over the years?  Seems the 3/8" belt may be a little light for this application but no way will a 1/2" belt fit these pulleys.


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## 34_40 (Jul 25, 2022)

It could be like mine,just a mish mash of parts and I can't really go by what "the book" says.  Mine was a 4 pulley setup originally, but a prior owner swapped it to 2 sheeve pulleys.  So when trying to swap speeds the belt is to wide to clear the mounting, there is no room between the pulley and the mount.


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## Soggy618 (Jul 25, 2022)

The M6-427 is one of the countershaft pulleys for the 618 lathe; this takes a 3/8" 3L belt.
I'd follow your instincts and use a belt that fits. 

BTW, the P/L for the lathe shows the belt as L9-125, which derives from an older 9" lathe model.


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## BGHansen (Jul 25, 2022)

I swapped a Harbor Freight segmented belt on my MFB.  Saves you from pulling the spindle and seems to work fine.

Bruce


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## intrepid (Jul 25, 2022)

BGHansen said:


> I swapped a Harbor Freight segmented belt on my MFB.  Saves you from pulling the spindle and seems to work fine.
> 
> Bruce


Yes Bruce, that is my plan for the spindle belt when needed.  For now I am just trying to figure out and understand the motor drive belt.  As Soggy618 suggested I will follow my instincts and go with the 3/8" belt.  Just hoping the small width belt can handle torque and power supplied by the motor.


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## JPMacG (Jul 25, 2022)

I use a 4L350 belt for the motor-to-countershaft of my MFC.  I think 4L means it is 1/2" wide.  By the way, I found that a ribbed belt runs smoother than a standard belt around the smallest groove of the the motor pulley.   No need for a link belt here (unless you just want to use one).  The countershaft is easily removed for belt replacement - unlike removing the spindle.


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## intrepid (Jul 25, 2022)

Just wondering JPMacG what is the number on your counter shaft pulley drive?  Is a also a two step pulley?


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## JPMacG (Jul 26, 2022)

Yes, it is a 2-step pulley.  The Atlas part number on the pulley casting is M1-80B.


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## intrepid (Jul 26, 2022)

JPMacG said:


> Yes, it is a 2-step pulley.  The Atlas part number on the pulley casting is M1-80B.


Thanks,  Its starting to make some since now.  It appears Atlas did use different size pulleys and belts on the various models.  Mine is a MF and from what I have been able to determine now it does have the correct 3/8" wide pulleys and belt.  Other models like the MFC they used the 1/2" motor drive pulleys and pulleys.  I suppose there are other differences between the models but at this time it is no big deal.  Now once I get mine in operation, like I mentioned before, I am hoping the 3/8" belt can handle the power and torque supplied from the motor.  If not, I now know how to upgrade.  Thanks all.


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## wa5cab (Jul 27, 2022)

The Alas mills all have two belts that some of the replies apparently confused.  The two belts are the motor to countershaft belt, commonly called the motor belt, and the countershaft to spindle belt, commonly called the spindle belt.  All 12 mill models used a 3/8" wide motor belt.  The three base models had 4-step cone pulleys and used a 3/8" wide belt.  The three A-models had 3-step cone pulleys and a 3/8" wide spindle belt.  The three B-models and the three C-models had two-step cone pulleys and used a 1/2" wide spindle belt.  There is no need for a 1/2" motor belt.  My 3996 12" lathe has a 3/4 HP motor and a 3/8" motor belt.  It was bought new in 1981.  I changed the motor belt about 5 years ago, more because I had the replacement belt on the shelf than for any other reason.


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## intrepid (Jul 27, 2022)

wa5cab said:


> The Alas mills all have two belts that some of the replies apparently confused.  The two belts are the motor to countershaft belt, commonly called the motor belt, and the countershaft to spindle belt, commonly called the spindle belt.  All 12 mill models used a 3/8" wide motor belt.  The three base models had 4-step cone pulleys and used a 3/8" wide belt.  The three A-models had 3-step cone pulleys and a 3/8" wide spindle belt.  The three B-models and the three C-models had two-step cone pulleys and used a 1/2" wide spindle belt.  There is no need for a 1/2" motor belt.  My 3996 12" lathe has a 3/4 HP motor and a 3/8" motor belt.  It was bought new in 1981.  I changed the motor belt about 5 years ago, more because I had the replacement belt on the shelf than for any other reason.


Thanks for this information and clearing this up.  I feel much better now knowing this about the 3/8” motor belt.  Knowing this, I’m wondering if I measured correctly.  Is the 3/8” motor belt 31”?  Thanks wa5cab


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## 34_40 (Jul 27, 2022)

And yes. I was confused about which belt you were asking about.  I was speaking about the spindle belt. Sorry.


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## wa5cab (Jul 28, 2022)

Intrepid,

I am sorry but the motor belt part numbers for the base and A-rev of the Atlas mill are about the only Atlas motor belt lengths that I do not have.  About all that I can suggest is to look up the Atlas belt part number and then call Clausing and order one.  I believe that parts lists for all of the various Atlas machines (except drill presses) are available in Downloads.  If you come up with it with that method, report it here and I will add it to Downloads.

I will also mention here that it is my understanding that Clausing sold out of the 3-groove and 4-groove Mill spindle and countershaft pulleys many years ago.  So if you find yourself needing either or both, your only options are going to be either locating either or both on the used market or converting to the 2-groove pulley configuration.


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## ub27Rocks (Jul 29, 2022)

Late to the party as usual but: I have an MF 4 sheave machine. Belt from motor to jack shaft is 3L320, jack shaft to spindle is M-28. I had to try a few to find this combination that works on my machine. Motor mount bracket and jack shaft casting are originals so those sized 3/8" belts should work for you as well.

I bought a brand new spindle pulley/gear assembly off eBay last year so they do pop up. I wanted spare for it and the power feed bevel gears just in case 

Gerrit


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## 34_40 (Jul 29, 2022)

ub27Rocks said:


> I bought a brand new spindle pulley/gear assembly off eBay last year so they do pop up. I wanted spare for it and the power feed bevel gears just in case
> 
> Gerrit


Would you be willing / able to make a drawing of that spindle?  I haven't been as lucky in finding a replacement as you have.


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## ub27Rocks (Jul 30, 2022)

I'm willing and able, just not sure as to when however  The main challenge with making a replacement is that the smallish gear is cast as part of the whole thing. Later ones (as in 3 and 2 step) had it as a separate item.


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## ub27Rocks (Jul 30, 2022)

And check your PM.


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## ub27Rocks (Jul 30, 2022)

wa5cab, is a M6-79 compatible with a MI-79? 4 step pulley.


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## 34_40 (Jul 30, 2022)

ub27Rocks said:


> wa5cab, is a M6-79 compatible with a MI-79? 4 step pulley.


Try this one, https://www.hobby-machinist.com/thr...-used-condition-50-shipped.93563/#post-866519    It may help clear up some things for you.  I did get the pulleys but I am uncertain if the spindle is also different.
That's why I was asking for the measurements.


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## wa5cab (Jul 30, 2022)

This post is mainly in answer to the question in Post # 18 above.

Probably not.  While there does not seem to be any way to know whether one part could be made from another if they both had the same suffix number, whether the two would be interchangeable or not is a definite NO.  The prefix (in this case M6 and M1) indicates the model of machine that the part was originally designed for.  M6 means that the part was originally designed to be used on the Atlas 618 and probably 612 (since both machines are 6" lathes.  Let me inject the comment here that no one still alive seems to know why they chose to use M6 instead of just 6 as they had done on the 9" and 10".  Anyway, the suffix number indicates the function of the part. in this case the spindle cone pulley.  Why they did not use the same spindle as the 618 uses no one seems to know.  The countershaft 4-step pulleys are the same and both have the earlier part number, M6-80.  But not the spindle one.  And although we have the 3 step and 2-step pulley and gear drawings, we do not have the 4-step drawing or the Mill spindle drawing or drawings.  I will try to call Clausing next week and check on the the situation.


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## ub27Rocks (Jul 31, 2022)

thank you for your sage advice as always. I will be pulling my MF spindle next week so can measure it all up then.


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