Still Trying to Fully Understand

[dusty]

the sheaves (operation of) in a Mark V and the pulleys in the Mark 7.

Does everyone agree that the Mark V sheaves are 5" and that this image (taken from a thread on this forum) accurately represents the belt position on the drive sheave when set at high speed (5200rpm).

and

Another simple question. Does the motor normally operate at 3450rpm or 3570rpm?

Drive Sheaves at High Speed.JPG (47.35 KiB) Viewed 22528 times

My issue is that I cannot reconcile pulley diameters on conjunction with the speed charts that are provided by Shopsmith. I do understand that there are some differing charts. I am assuming for this exercise that the idler sheave should move between 1120rpm to 8320rpm.

Yes! The numbers will not be exact and probably not consistent.

[garys]

I don't have a motor out to look at the ID plate on it, but in the US with 120v and 60cycle power, the two standards for motors are 1725 and 3450 rpms. Anything other than that would be have to be made non-standard.

[JPG]

What an excellent time consuming trip to lord only knows where(if indeed a destination is actually arrived at).

First of all an induction motor does not operate at a fixed speed. The resultant speed is a function of many factors with the major one being mechanical loading. The rated rpm includes usually the assumption of being fully loaded at the rated horsepower.

Now about v-belts. What is the effective 'diameter' when it is running on a pulley. It is somewhere between the outer(wide) and inner(narrow) portion of the belt.

Often (in the past) the question has been raised as to why the dial has letters rather than actual rpm numbers. As Nick once replied 'there is a lot of stuff going on there'. Accurate numbers simply are not consistant when all is taken into consideration including belt wear(that effective diameter thing again).

In spite of this the Mark VII did use actual numbers. They only got away with that before inexpensive tachometers became accessible.



So good luck Dusty. I think yer chasing yer tail. A ± 20% deviation is IMHO to be expected.

Now which of those differing speed charts are you attempting to reconcile?



Oh! BTW the idler pulley will rotate between 1120 and 8320 rpm.

[dusty]

I don't have a motor out to look at the ID plate on it, but in the US with 120v and 60cycle power, the two standards for motors are 1725 and 3450 rpms. Anything other than that would be have to be made non-standard.

Thank you for the response. The plate on my two motors both read 3450rpm as well. The motor (AO Smith) in my Shorty runs at 3570rpm.

I am through "chancing my tail" for now. I believe that I now understand the operation of the sheaves much better than simply knowing that they are variable pulleys. I also better understand the apparent inconsistencies in the Mark V speed chart that I have.

Sheaves, Shaft and Belt.png (72.58 KiB) Viewed 22188 times

This was a fun and educational journey for me. I find that no matter how much I use these machines there is always something more to learn.

[JPG]

Nicely done sketchup work. I am curious what the eccentric positioning was when the shaft spacing was measured.

[dusty]

Nicely done sketchup work. I am curious what the eccentric positioning was when the shaft spacing was measured.

I don't know but I really doubt that it is significant but to this machine and even then could be made different simply by adjusting belt tension.

What I did confirm for myself is that whatever amount the belt moves in one pulley it moves the same in the other. On my machine (The Shorty), the belt (when AT HIGH SPEED) is almost exactly the same distance from the edge of the other pulley when at low speed. This suggests to me that the change is linear for any given set of pulleys and belt. The speed chart have does not give me that impression. I am unable to closely match the speed chart but I suspect that is because the motor in The Shorty runs so much faster (3450rpm vs 3570rpm).

Oh, I also learned that my opening questions were not taken seriously because no one challenged the fact that the pulleys are 5" in diameter. They are actually 5 1/2".

[jsburger]

I don't have a motor out to look at the ID plate on it, but in the US with 120v and 60cycle power, the two standards for motors are 1725 and 3450 rpms. Anything other than that would be have to be made non-standard.

Thank you for the response. The plate on my two motors both read 3450rpm as well. The motor (AO Smith) in my Shorty runs at 3570rpm.

I am through "chancing my tail" for now. I believe that I now understand the operation of the sheaves much better than simply knowing that they are variable pulleys. I also better understand the apparent inconsistencies in the Mark V speed chart that I have.

Sheaves, Shaft and Belt 2.png

This was a fun and educational journey for me. I find that no matter how much I use these machines there is always something more to learn.

Just curious. Are you saying that the motor plate on your shorty says 3450 but it actually runs at 3570?

[dusty]

I don't have a motor out to look at the ID plate on it, but in the US with 120v and 60cycle power, the two standards for motors are 1725 and 3450 rpms. Anything other than that would be have to be made non-standard.

Thank you for the response. The plate on my two motors both read 3450rpm as well. The motor (AO Smith) in my Shorty runs at 3570rpm.

I am through "chancing my tail" for now. I believe that I now understand the operation of the sheaves much better than simply knowing that they are variable pulleys. I also better understand the apparent inconsistencies in the Mark V speed chart that I have.

Sheaves, Shaft and Belt 2.png

This was a fun and educational journey for me. I find that no matter how much I use these machines there is always something more to learn.

Just curious. Are you saying that the motor plate on your shorty says 3450 but it actually runs at 3570?

Yup.

[jsburger]

Thank you for the response. The plate on my two motors both read 3450rpm as well. The motor (AO Smith) in my Shorty runs at 3570rpm.

I am through "chancing my tail" for now. I believe that I now understand the operation of the sheaves much better than simply knowing that they are variable pulleys. I also better understand the apparent inconsistencies in the Mark V speed chart that I have.

Sheaves, Shaft and Belt 2.png

This was a fun and educational journey for me. I find that no matter how much I use these machines there is always something more to learn.

Just curious. Are you saying that the motor plate on your shorty says 3450 but it actually runs at 3570?

Yup.

And the other motor?

[JPG]

. . .

What I did confirm for myself is that whatever amount the belt moves in one pulley it moves the same in the other. On my machine (The Shorty), the belt (when AT HIGH SPEED) is almost exactly the same distance from the edge of the other pulley when at low speed. This suggests to me that the change is linear for any given set of pulleys and belt. Equal and opposite, but not necessarily linear.

Oh, I also learned that my opening questions were not taken seriously because no one challenged the fact that the pulleys are 5" in diameter. They are actually 5 1/2".

I had no doubt you can accurately measure the od of the pulley so no response was needed.