Changing Speed - Mark V

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dusty
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Changing Speed - Mark V

Post by dusty »

What actually causes the Idler Sheave to move? The button on the sheave is pushed in one direction (moving from High Speed to Low Speed) but what moves the Control Sheave in the other direction? Is it the the Motor Spring attempting to decompress?
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DLB
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Re: Changing Speed - Mark V

Post by DLB »

dusty wrote: Tue Oct 04, 2022 7:50 pm What actually causes the Idler Sheave to move? The button on the sheave is pushed in one direction (moving from High Speed to Low Speed) but what moves the Control Sheave in the other direction? Is it the the Motor Spring attempting to decompress?
I think it depends a bit on the condition of the machine. If all is working great, then yep, spring decompression will move the Control Sheave as the pork chop gets out of the way. This is why it (should) takes much less force to increase speed than decrease. As things gum up, maybe a bit of both the spring and drawing the control sheave away with the speed control via the clip and button.

- David
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dusty
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Re: Changing Speed - Mark V

Post by dusty »

DLB wrote: Tue Oct 04, 2022 8:34 pm
dusty wrote: Tue Oct 04, 2022 7:50 pm What actually causes the Idler Sheave to move? The button on the sheave is pushed in one direction (moving from High Speed to Low Speed) but what moves the Control Sheave in the other direction? Is it the the Motor Spring attempting to decompress?
I think it depends a bit on the condition of the machine. If all is working great, then yep, spring decompression will move the Control Sheave as the pork chop gets out of the way. This is why it (should) takes much less force to increase speed than decrease. As things gum up, maybe a bit of both the spring and drawing the control sheave away with the speed control via the clip and button.

- David
But let us assume that all is not great; that the sheaves have not been properly lubricated. What then brings the control sheave to open. I can not bring myself to believe that the spring steel arm on the porkchop pulls it back via the wire loop.
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chapmanruss
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Re: Changing Speed - Mark V

Post by chapmanruss »

When all is not great is when problems occur. If the movable sheaves on the Motor and Idler shafts no longer move, generally because of a lack of proper lubrication, trying to turn the Speed Control Assembly would be like trying to do that with the drive system (belts) not turning. Something has to give. That may be the wire loop coming off, damaging gear teeth on the Speed Control or other damage. If the Motor 's movable sheave is stuck that would act as a fixed pulley. If the Idler Shaft's movable sheave is moving properly it could open up by the Speed Control being turned. Closing the Idler Shaft's movable sheave would work up to the point it reengages the belt and would no longer be able to close further with the motor sheave not moving. If the belt wasn't there between the Motor and Idler Shafts pulleys It should take little effort by the Speed Control to "pull" the Idler Pulley open or push it closed.

As David said
If all is working great, then yep, spring decompression will move the Control Sheave as the pork chop gets out of the way. This is why it (should) takes much less force to increase speed than decrease.
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Re: Changing Speed - Mark V

Post by JPG »

It has been my contention for a long time that the sole purpose of the 'wire loop' is to not allow the center race of the bearing to rotate thus making it possible for the bearing to due it's job as the button is pressed(slid along) against the porkchop.

A properly lubricated and functioning reeves drive(belts, movable sheaves, fixed sheave) will respond to the control idler pulley opening(when the control sheave moves away from the fixed sheave) by first the drop in belt tension will cause the motor pulley spring the move the floating sheave towards the fan sheave this taking up the belt slack.

Only when the system becomes sluggish due to lack of lubrication or crud accumulation will the loop become active in the opening of the idler pulley. That may help for a while, but is NOT recommended procedure.

Sluggishness in the motor pulley will result in delayed speed increase(or outright slippage) even if the control sheave is moved with or without the assistance of the loop pulling on the control sheave.
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Re: Changing Speed - Mark V

Post by john_001 »

dusty wrote: Tue Oct 04, 2022 7:50 pm ... Is it the the Motor Spring attempting to decompress?
Basically, yes. Nothing “pulls” the control sheave (the little clip on the end of the pork chop is just there to keep the button bearing fixed; not to pull the control shaft back).

The spring on the motor shaft is trying to force the motor sheave closed (maximum diameter). Since the belt is a fixed length, in the absence of the pork chop the control sheave would be forced open (minimum diameter) and the machine would run at full speed. But when you lower the speed control, the pork chop, via the button bearing, pushes the control sheave closed, making it bigger. Since, again, the belt is a fixed length, this forces the motor sheave open against the spring and makes the motor sheave smaller, so the speed decreases. If you then raise the speed and back the pork chop away from the button bearing, the control sheave is now free to slide open (assuming the shaft is well-lubricated), so the motor shaft spring causes the control sheave to open by pushing the motor sheave closed, so the speed increases.

All of this is dependent on the two sheave shafts always being well-lubricated so the sheaves can slide back and forth freely.
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Re: Changing Speed - Mark V

Post by JPG »

Well said! john_001
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dusty
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Re: Changing Speed - Mark V

Post by dusty »

OKAY! I think I got it. The floating sheave and the control sheave move back and forth in lock step on their respective shafts under the control of the motor spring and the porkchop

The speed control (porkchop) pushes the floating sheave closed (against the spring) while the spring attempts to push back. The porkchop (with the mechanical advantage of the gears) controls all movement. If the speed control (porkchop) does not move -- nothing moves. The porkchop"pushes" the control sheave closed while the spring attempts to push the floating sheave closed. The belt is just along for the ride. It takes a position on the sheaves where evr the sheaves may push it.

The fan sheave and idler sheave do not change location with respect to one another.

The separation between the" fan sheave and the floating sheave" as well as that between the "idler sheave and the floating sheave" varies from 1/2" fully closed to approximately 1 1/2" fully open. The resulting ratio ultimately determines the speed of the idler chant. The diameters of these two sets of sheaves vary (depending on the speed setting) between 5 1/2" (fully open) and 2 1/2" (fully closed).

No matter what the speed is - the sum of the two diameters will always be 8".

I have been a long time coming to an understanding of how this all works but now, with thanks to all who have contributed to the many related threads, I understand.
Shopsmith Speed Control.png
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Re: Changing Speed - Mark V

Post by JPG »

One minor tweak to what you just posted.

The control sheave determines the location of the belt in the idler pulley.

When the control sheave is moved the belt will either be squeezed by the closing idler pulley or loosened by an opening idler pulley.

That change in belt tension(closing pulley will increase tension as the belt rides to a larger diameter location) will cause the floating pulley to be repositioned thus restoring belt tension to what it was before control sheave moved.
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dusty
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Re: Changing Speed - Mark V

Post by dusty »

JPG wrote: Thu Oct 06, 2022 10:47 am One minor tweak to what you just posted.

The control sheave determines the location of the belt in the idler pulley.

When the control sheave is moved the belt will either be squeezed by the closing idler pulley or loosened by an opening idler pulley.

That change in belt tension(closing pulley will increase tension as the belt rides to a larger diameter location) will cause the floating pulley to be repositioned thus restoring belt tension to what it was before control sheave moved.
What you say is absolutely consistent with what happens. I am just not sure of what causes what. Your introduction of "belt tension" being a control factor is what causes me pause. Regardless -the system works great and I think I understand how (maybe not why}.
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