Mark V Speed Control
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- dusty
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Re: Mark V Speed Control
When I use 2.53" as the max radius (5.03" Max PD) and do the calculations I find the min radius (Min PD) to be 1.449" and the idler speed to 6024 rpm (1234 rpm quill).
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Dusty
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Re: Mark V Speed Control
I'm still having a hard time understanding where you are coming from on this. When I read the words I think you have accounted for 14.5" + 15.895" + 5.1208" or a bit over 35.5" of belt, but you said the total accounted for is 23.087". By my measurements/math, the only number that is close to mine is the 14.5", and I'm not understanding where the rest of them are coming from.dusty wrote: ↑Sun Jul 24, 2022 12:40 pm ...
The numbers do not all add up.
With reference to this sketch I am unable to account for about 4" of the motor belt and the only place the difference can be introduced is in the circumference of the idler pulley.
The belt is 27" long. The pullet axis are separated by 7.25" thus accounting for 14.5" of the 27".
The idler pulley is at maximum diameter thus accounting for 15.895" while the motor pulley (by calculation) accounts for 5.1208", Total belt length accounted for is 23.087"
Where is the rest of that belt (4").
...
I'm applying my measured values to what I think you are trying to do here. I am using only the outside diameter of the belt. I'm simplifying the belt-path model as two semi-circles with a diagonal line connecting them. The Idler measured R=2.75" (belt was slightly proud), so accounts for 8.639". The Motor measured 0.8625, accounts for 2.71". The straight line distance between the points on the pulleys is calculated. It is the hypotenuse of an artificial triangle with "a" equal to the 7.25" difference in centers and "b" equal to the difference in radii, comes to 7.492". (Per Pythagorus.) Times two. All in, comes to 26.33" of what I believe is usually called a 26.5" (OD, not PD) belt. Pretty close.
My measured values, therefore, seem very close to correct. My spring appears to be fully compressed and my belt rides slightly proud on the Idler, so the pulleys are maxed/min'd out. (Both at, or very near, their mechanical limits aka stops.

- David
- dusty
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Re: Mark V Speed Control
14.5" is the sum of the 1/2 circumference measurements and can ve calculated by knowing the radius or diameter of the sheaves. The 12.5 " is the distance in space between the axis of the two shafts (idler and motor). 12.5 + 14.5 = 27" The belt length which obviously is a constant.DLB wrote: ↑Sun Jul 24, 2022 6:20 pmI'm still having a hard time understanding where you are coming from on this. When I read the words I think you have accounted for 14.5" + 15.895" + 5.1208" or a bit over 35.5" of belt, but you said the total accounted for is 23.087". By my measurements/math, the only number that is close to mine is the 14.5", and I'm not understanding where the rest of them are coming from.dusty wrote: ↑Sun Jul 24, 2022 12:40 pm ...
The numbers do not all add up.
With reference to this sketch I am unable to account for about 4" of the motor belt and the only place the difference can be introduced is in the circumference of the idler pulley.
The belt is 27" long. The pullet axis are separated by 7.25" thus accounting for 14.5" of the 27".
The idler pulley is at maximum diameter thus accounting for 15.895" while the motor pulley (by calculation) accounts for 5.1208", Total belt length accounted for is 23.087"
Where is the rest of that belt (4").
...
I'm applying my measured values to what I think you are trying to do here. I am using only the outside diameter of the belt. I'm simplifying the belt-path model as two semi-circles with a diagonal line connecting them. The Idler measured R=2.75" (belt was slightly proud), so accounts for 8.639". The Motor measured 0.8625, accounts for 2.71". The straight line distance between the points on the pulleys is calculated. It is the hypotenuse of an artificial triangle with "a" equal to the 7.25" difference in centers and "b" equal to the difference in radii, comes to 7.492". (Per Pythagorus.) Times two. All in, comes to 26.33" of what I believe is usually called a 26.5" (OD, not PD) belt. Pretty close.
My measured values, therefore, seem very close to correct. My spring appears to be fully compressed and my belt rides slightly proud on the Idler, so the pulleys are maxed/min'd out. (Both at, or very near, their mechanical limits aka stops.) If I had a tach I would expect it to measure about 4% higher than I calculated or I'd be wondering why. (4% because of virtually unloaded motor speed being slightly higher than 3450.)
- David
The diameter of the idler pulley is also a constant when at low speed. The variable sneaks in when PD is taken into consideration. With the idler pulley at max calculate the circumference, Subtract that and the 14.5" from the 27" and the result is the 1/2 circumference of the motor pulley.
The 27" (all of it) must be acvcounted for,
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Dusty
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- JPG
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Re: Mark V Speed Control
The 'achieved' slow rpm is indeed affected by the high speed adjustment.
Yes the floating sheave can come to a mechanical stop sorta, but since we are considering the open condition, any stop would also diminish belt tension or the belt dropping down into the vanes of the motor pulley sheaves. The closure of the control sheave can limit the attained slow speed since it cannot close more to increase the effective diameter.
The high speed adjustment starts with positioning the belt near the outer rim of the idler pulley. The hs adjustment is made to limit the positioning of the control sheave. When the adjustment is made, the floating sheave will be responding to changes made in the positioning of the control sheave(affected by the hs stop).
Many things can affect the end result including belt width and lengthdue to wear etc.), sheave wear, as well as the hs stop itself.
We need to realize there are many things that WILL affect the final result and that the HS adjustment is an approximation at best.
Using a tach to quantify things will lead thee on a merry chase( similar to chasing perfect rip fence alignment with a dial indicator).
Yes the floating sheave can come to a mechanical stop sorta, but since we are considering the open condition, any stop would also diminish belt tension or the belt dropping down into the vanes of the motor pulley sheaves. The closure of the control sheave can limit the attained slow speed since it cannot close more to increase the effective diameter.
The high speed adjustment starts with positioning the belt near the outer rim of the idler pulley. The hs adjustment is made to limit the positioning of the control sheave. When the adjustment is made, the floating sheave will be responding to changes made in the positioning of the control sheave(affected by the hs stop).
Many things can affect the end result including belt width and lengthdue to wear etc.), sheave wear, as well as the hs stop itself.
We need to realize there are many things that WILL affect the final result and that the HS adjustment is an approximation at best.
Using a tach to quantify things will lead thee on a merry chase( similar to chasing perfect rip fence alignment with a dial indicator).
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Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10E[/size](SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange
Re: Mark V Speed Control
I don't 'see' the correlation between high speed adjustment and low speed achieved. I do see the correlations between belt length/width and any speed. The high speed adjust, by setting the dial, does set the relationship between sheave position and where the slow detent will occur, but I'm going past the detent if needed in arriving at the slowest achievable speed. Just as I go past the high speed detent, usually without even knowing it is there.
Note - IIRC the slow speed detent occurs at 'SLOW' on the dial, and is based entirely on dial position. It may or may not be felt at slowest achievable speed, which is based entirely on sheave positions. If you want it to occur at slowest achievable speed, you can set the dial to do that as Steve advocated earlier in this thread. (Rather than at high speed.)
Lowest theoretical RPM would occur if the Idler sheaves were closed to max diameter AND Motor sheaves were opened to min diameter. With all of the things that vary, it is highly unlikely that we would ever get both conditions at the same time. So lowest speed achieved should be when either of those conditions are met, because the speed control will stop responding at that point. Unless you only adjust to the detent or to some dial indication. I agree that Motor sheaves fully open (min diameter) is the less desirable of the two, but I think it happens sometimes.
- David
Note - IIRC the slow speed detent occurs at 'SLOW' on the dial, and is based entirely on dial position. It may or may not be felt at slowest achievable speed, which is based entirely on sheave positions. If you want it to occur at slowest achievable speed, you can set the dial to do that as Steve advocated earlier in this thread. (Rather than at high speed.)
Lowest theoretical RPM would occur if the Idler sheaves were closed to max diameter AND Motor sheaves were opened to min diameter. With all of the things that vary, it is highly unlikely that we would ever get both conditions at the same time. So lowest speed achieved should be when either of those conditions are met, because the speed control will stop responding at that point. Unless you only adjust to the detent or to some dial indication. I agree that Motor sheaves fully open (min diameter) is the less desirable of the two, but I think it happens sometimes.
- David
- dusty
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Re: Mark V Speed Control
This is the best I can do to depict my sheaves. The sketch shows (in the far right side) the diameters of the sheaves at high-mid-low speeds. For this sketch I define high as when the belt is flush with the outside perimeter of the motor sheave.
Thusly, low speed would reposition the sheaves with the belt flush with the outside edge of the idler sheave.
On my machines the belts do not come flush with the sheaves. They are inset at least 1/8" which I believe at least compensates for PD in my spread sheets (used for calculations.
If explanation is required just say so. I am must willing to make changes or answer questions about this or anything else I post on this forum.
Thusly, low speed would reposition the sheaves with the belt flush with the outside edge of the idler sheave.
On my machines the belts do not come flush with the sheaves. They are inset at least 1/8" which I believe at least compensates for PD in my spread sheets (used for calculations.
If explanation is required just say so. I am must willing to make changes or answer questions about this or anything else I post on this forum.
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- SteveMaryland
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Re: Mark V Speed Control
In the interest of clarity, another post. See attached jpgs.
It helps to draw a picture. I have learned a lot by doing so during this thread. I am lucky to have a very good CAD program.
To address the OP's and Dusty's problem, they want lower min RPM, and it appears to me that the only way they will get that is to use a shorter belt length. See table. Shorter belt length results in lower min PD - which in turn results in lower min RPM.
It also results in higher max RPM, but that's how it is. Shorter belt = lower min speed, higher max speed. Longer belt = higher min speed, lower max speed. It is just geometry. Please review the attached materials and advise if unclear.
I also learned that there is a minimum PD under which we cannot go - because to go lower would result in the belt not fully engaging the sheaves and possibly falling into the gap between the sheaves. To be avoided. This makes the min practical PD = 1.88".
And if 1.88" is our practical min PD, and 5.06" is our practical max PD, then the lowest output speed we can get is - see table. That lowest speed is obtained by using, not the Official Shopsmith 26.57" long belt, but a shorter belt.
Likely such a belt of that length is available, or close - I have not shopped for one. I would try a link-belt instead.
I really am surprised that the Official Shopsmith belt will not allow 700 RPM output speed - isn't that a claim?
So as far as I am concerned, a remedy for the OP's and Dusty's issues were found, and we all learned.
It helps to draw a picture. I have learned a lot by doing so during this thread. I am lucky to have a very good CAD program.
To address the OP's and Dusty's problem, they want lower min RPM, and it appears to me that the only way they will get that is to use a shorter belt length. See table. Shorter belt length results in lower min PD - which in turn results in lower min RPM.
It also results in higher max RPM, but that's how it is. Shorter belt = lower min speed, higher max speed. Longer belt = higher min speed, lower max speed. It is just geometry. Please review the attached materials and advise if unclear.
I also learned that there is a minimum PD under which we cannot go - because to go lower would result in the belt not fully engaging the sheaves and possibly falling into the gap between the sheaves. To be avoided. This makes the min practical PD = 1.88".
And if 1.88" is our practical min PD, and 5.06" is our practical max PD, then the lowest output speed we can get is - see table. That lowest speed is obtained by using, not the Official Shopsmith 26.57" long belt, but a shorter belt.
Likely such a belt of that length is available, or close - I have not shopped for one. I would try a link-belt instead.
I really am surprised that the Official Shopsmith belt will not allow 700 RPM output speed - isn't that a claim?
So as far as I am concerned, a remedy for the OP's and Dusty's issues were found, and we all learned.
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Mark V, Model 555510, Serial No. 102689, purchased November 1989. Upgraded to 520
- dusty
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Re: Mark V Speed Control
Thank you very much, Steve.
The information that you have added is very informative and much appreciated. Your CAD documents are great.
We still are not on exactly the same page. I am out of step because I have not made the transition n to PD. Also, I have not been able to find official documentation on the Shopsmith belts (there have been several from different vendors); all sold by Shopsmith at one time. The numbers that I am working with are all from belts that I have and can measure.
It would be fair yo say that my numbers (other than PD) are rough averages of the belts I can measure.
I am curious though about what you have stated as the length of the official SS belt being 26.57" Where is that number stated?
For this specific application .47" makes a significant difference.
Unfortunately, we have not heard from the OP and there is no way to know if his concerns have been answered. Hopefully they have.
The information that you have added is very informative and much appreciated. Your CAD documents are great.
We still are not on exactly the same page. I am out of step because I have not made the transition n to PD. Also, I have not been able to find official documentation on the Shopsmith belts (there have been several from different vendors); all sold by Shopsmith at one time. The numbers that I am working with are all from belts that I have and can measure.
It would be fair yo say that my numbers (other than PD) are rough averages of the belts I can measure.
I am curious though about what you have stated as the length of the official SS belt being 26.57" Where is that number stated?
For this specific application .47" makes a significant difference.
Unfortunately, we have not heard from the OP and there is no way to know if his concerns have been answered. Hopefully they have.
"Making Sawdust Safely"
Dusty
Sent from my Dell XPS using Firefox.
Dusty
Sent from my Dell XPS using Firefox.
Re: Mark V Speed Control
SteveMaryland, Are you saying longer belts have too much slack to separate the motor sheaves far enough apart to reach minimum pitch diameter?
The upper sheaves are held to a fixed pitch diameter by the speed control so the lower sheaves have to absorb changes in speed created by changing loads. Shouldn't the minimum PD still leave a little uncompressed spring on the motor shaft to allow for that?
I don't recall where I learned of the following, not really sure it applies here. I thought the belt would push further between the spring loaded motor sheaves by some tension on the belt created from it being driven around around the sheaves. That would allow a slightly longer length belt than calculated above to still achieve the minimum PD.
The upper sheaves are held to a fixed pitch diameter by the speed control so the lower sheaves have to absorb changes in speed created by changing loads. Shouldn't the minimum PD still leave a little uncompressed spring on the motor shaft to allow for that?
I don't recall where I learned of the following, not really sure it applies here. I thought the belt would push further between the spring loaded motor sheaves by some tension on the belt created from it being driven around around the sheaves. That would allow a slightly longer length belt than calculated above to still achieve the minimum PD.
Ed from Rhode Island
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- dusty
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Re: Mark V Speed Control
Would running with the belt on the upper sheaves set proud (at low speed) make your point.edma194 wrote: ↑Mon Jul 25, 2022 4:13 pm SteveMaryland, Are you saying longer belts have too much slack to separate the motor sheaves far enough apart to reach minimum pitch diameter?
The upper sheaves are held to a fixed pitch diameter by the speed control so the lower sheaves have to absorb changes in speed created by changing loads. Shouldn't the minimum PD still leave a little uncompressed spring on the motor shaft to allow for that?
I don't recall where I learned of the following, not really sure it applies here. I thought the belt would push further between the spring loaded motor sheaves by some tension on the belt created from it being driven around around the sheaves. That would allow a slightly longer length belt than calculated above to still achieve the minimum PD.
See the sketch that I posted in this thread with the red ring around the sheave, The numbers that go with that sketch show what low speed was achieved.
"Making Sawdust Safely"
Dusty
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Dusty
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