Mark V Speed Control

[dusty]

We are right together at mid-range. Your estimate of 1.94" is dead on. Our estimates of what happens when speed is changed (up or down) from that point is what differs. I firmly believe that the radii of the sheaves change in opposite direction in equal amounts from that point (under the control of the quadrant with assistance from the spring).

[DLB]

We are right together at mid-range. Your estimate of 1.94" is dead on. Our estimates of what happens when speed is changed (up or down) from that point is what differs. I firmly believe that the radii of the sheaves change in opposite direction in equal amounts from that point (under the control of the quadrant with assistance from the spring).

I agree. That's a math prediction with some assumptions. An alternative math prediction with some assumptions is the average of max and min, that one gives us 1.788" datum line radius rather than 1.86". Not a huge difference, but getting far from your 2". Perhaps explained by the 14.5" number, which I think is another estimate and will vary from machine to machine because the eccentric adjustment changes the distance between the Idler and Motor shafts. Measurement is needed, though not currently practical for me. And then there is measuring belt length, an inherently inaccurate measurement unless one is willing to cut the belt or uses some calibration technique to correct for the inherent error.

- David

[dusty]

We are right together at mid-range. Your estimate of 1.94" is dead on. Our estimates of what happens when speed is changed (up or down) from that point is what differs. I firmly believe that the radii of the sheaves change in opposite direction in equal amounts from that point (under the control of the quadrant with assistance from the spring).

I agree. That's a math prediction with some assumptions. An alternative math prediction with some assumptions is the average of max and min, that one gives us 1.788" datum line radius rather than 1.86". Not a huge difference, but getting far from your 2". Perhaps explained by the 14.5" number, which I think is another estimate and will vary from machine to machine because the eccentric adjustment changes the distance between the Idler and Motor shafts. Measurement is needed, though not currently practical for me. And then there is measuring belt length, an inherently inaccurate measurement unless one is willing to cut the belt or uses some calibration technique to correct for the inherent error.

- David

Yes, much of the difference in how we acquire our numbers but now the 14.5" That is the measured distance between the idler shaft and the motor shaft. It is a variable as you point out but a vary small one.

[DLB]

I refurbished a Drive Sleeve and got the machine back together. Measured radius value was 1.949 to the belt surface, corrected to 1.869 at the datum line. Pulleys were equal at equal RPM, as expected.

- David

[dusty]

I refurbished a Drive Sleeve and got the machine back together. Measured radius value was 1.949 to the belt surface, corrected to 1.869 at the datum line. Pulleys were equal at equal RPM, as expected.

- David

This is good. I assume that if you either increase or decrease speed from that point the belt on one or the other of the sheaves can be moved so as to be nearly flush with perimeter of a sheave. At that point the measured idler shaft speed should be close to either 1120rpm or 8400rpm depending on which way speed was changed (up or down).

I am curious about how you make this measurement. I would measure from the perimeter edge of the sheave to the belt surface. At this speed (near motor speed of 3580rpm) I would expect the measurement to be about 3/4" which translates to 2" from belt surface to center of axis (the radius of either. sheave).

At this point - the sum of the two radii is 4" (2 x 1.949" carried to one decimal point).

[DLB]

This is good. I assume that if you either increase or decrease speed from that point the belt on one or the other of the sheaves can be moved so as to be nearly flush with perimeter of a sheave. At that point the measured idler shaft speed should be close to either 1120rpm or 8400rpm depending on which way speed was changed (up or down). Around 1200 to 9000 no-load on this machine. Which was the point of my earlier post, this conflicts with the data in the table you posted entitled Sheave Stats, both in dimensions and rotational speed. (1627 to 7876 Idler RPM)

I am curious about how you make this measurement. I would measure from the perimeter edge of the sheave to the belt surface. At this speed (near motor speed of 3580rpm) I would expect the measurement to be about 3/4" which translates to 2" from belt surface to center of axis (the radius of either. sheave). Same. I use a gage made from a SS T-nut, threaded rod, and jam nut, and adjust the threaded rod so it's giving me the distance from sheave perimeter to belt surface. Then measure the jig using dial or digital calipers using the depth feature. I've been using an offset of 0.080" from belt surface to estimated datum line. I use a previously measured sheave diameter (5.45") for reference.

Previous comment was something to the affect that the chart you posted seems to conflict with known measured data, or that I was completely missing the point of the chart.

- David

[dusty]

This is good. I assume that if you either increase or decrease speed from that point the belt on one or the other of the sheaves can be moved so as to be nearly flush with perimeter of a sheave. At that point the measured idler shaft speed should be close to either 1120rpm or 8400rpm depending on which way speed was changed (up or down). Around 1200 to 9000 no-load on this machine. Which was the point of my earlier post, this conflicts with the data in the table you posted entitled Sheave Stats, both in dimensions and rotational speed. (1627 to 7876 Idler RPM)

I am curious about how you make this measurement. I would measure from the perimeter edge of the sheave to the belt surface. At this speed (near motor speed of 3580rpm) I would expect the measurement to be about 3/4" which translates to 2" from belt surface to center of axis (the radius of either. sheave). Same. I use a gage made from a SS T-nut, threaded rod, and jam nut, and adjust the threaded rod so it's giving me the distance from sheave perimeter to belt surface. Then measure the jig using dial or digital calipers using the depth feature. I've been using an offset of 0.080" from belt surface to estimated datum line. I use a previously measured sheave diameter (5.45") for reference.

Previous comment was something to the affect that the chart you posted seems to conflict with known measured data, or that I was completely missing the point of the chart.

- David

I see your point! I need to think this through and evaluate how I created that chart.

Please comment on the entries at the bottom of the left hand panel. The numbers that relate to belt position at 3580 rpm. Do you agree with a 2" radius at 3580 rpm (idler speed)? That's 3/4" down from the sheave perimeter.

Do you also accept the premise that the diameters of the two sheaves change in equal and opposite directions from those numbers when the speed is changed?

[DLB]

I see your point! I need to think this through and evaluate how I created that chart.

Please comment on the entries at the bottom of the left hand panel. The numbers that relate to belt position at 3580 rpm. Do you agree with a 2" radius at 3580 rpm (idler speed)? That's 3/4" down from the sheave perimeter.
Essentially yes. 3580-ish RPM, 2-ish inch radius. Mine ran closer to 3570 RPM because motor RPM gradually decreases as headstock speed, and mechanical load on the motor, increase. And around 2 inches with some variation caused by variation in belt length/width and eccentric position. But those are likely small variations.
Do you also accept the premise that the diameters of the two sheaves change in equal and opposite directions from those numbers when the speed is changed?
No, I'm coming to the realization that they do not. Using this as a starting point, both radii (datum line) are 1.869". Move to slowest speed, and radii have changed to 2.66" and 0.916" respectively. The Idler sheave has changed +0.791 while the motor sheave changed -0.953. Opposite, but not equal. I think the tach proves these numbers as reasonably accurate.

- David

[dusty]

OKAY: You now have me doubting some of my assumptions. As a result I am going to have to do some testing with the tachometer included to convince m,yself one way or the other.

It will be hard for me to change my convictions because I am a strong believer in what I believe the mathematics tells me.

No matter what, our numbers will not be exactly the same because of "uncontrolled deviations" but those should be identifiable. Example: My belt measures 27". I measured it by attaching painters tape to the outer surface of the belt, cut it where the tape would overlap and then removing it to measure. Using that same piece of tape I checked two other belts. One checked to be the same and the other produced a slight overlap (about 3/a6"). Yes, the belts are not all identical.

Another Example: My idler shaft is offset by 7 1/4" from the motor shaft. There is potential for some difference here because of the eccentric. This deviation, however, will be very slight and will not vary at all on my machine unless I alter belt tension. On any other machine it might be different.

Another example that see is the motor speed. You have indicated that yours changes, If mine changes at all, it is very slight. I have set the tachometer and watched it for minutes with no change. I have checked it and then turned the motor off. When I bring it back on it measures withing 3-5 rpm the same. I am confident in saying that my motor turns at 3580 rpm +- 3 rpm. Yes, it may vary some under work load but not while just tesing idler shaft speed.

Off to do some testing.

[dusty]

No testing done yet but I have spent some time studying the numbers.

David - Looking at the numbers you provided for operation at mid-range it appears to me that all of the differences between your setup and mine can be directly attributed to the difference in belt length and rounding error We know that belt length differs by 3/8" (mine is 27" while yours is 26 5/8").

When I do a sketchup of your numbers and then run my spreadsheet against the two belt length differs by .785". We know the reason for 3/8" is belt length. The remaining .41" warrants more study.

When I run the same comparison using numbers at low speed I get a different picture. Your numbers and mine for dimensions of the control sheaves differ by only 3/32". Another story with the floating sheave. There we differ by more than 1/4". Your floating sheave (.961") being smaller than mine (1 15/64"). This would certainly explain the speed differences that we experience.

What I can't account for is the difference in belt lengths. Your numbers (sheave circumference plus 7.25" gap between sheaves) accounts for 25 3/4" of belt. My only GUESS is that the floating sheave has not expended as expected (motor spring is still compressed more than it should be) and the floating sheave is smaller than it should be.

Now I gotta do more testing. I am going to run the same tests on my other machine (The Shorty restored to Full Length). I am also getting close to being able to make saw dust once again.

This broken hip has been a real pain and a real nuisance in the shop. An accident waiting.