Schedule a Meeting · Talk to a real woodworker: +1 937-890-5197 · 8:00AM – 4:30PM ET

Mark V Speed Control

dusty

DLB wrote
dusty wrote I set it with the belt "flush" with the floating (motor) sheave.

This statement changes things quite a bit. Elsewhere, you've referred to set 'properly' which I interpreted as meaning per the manual or sawdust session. The manual I'm looking at says to set it at 5200 RPM (if using a tach, I suppose) or until the drive belt is 1/8" to 1/16" below the outside diameter... Same as the sawdust session IIRC. I agree with how you set it, but it's not per the manual. It is likely much faster than 5200 RPM, as well. Then it is purely coincidence that the slow speed belt position is also approximately flush, which it would be no matter where you set the high speed stop.

I used to set my high speed stop ~1/8" below the outside diameter because I didn't have a tach. So I set the stop=Fast (on the indicator dial) = 1/8" below... With a tach, I set the high speed stop faster for ease of maintenance (the only time I use the stop) and set the indicator dial for the best result in the useful speed range, which for me is from slowest achievable to ~3500 RPM. Best result, meaning closest fit to the speed chart independent of load.

- David

You rightly point this out. Flush is not per procedure. All of the documentation that I have seen says 1/16" to 1/8" below flush (to compensate for belts with diminishing dimensions). I don't have any of those on my machines - mine are all new or so nearly new .

I do not advocate this deviation from procedure even though I do it. Slightly below flush is proper.

dusty

Sheave Stats.png

DLB

dusty wrote Sheave Stats.png

The table appears to conflict with things we know to be correct.(?) My measured no-load Idler speeds range both faster (9006 RPM) and slower (1198 RPM) than what the chart indicates. Or am I missing the point?

- David

JPG

What is the column 2 number?

This reflects a quill speed range of 1017 to 4923 rpm.

dusty

JPG wrote What is the column 2 number?

In column 2 the fractional number (17/64") is the distance from the outer edge of the sheave to the top of the belt measured on the surface of the sheave. I measured that way because I could not get a good sheave radius due to the several obstacles that prevented me from using a dial caliper or steel rule. The hypotenuse of a right triangle formed by the sheave and the top of the belt.

This reflects a quill speed range of 1017 to 4923 rpm.

Yup. Using these pulley sizes and a belt of fixed length (27" for my calculations) and standard pulley ratios these are the speeds created by each pulley set. It was thedse numbers that led me to declare early in this thread and elsewhere that 700rpm was impossible to achieve.

Please - if you see an error in my thinking say so. I would very much appreciate being shown the light.

DLB

dusty wrote Please - if you see an error in my thinking say so. I would very much appreciate being shown the light.

Previous results, both measuring RPM and measuring minimum radius, suggest to me that there is an error in your modeling that suggests a 2.75" large radius corresponds with a 1.25" small radius. Since I don't know the logic that ties these together I can't guess. I consider the 2.75" to be correct for slow speed. My best estimate of minimum radius, measured at the datum line (also best estimate) is 0.916" for standard belt, fully closed Idler sheaves, proper eccentric adjustment, typical upper belt, etc. (sample of one, YMMV cuz this obviously vary a bit). So I think your error is in the small radius that corresponds with max radius: 1.25" Vs 0.916".

In an earlier post where I corrected my minimum radius value to 0.916", calculated RPM and measured RPM were within 1%. I'm pretty satisfied that this is an accurate number for the one machine I measured it on.

- David

dusty

DLB wrote
dusty wrote Please - if you see an error in my thinking say so. I would very much appreciate being shown the light.
Previous results, both measuring RPM and measuring minimum radius, suggest to me that there is an error in your modeling that suggests a 2.75" large radius corresponds with a 1.25" small radius. Since I don't know the logic that ties these together I can't guess. I consider the 2.75" to be correct for slow speed. My best estimate of minimum radius, measured at the datum line (also best estimate) is 0.916" for standard belt, fully closed Idler sheaves, proper eccentric adjustment, typical upper belt, etc. (sample of one, YMMV cuz this obviously vary a bit). So I think your error is in the small radius that corresponds with max radius: 1.25" Vs 0.916".

In an earlier post where I corrected my minimum radius value to 0.916", calculated RPM and measured RPM were within 1%. I'm pretty satisfied that this is an accurate number for the one machine I measured it on.

- David

If this is the machine with a belt that rides proud on the large pulley I may understand. According to my calculations with a 26.5" belt and a .916" radius small pulley the larger pulley needs to have a 2.9" radius. This produces an idler speed of 1080 rpm on one end and and 9357 rpm at the other end. That equates to 681 and 5847 rpm quill.

If you recalibrate to locate the belt on the large pulley to be 1/8" below the perimeter the idler speeds change to 7602rpm and 1485 rpm with the quill running at 4751 rpm and 928 rpm.

With a slightly shorter belt (26 3/4") The speeds become 7674 rpm and 1516 rpm or 4786 rpm and 947 rpm and the quill.

Shopsmith chart: 1120 and 8400 or 700 and 5250.

I guess it can be said that I am running with the wrong belts - 27" purchased from Shopsmith.

I must say though that except for not hitting the right speeds at the extremes - the speed control system works great and since I hardly ever go toward the high end I am quite satisfied.

Through all of this, I have developed a couple cludge tools (depth gauges) for measuring pulley radius.

DLB

dusty wrote If this is the machine with a belt that rides proud on the large pulley I may understand. According to my calculations with a 26.5" belt and a .916" radius small pulley the larger pulley needs to have a 2.9" radius. This produces an idler speed of 1080 rpm on one end and and 9357 rpm at the other end. That equates to 681 and 5847 rpm quill...

Yes, because I looked at two machines for this thread and both rode slightly proud at slow stop. No, to everything else. My best estimate of pulley radii (datum line) was 2.66" and 0.916" for a calculated Idler speed of 1232 at motor speed 3580. Measured Idler speed under those same conditions was 1246 RPM. So calculated and measured numbers were within 1%, and I'm satisfied they are pretty accurate. Since what is important is a ratio, both numbers could be slightly off but they could not be 2.75" and 1.25". 2.75" is the max plausible radius for the large pulley, would give a small radius of 0.947". The belt cannot run at a 2.9" radius, but if it could the datum line radius still cannot exceed 2.75".

But I was only trying to respond to your 'If you see an error in my thinking please say so' note. To state my response differently: Yes. Your sum of the two radii always add up to 4". That is different from real measured results and creates a significant deviation from the SS speed chart with significantly less RPM range. It is also inconsistent with measured RPM.

- David

dusty

DLB wrote
dusty wrote If this is the machine with a belt that rides proud on the large pulley I may understand. According to my calculations with a 26.5" belt and a .916" radius small pulley the larger pulley needs to have a 2.9" radius. This produces an idler speed of 1080 rpm on one end and and 9357 rpm at the other end. That equates to 681 and 5847 rpm quill...
Yes, because I looked at two machines for this thread and both rode slightly proud at slow stop. No, to everything else. My best estimate of pulley radii (datum line) was 2.66" and 0.916" for a calculated Idler speed of 1232 at motor speed 3580. Measured Idler speed under those same conditions was 1246 RPM. So calculated and measured numbers were within 1%, and I'm satisfied they are pretty accurate. Since what is important is a ratio, both numbers could be slightly off but they could not be 2.75" and 1.25". 2.75" is the max plausible radius for the large pulley, would give a small radius of 0.947". The belt cannot run at a 2.9" radius, but if it could the datum line radius still cannot exceed 2.75".

But I was only trying to respond to your 'If you see an error in my thinking please say so' note. To state my response differently: Yes. Your sum of the two radii always add up to 4". That is different from real measured results and creates a significant deviation from the SS speed chart with significantly less RPM range. It is also inconsistent with measured RPM.

- David

I'm trying to understand, David. The two radii (2.66 and .916 result in belt on pulley of 11.234"). Adding pulley separation of 14.5" accounts for a belt length of only 25.73". Are you using a belt that is that short.

If you have a tachometer, with idler speed set to equal motor speed are the two sheave radii equal (2" ea resulting in a 1/2 circumference of 6.25" each). Note: 12.5" + 14.5" (pulley separation) = belt length 27" (my belts).

DLB

I've disassembled the machine I was using for this because I needed to cannibalize it for a Drive Sleeve to fix my PowerPro.

dusty wrote I'm trying to understand, David. The two radii (2.66 and .916 result in belt on pulley of 11.234"). Adding pulley separation of 14.5" accounts for a belt length of only 25.73". Are you using a belt that is that short. No. Earlier in this thread I measured a couple of belts at 26-5/8" outer circumference. If I estimate the belt length at the datum line I get 26.17".

If you have a tachometer, with idler speed set to equal motor speed are the two sheave radii equal (2" ea resulting in a 1/2 circumference of 6.25" each). Note: 12.5" + 14.5" (pulley separation) = belt length 27" (my belts). I can't do this now. I did it before, the radii looked equal and physics says they are equal. I don't think I'd expect 2". (I'm using my belts. ;) ) Using that math in reverse I project 1.86" radius on the pulleys. That's datum line, I would expect 1.94" outer belt, so we are not far apart at mid-point on the sheaves and it is probably all attributed to belt length.

- 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).

DLB

dusty wrote 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

DLB wrote
dusty wrote 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

DLB wrote 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

dusty wrote 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

DLB wrote
dusty wrote 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

dusty wrote 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.

« Previous Page Next Page »