Mark V Speed Control

[dusty]

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 (86.37 KiB) Viewed 3031 times

[DLB]

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]

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]

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]

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]

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]

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.

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