Mark V Speed Control

[dusty]

I need some help. Hopefully there is someone here on the forum that can provide that assistance. I need to see the fan sheave and the floating from the inside. Hopefully someone has there that are not mounted and can take a couple photos.

I have made some assumptions about how they are shaped where the vanes inter-mesh. I am beginning to suspect that my assumptions are incorrect.

[JPG]

I believe all are pairs regardless of model/vintage.

Here is a MVII idler/control pair.

The 'male' hub is slightly larger than 1"(1.03)

The 'female' hub cavity is slightly larger.(1.06")

The vane tips are about 1.17" across.

sheaves.jpg (344.28 KiB) Viewed 922 times

[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

The 14.5" is not necessarily what you will measure but it is not an estimate for my machine. It is twice the distance between idler shaft and motor shaft (variable only by the eccentric adjustment - an adjustment I have not changed in at least two years-last belt change).

I checked this belt by crude measurement and believe it to be very close to 27". I used a piece of nylon lacing tape wrapped around the surface of the mounted belt and then cut at point of intersect. Do this in the drill press mode. I did it laying on the floor under the machine. After that I measured the lacing tape with a steel ruler. Pretty confident of its length being 27".

Subsequent testing has convinced me that the belt moves on the two sheave sets in "equal and opposite direction"

I'm about to button this up and go back to making some sawdust. I have requests from great grand daughters for jewelry boxes for Christmas. I said time was short - maybe not by Christmas. They then volunteered to come help. I really dislike sanding and painting. This may be an opportunity to deliver unfinished.

[dusty]

Just when I was beginning to think that I understood the Mark V speed control I learn that the fan and floating sheaves are not exactly what I had pictured. They function according to my current understanding but they do look different - especially the Fan Sheave. I guess I should have know - it is called a fan sheave for a reason.

4023.jpg (15.02 KiB) Viewed 853 times

4024.jpg (23.61 KiB) Viewed 853 times

4025.jpg (22.19 KiB) Viewed 853 times

4026.jpg (21.99 KiB) Viewed 853 times

4027.jpg (18.18 KiB) Viewed 853 times

Photo Manager works differently, too. Why these thumbnails??? I just cannot keep yup with the Microsoft changes.

[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

What tied those two numbers together was not based on logic. In fact, 4" being the sum of the two radii is not even correct. When I wrtongly came to that conclusion I was doing calculations with no decimal accuracy. Carrying the calculations to two or three decimals immediately reveals that. Also, I had been working on the numbers assuming belt length of 27" and with idler speed equal to motor speed. Under all other conditions, my error becomes obvious.

However, the sheave radii do add to a number very, very close to 4". Deviation greater than about 3/32" indicates a problem in the model.

With the testing and modeling that I have now done, I am totally convinced that the sheaves move in "equal" and opposite directions unless there is something not working correctly. Making this happen is the primary task of the motor spring. If belt tension is retained when the
control sheave makes a change the floating sheave will move in the opposite direction and by the same amount.

[dusty]

A major change in my thinking has occurred has occurred. I am still convinced that the sheaves "should" move in equal and opposite directions BUT mine do not. Opposite yes - equal - no. Of course you, David, already have declared that to be. I'm still testing to learn HOW and why.

[dusty]

Question regarding my post right before this.

Is it logical for me to consider that speed where idler shaft speed equals motor speed to be the middle starting point? That is - should I expect the sheaves to move equal distances from there to the two extremes?

[JPG]

Consider the following:

The quill speed range from 700 to 5200(nominally).

The mid point is 2250 (5200-700)/2.

The quill to idler speed ratio is 1.6 so idler speed is 3600.

So ignoring the motor slip, your assumption is reasonable.

Note the speed range from there is not identical 2250 - 700 = 1550 vs 5200 - 2250 = 2950

So linearity is not a valid assumption.

[dusty]

I have been laboring under an assumption that the sheaves are all very, very similar on the vain side while the major differences were on the other side. Yes, the sheaves are all "similar" and that is all I can say. I have been working with three different operational machines and three sets of sheaves (spare parts). I have found that no two sheaves measure the same. I am not saying and do not mean to imply that these parts don't work but I have concluded that they different from one another enough to introduce performance differences (especially speeds and pulley radii).

Dave commented here that he could not understand some of the "facts" that I stated and now I understand. As he said - my modeling and my test results just do not support one another. The sketches are close approximations but that is where it ends. Approximations that hopefully help some understand the speed control system but a general understanding is all they are good for.

This has been a successful session for me because I now understand how it all works. I am now faced with the task of repacking, marking and storing all of my "spare parts".

Side Comment: I bought a new drive belt for this but I doubt that I will ever install it because it differs dimensionally so much from all the others.
It measures .5835" across the top surface where all of the others are close to .50" to .53" wide. It does measure very close to 27"" long.

[JPG]

15 mm?

What are you using to measure a rubber belt width to .0001"?