Just A Glance at Speed Control (The Sheaves)

[dusty]

The Speed Control System. .jpg (187.45 KiB) Viewed 1673 times

Shown at Low Speed

[DLB]

Wanted to add a bit about the mechanical stops while it is fresh in my mind. The high speed stop is a long set screw on the speed control assembly that limits the travel of the quadrant (aka pork chop). The slow stop, at least on my machine, seems to be a combination of two. I can't distinguish which occurs first on this specific machine. The spring on the motor shaft reaches full compression at the same point, or very close, that the idler sheaves close to their limits. Unlike the high speed stop, the slow speed stop is not adjustable.

- David

[dusty]

True. The spring definitely
limits the idler sheave (hard limit) but I never thought of it as the speed stop. What is the lower speed (rpm) .
Mine is no where near advertised. My problem right now may be the high speed adjust. Calculating low speed based on pulley ratios does not support the eadvertised speed chart.

[DLB]

True. The spring definitely
limits the idler sheave (hard limit) but I never thought of it as the speed stop. What is the lower speed (rpm) .
Mine is no where near advertised. My problem right now may be the high speed adjust. Calculating low speed based on pulley ratios does not support the eadvertised speed chart.

What are you using for pulley ratios? Are you factoring in the ratio of of Idler to Main spindles? Target speed range is 700 - 5200 RPM at the upper spindles, so 1120 - 8320 at the Idler, I think. Using numbers I think are close, I'm seeing it pretty close at low speed but farther off at fast. I don't have a tach for testing assumptions. I think the sheaves themselves support a max diameter of 5+" and a min of under 2", with actual values determined by the mechanical stops, variation, belt wear, actual belt length, etc.

Note - The Idler speed range I gave is weirdly asymmetric in relation to 3450 nominal motor RPM. Probably means an undisclosed error in my thinking.

- David

[dusty]

I agree with you on all that you say with regards to speed control and target speeds. Also on pulley size. With that I would add a 27" belt and the 7.25" separation between motor shaft and idler shaft.

In my calculations I do not concern myself with with quill speed. Quill speed being the result of a fixed ratio between pulleys on the upper spindle and the idler shaft. Therefore I disregard the 700 to 5250 RPM stats and deal only with the 1120 to 8400 figures.

With that having been said, I conclude that the mid-range 3450 (variable dependent on motor speed) requires the sheaves (at 3450 RPM) to be 3.979" in diameter (1.9894" radius). Round it off where ever you want.

At that starting point, I believe additional calculations can be made by increasing the size of on pulley while decreasing the size of the other pulley the same amount.

[BuckeyeDennis]

Dusty, when you calculate the belt drive ratios, are you using the pitch diameter of the pulleys, or the outside diameters? If using the OD’s, there will be a small but possibly significant error in the calculated drive ratio.

https://www.gizmology.net/pulleysbelts.htm

[dusty]

Dusty, when you calculate the belt drive ratios, are you using the pitch diameter of the pulleys, or the outside diameters? If using the OD’s, there will be a small but possibly significant error in the calculated drive ratio.

https://www.gizmology.net/pulleysbelts.htm

Thank you for this reference. I have been totally ignoring v belt characteristics and using a fixed 1/2" for belt width. Including pitch angle will require more study on my part. However, I plugged some of my numbers into this calculator and came up with reasonably close results.

The Shopsmith 1/2" belts are typical class "A" V-belts so this calculator should work.

Thanks again for the new toy.

[dusty]

My problem/confusion has been the direct result of misusing ratios coupled with excessi8ve rounding. Once I got all my ratio errs fixed I simply had to do calculations to the 5th or 6th decimal point. This proved to be more accurate but also insane. The speed control simply does not allow adjustment to that level of accuracy.

[JPG]

The Speed Control System. .jpg
download/file.php?id=56367
Shown at Low Speed

Your drawing linked to above clearly illustrates that a previous statement by me re movable sheaves aligning with the opposing pulley fixed sheave at the extreme settings is WRONG!

Note the belt cross sections are not aligned (horizontally).

The three lines indicating the three belt positions in both idler shaft and motor shaft views should line up horizontally.

[dusty]

Maybe I cluttered the sketches with too much information (too many conditions depicted on one drawing).

The following is the same basic sketch but with the sheaves and belt cross sections moved to High Speed.

The Speed Control System. .. High Speed for Forum Post.jpg (105.02 KiB) Viewed 1470 times