Mark V Speed Control

[BigSky]

Plot of above speed chart submitted by OP. Shows a (moderately) nonlinear relationship between dial marker (equally spaced letters) and actual speed.

The geometry of variable belt drives can be tricky to predict. Exact linearity of output speed across the dial is not to be expected, but the deviation from linear appears to be not much. Why the '"real" speed differs so much from the chart speed is not clear. The 1.6 multiple does not explain it.

Thank You so very much. Your graph looks much more like what I expected than what I was getting. Obviously, I am using the excel chart tool improperly.

[edma194]

BigSky, do you still see a significant difference between the chart and measured RPM?

[BigSky]

BigSky, do you still see a significant difference between the chart and measured RPM?

Yes I do. Especially on the low end. I now have a hunch that I need to do a hi speed adjust which I have never done.

[SteveMaryland]

But according to OP's numbers it is the low-end deviation that is small and the high-end deviation large...

In any case, in order to "calibrate" the speed to the dial, you start the machine and crank the dial (slide the item 98 Belt Cover off first) until the top of the v-belt is just flush with the OD of the idler sheave. That's the minimum slow speed. Stop the machine. Then you remove (using a 3/32 hex wrench and a flashlight) the item 84 Speed Control Handle which allows you to disengage item 77 Speed Control Dial and rotate it so the SLOW mark on that 77 dial lines up with the 12 o'clock mark on the headstock. Then setscrew (get the flashlight again) item 84 back on and you are done.

Try never to go into the top speeds. Just don't...

Whatever RPM SLOW and FAST turn out to be, that's it. They might never be copasetic with Shopsmith's official RPM numbers but doesn't matter. Using an optical speed meter is the best way to get the desired RPM if it has to be exact, which it almost never needs to be.

[edflorence]

Try never to go into the top speeds. Just don't...

Why not?

[SteveMaryland]

For the same reason you don't drive your car 100 mph around a corner. You might get away with it but it's not a good idea.

There's a reason Shopsmith casts features in the dial to "discourage" going into the high RPM's.

[jsburger]

For the same reason you don't drive your car 100 mph around a corner. You might get away with it but it's not a good idea.

There's a reason Shopsmith casts features in the dial to "discourage" going into the high RPM's.

What "features"? On the early SS you had a stop to override to go above a certain speed. IMO that was a safety feature. That stop has not existed for over 50 years so why is SS discouraging going to high speeds?

[DLB]

But according to OP's numbers it is the low-end deviation that is small and the high-end deviation large...
...

I'll admit to not being completely in the clear on this thread, but I don't think the OP provided actual (i.e. measured) numbers. I think you are interpreting the second column of numbers as measure RPM, I interpreted the same numbers as Idler shaft RPM. I only sampled a couple of them, but they were 1.6X.

About high speed - If you are using current generation parts, then those same parts in the PowerPro are good (-ish) to 10K RPM. The PP builds up too much heat, but as far as I know the bearings etc. are all good for 10K continuous. (Not an endorsement of the new style Idler bearings.)

- David

[SteveMaryland]

It has been my experience that at the highest speeds, vibrations can set in which loosen the speed control - i.e., loosen it up so that it drifts off toward higher speeds. I attribute this loosening to a lower static friction due to the vibration.

The speed control holds its position essentially by static friction. Under high-frequency vibration, that holding friction diminishes a lot, and speed drift can and does occur. I have observed it. A danger.

It's the same thing as when an otherwise tight nut vibrates off a threaded stud, and for the same reason. Also dangerous.

High speed drift is not going to happen on every machine every time, but when it does it is a danger. I don't want the OP to encounter it, or any other Shopsmith owner.

I am not talking about or worried about bearing failure at high speed. I am referring to the speed dial's ability to reliably and safely hold set speed under the vibratory environment that can set up when output speeds are high. Obviously Power Pro does not have this problem because it does not have a mechanical speed control.

I believe that is why early Shopsmiths had the stop. They saw a problem with high speeds early. Why did they later get rid of it? I don't know. Maybe they thought the stop looked like a band-aid on a larger problem - which it was. I don't think they should have removed the stop. But really, they should have redesigned the speed control to hold tight under high-frequency vibration, drift being a weakness of the speed dial control then and now.

[JPG]

That plot is fairly linear and the 1.6 ratio is consistent.

Considering the hardware, I consider it 'normal'.

Adjusting the high speed stop down to closer to 5100 will cause the slow setting to approach 700.

Realize belt wear will also cause a shift upward.



Re the scenario presented above, the control sheave is the 'input' and the motor sheave spring brings up the rear by responding to belt tension changes caused by the control sheave.

The high speed stop IS set at "Fast".

The early stop has been replaced with a tactile feedback ramp. Subtle, but is is there.

Realize the early model had a 3/4 hp motor. It likely strained under load at high speeds.

Yes the faster it runs, the more noise/vibrations occur.

FWIW the mechanical models also will heat up at highspeeds due to friction etc..