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Mark V Speed Control

BigSky

SteveMaryland wrote 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

edma194 wrote 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

SteveMaryland wrote

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

SteveMaryland wrote 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.

:confused: :confused: :confused: 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

SteveMaryland wrote 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..

BigSky

JPG wrote 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..

If the plot you say is "fairly linear" is the one presented by SteveMaryland then I know why I am confused.

If I understand --- you are telling me that I should not strive for an operating range of 710 to 5250. Admittedly that would eliminate my dilemma,

????Belt wear causes a shift upward ???? With no belt attached the motor pulleys are 1/2" at the outer edge. Maximum spring expansion.

JPG

Linear means straight line. Yes the plots have a slight curvature. The two plots have a different slope (rise/run) due to the 1.6 ratio.

A narrower belt will ride further into the pulleys causing an upward shift of the speed attained.

The high speed adjustment will be reflected in the entire range thus causing a similar shift at the slow setting.

Realize the first step in the high speed adjustment is subjective and will affect the end result over the entire range.

edflorence

There was a thread a few years back about using a handheld laser tachometer to monitor output speeds and to make high speed adjusting more accurate. Just thought I would bring it up again, since these little devices work so well and are not expensive...under $20. I use one to check speeds a couple of times a year, and have found that I only need to do a high speed adjustment every couple of years or so to keep the speeds where they should be, relative to the letters on the dial.

Shopsmith's chart of recommended speeds does not show speeds above 3600 rpm (speed dial setting of R-S). 3600 rpm is the speed recommended for dadoing and molding. Editions of PTWFE previous to the current one recommend speeds of 4000 to 5000 when routing in drill press mode. However, the manual for the speed increaser says that the speed increaser must always and only be used with the speed dial on "V" (4700), and goes on to say "...Do not go below or exceed this speed setting." Emphasis as shown in manual.

Staying with these recommendations has always worked well for me.

BigSky

Thanks for all the response. I need to digest it all.

HopefulSSer

You can also get cell phone apps that flash the camera flash to allow you to determine rpm. They kinda-sorta work. You might need to set the app for a multiple or fraction of the actual speed to get it to work properly.

dusty

BigSky wrote
edma194 wrote
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.

Doing a high speed adjust may alter the numbers but not enough to match the Shopsmith speed chart (especially on the low end.

The closest I can get to 700rpm quill speed is 1008.5rpm "measured". This occurs with the speed control adjusted such that the belt is even with the outer edges of the control sheaves.

Mathematically it can be determined that the Control Sheaves would have to be nearly 1" larger in diameter than they are to have a Quill speed of 700rpm.. I measure my sheaves to be 5.4" in diameter and I strive to keep the belt inside of the edges by about 1/8" therefore I get no where near the Shopsmith numbers.

This shows why I believe that achieving 700 rpm quill speed is a no-go:

If you believe I am wrong - please do so comment to this thread. This is how we all learn.

700 rpm a no-go.png

no-go for 700 rpm quill.png

SteveMaryland

What I do not understand is how adjusting the high-speed stop (the setscrew) can have any effect on the low speed.

Others here have suggested a connection.

Low- and high-speed limits are independent of each other, as far as I can tell.

DLB

SteveMaryland wrote What I do not understand is how adjusting the high-speed stop (the setscrew) can have any effect on the low speed.

Others here have suggested a connection.

Low- and high-speed limits are independent of each other, as far as I can tell.

I agree. I think the 'connection' is that we typically reference the dial at fast right after setting the high speed stop. But I agree with you that this could also be done at the slow stop. Or anywhere else, for those that have a good tachometer.

As I see it there are two low speed stops, and no easy way to tell which one a given machine is hitting. 1) The Idler sheaves will only close so far (roughly a 1/2" gap at the outer rim) and 2) The spring on the motor shaft will only compress so far. Either or both of these act as a hard stop in the Slow direction. Both are completely independent of the high speed stop.

- David

DLB

dusty wrote If you believe I am wrong - please do so comment to this thread. This is how we all learn.

Dusty - I was going to stay out of this discussion because I don't have a tach for the SS. But I'm lost on your math right now. Where is Radius coming from? These numbers look wrong to me, and I worked in radius because I felt I could reasonably measure it. My results indicated no problem getting to 700 RPM, but neither radius is particularly close to yours. And I didn't have a tach to prove/disprove what I calculated, so I quit.

Note - To be accurate we need to know or do a good estimate of "pitch diameter." For simplicity, this is the effective diameter of the belt riding in a pulley. It is a bit less than the outer diameter of the belt in the pulley.

- David

dusty

DLB wrote
dusty wrote If you believe I am wrong - please do so comment to this thread. This is how we all learn.
Dusty - I was going to stay out of this discussion because I don't have a tach for the SS. But I'm lost on your math right now. Where is Radius coming from? These numbers look wrong to me, and I worked in radius because I felt I could reasonably measure it. My results indicated no problem getting to 700 RPM, but neither radius is particularly close to yours. And I didn't have a tach to prove/disprove what I calculated, so I quit.

Note - To be accurate we need to know or do a good estimate of "pitch diameter." For simplicity, this is the effective diameter of the belt riding in a pulley. It is a bit less than the outer diameter of the belt in the pulley.

- David

Maybe I can't do this and still be correct but I did (do) not use pitch diameter. I have done all my calculations and sketches based on the outer surface of the belt.

I'm curious. Which numbers do you find to be in error and what do you have.

When at low end what rpm do you have or calculate. At 700 rpm (or the very lowest you can achieve) where does the v-belt ride on the idler pulley.

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