Mark V Speed Control

[BigSky]

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, 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:

700 rpm a no-go.png (43.04 KiB) Viewed 1596 times

no-go for 700 rpm quill.png (62.03 KiB) Viewed 1594 times

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

[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]

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]

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]

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.