Shopsmith Forums

wa2crk wrote:Dusty
How accurate is your tachometer? Everything has tolerances. Some more than others!
Bill V

It is a cheap one from China but accuracy is not the issue. That is to say if it reads 3600 when it should read 3650 would not cause my issue.

When looking at the shaft speed when set to low speed I want to read 700rpm.

One machine reads 758 and the other 749. Not bad.

At J Speed, one reads 2026 and the other reads 1889.

dusty wrote:It is a cheap one from China but accuracy is not the issue. That is to say if it reads 3600 when it should read 3650 would not cause my issue.

When looking at the shaft speed when set to low speed I want to read 700rpm.

One machine reads 758 and the other 749. Not bad.

At J Speed, one reads 2026 and the other reads 1889.

And 1900 seems to be the intended speed(from various charts etc.).

If so, one is about 7% fast, and the other about 1% slow.

This whole system is not linear.

You have one pulley causing the belt to position on the idler pulley and a second responding to the difference in belt tension in a compensating manner.

Thus as the control sheave is positioned from slow, the belt takes a new position on the pulley. What that position is, is determined by not only the control sheave position, but the belt width, the slope of the pulley sheaves, the belt length, the spring tension on the floating sheave, the motor pulley sheave slope, the phase of the moon, the temperature(both ambient and belt), and the humidity, and the time of day, and the gps coordinates, and lord only knows what else.

And you wondered why there are no rpm graduations on the dial.


Yes the Mark VII guys just plain goofed(or did not understand the foolishness of the number, nor the reason for the letters).

Realize the intent is to set to an acceptable speed range, not a specific speed.

Read my comments in Post #5.

I do not have an issue. I am not trying to fix anything.

I am trying to better understand how the speed control system works and what causes it to work differently under different circumstances. I rather doubt that phase of the moon or relative humidity will have an effect.

For me, this is a learning session that is most likely not needed my the "mechanically astute".

dusty wrote:Read my comments in Post #5.

I do not have an issue. I am not trying to fix anything.

I am trying to better understand how the speed control system works and what causes it to work differently under different circumstances. I rather doubt that phase of the moon or relative humidity will have an effect.

For me, this is a learning session that is most likely not needed my the "mechanically astute".

I was attempting to share my understanding of 'why' two different sets of hardware would produce different results.

Yes towards the end of the 'list' of contributing factors it contains pure silliness, but does so to illustrate the 'point' that many things affect the outcome.

Since we are not likely to be successful in measuring all that affects the speed, a lot of intuitive thinking is required to 'understand' or 'accept'.

Dusty...Very interesting observations...I will have to check my lower spindle/upper spindle ratio with a tach. I have just assumed 1.6 but never checked. A couple of years ago I did get a laser tach and checked the main spindle speeds. I found, as I suspected I would just based on sound, that the spindle speeds were consistently higher than the posted speeds for each letter on the dial. I did a high speed adjustment and brought the FAST setting to about 5260. At that setting, when I turn to the SLOW setting I record 770 (posted speed for SLOW is 700).. But at C, with a posted speed of 950 I read 930 and Q with a posted speed of 3250 I read 3200. So, I am running a little high on either end but low at all the intermediate settings. Since all the numbers are reasonably close to what they "should" be, I didn't worry about them not being right on the money, but instead I made up a chart of the speed settings and use it to get to the speed I need, according to the Shopsmith Operational Speed Chart, for whatever operation I am doing. In other words, I adjust the dial to the speed I want, regardless of the letter on the dial.

I also checked the spindle speeds at the output ends of the speed reducer and the speed increaser. The reducer at SLOW turns at 120 and the increaser on V turns at 10,800.

Though I'm pretty much at sea in this discussion it sounds as though a tach would serve a useful role as standard equipment for every one of these machines.

Based on what I'm reading here I'm not quite certain how important this varying speeds issue is or isn't so long as the readings are close to what's intended.

So, ummmmmm, how important is it?

The way I see it, (and, remember I've never worked on a Mark series) the normal wear on the motor and control pulleys would change the speeds. You ever see any signs of wear on either pulley, in a certain spot, like the setting you use the most? You ever see any aluminum (pulley) dust, when you clean up?

It just may be that the pulleys have some (perfectly acceptable) wear in some spots.

The Model 10 speed changer works in a similar fashion to the Mark series, speed control, and I've SEEN wear on the center sheaves. Still works just fine.

steve

skou wrote:The way I see it, (and, remember I've never worked on a Mark series) the normal wear on the motor and control pulleys would change the speeds. You ever see any signs of wear on either pulley, in a certain spot, like the setting you use the most? You ever see any aluminum (pulley) dust, when you clean up?

It just may be that the pulleys have some (perfectly acceptable) wear in some spots.

The Model 10 speed changer works in a similar fashion to the Mark series, speed control, and I've SEEN wear on the center sheaves. Still works just fine.

steve

I always machine the 4 sheave vane faces when rebuilding a headstock. I find the wear areas can be up to .030" deep in areas on the vanes. I found this wear can cause different headstock noises as you go through the speed ranges and can make trouble shooting difficult at times. I only check the low and high speed RPM limits after rebuilding a headstock