Belt hitting way tube

[JPG]

Re motor positioned closer to the operator side way tube.

That may have done to partially compensate for the off centering of the of the idler shaft due to eccentric positioning.(*see below!)

It is my contention that the poly-v belt tensioning should be accomplished by rotating the eccentric clockwise(as viewed from the outside) which places the wider portion of the eccentric to the (left) rear that moves the idler shaft closer to the (right) front. Reason being normal torque due to running will tend to rotate the eccentric towards the tighter belt position.

* But that is bass ackwards from what I said above.


So much for initial thoughts.


Now for second thought:

The belt will exhibit a tight tension on the front due to the motor creating tension as it pulls the belt. Conversely the belt will exhibit less tension on the rear due to the motor pushing the belt there. That is where any belt flutter will occur.

So perhaps it is offset towards the front to allow room for greater flutter on the back side.

Drawings would be nice, but they only reveal what, not why.









NOW howcome the belt flutter causes damage to the way tube gear rack on the Mark VII???

[DLB]

Considering the new (to me) information on the motor position it seems clear that minimum clearance occurs at maximum speed. (Also, that's as shown in Steve's latest drawing.) On my machine, that clearance is less than 1/16", the smallest drill bit in the set I was using to gauge clearance. I put a piece of blue painter's tape on the way tube and ran the machine at high speed, and IMO the tape indicated intermittent belt contact, probably consistent with belt flutter. I have little doubt that a faster high-speed stop setting would result in consistent contact between belt and way tube on this machine. I don't have a problem with zero clearance at the high speed stop, we know from another thread and a handful of owners making speed measurements that out machines tend to run faster than the specified max RPM. But, like the OP, I would be concerned with zero or negative clearance at saw speed.

Jumping back, one of the OP's pictures showed the belt running proud relative to the motor sheaves. That can only (?) be caused by incorrect high speed stop adjustment. In that case, the speed and relative position of the belt would also be fast at a Saw setting. Correcting the stop setting and resetting the speed dial with the belt down 1/16" to 1/8" into the pulley might fully resolve the belt clearance issue.

As we know, there is always going to be some variation from machine to machine. Idler position varies both horizontally and vertically with the upper belt itself and user preference of belt tightness. At high speed, both pulley diameters vary with user preference on high speed stop setting, belt variance with any one supplier, belt variance among belt suppliers, and belt wear.

My machine is still somewhat different than Steve's model. While I'm not concerned about that, here are more detailed measurements:
Motor pulley diameter measured/calculated at the outside of the belt at the high speed stop: 5.363".
Vertical distance from top of way tubes to center of Idler: 2.827"
Vertical distance from top of way tubes to center of Motor shaft: 4.264"
Since the center lines of those two pulleys does not lie on a vertical line, the center to center distance is not equal to those numbers added together. Instead of calculating or measuring a correct center to center distance, I'll presume that Steve's model does that.

- David

[edma194]

Melindacrosby, welcome to the Shopsmith Forums.

Based on the following statement from JPG could you verify that the belt contact has been with the rear way tube? Sorry, if I missed something in your posts that clarifies that. Also, thank you for posting detailed descriptions and annotated pictures, you're gonna fit right in at this place

The belt will exhibit a tight tension on the front due to the motor creating tension as it pulls the belt. Conversely the belt will exhibit less tension on the rear due to the motor pushing the belt there. That is where any belt flutter will occur.

[JPG]

The high speed stop adjustment has been mentioned herein, but pix indicate it was not done properly.

SOP says to adjust the speed control so the outer surface of the belt tracks slightly inside the outer periphery of the motor pulley. Then the high speed stop is adjusted so the travel is limited to that setting.

Next the indicator ring is set to fast.

That concludes the adjustment process.

However we tend to 'test' the success by determining where the indicator positions at the slow limit of the speed adjustment. That limit is the result of the interaction between the control sheave and the floating sheave travel. The control sheave can only be closed so far and excessive opening of the floating sheave can cause the belt to jam in the sheaves vanes..

I am guilty of that desire for fast/slow travel limits and will readjust the high speed stop in an effort to achieve it as long as interference between the control sheave and the speed control bracket is avoided. A secondary objective is to allow the lower end to actually be altering the quill speed all the way to the slow stop.

[dusty]

I still cannot see how, even in the worst case, that a Shopsmith Mark V drive belt could contact a way tube.

Even when the eccentric is set to the 3 or 9 o'clock positions, the closest the belt comes to the way tube is 1/2".

Could the motor mounting position be off?

You requested a dimension earlier in this thread when you had distance from top of tubes to upper drive shaft indicated at 8;00", You now have it indicated as 7.625". I did not reply but I must now. By my drawings(measurements) the separation from top of ways to center of axis of the upper drive shaft is 7 1/8". This is 8" if taken from center to center

[dusty]

I am unable (at this moment) to do this in the shop (on a machine) but I have modeled this in Sketchup,

Using the Sketchup model I I can see that if the drive belt does not move properly (smoothly and equally) within the sheaves during speed change the belt could certainly rub the tubes but NOT on a proper;y assembled and operating machine.

I'll work on this some more and maybe I can get a sketchup model to work here on the forum.

[JPG]

I am unable (at this moment) to do this in the shop (on a machine) but I have modeled this in Sketchup,

Using the Sketchup model I I can see that if the drive belt does not move properly (smoothly and equally) within the sheaves during speed change the belt could certainly rub the tubes.

I'll work on this some more and maybe I can get a sketchup model to work here on the forum.

I think that describes what I surmise occurs when changing speed towards slow.

The closing control sheave creates a tightness to the advancing belt that in turn creates slack in the retreating belt that then allows the floating sheave to close slightly on that side of the pulley. That creates a larger track on the motor pulley than the opposing side(temporarily).

All this squeezing and slow reacting is why thee must not be aggressive when adjusting towards slow.

[dusty]

This has been interesting for me. Just wish I could get hands on the machine in question.

After dwelling on the issue (using a Sketchup model) I can see only one possible cause (assuming the machine is assembled properly).

TYhe second image in this thread got me thinking about this. I conclude from the image that the machine is at high speed (belt position in motor sheave). Then looking at Idler Sheave. Belt appears to be too high in the sheave.
If the idler sheave was not closing properly causing the belt to ride too high in the sheave with respect to where the belt is in the motor sheave the belt would be closer to the way tube than it should be.

Just my two pennies worth. Thanks for the challenge.

[dusty]

Considering the new (to me) information on the motor position it seems clear that minimum clearance occurs at maximum speed. (Also, that's as shown in Steve's latest drawing.) On my machine, that clearance is less than 1/16", the smallest drill bit in the set I was using to gauge clearance. I put a piece of blue painter's tape on the way tube and ran the machine at high speed, and IMO the tape indicated intermittent belt contact, probably consistent with belt flutter. I have little doubt that a faster high-speed stop setting would result in consistent contact between belt and way tube on this machine. I don't have a problem with zero clearance at the high speed stop, we know from another thread and a handful of owners making speed measurements that out machines tend to run faster than the specified max RPM. But, like the OP, I would be concerned with zero or negative clearance at saw speed.

Jumping back, one of the OP's pictures showed the belt running proud relative to the motor sheaves. That can only (?) be caused by incorrect high speed stop adjustment. In that case, the speed and relative position of the belt would also be fast at a Saw setting. Correcting the stop setting and resetting the speed dial with the belt down 1/16" to 1/8" into the pulley might fully resolve the belt clearance issue.

As we know, there is always going to be some variation from machine to machine. Idler position varies both horizontally and vertically with the upper belt itself and user preference of belt tightness. At high speed, both pulley diameters vary with user preference on high speed stop setting, belt variance with any one supplier, belt variance among belt suppliers, and belt wear.

My machine is still somewhat different than Steve's model. While I'm not concerned about that, here are more detailed measurements:
Motor pulley diameter measured/calculated at the outside of the belt at the high speed stop: 5.363".
Vertical distance from top of way tubes to center of Idler: 2.827"
Vertical distance from top of way tubes to center of Motor shaft: 4.264"
Since the center lines of those two pulleys does not lie on a vertical line, the center to center distance is not equal to those numbers added together. Instead of calculating or measuring a correct center to center distance, I'll presume that Steve's model does that.




- David

I have modeled the shafts, sheaves and tubes and I find thart my resulting dimensions are very very close to your measurements (stated in this thread). My model depicts the 3 shafts in question as being aligned on the vertical plane (center of rotation of the upper shaft). The differences that I see would not create the problem that we are discussing.

What I wish I had was clarification of where a plumb bob dropped off the rear edge of the idler sheave would be with respect to the inside circumference of the upper, rear way tube.

[DLB]

What I wish I had was clarification of where a plumb bob dropped off the rear edge of the idler sheave would be with respect to the inside circumference of the upper, rear way tube.

I didn't use a plumb bob. My measurement is perpendicular to the tops of the way tubes rather than to the center of mass of the earth. (Consistent with other measurements I've provided in this thread.) 2.3845"

Measurements on my machine aren't going to tell us why the OPs machine had zero or negative clearance between belt and way tube at TS speed. My machine has about 3/32" clearance at "R" (nominally 3500 RPM) on the speed dial.

- David