SteveMaryland wrote: ↑Tue Dec 31, 2024 3:02 pm
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?
I agree, I'm sure that the engineers designed the machine so that in the worst case the drive belt would not contact the way tubes. My eccentric is positioned close to worst case, which I suspect is also pretty close to nominal, and I measured ~3/32" clearance. So the first difference I see between my machine and your model is I measured at speed "R" and you are modeling two speeds, very fast and very slow. So I measured again at the Slow stop and clearance was ~11/32". I have no reason to think "R" is the worst case speed for belt proximity to way tubes, but it is ~1/4" worse than Slow. My untested hypothesis is that worst case speed occurs when the belt is vertical, I think that is around "L".
Conclusions from that: 1) Speed matters, so real world worst case is different than the model shown. 2) Besides speed, there is an unexplained difference of about 5/32" between my machine and your model at Slow. 3) There is an unexplained difference of about 3/32" (or more) between my machine and the OP's machine.
- David
Unexplained?? How deep are the belts into the sheaves and where is the eccentric? Where is the Motor Sheave with respect to the Variable Sheave?
Get an exact measurement of the two shafts (Idler and motor) with respect to one another.
"Making Sawdust Safely" Dusty
Sent from my Dell XPS using Firefox.
SteveMaryland wrote: ↑Wed Jan 01, 2025 1:08 pm
...The above layout shows the Shopsmith at the midrange speed + we have added the eccentric effect. Still looks like we have at least half an inch of clearance...
Focusing on the differences(s) between Steve's model and my hardware... I'm surprised to find that the motor shaft axis is somewhat nearer to the front way tube (right way tube on Steve's 2D picture) than to the rear. More so than the Idler at the eccentric's max bias. I used a combination square placed over each way tube and measured to the center of the motor shaft, and the motor axis was about 3/4" closer to the front way tube. (Measured on the angle, which I didn't determine, so this is not an accurate measurement.) I used the same method to measure the Drive Sleeve spindle and found it to be exactly centered.
Somewhat tentatively, I conclude that the motor position as shown in the model is incorrect. Factoring in a front bias of both the Idler and the motor, the belt comes much closer to the front way tube than to the rear. And therefore much closer than the model would predict.
DLB, you have made an important discovery. Thank you. I had ass-umed that the motor axis was "centered " on the headstock plane of symmetry. I really had not noticed an offset. I previously modeled the physical headstock (using ruler, tape measure, etc.), but I sure missed that feature.
I don't often have the headstock dismantled, and whenever my headstock is dismantled, it's for repair and not measurement. I can't remember exactly how the motor is mounted.
Please advise the offset dimensions, and if the offset looks to be "fixed" in the mounting or if it can be varied by slotted holes or similar means. Let's find out if it answers the present mystery.
Also, what might be the design reason Shopsmith mounted the motor with an offset from the center plane? Has to be some reason.
Getting accurate dimensions from the physical headstock is tricky. What would be really good to get, are the original Shopsmith engineering drawings that were used to fab the headstock castings and other parts, because from such drawings, the "actual" dimensions could be exactly obtained. Has anyone on this forum seen those drawings, and are they viewable?
Mark V, Model 555510, Serial No. 102689, purchased November 1989. Upgraded to 520
I'm not certain that I follow this latest discussion but allow me to add this bit of trivia.
With the way tubes level from one to the other if you drop a plumb bob from the center of the idler shaft it should be in line with the center of the motor shaft. That is to say that the two shafts should align in the "vertical plane". In fact, all three shafts align with one another in that same vertical plane.
"Making Sawdust Safely" Dusty
Sent from my Dell XPS using Firefox.
dusty wrote: ↑Thu Jan 02, 2025 9:28 am
With the way tubes level from one to the other if you drop a plumb bob from the center of the idler shaft it should be in line with the center of the motor shaft. That is to say that the two shafts should align in the "vertical plane". In fact, all three shafts align with one another in that same vertical plane.
Is that really so? Wouldn't the position of the idler shaft change with the orientation of the eccentric bushing?
My results differ from Dusty's. My measurement was more complicated, but then I used a simple setup to confirm. I laid a combination square across the way tubes with the 90 degree head in contact with the outer edge of whichever I was measuring. Then but a Starrett right angle rule clamp on the combo square rule, with a 6 inch rule on the clamp and therefore at a right angle to the combo blade. I moved the clamp until the 6" rule crossed the center of the motor shaft, clamping it when it was properly located. The motor shaft was centered 3-29/32" from the outside of the front way tube and 4-27/32" from the outside of the rear way tube. A difference of 15/16", of a bias of half that, or 15/32". I'm not going to claim this is the exact value, but I'm reasonably confident it is within 1/16" at worst.
The headstock I measured has an Emerson motor IIRC. I don't think this actually matters, as far as I know all Mark 5/V motors use the same air plenum which also is the shaft end motor mount. My best guess at a reason for this offset is to make room for a startup capacitor that on some motors is mounted on the case.
I sure wish we could put these three machines together in the same shop. I cannot imagine why the differences. David, if you drop a plumb bob from the upper shaft does it reveal the same differences.
"Making Sawdust Safely" Dusty
Sent from my Dell XPS using Firefox.
I don't recall when or where, but I have heard about the motor shaft being off center before. I would assume it was here in the Shopsmith Forums. There's no clear need for the motor shaft to be centered relative to the way tubes or the idler shaft, and the latter moves along with the eccentric orientation.
The difference between the narrowest and widest section of the eccentric bushing is not that much. Possibly that was taken into account in the design. I think leaving space for the capacitor or other variations in the motor is the more likely reason makes sense.
To avoid being misleading I should probably delete all of the posts/comments that I have made in this thread. They are wrong, wrong, wrong as are posts on this general topic I have made elsewhere. The three shafts MAY NOT align in the verticle plane as I have previously stated. I do not no where or why I have gone wrong but today I dropped a plumb bob down the output side of the upper drive shaft only to find that It did not come near being in line with the motor shaft.
I'll post later IF I ever learn what I have done wrong. Given my diminishing eye sight and stamina..that may never happen.
"Making Sawdust Safely" Dusty
Sent from my Dell XPS using Firefox.
