Shopsmith Forums

The following pics show the measurements. There are some differences between your figures and mine. I added an extra pic showing the idler sheaves closed when disconnected from the quadrant. I couldn’t get a pic of the motor sheaves manually separated (two hands and holding the sheaves open and the tape and the camera) but the measurement was 1 1/2”.

When I was moving the speed dial down toward the low end the system started to bind up at “C”. But while the dial could turn more toward “B” the idler sheaves had already closed. And the loop on the idler bearing became proud of the quadrant spring. This pic shows the quadrant at “C” with the idler loop just resting on the spring. There is virtually no tension here and when the dial is turned toward “B” the loop becomes free. I can move it with my finger nail.

You have an 'idler' sheave installed on the motor shaft instead of a 'floating' sheave.

The 'hub' is about 1/4" shorter on the floating sheave. With the extra 1/4" on the incorrect floating sheave the range of motion is restricted to 1/4" less(grounds out prematurely at "C").

The correct floating sheave hub is about 1" in length from the aluminum casting projection.

Another difference in the floating/control sheaves is the control sheave has the inset for the button bearing whereas the floating sheave hub is smooth across the end.

I DO hope this resolves this mystery!!!

Oh! . And thank you. I just ordered one. Will install it and let you know the results

Well, the good, the bad and the ugly. JPG is spot on. For whatever reason I had an “idler” sheave on the motor shaft. To add visuals to his observation I have these pics. With a new floating sheave and the OEM belt I ran the machine and turned the speed control. It stopped at “C”. The same place.
The stub is 1” long to the spring seat.

At “C” -
The stub is grounded against the nut.
The RPM is 1080
The motor sheaves are 1 11/16” outer to outer rims.
The idler sheaves are 7/8” outer to outer rims.

At “Fast” -
The RPM is 5280.
The motor sheaves are 15/16” outer to outer rims.
OEM belt is about 1/8” inside outer edge of rim.
Idler sheaves are 1 13/16” outer to outer rims.

Any thoughts (positive)?

I’ve gotten the speeds down to the point where I can run my belt sander , et al, safely. So if there are no new insights to this issue of being unable to get the bottom speed down to 700 RPM I’m really tempted to stop here.

An engineering note - When I bought the floating sheave at Shopsmith (I live 20 minutes away) one of their engineers told me that back in the day, when they upgraded their motors and changed from the nut on the end of the motor shaft to the clip, they made two other changes. They increased the shaft diameter by .003” and they increased the length of the stub on the floating sheave by 3/8”. So, an older floating sheave will not fit on the newer shaft and a newer sheave will have a sloppy fit on the older shaft and stop earlier.

I’m always disappointed when I read a thread and the postings stop in the middle of solving a problem without a successful solution. I always wonder if the original poster died, simply lost interest, found a solution independent of this forum or forgot what he was doing. So I want to close out this thread so anyone interested won’t have this wondering.

It appears there is no insight to my issue of not being able to get my speed controller down to the slowest speeds. Maybe my machine has some internal uniqueness (at least two sets of hands have had a chance to get inside it and mess around). So, I’m stopping here. I can get my machine to safely do what I want it to do.

Thanks to those who tried to help.

I am disappointed(and enlightened) as well. It seems your initial suggestion that we pooh poohed was partly correct.

Only suggestion I have is to shorten the floating sheave(actually I would shorten the control sheave that is in the pix above[NO BEARING]).

I am chalking his up to an education re history of floating sheaves. I wish I had already had that education earlier in this thread.

oddie,
As I ran out of ideas on your problem I left it in JPG's hands. He has a long history with the Shopsmith having owned his Goldie since new. There were a lot of changes made inside the headstock during the first ten years. Those sheave differences are one I have not seen in any documentation or I missed it. This shows how important it is to have the parts for the correct era of the Mark 5.

JPG and oddie,
Thank you for following through on this so we all have this important information available when restoring older Mark 5's.

Well, I forgot. The large lady hasn’t sung yet. JPG had said earlier there were too many variables. How true. We resolved just one of them.

I had left my headstock open while we worked this issue. Because it was over I wanted to close it up. But part of that was to replace the belt from the OEM one to the new one. Please recall I bought a new one because the OEM one was too small (less than 1/2”). But all our testing had been done with the OEM one.

I installed the new belt and using a tach set the high speed stop at 5200 RPM. The belt is about 1/8” shy of the outer rim of the motor sheaves. The high speed stop screw is flush with the top of the jam nut.

The speed controller turns down to “A”! But the speed at “A” is 1170 RPM. SS specs are 750 RPM. I have recorded all the speeds from “Fast” to “A” so I can still set the proper speeds for my sanding accessories. But if following SS specs all the speeds are too high.

Does this shed new light? Is the rest of the cast still singing?

Hmmm. I don't know what to make of this, having never needed to delve into my 2005 machine's innards. But maybe JPG or Russ will.

1170/750 = 1.56. That's suspiciously close to the normal idler-shaft drive ratio. Have you measured your idler-shaft speeds?

In the interest of further understanding(this all still does not totally add up), when set to 'A', what is the position of the 16 x 625 belt on the idler pulley(distance from top of belt the edge of pulley[same as the motor pulley at fast measurement])?

16 mm is a slightly wider belt than OEM. All things being 'typical' that should cause the belt to ride higher in the pulleys. At 'fast' the belt fpm should be faster than 'typical', but the belt is also riding higher in the idler pulley which reduces the resultant speed.

I think seeking equal position of the belt/motor(a) to the belt/idler(b) pulleys at fast(a) and slow(b) is a goal of the high speed adjustment(assuming that does not create some unanticipated condition such as control sheave interfering with the speed control body). I go there only because the 16 x 625 belt is slightly wider than an OEM belt.

Probing for understanding!!