misaligned floating sheave on motor shaft

[peterag]

Hi All,

I have just inherited a Mark 500 (grey) that once had been very busy, but has in the last five years seen much less action (my very skilled father-in-law is now ninety).

So I conscientiously followed the instructions (manual and video), and cleaned and lubricated the machine before using it.

However, when I came to try the clean machine, the belt loosened as I put it into the higher speed setting (to the point that the top shafts no longer turned). On inspection, it seemed that though the lower floating sheave was not stuck, and I could pull it back on the shaft against the spring, it was coming into contact with, and butting against, the fan sheave, when released; namely the sheaves did not mesh. As the belt had a torn interior section, I decided to wait and get a new belt, figuring that the torn belt section might have caught the floating sheave and brought it out of alignment.

The damaged belt does not seem to have been the issue though, as the problem continues with a new belt (I changed the belt last night). I can get the machine to go through the full range of speeds, but it does happen that the problem repeats itself when I bring the Mark V into high speed. I think I fixed the issue once or twice by moving the sheave manually, and at least one other time by slowly changing the speed on the unit back down and up, causing the belt, I guess, to catch the sheave and bring it into position...

I've done a search on the forum, and certainly 'stuck sheave' turns up. However, I was hoping for any suggestions? I am certainly game to open it up (bless youtube).

Thanks in advance for any help....

Peter (in Ringwood, NJ)

[JPG]

The top(widest) of the belt should be about 9/16" wide.

When fully 'closed' the motor pulley should be about 1/2"(or less) wide at the inside of the outer diameter.

Also the belt length should be 26 1/2".

Did you obtain the new belt from Shopsmith?

Standard automotive belts are ineffective.

[peterag]

Thanks for the response.

Yes, I bought the belt from SS... And with it certainly everything behaves correctly - except when it doesn't. I don't think the issue is the belt.

[JPG]

OK so we back to the sheave.

When it 'fully' closes, what is the width across the outer rim of the pulley(inner surfaces where the belt rides).

And when it slips at high speed, where is the belt in the pulley?

Is it possible it is riding 'off' the pulley?

Is the eccentric on the idler shaft flush with the headstock bore?

Is the bearing inserted correctly in the eccentric?

Brain storming things that will cause a correct belt to get loose.

If the control sheave opens the idler pulley too far.(typically that results in jammed belt).

[wa2crk]

we just had a similar condition on our community shop Shopsmith. The floating sheave did not travel through it's full range. I could pull the floating out and let it go back in but the range of travel was restricted due to dirt on the shaft of the motor. If the sheave is not able to travel through it's full range then the belt will go slack at some point of it's travel. (The point at which the floating sheave gets stuck.) This condition will vary with different machines depending on the amount of dirt on the motor shaft. The most expedient way of correcting this is to remove the motor and the spring from the motor. Then remove both sheaves and thoroughly clean the bores of both sheaves and the motor shaft. Also check for burrs on the groove on the motor shaft, on the edges of the grooves in the sheaves and on the key.
Bill V

[wa2crk]

I tried to post this earlier but my computer occasionally loses contact with the server.
Will have to talk to the computer techs again'
Bill V

[peterag]

Thanks - this sounds like my issue. As I wrote in my description above, the problem is intermittent - sometimes the floating sheave meshes properly into the fan sheave, and sometimes it doesn't.


In any case, I'll try your suggested cleaning/maintenance over the weekend. I'll let you and the world know how it goes.

[JPG]

Thanks - this sounds like my issue. As I wrote in my description above, the problem is intermittent - sometimes the floating sheave meshes properly into the fan sheave, and sometimes it doesn't.


In any case, I'll try your suggested cleaning/maintenance over the weekend. I'll let you and the world know how it goes.

Beware that compressed spring!!!!!!

[peterag]

Thanks - this sounds like my issue. As I wrote in my description above, the problem is intermittent - sometimes the floating sheave meshes properly into the fan sheave, and sometimes it doesn't.


In any case, I'll try your suggested cleaning/maintenance over the weekend. I'll let you and the world know how it goes.

Beware that compressed spring!!!!!!

Thanks for the warning... youtube's Jacob Anderson has a nice explanation.

BTW, I was answering your measurement post(s):

The top(widest) of the belt should be about 9/16" wide.

If I trust my cheap gauge, the new SS belt is a bit thinner - say, 17/32".

When fully 'closed' the motor pulley should be about 1/2"(or less) wide at the inside of the outer diameter.

Yesterday, I would have guessed that that was the case. Tonight, it is not, and I can't get the unit to full speed (the belt stays 1/8-1/4", say, below the rim). But perhaps that's a different problem.

Also the belt length should be 26 1/2".

TBD

Did you obtain the new belt from Shopsmith?

Yes

When it 'fully' closes, what is the width across the outer rim of the pulley(inner surfaces where the belt rides).

See above

And when it slips at high speed, where is the belt in the pulley?

The sheaves are butting against each other, so that the interior of the rims are about 1 3/8" apart.

Is it possible it is riding 'off' the pulley?

I don't quite know what that means: the belt hangs loose from between the upper pair of sheaves when the problem occurs...

Is the eccentric on the idler shaft flush with the headstock bore?

Yes

Is the bearing inserted correctly in the eccentric?

I hope and think so!!!!

As I wrote above, I'll let you all know how things turn out.

And, of course, thanks for the help.

[JPG]

When fully 'closed' the motor pulley should be about 1/2"(or less) wide at the inside of the outer diameter.

Yesterday, I would have guessed that that was the case. Tonight, it is not, and I can't get the unit to full speed (the belt stays 1/8-1/4", say, below the rim). But perhaps that's a different problem.


The sheaves are butting against each other, so that the interior of the rims are about 1 3/8" apart.

1 3/8" is a WOW!!!!!!! IIUC It also contradicts the previous 1/8 - 1/4" observation unless it is loosly hanging down that low ?????

I am taking those answers to imply the motor pulley is NOT fully closing as you have already voiced suspicion. So cleaning/lubricating the motor shaft/floating sheave is de fix.