Shopsmith Forums

Hi all,

While rebuilding my shortie I didn't make any adjustment to the high speed set screw so I didnt do a speed adjust when I reassembled. I was using it a few days ago and it just sounded fast. So last night I got out my Tach and the low speed was 1150 RPM!. So checked that the sheaves are well oiled and free to move, keys are in place, etc and then I went about doing a speed adjustment. The top end has no problem reaching 5200 RPM (which I really done need) but the low end can't get below 875 RPM. Even when I unplug and manually work the driven sheave to where the v-belt is near the OD of the driven sheave and the motor sheave is about as wide as it goes, I can't seem to get it to run below about 870 RPM. According to the website, I should be able to reach 700 RPM at 'SLOW'. I was stumped but didn't have time to dig into further last night. Will get at it again in another few days. I'll also tach my other units to see exactly what they're doing when at 'SLOW'. I'd be appreciate knowing what you did if you've ever encountered this situation or have any ideas.

- Nick

Is the 'Motor' belt OEM(i.e. from Shopsmith?)

P.S. Is the belt < 1/2" wide?

I snapped a quick picture but didnt measure. The belt is a 504193. It's an older belt but looked to be in good shape so I reused it. I believe the current number is different.

UncleSnick wrote:I snapped a quick picture but didnt measure. The belt is a 504193. It's an older belt but looked to be in good shape so I reused it. I believe the current number is different.

Correct belt. Appears 'normal' width.

So that path is non-fruitful.

Since the belt positioning on the pulleys is 'normal' I am suspect of the tach. The motor is highly unlikely to be running fast especially 25% so.

Thanks for the tip JPG. Now the plot thickens ...

I thought I'd verify the tach against a known entity. So I tach'ed the motor shaft and got 3580 PRM which I thought was fairly close to a 3600 RPM motor. But when i looked at the nameplate, it said the output should be 3450 RPM! So I was getting a reading 104% of nameplate. So the tach might be off but doesn't fully account for the 24% increase in speed I am seeing at the Quill.....

I had to put it back together to use it Sunday afternoon so I just adjusted the speed indicator wheel to match the RPM I was reading so I don't overdrive my bandsaw. But now the lowest I can mechanically go is about 'C' on the dial.

I'd gladly pull it apart and fix it if I knew what the problem was ....

Tell me some 'details' about the tach sensing revolutions.

Hi JPG,

I'm using a Shimpo Tach. I took a picture of how I checked the quill shaft speed. I did the same on the motor shat before I reassembled it. I also shot a picture of the certification. Seems it's almost 12 years overdue for a re-calibration.

What is the laser detecting/responding to?

Reflective strip, flag, ...?

Look closer JPG. Do you see the shaft touching he coupler? Think mechanical, not digital.

UncleSnick wrote:Thanks for the tip JPG. Now the plot thickens ...

I thought I'd verify the tach against a known entity. So I tach'ed the motor shaft and got 3580 PRM which I thought was fairly close to a 3600 RPM motor. But when i looked at the nameplate, it said the output should be 3450 RPM! So I was getting a reading 104% of nameplate. So the tach might be off but doesn't fully account for the 24% increase in speed I am seeing at the Quill.....

I had to put it back together to use it Sunday afternoon so I just adjusted the speed indicator wheel to match the RPM I was reading so I don't overdrive my bandsaw. But now the lowest I can mechanically go is about 'C' on the dial.

I'd gladly pull it apart and fix it if I knew what the problem was ....

The speed rating listed on an induction motor is the "full-load" speed ... in this case about 96% of the 3600 RPM "synchronous speed". The motor speed decreases with load, fairly linearly, and 4% "slip" is typical at rated continuous output power. If you measure the speed at no load, however, it should be pretty close to the synchronous speed. So there's no reason to suspect gross inaccuracy of your tach.