Mark VII Motor Hums in Reverse

[GerikBensing]

I recently bought a Mark VII Shopsmith that needs some TLC. It initially ran in forward and reverse, though I noted when it got higher up in RPM it seemed to slow down. My guess was something to do with the pulleys being pretty gummed up. I decided to do a tear down and make a YouTube video about it since there isn't much on the Mark VII's and went to record it going in forward and reverse and... reverse just hums and makes the saddest little effort to spin but nothing happens now. I turn it off right away, but even after tearing it down with nothing attached it has the same issue, so it's certainly just a problem at the motor / wiring level. The motor spins freely in both directions, though there is a bit of a rough sound internally that I suspect is bearings that would appreciate being replaced.

Thoughts? Motor is the A.O. Smith Corp. C48L2A10 model.

IMG_6244.JPG (479.92 KiB) Viewed 877 times

[JPG]

The switch is the culprit.

The 5 terminals on the right control the direction. They switch the polarity of the start circuit.

The switch reverses the polarity between the two pair of wires.

The two wires in the rear(behind the forward three) are connected to the near terminals to their right for one direction and to the near terminals to their left for the opposite direction. The two outer near terminals are jumpered to each other.

Getting into the innards is easy, and a bit risky, but necessary to correct this.

[miken]

I have to agree with JPG, on my MarkVII it was a poor contact in the switch. I have the same motor. Here is a link to my posts with wiring to the switch explained viewtopic.php?t=24293. You can disconnect the switch from the motor and apply power to the motor leads directly to test both forward and reverse once you get the wiring figured out.

Mike -

[GerikBensing]

Alright, so I got a chance to continue troubleshooting and noted how tough it was to press the reverse button. I tested the connections and everything passed. I decided to try cleaning it up a little anyways and then the buttons got harder to press. I decided to do the drill and spray procedure and that all went fine but now the buttons are extremely hard to press. I suspect the process has dislodged lots of gunk that was building up and now it’s stuck between the three boards in there. They all function as they should still when you get them in position. If you fill it with electronics cleaner it seems to lubricate everything and the buttons function pretty normally until the cleaner dries up.

I tested the motor and it does go in forward and reverse without incident.

So, thoughts on what I should do next? I imagine if I could open the switch up I could resolve the issue, but I’m guessing it’s fairly destructive to do so. I do have a 3D printer at my disposal if case reconstruction will be necessary.

[miken]

I opened my switch as I really had no other options. There are 3 sliding plates (boards you called them) in there in a specific order, don't mix up the order. I put powdered graphite between each plate as I reassembled. There is a picture on my post linked above of the opened switch. The powdered graphite really makes the plates slide easily. If I remember correctly, the back plastic cover plate was pretty easy to pry off. Push in on the contact pins as you lift off the cover plate so the contacts stay in place under the cover inside the switch. They are not glued in and will want to come off with the cover plate. If that makes any sense at all.

Mike -

[JPG]

IIRC a couple of screws/nuts hold it together. A small washer under the nut when reassembled is recommended.

[GerikBensing]

Okay, so the case and the male connectors aren’t attached to each other directly? It looked like the connectors were sort of pressed into the case. I have not noticed any screws that can be removed besides the one that holds the lightbulb post. I was thinking about graphite or something similar too but was concerned about conductivity. Sounds like it’s not an issue.

[BuckeyeDennis]

I’d be very cautious about using graphite powder inside of a switch. The stuff is both conductive and combustible, so you don’t want it anywhere that it could cause a short-circuit between conductors.

Teflon spray would be much safer. But as teflon is an excellent insulator, you wouldn’t want to get it between the switch contacts.

Based on a quick Google search, it appears that a dielectric grease, applied to the mechanical sliding points but not to the switch contacts, would be the preferred approach.

[miken]

At the time I did mine I didn't even consider conductivity. Good point Buckeye. I just wanted a dry lubricant because anything else is somewhat sticky and wouldn't slide as well. Also sawdust will eventually stick to any grease/oil like lubricant. I only put it between the plates and haven't had any issues, but if there are safety concerns please don't follow what I did. Maybe try baby powder, or silicone spray on the sliding plates only?

Gerik, the male pins that go through the back plate are a tight fit through that back cover plate. I think they were supposed to be a tighter fit in the switch part on mine but they just lifted out when I took off the cover. It's no big deal if they do, you just need to reinsert them back into the switch. My contacts were really loose in the switch which I think contributed to arcing which eroded the switch contacts. I epoxied them in place when I reassembled, and built up new contacts with electrical solder then filed them flat. My repairs were never originally meant to be long term, i had plans to replace the switch completely, but it has worked out well, and I will run it until I'm forced to replace it.

Mike

[JPG]

viewtopic.php?t=11986 Scroll down for nut detail.