Intermittent Drum Switch Operation

[Rick Kruger]

I have a 1946 MG 10EE. Recently, the drum switch operation has become intermittent, meaning it does not turn on to run when the drum switch is rotated either left (forward) or right (reverse) at times. It can be very intermittent in that it will run at times and not run with repeated attempts. Other times, it will start out working, but then goes into complete not-running. Even more scary and dangerous is that if left in the ON position, the machine will start up without warning after not working for a few or many seconds. Link to a video showing this behavior.

One person I asked about this suggested the contacts could be dirty or worn such that it is not making good contact. I have drawings and see there is an access plate on the back of the headstock. I have the machine pretty close to a wall and it will be difficult for me to get back in there to get the plate off and then be able to look inside. I may have to move it away from the wall to work effectively.

The drawings I have show a cross section and I can see there is a coupler between the shafts of the rotary switch and the drum switch with set screws. It would appear I need to loosen one of those to get the drum switch out to work on it. But it is not evident from the drawings what else may be needed to get it out.

What other reasons could there be for the switch behaving this way and what else do I need to know for getting the drum switch out?

Thanks,

Rick

 

[BugRobotics]

Is this machine using the original drive electronics or has it been updated? If it has been updated what is the model of the VFD?

 

[zamboni2354]

Here's the switch that was in my 50s or 60s parts machine and one for the 1988 machine. Either way the switch comes out and a roll pin simply slides into a slot on the lever portion.

Hope that helps
Jeff

Sent from my SM-G998U using Tapatalk

 

[Rick Kruger]

Original, motor generator, no VFD.

 

[Rick Kruger]

Here's the switch that was in my 50s or 60s parts machine and one for the 1988 machine. Either way the switch comes out and a roll pin simply slides into a slot on the lever portion.

Hope that helps
Jeff

I'm not clear on what you mean by the switch comes out. I see what appears to be a roll pin on the shaft in the left photo. Is that the roll pin you are referring to? The switch has to come out the back and from the drawing I have it appears either a roll pin or set screw has to come out in the on the collar between the front switch and the drum switch.


Rick

 

[Rick Kruger]

Here's the switch that was in my 50s or 60s parts machine and one for the 1988 machine. Either way the switch comes out and a roll pin simply slides into a slot on the lever portion.

Hope that helps
Jeff

I'm not clear on what you mean by the switch comes out. I see what appears to be a roll pin on the shaft in the left photo. Is that the roll pin you are referring to? The switch has to come out the back and from the drawing I have it appears either a roll pin or set screw has to come out in the on the collar between the front switch and the drum switch.


It looks like I need to take the plate off the back, but your photos show the drum switch being attached directly to the plate. If that is the case, how do I get in there to loosen anything?

Rick

 

[BugRobotics]

With the machine off can you get at the leads to check continuity?

 

[Rick Kruger]

With the machine off can you get at the leads to check continuity?

I can probably do that, but I don't even know which leads or where. I haven't opened the back to expose any leads if that is where.

 

[Cal Haines]

You don't need to move the machine. You can lean across the bed and remove the switch.

You can check the switch contacts from the terminals at the bottom of the DC control panel. With the machine off, you should see continuity between terminals C1 and C3 with the headstock switch in left-leaning position, and between C2 and C3 with the switch in the right position.

Cal

 

[BugRobotics]

I can probably do that, but I don't even know which leads or where. I haven't opened the back to expose any leads if that is where.

Here is a wiring diagram posted a while back: https://www.practicalmachinist.com/...matic-round-dial-10ee-10ee_schematic-copy.jpg

Here is the thread:Schematic for Round dial 10EE

 

[zamboni2354]

Yes the switch is attached to the rear plate. You remove the screws on the rear plate and pull it out with the switch. It all just slides out. The roll pin doesn't pin it into anything, it slides in a slot in 1011-20

 

[Rick Kruger]

You don't need to move the machine. You can lean across the bed and remove the switch.
...snip...
Cal

Got the screw out but the plate is stuck, by paint? Been tapping on it but hasn't budged. Tried some gentle prying, no movement.


Rick

 

[Cal Haines]

There should be 4 screws.

Go around the perimeter with a V-shaped X-Acto blade to break the paint. If you have a pin-type face spanner and can give it a twist, that will usually break it loose. You may need to use a spring hook to get between the plate and the headstock to pull it free.

Cal

 

[Rick Kruger]

There should be 4 screws.

Go around the perimeter with a V-shaped X-Acto blade to break the paint. If you have a pin-type face spanner and can give it a twist, that will usually break it loose. You may need to use a spring hook to get between the plate and the headstock to pull it free.

Cal

Took a bit more prying but it came out. Cleaned the contacts and there is continuity between terminals C3/C3 on one side and C1/C2 on the other. Reassembled, but did not correct the intermittency.

Any point to and would it be safe to turn the lathe on and try rotating the drum switch while out of the headstock?

Before
View attachment 343894View attachment 343895

After
View attachment 343896View attachment 343897

(Curious, previous inline photos display as thumbnails but these are showing as URLs).

Rick

 

[BugRobotics]

Can't see your most recent attachments for some reason. I'd be checking for loose/broken wires or terminations at the controller.

 

[Cal Haines]

To check the contacts at the switch, disconnect C1, C2 and C3 from the bottom of the DC control panel. You should see zero Ohms between C1 and C3 in one position, C2 and C3 in other. There should never be continuity between C1 and C2.

The contact fingers can be removed for cleaning by first taking out the screws.

Check continuity between both end of leads C1, C2 and C3 (drum switch to DC panel end of each wire) while they are disconnected at the DC panel.

The fact that you're having problems in both directions suggests that you have a problem with the C3 wire or its contacts.

Cal

 

[Rick Kruger]

Can't see your most recent attachments for some reason. I'd be checking for loose/broken wires or terminations at the controller.

Yeah, I find that curious too. They show up as links/URLs on my display and clicking on them brings them up.

I've never been inside before on this lathe. Where is the controller?

Front panel off, wiring box exposed. Wiggled each one, nothing seems loose here. I can't match any of the terminals in this panel to to drum switch either.



Rick

 

[Rick Kruger]

Where is the DC control panel? I have a full sized hardcopy of the wiring diagram, part of the manual ordered from Monarch. It doesn't identify anything as DC control panel. I have the front door off. Is it inside either of the end doors?

Rick

 

[Cal Haines]

...

I've never been inside before on this lathe. Where is the controller?

Front panel off, wiring box exposed. Wiggled each one, nothing seems loose here. I can't match any of the terminals in this panel to to drum switch either.

View attachment 343899View attachment 343900

Rick

That's the motor/generator (MG) terminal panel. It has nothing to do with your problem.

There is no "controller". The DC Control Panel is located behind the big cover on the headstock end of the machine. It's a large box, on the the bottom, to the right of the spindle motor.

If you didn't find wires on the headstock drum switch with metal tags C1, C2 and C3, say so.

Cal

 

[BugRobotics]

I believe yours is accessed behind the covers at the rear of the machine (spindle end).