10EE RPM Jumps

[Will McRay]

I have a 1947 10EE and all works fine except I have developed an issue with the spindle speed. When the spindle speed is turn down to say 300-500 rpm and the spindle is stopped. When I turn the spindle back on, the speed is now at its lowest rpm. I then have to increase the speed via the knob and around 1000 rpm the spindle speed will jump to that speed. From there I can control the rpm as you normally would. This only happens after stopping the spindle while in a low rpm. If the rpm was say 700 rpm and stopped then started, it would start just fine back at 700 rpm.

Not sure if motor brushes could cause this or if the rheostat is bad.

Anyone experienced this before or have any recommendations?

Thank you all in advance.

Will


Sent from my iPhone using Tapatalk

 

[rke[pler]

It would help if we knew the drive type. From the mention of 1947 and rheostat I'm assuming that it's a motor/generator drive.

Check the wiper and wides area on the rheostat, make sure both are clean. It's possible some oil dropped on the windings and is affecting things. But the symptoms aren't entirely that. If cleaning doesn't improve things it might be a good idea to put a meter across the field on the motor (F1 and F2 in the front panel) and see what the field voltage as well as the armature voltage (A1 A2). This shouldn't be in field weakening area yet but it'd be a good check on the exciter.

Also check the brushes, make sure they're long enough and the springs are good and engaging the brushes. Check the brush holders that they're not shifting. play with stuff to make sure there's nothing loose on a contact.

Keep one hand in your pocket if you're checking live voltages, there's enough voltage and current in there to kill you and it'll hurt the whole time you're dying.

 

[Cal Haines]

... If cleaning doesn't improve things it might be a good idea to put a meter across the field on the motor (F1 and F2 in the front panel) and see what the field voltage as well as the armature voltage (A1 A2). This shouldn't be in field weakening area yet but it'd be a good check on the exciter.

Assuming that this is a motor/generator (MG) drive:

You won't find a terminal F1 on the bottom of the DC Control Panel (the big box next to the spindle motor). You need to measure from F2 to E2 to check the spindle motor's field voltage.

If Russ' suggestions don't help, go to the terminal panel on the MG (behind the cover at the operator's feet and make the following checks: Check the voltages between GF2 and E2 and between E1 and E2 when the spindle is running normally at 400 RPM and then after restarting, when the spindle is running too slowly. The GF2-to-E2 voltage is what controls the speed of the spindle when the motor is below 640 RPM. It should always read the same for a given speed setting. E1-to-E2 is the output of the exciter and it should always be around 115 VDC, regardless of load or speed setting.

Also pay attention to what DC Control Panel relays operate when you turn the speed up, after restarting.

Cal

 

[Will McRay]

Thanks everyone. I get to checking. This is a motor/generator set up so all your recommendations are relevant.

Will


Sent from my iPhone using Tapatalk

 

[Will McRay]

It took a bit, but I finally got around to checking the recommended volatges. Life and family has a way to getting into the way of hobbies.

I checked the voltages at four RPM ranges. Here is what I got:

SPINDLE OFF MOTOR RUNNING:
F1-F2: .001 VDC
A1-A2: 5.6 VDC
GF2-E2: .001 VDC
E1-E2: 114.5 VDC

SPINDLE ON (400 RPM)
F1-F2: 24 VDC
A1-A2: 36 VDC
GF2-E2: 24 VDC
E1-E2: 110 VDC

SPINDLE ON (RPM DROPPED OFF AFTER SPINDLE STOP THEN START, ROUGHLY 10-20 RPM)
F1-F2: 0.18 VDC
A1-A2: 7.3 VDC
GF2-E2: .12 VDC
E1-E2: 113 VDC

SPINDLE ON (640 RPM)
F1-F2: 52.3 VDC
A1-A2: 63.0 VDC
GF2-E2: 52.3 VDC
E1-E2: 109 VDC

SPINDLE ON (1000 RPM)
F1-F2: 101.4 VDC
A1-A2: 85.8 VDC
GF2-E2: 101.7 VDC
E1-E2: 105 VDC

So what do these numbers tell me? Cal stated the voltage from E1-E2 regardless of RPM should be 115 VDC. I am seeing fluctuations of voltage at different RPMs. Is this brushes?

The brushes look okay. I do see one of the brush on the DC motor that is not sitting even with the other side. The spring pressure retainer (not sure what its called) has one lower then the other, but is making contact that I can tell.

Looking at the relays in the panel by the AC motor on the back of the lathe, the contacts are dirty and could use a cleaning. What is the best way for this? When running in either direction and stopping the spindle a large spark does happen. When engaging, no spark.

Another observation is when running in reverse, the RPM gage does not read obviously, but the speed seems faster at the top end then forward. I did observer while in reverse and full speed, it spun up strong, the back off on RPM. Not sure how much, but I'd guess about 500 RPM.

In forward, I can not longer obtain the full 2500 RPM. I can only got to around 2000 RPM. I don't see anything burnt or damaged electrical components (visually).

Based on what I stated, what are some recommendations? I am not a strong electrical guy so please be patient with me and break them down barney style.

As always, thank you everyone for your assistance.

R/S
Will

 

[Cal Haines]

...
I checked the voltages at four RPM ranges. Here is what I got:

SPINDLE OFF MOTOR RUNNING:
F1-F2: .001 VDC
A1-A2: 5.6 VDC
GF2-E2: .001 VDC
E1-E2: 114.5 VDC

SPINDLE ON (400 RPM)
F1-F2: 24 VDC
A1-A2: 36 VDC
GF2-E2: 24 VDC
E1-E2: 110 VDC

SPINDLE ON (RPM DROPPED OFF AFTER SPINDLE STOP THEN START, ROUGHLY 10-20 RPM)
F1-F2: 0.18 VDC
A1-A2: 7.3 VDC
GF2-E2: .12 VDC
E1-E2: 113 VDC

SPINDLE ON (640 RPM)
F1-F2: 52.3 VDC
A1-A2: 63.0 VDC
GF2-E2: 52.3 VDC
E1-E2: 109 VDC

SPINDLE ON (1000 RPM)
F1-F2: 101.4 VDC
A1-A2: 85.8 VDC
GF2-E2: 101.7 VDC
E1-E2: 105 VDC

So what do these numbers tell me? Cal stated the voltage from E1-E2 regardless of RPM should be 115 VDC. I am seeing fluctuations of voltage at different RPMs. Is this brushes?

...

In forward, I can not longer obtain the full 2500 RPM. I can only got to around 2000 RPM. I don't see anything burnt or damaged electrical components (visually).
...

Beg to differ, but the symptom is that you have no field voltage, which is a real problem. Brush timing may be an issue, but certainly not the first thing that you need to address. Leave the brushes alone for now!

Field voltage should never drop below about 40 VDC and should be at 100% (about 115 VDC) until the speed control is at the midpoint. You probably have something going on with your motor rheostat, probably an open winding. The motor rheostat is the one that's connected in series with the field and what weakens the field to allow the motor to run above base speed. It's the one with two wires, F2 and E1-2. However, with the spindle stopped, the NC contacts on the Forward/Reverse (F/R) contactor should bypass the rheostat and you should see full field voltage, so I'm not sure what's going on there. Perhaps the dirty contacts that you mentioned are keeping the NC contacts from working.

Disconnect one of the leads to the rheostat and move it through its full range while watching the resistance. The resistance should read close to zero for the first half of the rheostat, then increase to about 400 Ohms at the end of motion.

Cal

 

[Cal Haines]

Zero field power WHAT? It can hit some crazy speeds with no field, you should know that. The field acceleration relay is probably all that's keeping the motor from running away completely.

You can't check the brush timing when the motor isn't running correctly. Which it isn't when it has no field.

LEAVE THE BRUSHES ALONE. FIX THE FIELD PROBLEM.

Cal

 

[rke[pler]

F1-F2 should have been E1-E2 for most all of the tests (I'm not completely sure about spindle off but I think even there). The field voltage should be high until the armature voltage reaches it's max, then decrease slowly as the motor speeds up until the max speed is reached. The rheostat controls the field voltage and if you look at the resistance over it's travel you should see very low resistance at the low speed to about half the travel then a slow increase in resistance to the max speed (I'm unsure what the max resistance you'll see might be). I'd hook up and analog meter to the rheostat and watch the meter as you move the rheostat, and weird blips on the needle means you need to clean or replace the rheostat.

Once you have the field working correctly we can look at the armature voltages, they don't look quite right. Low at the 1000 rpm even if you're running a 2500 rpm machine.

Once all that's done we can see if the brush timing is off, but if the voltages are OK and it's not arcing a lot I'd be tempted to leave it alone.

 

[Will McRay]

I got a lot to research and learn with all the discussion. Seems the rheostat should be checked first through the whole range.

For the brushes, I don’t have any sparking going on. If this is a brush timing issue, how do I verify the timing and what is the procedure for setting the timing? What’s entailed? Pulling the M/G?

Uncharted waters for me but willing to learn.

Will


Sent from my iPhone using Tapatalk

 

[Cal Haines]

If the forward and reverse speed sounds the same, by ear, the timing is close enough. You can use a laser tachometer to dial it in closer if you like, or if your hearing isn't very good. The timing is adjusted by rotating the black, insulating ring that support the brush holders. The split in the ring and the lock bolt is at about 10 O'clock when you're looking at the pulley end of the spindle motor. Witness mark the ring before attempting to adjust it, so you can return to the starting point. Rotate the ring a small amount (with the motor off) and see if the timing improves, if it gets worse, go the other way.

But again, when the field voltage is all over the place, you need to fix that first or you'll just be chasing your tail.

Cal

 

[Will McRay]

Cal,

I tried to send you a PM but you inbox is too full. Do you have an email or text I can send questions to you about my 10EE issue with the RPM jumping issue I have?


Sent from my iPhone using Tapatalk

 

[Cal Haines]

Cal,

I tried to send you a PM but you inbox is too full. Do you have an email or text I can send questions to you about my 10EE issue with the RPM jumping issue I have?

...

Sorry about that. I made a little space in my inbox. You can always e-mail me by clicking my name in the upper-left corner of any of my posts. I prefer e-mail to PMs.

BTW, you have e-mail turned off for your account. (I think that it's off by default.) If you enable it, it's easier for people to contact you. You don't have to worry about getting spam from it, senders don't get your e-mail unless you reply to them via e-mail. In 20+ years here I've never gotten spam via Practical Machinist's e-mail system.

Cal