Dreaded LB15 Spindle issues again

Hi, last year I had trouble with the spindle on my mid 80's LB15. With help from here I was able to get the old girl going, but the problems have started again. It seems that as soon as the weather starts to cool off, she doesn't like to start in the mornings. Later in the day all is good.

I have isolated the problem to the speed sensor on the spindle motor. I proved this today by pulling the motor out , removing the fan & then the sensor cover & heating the sensor with my daughters hairdryer. After only a couple of minutes of warming, the motor runs fine in both directions

My question is, what components on the sensor can be effected by warmth in this way

Here is a pic

Any thoughts would be appreciated. Thanks

Ok, I have worked out that it must be a weak magnet that in someway responds to heat. I adjusted the clearance between the toothed wheel & magnet to 0.05mm & she runs fine. Does anyone know how much "air gap" there should be? I am concerned that having too little gap may lead to interference between the two once everything warms up. Cheers.

A big thanks to Jim (doctorcnc) for helping me out again. It is great having people with such extensive knowledge of these machines & who are willing to share it. Regards wc56

Thought I would do an update in case someone else has this problem. I purchased a used sensor from the US & had it fitted & tuned in over the weekend. The old girl is going good once again. I still don't know what was wrong with the old sensor. I thought maybe a weak magnet, but the replacement didn't feel any different. The tech who tuned the new one thought maybe a dodgy solder joint, but doesn't know for sure. Regards WC56

I would tend to agree as well with the solder joint theory, but could also be gap. From what I was told they should be about .5mm or .02" for a correct gap. I usually tend to set them a little closer, but would not get too close because you can wreck them if they rub. I personally like the .01-.015" range.

Best regards,

WC56
Do you think my issue could be related to yours? See below description.

PASTE:
After I discovered the two small 5 amp fuses blown with the advice given here I did indeed find the fault at the spindle cooling fan which had seized solid and was fried.
So with the motor removed I took off the fan and disconnected it for now.

The then proceeded to remove the back cover and of the motor and expose the pulse generator "thingy" on the rear of the shaft. It was spotless in there! Anyway, I reset the gap using some thin paper.

While the motor was out I connected the wires and tried to run it on the ground just to the side of the machine. First few times it was jerking and making noises just like before. I rechecked the plugs on the Fanuc drive and when I can back the spindle worked perfectly! I put it back in the machine and ran some parts, no issue.

Then the next day, cold I noticed it jerking again, so I let it warm up, then once warm it ran fine. That was a few weeks ago.

Today it ran for a few minutes smoothly than while spinning smoothly and warming up at say 500 rpm its started making short jolts and jittering noises, got worse and now I'm back to where I started. with the Alarm A SDU 110.

Any ideas before I call Fanuc in?

Quote:

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Originally Posted by rotec

WC56
Do you think my issue could be related to yours? See below description.

PASTE:
After I discovered the two small 5 amp fuses blown with the advice given here I did indeed find the fault at the spindle cooling fan which had seized solid and was fried.
So with the motor removed I took off the fan and disconnected it for now.

The then proceeded to remove the back cover and of the motor and expose the pulse generator "thingy" on the rear of the shaft. It was spotless in there! Anyway, I reset the gap using some thin paper.

While the motor was out I connected the wires and tried to run it on the ground just to the side of the machine. First few times it was jerking and making noises just like before. I rechecked the plugs on the Fanuc drive and when I can back the spindle worked perfectly! I put it back in the machine and ran some parts, no issue.

Then the next day, cold I noticed it jerking again, so I let it warm up, then once warm it ran fine. That was a few weeks ago.

Today it ran for a few minutes smoothly than while spinning smoothly and warming up at say 500 rpm its started making short jolts and jittering noises, got worse and now I'm back to where I started. with the Alarm A SDU 110.

Any ideas before I call Fanuc in?

---

Sounds like it may be the same faulty sensor. Mine is still running great...touch wood.

Quote:

---

Originally Posted by rotec

WC56
Do you think my issue could be related to yours? See below description.

PASTE:
After I discovered the two small 5 amp fuses blown with the advice given here I did indeed find the fault at the spindle cooling fan which had seized solid and was fried.
So with the motor removed I took off the fan and disconnected it for now.

The then proceeded to remove the back cover and of the motor and expose the pulse generator "thingy" on the rear of the shaft. It was spotless in there! Anyway, I reset the gap using some thin paper.

While the motor was out I connected the wires and tried to run it on the ground just to the side of the machine. First few times it was jerking and making noises just like before. I rechecked the plugs on the Fanuc drive and when I can back the spindle worked perfectly! I put it back in the machine and ran some parts, no issue.

Then the next day, cold I noticed it jerking again, so I let it warm up, then once warm it ran fine. That was a few weeks ago.

Today it ran for a few minutes smoothly than while spinning smoothly and warming up at say 500 rpm its started making short jolts and jittering noises, got worse and now I'm back to where I started. with the Alarm A SDU 110.

Any ideas before I call Fanuc in?

---

Sounds like it may be the same faulty sensor. Mine is still running great...touch wood.

Quote:

---

Originally Posted by WC56

Sounds like it may be the same faulty sensor. Mine is still running great...touch wood.

---

Thanks for getting back.

Well shortly after my last post here, I thought what the heck, on the SDU I'll try just change out the circuit board only. I did have a spare off another LB15. And it worked! ran all day.
Then this morning (very cold) I fired it up and expected issues. As the old one hated the cold. To my surprise, it ran with no issues. So looks like it may have just been a circuit board issue.

One thing I will say is that this machine came from a very busy 24/7 auto production shop. The old board looks so much worse than the replacement board which by comparison looked new.
Let's see how she goes.

I love this little lathe. I've spent some money on her over the years, but I think it's been worth it.

PS: For LB15 to PC coms, I use an eBay USB - RS232 converter on a laptop. After I found the correct driver I was surprised to find it worked!

Glad to hear she is running again...fingers crossed you have nailed the problem. They are a great old lathe & usually very reliable.