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Fanuc spindle drive help

Mopar73

Plastic
Joined
Jun 30, 2022
New member here. I will try to include any info that I think relevant in this initial post. My employer has a 1989 Wasino lathe with a Fanuc A068-6044-H742 AC spindle servo unit. The spindle braking has not worked properly for several years and has now regressed to the point that I have to ramp rpm down in 250 rpm steps and dwell 5 seconds between steps to slow spindle rpm down from any speed over about 400 rpm. If I do not do this, spindle drive will shut down with Alarm 2 after 4-5 seconds of attempting to brake. This shutdown occurs in both low and high range. Alarm 2 is (Speed is deviated from the command value due to overload or other) according to the drive manual I have. I have experienced no problems with the spindle accelerating up to speed in forward or reverse nor have I noticed any lack of power. I also spent the last 2 weeks double lead single point threading with no repeatability issues which makes me assume that I do not have an encoder or speed sensor problem. I am hoping that someone on this forum will be able to narrow down what part of the drive I need to look at. I am just an programmer/operator and the only "tech" experience I have is from doing what I can to try to keep our old machines going for the last 20 years so my knowledge of electronics terms and such is fairly limited. I know, in a perfect world, this drive would just be replaced with a rebuild but the cheapest rebuild found so far was almost $8000. I understand going in, that even if we can determine what components are bad, we may just find the next weak link in our 33 year old electronics. Thanks in advance to anyone who reads this book and is able to offer assistance.
 

Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
Check the regen IGBT's. The manual for that drive will explain it in detail. The parts are not expensive. Changing them out is not fun. It's about a full day job start to finish.
 

Mopar73

Plastic
Joined
Jun 30, 2022
Thanks, those were the components that I had my eye on. I assume what I would be looking for is that at least some of them have failed open, therefore the rest of the drive functions normally? Would I also want to check the 3 capacitors?
 

wmpy

Hot Rolled
Joined
Dec 16, 2011
Have you checked that the belts between the motor and the spindle are tight? Loose/slippery belts can cause these issues as well.

Also, you can get this drive repaired for around $4k. See here.
 
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Mopar73

Plastic
Joined
Jun 30, 2022
Have you checked that the belts between the motor and the spindle are tight? Loose/slippery belts can cause these issues as well.

Also, you can get this drive repaired for around $4k. See here.
Actually, I know this machine has 6 or 7 drive belts and they are a greasy slimy mess and they do slip occasionally when starting spindle in high range. I know those last two sentences make me sound like a moron but getting my employer to fix something that is still remotely functional is very difficult. Wouldn't worn drive belts also cause problems taking heavy cuts or with repeatability during threading, not just with the spindle slowdown? Not trying to argue, I just need really good evidence to convince the holders of the purse that it could just be the belts.
 

Mopar73

Plastic
Joined
Jun 30, 2022
Have you checked that the belts between the motor and the spindle are tight? Loose/slippery belts can cause these issues as well.

Also, you can get this drive repaired for around $4k. See here.
Even 4k is more than my boss wants to put into this old girl at this point. I already told him, if that's the case, that he needs to start shopping for a newer lathe. I don't know how much longer this one is going to function in "limp mode."
 

wmpy

Hot Rolled
Joined
Dec 16, 2011
Actually, I know this machine has 6 or 7 drive belts and they are a greasy slimy mess and they do slip occasionally when starting spindle in high range. I know those last two sentences make me sound like a moron but getting my employer to fix something that is still remotely functional is very difficult. Wouldn't worn drive belts also cause problems taking heavy cuts or with repeatability during threading, not just with the spindle slowdown? Not trying to argue, I just need really good evidence to convince the holders of the purse that it could just be the belts.

Slipping belts would not cause threading issues. There is most likely another belt that is toothed connecting the spindle to a tach. As long as that belt is ok, slippage between the motor and spindle does not affect threading.

In my experience, spindle belts have to be really loose and slipping a lot in order to cause problems taking heavy cuts. But they only have to be a little loose to cause problems stopping the spindle.

I don't have a complete grasp on how it works, but roughly speaking, if you stop your spindle when it's going, for example, 2000 rpms, the drive knows that it should take 1.5 seconds (made up number) to come to a halt. So, it "applies the brakes" for that amount of time. If the belt is slipping even a little, instead of coming to a complete stop in that time, it slows it down to only 50 rpm or whatever. Then it gives up trying to stop the spindle because time is up, and you have a spindle that is coasting. Maybe someone else can chime in and give a better explanation of how it actually works, but that's how I think of it.

I don't know if that's your problem, but it's the first place I would look whenever I had a problem with spindle stopping. Add to that what you said about the condition of the belts, and ... yeah, you should get a set of new, properly tensioned belts on there- especially before you start taking apart old spindle drives. Hopefully, the pulleys aren't too worn from all the slipping that's been going on.
 

Mopar73

Plastic
Joined
Jun 30, 2022
Thanks, yes it does have a small toothed belt that goes to an encoder. All I can say is duh. I guess it wouldn't make sense to rely on v-belts for timing of threads. I'll try to get them to spring for a set of belts before I go much further.
 

aj

Cast Iron
Joined
May 12, 2006
Location
Burlington, North Carolina
New member here. I will try to include any info that I think relevant in this initial post. My employer has a 1989 Wasino lathe with a Fanuc A068-6044-H742 AC spindle servo unit.
You might also contact Tennessee Industrial Electronics. They're our "go to" source when we need anything Fanuc. They've always had what we needed in stock and it's on our door step the following morning via FedEx.
 

Mopar73

Plastic
Joined
Jun 30, 2022
Thanks, I'm actually corresponding with one of their techs as we speak as we got their contact info from this forum. I was expecting a call-back and didn't realize that they had sent me an e-mail 2 days before. No internet access at work.
 

Milling man

Aluminum
Joined
Aug 6, 2021
Location
Moscow, Russia
New member here. I will try to include any info that I think relevant in this initial post. My employer has a 1989 Wasino lathe with a Fanuc A068-6044-H742 AC spindle servo unit. The spindle braking has not worked properly for several years and has now regressed to the point that I have to ramp rpm down in 250 rpm steps and dwell 5 seconds between steps to slow spindle rpm down from any speed over about 400 rpm. If I do not do this, spindle drive will shut down with Alarm 2 after 4-5 seconds of attempting to brake. This shutdown occurs in both low and high range. Alarm 2 is (Speed is deviated from the command value due to overload or other) according to the drive manual I have. I have experienced no problems with the spindle accelerating up to speed in forward or reverse nor have I noticed any lack of power. I also spent the last 2 weeks double lead single point threading with no repeatability issues which makes me assume that I do not have an encoder or speed sensor problem. I am hoping that someone on this forum will be able to narrow down what part of the drive I need to look at. I am just an programmer/operator and the only "tech" experience I have is from doing what I can to try to keep our old machines going for the last 20 years so my knowledge of electronics terms and such is fairly limited. I know, in a perfect world, this drive would just be replaced with a rebuild but the cheapest rebuild found so far was almost $8000. I understand going in, that even if we can determine what components are bad, we may just find the next weak link in our 33 year old electronics. Thanks in advance to anyone who reads this book and is able to offer assistance.
The symptoms you describe indicate some kind of malfunction in the spindle braking circuit - the regeneration system and / or the braking resistor circuit (I don’t know if they are in this drive).
My advice is, first of all, to coordinate with your superiors ALL your attempts to fix something in this machine, so that you will not be made guilty later. Or, even worse, they didn’t put any expenses on you.
 

Mopar73

Plastic
Joined
Jun 30, 2022
Related to the issues I am experiencing with this spindle drive, some of the checks the manual want you to do require an oscilloscope which we also do not have. I have been looking on ebay and amazon and notice that there are a number of very reasonably priced digital versions available. I know nothing about them and am just curious if a scope is a fairly user-friendly item and if these small digitals would be sufficient or if an older full-size analog version is needed. We have other machines in the shop that a scope would be beneficial for at times.
 

cnctoolcat

Diamond
Joined
Sep 18, 2006
Location
Abingdon, VA
For a great, user-friendly oscilloscope at a good price, check out the Rigol DS1054Z. It is a 4-channel unit, and has a very handy "auto" function which finds, scales, and displays the signal you're wanting to monitor like magic.
No affiliation, just a satisfied user....

ToolCat
 

Mopar73

Plastic
Joined
Jun 30, 2022
Quick update for anyone that has the same problem in the future. We have spent the last couple weeks diagnosing in between part runs. Tennessee Industrial Electronics has been very helpful as suggested. My owner purchased both a megohmeter and an oscilloscope. Our spindle motor megged fine and the motor power cable megged a low so we did replace it, however no change in operation. Our next course of action was to adjust RV18 and RV19 spindle feedback pots with the scope. As some of you probably know, to access the some of the checking points and pots, the spindle orientation board has to be swung up out of the way. I prepared the drive so we could do the checks yesterday morning and then found out the owner would not be in and needed to run the machine. I returned the orientation board back to its normal position and re-fastened it. Imagine my surprise when I found that the spindle-braking has magically returned to normal. I don't know yet if one of the cables on the orientation board has an issue or maybe debris on one of the boards was disturbed. No idea, all I know is the lathe ran flawlessly all day today. Nothing like "fixing" something by accident. I will post an update if and when I determine for sure what the actual cause was. At least it's narrowed down to an area now. I still have to get the boss to spring for a new set of drive belts. Thanks to all for the help.
 

Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
Quick update for anyone that has the same problem in the future. We have spent the last couple weeks diagnosing in between part runs. Tennessee Industrial Electronics has been very helpful as suggested. My owner purchased both a megohmeter and an oscilloscope. Our spindle motor megged fine and the motor power cable megged a low so we did replace it, however no change in operation. Our next course of action was to adjust RV18 and RV19 spindle feedback pots with the scope. As some of you probably know, to access the some of the checking points and pots, the spindle orientation board has to be swung up out of the way. I prepared the drive so we could do the checks yesterday morning and then found out the owner would not be in and needed to run the machine. I returned the orientation board back to its normal position and re-fastened it. Imagine my surprise when I found that the spindle-braking has magically returned to normal. I don't know yet if one of the cables on the orientation board has an issue or maybe debris on one of the boards was disturbed. No idea, all I know is the lathe ran flawlessly all day today. Nothing like "fixing" something by accident. I will post an update if and when I determine for sure what the actual cause was. At least it's narrowed down to an area now. I still have to get the boss to spring for a new set of drive belts. Thanks to all for the help.

The top board on the drive connects to the heavy lifting components through a bunch of heavy spring pin contacts. I bet jiggling the board a bit improved some contact there.

A spritzing of De-Ox and reseating boards/connectors is standard procedure for anyone owning older machines.
 
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