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I have a tree 250 with a 3HP spindle motor with a VFD. Right now the motor turns at about 4800rpm with a final spindle speed of 4k rpm. We want to bump to a 5HP spindle motor and get to a final spindle speed of 8-10K. OUr spindle is an Erickson QC 30 taper with dual taper bearings at the head and three ball types up top. All are sealed grease. We are looking for a cheap 5HP 184TC frame, 4pole probably.
We are looking for recommendations on brands of motors, max safe motor speeds, economical solutions, and what that spindle can take before we see issues with it. I know it scares most to wonder from the OEM path but we do it for a living in the race world.
Wether or not the spindle can take it, I would say you are pushing the limit right now with a standard induction motor at almost 5k. Especially if you are looking at a cheap one.Originally Posted by viper6383
If the spindle itself can take it, I would look at using a larger HP standard motor and gear up. 3:1.
At 10K the motor bearing and motor balancing are super critical.
Al.
CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
I'll add this:
Unless you know what kind of bearings are in the spindle (tapers, rollers, A/C ball, lite/med/heavy preload), simply over-revving the spindle can get dangerous and/or expensive.
As you go UP in speed, you generally go DOWN in preload - you do that to reduce heat rise potential.
Grease type (oil vs grease) and amount (lite for high speed, more is ok for lower speeds) also need to be reviewed and adjusted.
In an economy of words, you can't simply double the speed of a spindle and expect it to live half as long - it might fail in 1/10th the time or maybe even sooner - or later. It really is too hard to tell.
Yes, balancing are supler critical, but bearing alignments, fits, preloads and tolerances become hypercritical as speeds go up as well. NOT a place to SWAG unless you have money to spend/burn.
If you do (have money and time to burn), buy a good high speed spindle and you'll be MUCH happier in the long run - you'll make more money too.
Well the spindle has dual A/C ball types at the bottom and three standard ball types at the top. The plan was to run our machine out at its rated 4K for X amount of time and allow the heating to meet equilibrium and then start pushing the Rs and monitor heating in the motor and spindle. We may install thermocouples on the spindle to monitor that since loading will have a large effect on heating. I have done some research on the A/C bearings and the minimum rating for any of them is 11K. Now I have no way of knowing which bearings I have until I go in. The thought was that if it "pops" we know the bearings were not good for it. A 500 dollar mistake but one that we would have to cross anyway since we are not taking no for an answer on more Rs.
We would have to make a spindle bearing change anyway. We plan to build it ourselves and I know that would scare most people but we build race engines and parts everyday and I just love it when someone tells me I cannot do it. Actually, I am looking forward to it just to see what is going on there. Rest assured, I will school myself before attemping that.
I don't see anyone is telling you 'You cannot do it' just pointing out the pitfalls that you may see when you do try.
The rotor of a standard 4 pole 5 HP motor has quite a mass, I would be hesitant to be close this motor if you intend running it up to 10krpm.
Al.
CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
NO, no, sorry, I was not refering to anyone from the site. Actually, the reason I signed up is I saw several guys modding some custom mills and thought someone here cound help. Actually, I don't plan to push the motor further than 6-7K and plan to overdrive the spindle to 8-10K. I just rebuilt the motor today and found that indeed my spindle upper bearings are talking so it is time to check that out.
Now my big and hopeful question on that spindle is can I install upper bearings without having to mess with the A/c Bearings at the bottom? I will bet someone overtensioned the belt and caused this failure and I am sure the A/c bearings are still good. I will also start another thread just on that to get some advise and that rebuild.
B
Famous last words " but the bearings were rated for 11,000 rpm...."
Bearing "ratings" are theoretical values that the bearing should be capable of IF all the proper precautions for a particular environment are followed TO THE LETTER with all I's dotted and T's crossed. This also means that the bearings are warmed up prior to full tilt operation and all sorts of other normal and customary precautions. It also means proper lube and NO lube contamination.
Believe it or not, there are people who install stuff, turn on the switch and expect it to run. Like buying a crate motor and trying to run it at Daytona to win the 500. Ain't gonna happen.
High speed spindles typically run low preload bearings. THe better ones also tend to run constant pressure preloads as opposed to position preloads of the non-A/C support bearings. Thus, when the thing grows with heat, it doesn't start adding or changine preload in an unexpected fashion.
Grease becomes less desireable a lube at high speed - oil/air mist becomes the preferred medium of lube. The air cools and the misted lube gives all the lube needed - the mist also doesn't cause the balls to hydroplane as grease or oil bath will/might at high speed.
Your plan is valid and probably viable but there may be some legacy gremlins in your existing spindle design that may not be as conducive to high speed operation as you might hope. See if you can find some high speed spindle cross section dwgs - these would point out OBVIOUS differences that you should be aware of.
The creation of a 10K spindle is NOT unike the attention to detail that the construction of a 9500rpm race motor entails. Care, details, premium hardware and patience. Without them, you can readily create junk.
Yes, I am not telling you it is NOT possible - ony pointing out the challenges you face. one can never tell if the poster is a stroke or a PHD so, sadly, some of us merely assume lowest commond denominator in our replies.
You also want to revisit your tool paths and infeeds for any part programs once you get the spindle built. Have seen where guys went to high speed and figured that they could do things the same way as they did with their high preload/bury the tool programs. Only comment is as followsnuts)
Finally, there are no "that's good enough" "this is only DIY" excuses allowed when you're using/buidling H/S machine tool spindles. But you already know most of what can go wrong when one uses these bogus excuses if you do build race engines every day.
Good luck
viper6383....well it seems that you have all the answers....so go for it!
If the upper bearings are whining and have started to deteriourate, they may have already transferred vibratory distress to the A/C's.
If debris from raceway detriouration of the uppers got circulated thru the lube system, the A/C's are probably hurt.
Pull the A/C's and wash them very, very well. Then get a magnfiying glass and look very carefully to see if the balls in them are "frosted" or have "cut lines" in them - ditto for the raceway. NEITHER should be present on either.
If they are plastic caged, you can probably run them at high speed. Riveted steel cages are not as robust in high speed bearnigs as molded, reingforced nylon. Machined brass is OK but not as good as nylon
Cut lines come from debris and or overload - frosting comes from lube contamination. Both dreastically shorten the remaining service life of ANY bearing
If you do NOT replace the A/C's and they go bad later on, any misalignment generated will probably tear up the new top bearings. False sense of economics in my opinion but I"m not funding this program either.
How lucky do you feel about your ability to clean, inspect, judge the integrity of used bearings as well as your "machine tool engineering, self taught" classes???
The answer to this question would better determine whether or not to replace all the bearings as a one-shot repair.
NC Cams, I absolutely agree on replacement of the A/C bearings during repairs. I only ask because per OEM, the bearings should have lasted a lifetime. Actually, I am rather surprised the upper bearings are out since they are much larger and double stacked compaired to the motor bearings which were still good when I pulled them and replaced them. I know, *$%# happens.
I normally would not question bearing replacement but the cost of the bearings alone is hard to swallow. Now you can bet I will do a full inspection while I am there but I was somehow (I know) hoping the uppers were an easy swap. I should know better anyway. I should note that the original reason for our mods was that we have a vibration in the mill coming from an out of balance condition somewhere. Runout checks could very possibly give us the answer we don't want.
I agree that we need to better understand our spindle design and flaws. I am hoping that if we do replace the bearings, we can replace with better and higher rated bearings that will suite our needs better. I know the sealed grease bearing design could hurt us so I need to do some more research. Unfortunently, I really do need this thing apart to know what I have huh?
Disassembling and reverse engineering to see exactly what you're starting out with sure beats the hell out of the buy something off of E-bay and make do/it'll have to work like some guys do.
Once you "see" what you have, perhaps we can give more assistance.
The upper bearings could have failed if they were subjected to contamination - environmental or particulate, it doesn't matter, same effect.
Although bearings may have a theoretical mechanical capacity, most guys fail to consider grease life. Overheat it or contaminate it and the grease life plummets. That will cause premature bearing wear/failure REGARDLESS of the theoretical mechanical life.
Either that or a over reefed on belt - perhaps a misplaced blow to "seat the bearing" could have resulted in a brinnell. Life often plummets like a rock when hammers and bearings meet.
Or, if the spindle was position preloaded and got overheated, the expansion could have shoved the balls to the edge of the groove and consequently the balls got cut while running in that state.
To prevent a recurrence, you're really gonna want to do a post mortem or else it could happen again - only with more disastrous results.
There surely is a reason for the failure if you want to take the time to figure it out - I would if it were my spindle.
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