CNC Lathe CSS (G96) Wear & Tear

Flash Gordon · Feb 23, 2019

I'm running a job right now that's programmed with G96. There's lots of ramping up and down between about 800rpm and 3500rpm.
I know the machines are designed for this, but does this produce more wear and tear on the spindle motor and the electronics?

Mike1974 · Feb 23, 2019

I can't answer your question, but if you are going from 800 to 3500, I ass-u-me your part is pretty large diameter? You could limit your spindle to 2500 maybe, probably won't see much difference in cycle time or surface finish IMO. Once you get to the center your sfm starts getting close to zero pretty fast so...

Is this a big production job with lots and lots of parts? If not I wouldn't worry too much, if it is, maybe look at your programming to see if something can be done differently, IE rough drilling the center bore before facing so you don't have to go down to zero diameter. I know some people frown on this, but I've had no problems unless the stock is really bad out of square from the sawcut.

litlerob1 · Feb 23, 2019

It's not good for the Machine.

On top of what Mike posted, you can turn CSS off before sending the turret home. You can play with known speeds at the end of operations, from Tool to Tool, so it doesn't fall off much. The wind up is worse than the wind down (I assume). So just don't wind down, then it never has to wind up. I only stop it when engaging the C.

Vancbiker · Feb 23, 2019

Not hurting the motor as long as no issues with the fan. It does pull high currents through the transistor modules and DC bus of the drive, but they are sized for it. Again, cooling is important here. There are often fans and heatsinks that go uncleaned which reduce their ability to keep the modules cool.

Personally I do not think using CSS will noticeably shorten the life of the drive. Lots of AC drives go 20+ trouble free years.

SeymourDumore · Feb 25, 2019

I'm not seeing a dilemma here.
Your motor and the drive is designed for acceleration/deceleration, so a controlled up/down is better than a full start/stop anyway.

As far as 800 through 3500 ... so what? If that is how fast you need to turn with CSS, then that is what it'll be.
Would you rather bust tools or under utilize the machine?

Now if you're talking about keeping CSS on during toolchanges, then that's on you.
I for one ALWAYS go back to G97 Sxx before moving to the index position, where Sxx is the approximate starting spindle speed for the next tool.

doug925 · Feb 26, 2019

Like Rob said (maybe others too), it does not hurt it, but it may well wear out things faster than the norm.
I had to change out the spindle brake resistor on my HL-4 (years ago) due to the constant RPM changes of CSS on a small part.
I have since learned not to run my lathe the same way. I keep the G50 at 2500 for most turning on that 10" chuck.

If it does the majority of spindle ramping at tool change, switch to a G97 prior to the turret retracting to a clearance position for tool change.

If it from a facing cut, then "you gotta do what you gotta do"

Doug.

adama · Feb 27, 2019

Wear wise, no IMHO not a issue, but power cost wise, i think it might be, sure if your doing large facing type work you want to use it, but i think a lot of people miss what it costs them energy wise.

Vancbiker · Feb 27, 2019

adama said:
Wear wise, no IMHO not a issue, but power cost wise, i think it might be, sure if your doing large facing type work you want to use it, but i think a lot of people miss what it costs them energy wise.

Definitely a location specific concern. Around my area residential power is only $.08/kWh and industrial power is cheaper.

SeymourDumore · Feb 28, 2019

doug925 said:
I had to change out the spindle brake resistor on my HL-4 (years ago) due to the constant RPM changes of CSS on a small part.

Doug.

Sorry Doug, just read your post!

I don't know how the HL-s were set up and designed back then, but I will challenge ANYONE to show me how one can burn-up a stove coil filament brake resistor as-used
on EVERY Haas machine since at least 1998!
Seriously, while Haas has made some incredibly idiotic designs, on the other hand they've also had more than their share of "Why didn't I think of that" ideas!"

The stove top heater elements used as a brake resistor happens to be on the very top of that list!
Shiit, the f.in protective sheetmetal around them with the word "HOT" punched through cost more than the resistor itself!

doug925 · Feb 28, 2019

SeymourDumore said:
The stove top heater elements used as a brake resistor happens to be on the very top of that list!
Shiit, the f.in protective sheetmetal around them with the word "HOT" punched through cost more than the resistor itself!

True.
I was surprised it burned up. but it was inexpensive enough. IIRC
Since then, I use a G97 to cancel CSS prior to G00 X18. retract moves.

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