manual turret lathes: the part I don't get (multitude of spindle start/stops)

[Arthur.Marks]

This problem has confounded me, and I have had real-world repercussions regarding it. HOW do manual turret lathes deal with the incredible amount of starting and stopping of the spindle needed to do their job?? Now, I know there are capable machines which have clutches which allow the motor to not be stopped for each cycle. I don't have one of those. In fact, I learned my lesson a couple years ago when I did a couple-hundred run of a little part on my bench lathe with turret tailstock. One final aspect of the job was to face all the little pieces to exact length. Before I was done---my motor was. and needed a complete rewind to run again. too many starts, too quick in a row.

YET, one of the most prolific production machines, the Hardinge DSM59, as far as I know, doesn't have such a clutch: http://www.lathes.co.uk/hardinge/page3.html Neither does my lathe, a Schaublin 102. These were also made in great numbers as production machines.

So, the questions...
*was there any way to run these as production machines without the lever collet attachment?
*(related to above)was it accepted that the spindle was never meant to be stopped/started---instead, that a lever collet closer was to be used to release/close the collet while running? For example, the collet is always spinning while you remove/install the new part against a hard stop?
*is there any way to NOT to blow up a motor and do 100+ starts in an hour's time other than an independent clutch mechanism?
*do modern-day, bar-fed, CNC lathes overcome this issue in any OTHER way than an independent clutch mechanism?

I once again have a production run to accomplish, and I want no part in smoking out my motor again

Signed,
"Confused on my Available Options"

[wierdscience]

Have ran a Hardinge off and on for years,also a Gisholt and a WS.

The Hardinge has a low/hi range and a fwd/rev lever all done electrically.The motors on those(2spd) are built for multiple starts/plug reverses per hour.Also the speed ranges generally work out for turret work so you have a high speed for turning/drilling and a low speed for reaming/tapping all without stopping the motor,but simply"downshifting" the motor electrically.Small parts do get runout against a stop or changed while the spindle is turning simply because it's faster.

The old Gisholt has a fwd/neutral/rev clutch and a low/hi speed range clutch in addition to the 10 spd gearbox.On that one the clutches run in an oil bath and the motor runs a constant speed.No rapid starts there.

CNC machines,not much experience with those,but I would assume big honking resistors for breaking and constant voltage for starting.Also just like the old Gisholt the motor never really stops during operation.

[wbleeker]

What about using an automotive air conditioning clutch in your drive train? that way you could leave the motor running, you could also incorporate a brake into the setup. You would only need a 12volt power supply for the clutch.
Will

[John Stevenson]

Three phase motors can plug reverse with no problems provided the switchgear is up to it.

Take a look at one of the old swing saw sharpening machines.
Every time the grinding head swings the motor changes direction so the grinding wheel is always grinding off the tooth.

These can run 24/7 probably doing up to 50 teeth a minute, stop start, stop start.

[Mark McGrath]

We used to run a Herbert tapper,800 rpm,change direction every 5 seconds.Ran nine hour shifts,never stopped.
If it uses a quality motor and good switchgear as John says,no problems.

[philbur]

I believe that three phase motors are much more suited to repeated starts. Also single phase motors can be built/designed specifically to best withstand repeated starts.

Phil

[Doc Nickel]

Basically, the simple answer is that the lathes are built for it. The typical home-shop sized lathe is not necessarily meant or designed to start and stop dozens or even hundreds of times an hour. A dedicated production machine, to put it simply, is.

The above mentioned Hardinge switches electrically, via a motor (and contactors) designed to take the start/stop cycles. I have an older Logan 11" that I ran for a while with a single-phase motor, but I too began to worry about the constant start/stop- besides the fact it "slammed" to a start thanks to the compressor-duty caps in the motor.

I swapped it for a bigger 3-phase and a VFD, and now even after three hours of constant start/stop parts, the motor is hardly even warm. (The VFD is set at about 1.5 sec each ramp-up/ramp-down.)

If you have a small turret and are having problems with the motor, I'd suggest a similar 3-phase/VFD swap. The ramp-up/ramp-down reduces the strain on the belts and drive, it lets me change speeds rapidly (for the different tools) and I can reverse on the fly for tapping and other procedures. (Though only with the collets, the Logan has a threaded chuck.)

*was there any way to run these as production machines without the lever collet attachment?

-I'm not directly familiar with the Schaublin, but I would assume there's a way to mount a chuck. Is the spindle nose threaded?

(related to above)was it accepted that the spindle was never meant to be stopped/started---instead, that a lever collet closer was to be used to release/close the collet while running?

-I've seen people do that, but I'm given to understand it's not the norm. For manually placing and removing parts- by hand- the common- and in my opinion, correct- practice is to stop the spindle, open the chuck, remove the prior part, insert the next part, close the collet, and restart the spindle.

The only time I've seen not stopping the spindle commonly done is when using a bar feeder, where you open the collet, the feeder pushes the bar against the stop, you close the collet, and start cutting. In other words, you never physically handle either the part or the stock.

*is there any way to NOT to blow up a motor and do 100+ starts in an hour's time other than an independent clutch mechanism?

-Yes. As above, try a 3-phase motor with a good VFD (assuming you haven't already.) Give it reasonable ramp-up and ramp-down times and it should happily while away the hours.

*do modern-day, bar-fed, CNC lathes overcome this issue in any OTHER way than an independent clutch mechanism?

-Certainly. I know some modern CNC lathes run a computer-controlled servo as a drive motor, which acts much like I described with the 3-phase, but that's probably not an economical option for you.

Doc.

[willmac]

Arthur-

I think you can get some answers to your question by thinking about why you were stopping and starting the motor so frequently. It is likely that these stop/starts were required because the lathe you are using is not really intended for production work and whilst it has an turret tailstock, that is only a small part of what a proper production lathe would offer. Adding a turret to a ordinary bench lathe does not make it into a machine suitable for significant production.

For example, You probably need to stop the motor to change speeds; popular turret lathes like a Herbert preoptive avoided this time wasting by having a pre-selector gearbox - select the speed you want while the spindle is running then push in the button to change speed on the fly.

You would have been stopping and starting to feed stock to length at the start of a cycle. That would happen on the fly with a production machine with a bar feed.

It is possible that your lathe has a single phase motor. As others have pointed out, that is not the best choice for this type of work. The kick that is needed to get a single phase motor running and the centrifugal switch combine to produce a motor that is not intended for this type of duty. A three phase motor is simpler and much more robust.

[Arthur.Marks]

The feedback so far has me leaning toward the following end of the spectrum: it was an old motor. It had reached the end of its life. My operating it such didn't let the magic smoke out; its insulation had just plain worn out after 50+ some years. These lathes were made to a very high standard. The catalogs show the same equipment I have as being sold for "production" use. The motor is/was 3-phase, and the control setup is very close to the Hardinge machines, which is why I referenced them. i.e. two-speed switch which halves the motor speed without needing to change belt position. Reversing also.

I had hoped to run this job on my new vfd setup, but as per my prior thread that is not happening any time soon. I was lucky enough to receive a brand new, faulty motor from Marathon I just can't catch a break. Meanwhile... my deadline is fast approaching. So back to the 'old' setup. I guess I will run it and try not to worry. I did have the old motor re-wound by a professional motor shop, so it should be up to par. That'll be my theory anyway...

[moe1942]

Ask the people who rewound the motor if it is up to that task. They, if anyone, should know..

[wierdscience]

The feedback so far has me leaning toward the following end of the spectrum: it was an old motor. It had reached the end "



That very well could be,insulation does break down over time and being an old used machine there is no telling what kind of abuse it may have seen.A good rewind and a dip may put the whole situation to rest.

[Bob Fisher]

My 9X20 Jet has a clutch arrangement that allows multiple stops without problems. It is one of the reasons I kept it when I found my Logan. It irritates me to turn the lathe off to mike something. The air conditioning clutch idea intrigues me, though. Bob.

[Arthur.Marks]

I've been stopping and starting this motor quite a bit today with no complaint. I'm not finished yet, so I still could do a bang-up job tomorrow Can't say I'm worried about it anymore.

While I was in the midst of my Marathon motor trouble, I was trying to educate myself on C-face intermediary clutches such as those made by Warner Electric http://www.warnernet.com/industrialframe.htm Seemed like a good, if very expensive, option. They mount right onto standard frame motors and provide the same size output shaft for mounting the drive sheave. Ignoring the high cost of the units, I had one other sticking point. If I was to have a clutch at all, I would want a brake to arrest movement on disengagement of the clutch. Using the VFD for stop/starts allows a nice, controllable ramp time for the stop. The brakes on the clutch units seem to be all very abrupt. My setup goes: motor - V-belt to countershaft - flat belt to lathe headstock. With such a hard stop, wouldn't it be likely the belts would be prone to jump out of position? Or is that another one of my misconceptions... (probably)

I am familiar with the belt clutch you mention on the 9x20 lathes. You're right. It works quite well. I find that a de-tensioning lever doesn't work too well as a clutch when the belts are much larger though. Those 9x20 drive belts have a really, really small profile. De-tensioning flat belting doesn't work either. If you really release the tension, the belts foul their sheave position often. If you keep the tension much closer to retain position, I find the belt rubs and begins burnishing parts of the belting. This ruins the effectiveness of it---lessens the ability to transmit torque. It was my initial idea as well to use the tensioning of the countershaft as a clutch. Didn't Myfords use a similar set-up and somehow make it work?

[philbur]

With such a hard stop, wouldn't it be likely the belts would be prone to jump out of position? Or is that another one of my misconceptions... (probably)

My Boley has the same drive train you describe and also has twin electric clutches and an electric brake on the "return gear", equivalent to your counter shaft. It is primarily used for threading (metric). It stops the chuck in a fraction of a revolution and then provides a 4 speed return of the carriage, all at the flick of a switch and without stopping the motor. No belt jumping involved.

Phil

[DR]

Production machines were built to run sometimes 24/7 with constant starting stopping/reversing etc. That's why they cost so much. The motor out of a Hardinge machine typically was two speed with 1hp and 1/2hp on the lower speed. It takes two men and a boy to pick one of those up. Not to mention the cost.

Here's a teaser for you guys and girls. Swiss machines (that's a special type of lathe, not meant to refer to country of origin) had an unusual method of tapping the end of the workpiece. Since the machines were designed to make very tiny parts they had to efficient , price per part was low.

The tapping was done, tap screwed into part and unscrewed, without reversing the machine's spindle or changing it's speed. This saved the time/cost of reversing the spindle so other tools could be cutting on the part's OD while the tapping was occurring.

How was that done?