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Constant Surface Speed Setup on Lathe

Mr. Fixit

Aluminum
Joined
Mar 16, 2009
Location
Wellington, FL, USA
Hello and Happy New Year to All..

I have an Electronic Variable Speed Manual Lathe and would like to set up a CSS function. The Frequency Drive Unit is a Yaskawa G7 and according to the engineers there, the drive will support this function, but they could not provide any specifics on how to physically set up the cross slide or what was needed to accomplish this. Since the Lathe has a spindle speed sensor and tachometer, I am assuming that all that is needed is some sort of scale that puts out an analog signal (but I am just guessing) to send to the EVS. I would appreciate any information that you guys could provide. I should also mention that the lathe has a Fagor 2 axis DRO, although I dont know if this helps.

Thank you,

Steve
 
Hello and Happy New Year to All..

I have an Electronic Variable Speed Manual Lathe and would like to set up a CSS function. The Frequency Drive Unit is a Yaskawa G7 and according to the engineers there, the drive will support this function, but they could not provide any specifics on how to physically set up the cross slide or what was needed to accomplish this. Since the Lathe has a spindle speed sensor and tachometer, I am assuming that all that is needed is some sort of scale that puts out an analog signal (but I am just guessing) to send to the EVS. I would appreciate any information that you guys could provide. I should also mention that the lathe has a Fagor 2 axis DRO, although I dont know if this helps.

Thank you,

Steve

I would have thought a linear pot on the cross feed would do it. Anchor one end on the carriage and the other on the cross feed. Yaskawa should be able to tell you what range the pot needs to be and how to connect it to the drive.
 
I would have thought a linear pot on the cross feed would do it. Anchor one end on the carriage and the other on the cross feed. Yaskawa should be able to tell you what range the pot needs to be and how to connect it to the drive.

The guy at Yaskawa did mention a liner pot as a possible method. I will check into this as a solution and then get with them for connectivity.

Thank you..
 
A log taper is one that the resistance change is not proportional to the change in length or rotation. In the case of the constant speed control, in order for the cutting speed to be constant, the spindle rpm would have to go to infinity which is clearly not possible. With a non-constant resistor the speed levels off as you approach the center. The term "log taper" refers to change as being logarithmic in shape.

Tom
 
What Tom said w/r potentiometers.

That said, commonly available log tapers (Audio, mostly) aren't a great fit to your need anyway.

If you want different RANGES of CSFM, you mought be better served with digital scaling from stored tables in a programmable device. One-axis CNC?

And therein lies another challenge.

Even when you HAVE such, constant surfacing speeds are not as easily utilized on a truly 'manual' (not tracer, etc.) lathe as all that.

Going whole-hog CNC might not cost all that much (SMALL lathe, no?) could end up more useful all around.

Bill
 
A log taper is one that the resistance change is not proportional to the change in length or rotation. In the case of the constant speed control, in order for the cutting speed to be constant, the spindle rpm would have to go to infinity which is clearly not possible. With a non-constant resistor the speed levels off as you approach the center. The term "log taper" refers to change as being logarithmic in shape.

Tom

Thank you for the explanation, I appreciate it..
 
What Tom said w/r potentiometers.

That said, commonly available log tapers (Audio, mostly) aren't a great fit to your need anyway.

If you want different RANGES of CSFM, you mought be better served with digital scaling from stored tables in a programmable device. One-axis CNC?

And therein lies another challenge.

Even when you HAVE such, constant surfacing speeds are not as easily utilized on a truly 'manual' (not tracer, etc.) lathe as all that.

Going whole-hog CNC might not cost all that much (SMALL lathe, no?) could end up more useful all around.

Bill

Hmmm, more to think about and explore. Thank you
 
Please report back your outcome - success or modifications required - I've been wracking my brain how to set this up too.
Advice I had from others was that some DROs (not mine) have an output port which can give you analog voltage of OFFSET froma 0 point. That seemed a likely candiate to me (not for me). You would set a starting speed of your choice at a diameter or your choice and set the DRO to zero (0). The output from the DRO then will give the offset voltage to CHANGE the speed as your diameter changes.....
Looking forward to the solution!
Cheers,
Joe
 
Please report back your outcome - success or modifications required - I've been wracking my brain how to set this up too.
Advice I had from others was that some DROs (not mine) have an output port which can give you analog voltage of OFFSET froma 0 point. That seemed a likely candiate to me (not for me). You would set a starting speed of your choice at a diameter or your choice and set the DRO to zero (0). The output from the DRO then will give the offset voltage to CHANGE the speed as your diameter changes.....
Looking forward to the solution!
Cheers,
Joe

Joe,

I too have heard about the DRO with output scenario, but my Fagor DRO doesn't have an output either. Additionally, in speaking with the engineers from Yaskawa, and after they understood my current setup, they explained that there can only be one "Analog" output used with the drive. There is however, the ability to use a digital signal along with the already used analog one. I anticipate having more information in the next week or so, and as soon as I do I will report back.

Would you mind sharing which machine you have and how it is currently set up?

Regards,

Steve
 
Not sure people are getting the max and base speeds set up in the vfd and how the remote pots maps it's output to this range.
You sort of need to read this section of the manual and understand the interaction.
This is not a hard controls design problem but maybe a bit confusing at first.
Perhaps a bit of playing with a outside pot marked with some values would help.
Bob
 
Joe,
Would you mind sharing which machine you have and how it is currently set up?
Regards,
Steve

Not at all, Steve,
except that it won't be helpful :)
My lathe startedoff as a double-headed purpose built boring machine. I removed the right-hand head and replaced it with a Southbend tailstock. Then modified the saddle and crss slide to take lathe tooling on a top slide (which originally was part of a self centering cross-slide on top of a concentional cross slide.....).
The drive is now a 3hp 960rpm motor in the base, driving the headstock spindle via two V-belts - no back-gear.
I run it with a Huanyang VFD set to go 0 - 120Hz, whihc the motor is happy with. It has enough torque to do reasonably heavy cuts from about 12Hz, fine cuts down to 6Hz and runs out of steam around 120Hz with fine cuts, but heavy cuts are fine at 90Hz.
Max spindle speed is set to 1500rpm - due to the bronze main bearings and the smallest chuck I have at 6".
I intend to rebuild the removed right hand headstock to a fatter ball bearing spindle one day. The casting is indentical to the left one.
Here is a photo of it when I was finalising its setup:
IMAG1255.jpg
 
yes, my thinking is to have several different max rpms.
for example,. in my case spindle and bearings max @ approx 2500 = max ever rpm.
my 6" 3jaw steelchick has max 3000+ rpm = no problem.
but my 12" 4 jaw cast iron I believe is approx 1000 rpm.
Hence I want to easily max rpm in a highly visual way. maybe by default at startup it's always 500 or something as also an unbalanced part can be awkward if the during facing it can speed up to max spindle speed.
maybe I'm missing something here
 








 
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