eccentric turning

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27 Dec 2013 22:55 #42061 by lelef
eccentric turning was created by lelef
Hi,
I'm doing some mods on my retrofitted lathe, the fist one is to add an encoder for threading.
Searching on the web I've find this video CTX gamma 2000

Can linuxcnc do something like this? it seems not to different from threading..

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27 Dec 2013 23:27 #42064 by PCW
Replied by PCW on topic eccentric turning
Andy Pughs video of eccentric turning with LinuxCNC:

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27 Dec 2013 23:32 #42065 by lelef
Replied by lelef on topic eccentric turning
WOW :)

For configs or Gcode how it works?

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28 Dec 2013 00:04 #42066 by tenaja
Replied by tenaja on topic eccentric turning
Read the "about" on the YT page.

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28 Dec 2013 07:47 #42087 by andypugh
Replied by andypugh on topic eccentric turning
wiki.linuxcnc.org/cgi-bin/wiki.pl?NonCircularTurning

I have an updated component permanently installed now that lets me choose how many polygon facets I want. (normally set to zero).
That uses a calculated offset rather than the lookup table in the Wiki page above.

You do need either a very slow spindle or a very fast X axis, otherwise it barely works. My system is in the "barely works" category, and when I want to make a hexagon hole I end up turning the spindle by hand with a handle in the back end of the spindle
My next lathe will have a back-gear...

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28 Dec 2013 18:15 #42104 by lelef
Replied by lelef on topic eccentric turning
Thank You,
it is a really good work ,do poligons is also a great thing!
My lathe can turn very slowly but my x axis isn't very fast and powerfull with a stepper so I will change it with a better sized dc servo

If I've understand this componentis can be used also for the Z axis

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29 Dec 2013 06:02 #42131 by tenaja
Replied by tenaja on topic eccentric turning

lelef wrote: ... but my x axis isn't very fast and powerfull with a stepper so I will change it with a better sized dc servo

Sounds to me like your stepper is either grossly undersized or grossly underpowered, or both. A properly sized stepper that is properly powered could easily make the moves shown in those videos. I have a nema 23 stepper system running 500 inches per minute without fear of stalling (on a cast iron dovetail slide), and 500 ipm is faster than anything in those videos, and it was not expensive--just chosen with care.

One of the bigger expenses to a great stepper system is the power supply, so instead of spending $200, people often spend a fraction of that, and get a cheapass $30 power supply and expect "almost as good" performance, because "afterall, the motor is only rated for 5v." Then they end up with a crummy system, and blame it on the steppers rather than a poorly chosen system. There is a huge difference in performance between a 40v and 70v power supply...it is the difference between mediocrity and possibly outperforming a cheap servo system. (Obviously, the definition of "outperform" depends on the system goals.)

You pinch pennies on your power supply, and you will be wondering why your so-called 300oz-in stepper stalls at 50 inches/minute, and you will be thinking you need a 1,000 oz-in servo to get the speed you want, but in reality all you needed was an adequate power supply. The big difference between steppers and servos is the mindset. Servo drives are not considered "cheap" systems, so shoppers don't have the penny pinching mindset and the resulting systems are less likely to be underpowered with a crummy power supply.

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30 Dec 2013 00:05 - 30 Dec 2013 00:07 #42159 by lelef
Replied by lelef on topic eccentric turning
thank you, I know about the steppers, it is good sized and the power supply is good but the lathe is quite big, it is a Grazioli Dania it is capable of 20 and more mm of cutting on C45 and harder materials ,the dc servo of the Z has no problem ,the stepper with the load of just 12mm has problems,.
Till now it wasn't a big problem, doing works with the cnc control but doing eccentric turning I think the more fast the stepper goes the less load it can stand so I've thinked to put a dc servo (or a brushless servo ) also for the X ,servos can go faster with more constant torque
Last edit: 30 Dec 2013 00:07 by lelef.

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30 Dec 2013 06:01 #42180 by andypugh
Replied by andypugh on topic eccentric turning

tenaja wrote: A properly sized stepper that is properly powered could easily make the moves shown in those videos.

In fact, in my video, it is a stepper motor making the moves (NEMA23, 2 stack, 32V)

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26 Nov 2018 20:39 #121397 by Peter_Cassar
Replied by Peter_Cassar on topic eccentric turning
Hi Andy, Do you have any further details on this component? I have an idea to make form relieved gear cutters and produce the backing off with this technique. What I'd like to do is specify the number of lobes on the OD of a turned part , say 12 which will be the number of teeth. The X axis travel only needs to be 15 to 20 thou.

Peter.

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