Developments on my Home built 5C CNC Lathe - Polar interp. and Live tooling

Aciera wrote:

VFD is what I meant.
I guess the best would be to have some kind of gear (low for c-axis and high for lathe work) with some way to electrically switch from one to the other.

 

My commercial lathe has a big gear on the spindle, and a servo with a pinion.  Servo is mounted on a swinging bracket connected to an air cylinder.

Engage the C-axis and the main spindle motor is deactivated and the air cylinder shoves the servo (actually a 5-phase closed-loop stepper) against the spindle gear.  Once they're engaged the C-axis immediately homes before anything else happens.  Looking at the gears, I think it's about 40:1 reduction.

Main spindle motor is a 5kw, 7k rpm 3-phase induction motor with a Lenze VFD, driven via a 1:1 10-rib micro-V belt.  The main motor and the stepper both have encoders, but there's also a separate shaft encoder with a 1:1 timing belt connected to the spindle.

The two motor encoders are fed in to the respective drives, but my guess is that the spindle encoder is what the control uses for velocity and positioning control.

As an alternative configuration, there's a guy on YT who's been doing some interesting stuff with his lathe and a Centroid Acorn.  Specifically, he's got a standard VFD/induction motor, and separate servo connected via a timing belt.  The servo has an electric clutch to engage/disengage when the C-axis is active.

I considered going that route, but toothed electric clutches are very not-cheap new.  And I don't want to depend on an ebay score only to have a scorchingly expensive replacement bill if it dies int he future.

@NoJo -

Thank you very much for the updates and files.  This will go a long way towards a number of us making progress.

-Ralph

Ralph,
I think your lathe's spindle motor/C axis drive servo mechanism is fairly standard in the industrial machine world. My little lathe was one of those things that grew beyond my control. The cost of the lathe at the end was quite stupid and could have bought a really nice small Emco machine! And as these things go, the final result would have been better thought out had the original idea encompassed the end product! The original idea was a MACH2 cnc control, and a SMALL lathe using a small (5NM) Clearpath servo on the spindle ( 4000rpm), with an ER40 spindle. The bed was to be maybe 350mm long, no C axis......And the idea got out of hand. I really enjoyed the mechanics though, and using all the other machines to build this one ( an 85 year old shaper, for instance!).

If you need any of the other software let me know - the tool changer deviates substantially from the LCNC examples, but is very specific - also with the live spindle and so on..The live spindle is driven by a 500watt (1.5KW peak!) RC Brushless motor ( about 80mmOD 100mmLong), to which I fitted 3 hall sensors and wrote some Vector control SW to drive it. That works well - good torque @ 100rpm, max rpm of around 8000 @ 40VDC source drive.

You will have noticed I am running V2.9Pre - Dgarret updated that to a next release I believe - the Pre included fixes for a bug my Wife found in the LCNC code, but I am to scared to update to the latest build - who knows what else is different and what stops working on my machine!
Joe

NoJo,

6 months later and the lathe is built, both spindles connected and working (as spindles).  Ready to start integrating your C-axis arrangement if you don't mind me pestering you a bit more.

I've got both of your comps (caxis and gn_userkins) open as well as your HAL, INI, and G12.1/G13.1 ngc files.

First question:

How do you switch between spindle and c-axis mode?  Is it a G-code, M-code, or some other method?

Using 12.1/13/1 look like they enable polar interpolation, but not trigger C-axis mode.

Second question:
You mentioned earlier  - I think a number of us discussed this - that the C-axis homes each time it's enabled.  I can't figure out from your config how this happens - can you point me in the right direction?

Thanks,
Ralph

I have a question in the hal file at the end they load a component called livetool, is this component standard in the linuxcnc distribution or is it special for your application? Where can I get it?

COFHAL wrote:

I have a question in the hal file at the end they load a component called livetool, is this component standard in the linuxcnc distribution or is it special for your application? Where can I get it?
 

NoJo has a number of non-standard comps in his config.

caxis.comp
livetool.comp
gn_userkins.comp
jntoolchanger.comp

As well as (I think) the two remapped g-codes to switch on/off polar interpolation of the C-axis:
g121.ngc (remapped to G12.1)
g131.ngc (remapped to G13.1)

All of the comps and files are in the config he posted here:
forum.linuxcnc.org/10-advanced-configura...ling?start=30#272334

Oops.  Spoke too soon... his other comps are not in that zip file.

I think I found them in another thread he posted.  I'll see if I can find it again.


EDIT - complete config here.
www.forum.linuxcnc.org/10-advanced-confi...lfunction-bug#223654

However... I think this config has some older versions of files that were superseded.  This date was 2021-10-20, but the files he included in the 2023-05 post had a HAL and INI file from 2022-01.

I suspect the config is a combination of all the latest files, but hopefully NoJo will chime in and sort things out for us.

EDIT 2
Based on reading through the posts and files, it looks like the latest version switches from spindle mode to C-axis mode using the G12.1 remap to set the motion.switchkins-type pin.  I still don't follow what 'triggers' the switch in caxis.comp though.

Hopefully whatever is doing the switching doesn't require/force a change to polar mode at the same time.  I can think of situations where simple cartesian rather than polar interpolation is needed.