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

Hello JoeNoci,

I saw your 5C CNC lathe blog. You did a very nice job. Great report, very inspirational!

I am also into mills and lathes, CNC and manual, and more fun stuff ... I work with Fusion 360 CAD/CAM, using my own post processor routine in Fusion to tailor the G-code for my CNC mill. My plan for this year is to build a small "custom" CNC lathe and thus my interest in your approach to this subject

Greetings from Germany

Stefan

Thanks Stefan. I am 'almost' complete with the lathe..Not sure something like this is ever complete though. I will post some of the final photos and construction in my post within the 'Show your Stuff' topic, in the coming week or two..

Looking for the next project now...

Hello JoeNoci,

great. I will look at your pictures once you have posted them. I own a manual Weiler Condor lathe and I really miss CNC lathe capabilities. Hence, my plan for 2020 to build a small CNC lathe.

Stefan

NoJo,

I'm starting my own C-axis lathe project similar to the one you documented here and in another thread.

The two really murky areas for me are:

• Polar interpolation
• Spindle/C-axis switching (using the same motor)

Would you be able to provide your (hopefully working) configuration and comp files?  And perhaps an explanation of how you managed to glue everything together?  I found a single post from you a while back where you attached a comp and hal file, but they look like they were created during development and not 'final' files.

You mentioned working with Andy Pugh on it, but I've been unable to find any discussions you and Andy had regarding the switchable C-axis/spindle function.  Perhaps those were done outside this forum.

Thanks,
R

Hi there,
Well, this is not an easy task. I spent many months on the project, and the software side was not trivial. Polar interpolation and the finer nitty gritty did result in some 'custom' mods on the linuxcnc code, which is not really in line with the open-source distro norms, but there was just no other way. The C axis, when used with Polar modes, is treated in the same way as you would a mill XY axes, with the spindle doing polar rotations to cut straight lines on the workpiece.... There are many issues to take care of, not only in software, but in live spindle control and especially in live spindle tooling positions WRT tool heights and centers - it plays a huge role in accuracies. I am surprised you find only a single post - I think there must be a hundred plus posts, between myself, Andy and a half dozen others, with MANY tries, retries, new code, etc, etc - many many posts...You would do well to find all of them and read through them first - me giving you my comp/hal and software mods will not help you at all in the beginning - the hurdle to C axis interpolation is rather high and my hardware , spindle servo motor, etc is very specific.
You also need to use a big, powerful ( lathe size depending..) positional servo motor for the spindle motor - NO backlash in spindle positions, and depending on the servo you may need a servo brake, etc. Positioning for accurate C axis performance should be better than 0.1deg on the spindle servo....If you have not done something like that, you are in for some deep dollars, and headaches. Servo positioning to 0.1deg, with no jitter, shudder, and very small deadband is a dark path...

For links - try here:

www.forum.linuxcnc.org/show-your-stuff/4...-with-atc-and-c-axis
forum.linuxcnc.org/10-advanced-configura...-stop-command#205271
www.forum.linuxcnc.org/show-your-stuff/4...ss-on-the-atc#220862
www.forum.linuxcnc.org/10-advanced-confi...ible-malfunction-bug

NoJo,
Thanks for the fast reply - I didn't expect a response so quickly.

I was imprecise when I mentioned 'only one post' - I've poured over many, many posts of yours.  Just wasn't able to find the specific discussion on switching a single motor between velocity and positioning mode where you all developed the answer.

I did find, since my first post in this thread, a zip file from ~10/2021 with your config, including the g121 and g131 remaps and the three user-specific comp files you seem to have come up with.  I've been trying to digest them to get the overall picture.

I'm not surprised at your advice regarding the precision and torque requirements to manage a C-axis properly.  I do have a rather large (compared to the lathe/part size) servo, but no brake as of yet.  My particular use case is more for indexing rather than continuous machining, and no off-axis loads are anticipated right now.  But I'd like to have the ability to do continuous positioning even if it's for simple OD engraving.

I think I can accomplish that with what I've got, but if I need to fabricate a spindle brake and a clutched reducer system to increase torque and resolution - so be it.

I am in no rush.  The lathe is still only in CAD at the moment, but based on my recent experience LCNC'ing my mill I thought it prudent to get a better idea of the LCNC hurdles before simply assuming that everything would be a cake-walk.

Regards,
Ralph

Ralph,
If you read all, or most, of my posts you may have seen that I almost threw in the towel - a few times...! My wife is a software Artist, and without her efforts and involvement with the techno-guru's on this site, I would have thrown it in. LCNC is hugely versatile, does the basic machines very easily with very little effort and thought by the user, but a dinkum C axis machine is NOT where LCNC is easy at all. It was a real swine...
I mentioned somewhere in my posts and re-iterate - the lathe I did has actually no purpose - It was a mechanical challenge to me, one that I thoroughly enjoyed from that point of view. Accuracy in a C axis homebuilt lathe demanded jumping through many hoops, and that was what it was about. I think I completed it end 2021 and I am ashamed to say that I have not turned it on since mid 2022..!

It will probably take me a while to learn it all again! I can find the software and modules for you - all the mesa cards I used, etc - you need to say what you need!

Just give us everything!

[edit]
I'll take the machine too.

Hah! If I recall, you were one of the very active helpers back then!!

Everythings??? - You can come collect the lathe too if you want!

You see???!!! Your edit was in before my offer!!!

NoJo wrote:

Ralph,
If you read all, or most, of my posts you may have seen that I almost threw in the towel - a few times...!


 

I've been there, too.  Loudly threatened to give up on LCNC until a few other folks here pulled me back from the edge.

As to your offer... frankly, I don't need anything right this minute.  Mostly just confirmation that you got it working - which you've provided, thanks.  I've just ordered servos this evening and the stock for machining the hard parts... so I've got some time on the control side.

On the other hand, if you've noting for that poor old lathe to do, I can give it some gainful employment as my 2nd op lathe until the new one is done.  Just send it over and I'll pass it along when I'm finished with it.

If you do feel like revisiting your project, I'd appreciate anything you can send my/our way.  Final configs, any screen/GUI mods you may have done to improve usability, ect.  I'm starting to think I'll need a mostly-custom GUI for mine as it's mission in life will be more of an automation device than a general purpose lathe.

Cheers,
Ralph