gangtool setup / backtools

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01 Oct 2012 13:25 #24799 by andypugh
gmouer wrote:

I am already getting the impression that negative values of X "might" be the standard for rear tools. Again, further research needed..


Negative X commands certainly work easily and automatically, (no changes needed).
Negative X _offsets_ in the tool table are not really an option, as it is not at all unusual to have a "reference" tool (or probe) with zero length and the other tools both longer and shorter than that one.

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01 Oct 2012 14:53 - 01 Oct 2012 15:15 #24804 by andypugh
Touching-off wrong-side tools to negative values and commanding negative diameters seems to be not too unusual.

I asked a guy at Tormach how they program their lathe and he said
"As an example, in the video we posted a little while back, all the rear mounted TP code has positive X, but the threading tool (front TP) has negative X values."

Last edit: 01 Oct 2012 15:15 by andypugh.

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01 Oct 2012 15:05 #24806 by gmouer
Strange, the video you posted covers up much of the text in your post. Anyways....

Did you notice the turning tool is mounted inverted? That takes care of the need to reverse the spindle. To me, that seems like the preferred method however some guys may have a bunch of tooling with their gang tooled lathes that do not permit inverted mounting so they would have to be accomidated also.

Thinking further, I come back to cad/cam and such and how it would handle such matters. BigJohnT did some fantastic lathe ngcgui routines which will probably not like negative X values I would assume. Interesting stuff.

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01 Oct 2012 15:05 #24807 by BigJohnT
That video is a bad example for lathe operators... leaving the chuck key in.

John

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01 Oct 2012 15:12 #24809 by andypugh
gmouer wrote:

Strange, the video you posted covers up much of the text in your post.

Actually all the text is still there, just interspaced with a video.

Did you notice the turning tool is mounted inverted? .

Yes, and that was mentioned in our discussion. The spindle direction really needs to be determined by the G-code, not the tool table. You can, in principle, have both front and rear tools, and conventional and inverted tools, all at the same time.

Arguably there isn't much need for CAM with a lathe anyway.

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01 Oct 2012 16:41 - 01 Oct 2012 16:42 #24814 by gmouer
Yea, I agree that a lot can be done on a lathe without cam but there is those times that it comes in nice for more complex parts with lots of passes.

Well, I have my mission cut out it appears. I have to make up some toolholders for the lathe and now there is no doubt that some of them will be for inverted tool holding. I also have to read up on how the rest of the world handles programming for back tools on various lathes. IF additional functionality is to be added to linuxcnc for such purposes then it should be in line with the way the rest of the world handles such things.

I still have my 14x40 lathe to re-retrofit from mach over to linuxnc but that should be a pretty easy task. Then there is my bridgeport to reretrofit also from mach to linuxcnc. I am a linuxcnc guy now to stay. The garage play area is about full anyways so I don't see more machines.
Last edit: 01 Oct 2012 16:42 by gmouer.

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05 Oct 2012 00:44 - 05 Oct 2012 00:46 #24959 by gmouer
Talked to my friend tonight who has been a cnc lathe man for years, including many with front and rear turrets. I now understand how industrial controllers handle front/rear tools on a lathe.

More modern controls use G68 and G69 for front/rear turrets, those G codes are pretty much industry standard for front/rear turrets and their function is to "rotate the coordinate system". That allows X values to be positive for both front and rear turrets This makes programming the same for front and rear turrets (except for the preceding G68 or G69) Both are programmed as positive values of X.

Older controls do not support G68 G69 and rear tools have to be programmed as negative values of X.

So, maybe linuxcnc might want to add the G68 / G69 commands for coordinate system rotation for support of front and rear turrets.
Last edit: 05 Oct 2012 00:46 by gmouer.

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05 Oct 2012 00:58 #24960 by andypugh
gmouer wrote:

So, maybe linuxcnc might want to add the G68 / G69 commands for coordinate system rotation for support of front and rear turrets.

Do you know if it changes the sign in the DRO? (I can see arguments both ways)
Does it do more than negate X-words in G-code prior to sending them to the planner?
If the same tool is put in a front or rear tool post, does the G68/69 adjust the offsets to suit?

The codes are available.
www.linuxcnc.org/docs/devel/html/remap/s...nallocated_g_codes_a
But I think would need to go rather deeper into the structure of LinuxCNC than G-code remapping allows.

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05 Oct 2012 01:12 - 05 Oct 2012 03:08 #24961 by gmouer
Been kicking all those considerations around tonight. I think the key words are "rotates the coordinate system", and that would be around the z axis.
Rotating the coordinate system automatically would take care of the dro remaining positive, arcs and linear moves programming the same regardless of front or rear toolpost in use.

I looked around a bit on the net, many lathes support the G68 G69, exactly how they implement it will take further reading and I would imagine different controllers might have variances.


Edit!! Look at what I just found wiki.linuxcnc.org/cgi-bin/wiki.pl?CoordinateSystemRotation
apparently this concept is being tossed around

Further looking found this which claims coordinate system rotation has been implemented but it appears not as G68 but via the G10 command. www.mail-archive.com/emc-users@lists.sou...ge.net/msg17072.html It was also found on a requested features page, listed as done (Via G10 again, not G68)

Maybe the capability is there? Just through G10 rather than G68?
Last edit: 05 Oct 2012 03:08 by gmouer.

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05 Oct 2012 10:54 #24971 by BigJohnT
G10 L2 Pn Rn will rotate the coordinate system around the Z axis.

linuxcnc.org/docs/html/gcode/gcode.html#...em_a_id_sec_g10_l2_a

John

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