On 12/3/22 19:27, John Dammeyer wrote:
What with playing around with my new tool setter and trying to decide where to
put it I've come up with another set of questions which I've not really asked
but now has been bugging me for a while.
Home switches for a LinuxCNC controlled lathe. For the X axis I can see this as pretty simple as usually nothing impedes movement outward. Place it at the end of travel and it can serve as both a home and limit switch.
The Z axis is more interesting. Before homing I imagine the tail stock has to be loosened and moved all the way to the right as far away from the headstock to ensure finding a home switch. Or a home switch could be somewhere in the middle but then which direction to search?
If you arrange the switch to be closed on one side, and open on the
other, linuxcnc knows which way to move to find the switch.
Mine on the Sheldon is around 16" from the chuck, and it can't move far
enough toward the tailstock to reopen the switch. It is mounted on the
baxk of the bed, rigged so the gib strip on the rear of the carriage
actuates it.
Home offset is arbitrary and places it about 2" from the chuck jaws.
Anyplace will do, but I pull the tool to prevent collisions if there is
work chucked. You'll touch off both axis's in normal use anyway.
Alright. So we've established a pair of X=0, Z=0 for home and this is set into
the G53 X and Z locations. As I see it the next problem is with tools. Put a
carbide insert cutter into the tool holder and it extends out to the centerline
and to the left of the carriage.
How does one determine, with that tool tip, where the lathe centerline is and set that so G54 X is 0.000?
You don't worry about that, you measure the work and touch off at the
works radius. Its a good idea to take a light cut first to assure roundness.
The chuck can be 3 jaw or 4 jaw, 5C collet or even a faceplate or the arbor for turning between centers. In other words 5 different Z locations relative to that G53 Z=0 position found when homing.
And if the work is chucked in and sticks out 3" then do we try and make that end G54 Z=0?
That is what touch off is for.
In the past for non-CNC, say I have a DRO on the lathe, I'll face off the end and then set Z to 0.000. If I want to turn 2" I'll move the carriage until the DRO reads -2.000. At this point I could reset Z to 0.000 or just make all cuts go from 0.000 to -2.000.
Next if scratch the surface with the tool and set G54 Z=0.000 and then cut a pass at 0.010" I've now made the surface round with respect to the rotation. If I measure it at 1.020" in diameter then I now know the real X 0.000 centerline is 0.510". Set the G54 X value to 0.510" and from then on I can specify a final diameter and X positions for each cut which may already exist in the G Code.
It's all about finding the reference positions on the lathe. Change tool and it needs to be done again. How is it generally done with LinuxCNC. Is there a tutorial for that somewhere?
That habit doesn't change. With tp rotation for various cuts, your tool
table is always out of sync, measure and touch off.
Thanks
John
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Cheers, Gene Heskett.
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