Lathe axis "positions" - warning stupid beginner ?

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21 Nov 2010 20:11 #5497 by yugami
Starting to play around with my little lathe and I noticed that if I set Z to 0 (home) at the chuck moving to the tail is negative.

so my guess is that 0 is the far limit of the bed in CNC parlance (or my lathe is backwards)

Where should X and Z home be in relation to the center of the bed and the chuck?

This is the lathe in question:

maxnc.com/t2_cl.htm

There's a limit switch at the end of the bed and by the motor (far side of the picture) are the limit switches 0,0?

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21 Nov 2010 20:34 #5498 by BigJohnT
Typically a lathe with front tooling the machine Z0 is to the far right and X0 is to the front with the spindle on the left. Pressing +Z should make the tool move away from the spindle and pressing +X should make the tool move toward the front of the lathe. This makes the imaginary Y positive below the lathe. It is important to know that when your programming arcs. With a lathe like yours you will have to touch off the tool each time you put one on I assume.

In the subroutine section there are some subroutines written for a lathe to make simple operations a snap without any programming.

John

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22 Nov 2010 02:51 #5517 by yugami
Thanks again John, I glanced at and, will read more in depth, the subroutine stuff. I installed the program earlier today.

The lathe cross slide can hold multiple tool holders, I'm gathering from what I can tell that their software took coordinates to enact "tool changes" (assuming no tailstock) This is all a guess but I'm guessing on toolchange it cleared the stock moved the X forward and reset the perceived 0.

Again this is all a guess as there's not a lot of information on these lathes out there. The Max-nc user group seems to be 99.9% mill related and some tiny bit of old lathe info.

I just need this to make a few pre-programed parts once I figure out all the programming. The turning down to size subroutine will be a big help.

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22 Nov 2010 12:47 #5530 by andypugh
Lathes generally get use bigger Z numbers as you get further from the chuck, so if you zero the axis at the chuck face then face off at 6" you will have a 6" bar.

Quite often you will zero at the tailstock end of the material, and all Z values in the G-code will be negative, becoming more negative as you get closer to the chuck.

In G7 (lathe) mode the X value measures diameter directly. This saves a fair bit of mental arithmetic in general use, but can cause a bit of confusion when programming arcs.

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22 Nov 2010 13:20 #5532 by BigJohnT
I looked again at the photo and I see where you can set up multiple tools on the slide. Once you touch off each tool you can use the manual tool change window to change tools.

The way I touch off is to change to G55 (so no work offsets are in effect) and using a dowel I touch off the Z for each tool on the spindle face. I move the tip close enough so the dowel won't roll between the slowly back away till it does. Then I touch off the X on some material in the spindle that I have turned and measured and enter the diameter or radius (depends on which mode your in). Then I go back to the G54 and take any tool (after loading it with Tn M6 then G43) and touch off (G54) the Z of the work piece. This places all the tools Z offset in sync. After setting up tools I do a chicken check to make sure when I select a tool the tip position is where I think it should be as a few times I have messed it up by touching off X instead of Z etc. just being in a hurry.

John

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22 Nov 2010 14:16 #5535 by yugami
Follow up dumb question:

If I reverse the pins that the phases are connected to (step type 2) will that change the direction the motor turns, changing how the axis respond?

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22 Nov 2010 14:26 #5536 by andypugh
Just change the sign of the scale in the ini file.

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29 Nov 2010 18:20 #5740 by yugami
I used Geometry in the Display section with X-Z and now when I go Minus it moves along the correct path (per the image) but still goes negative.

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29 Nov 2010 19:01 #5742 by andypugh
I meant that you should change the scale of the stepgen in the relevant [AXIS_N] section of the INI file.

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29 Nov 2010 19:27 #5744 by yugami
I'm afraid I can't find any documentation on this variable. I do see that I have one in my INI file, but the Integrators manual doesn't seem to cover what it means.

Do you mean just to put a negative in front of the number?

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