C Axis Lathe Situation

[scatgo]

In do have some experience with X Y Z programing on a milling machine but i know nothing about C axis programming. Centroid has a video of the type of work i would like to do and a sample program. I was hoping someone could help me decipher the sample program so I can learn how to do some c axis programming. I would guess that all the programming would start at zero degrees. And C- would rotate the spindle clockwise and C+ would rotate the spindle counterclockwise. But if you look at the program all C axis move are C-???? If anyone can point me to any good tutorials on C axis programming that would be great. I have spent many hours online looking for tutorials but I haven't found a thing.

https://www.centroidcnc.com/cnc_c_axis_lathe.html#:

G20 ; INCH
G28 ; TOOL CHANGE POSITION
G97 G98 ; Cancel Constant Surface Speed and Feed per Minute
; This set up was the a gang style lathe.
; Tool 1 is a 1/4" end mill in a Live tool holder.
; Live tooling has the 1/4" end held horizontal to the X axis plane.
T0101 ; CHANGE TO TOOL 1 WITH OFFSET 1 for 1/4" ENDMILL
M51 ; TURN C AXIS ON
M23 ;Turn Live tooling ON
G0 G54 X1.5 M8
G0 Z-2.0035
C-75.068
G0 X1.25
G98 G1 X.95 Z-1.8975 C-87.222 F1396.21
Z-1.1904 C-168.251 F2000.
Z-1.1769 C-170.046
Z-1.1657 C-172.04
Z-1.1571 C-174.196
Z-1.1513 C-176.47
Z-1.1483 C-178.815
C-181.185
Z-1.1513 C-183.531
Z-1.1571 C-185.805
Z-1.1657 C-187.961
Z-1.1769 C-189.955
Z-1.1904 C-191.746
Z-1.8975 C-272.778
Z-1.9131 C-274.326 F1911.47
Z-1.9305 C-275.607 F1571.38
Z-1.9493 C-276.592 F1200.22
Z-1.9692 C-277.259 F810.25
Z-1.9897 C-277.597 F408.11
Z-2.0103 F25.
Z-2.0308 C-277.259 F408.1
Z-2.0507 C-276.592 F810.25
Z-2.0695 C-275.607 F1200.21
Z-2.0869 C-274.326 F1571.37
Z-2.1025 C-272.774 F1916.53
Z-2.8096 C-191.749 F2000.
Z-2.8231 C-189.955
Z-2.8343 C-187.961
Z-2.8429 C-185.805
Z-2.8487 C-183.531
Z-2.8517 C-181.185
C-178.815
Z-2.8487 C-176.47
Z-2.8429 C-174.196
Z-2.8343 C-172.04
Z-2.8231 C-170.046
Z-2.8096 C-168.255
Z-2.1025 C-87.222
Z-2.0869 C-85.675 F1910.84
Z-2.0695 C-84.394 F1571.38
Z-2.0507 C-83.409 F1200.22
Z-2.0308 C-82.742 F810.25
Z-2.0103 C-82.404 F408.11
Z-1.9897 F25.
Z-1.9692 C-82.742 F408.11
Z-1.9493 C-83.409 F810.25
Z-1.9305 C-84.394 F1200.21
Z-1.9131 C-85.675 F1571.37
Z-1.8975 C-87.227 F1916.53
Z-2.0035 C-75.068 F2000.
X1.2 F7.
X.9 Z-1.8975 C-87.222 F1414.39
Z-1.1904 C-168.251 F2000.
Z-1.1769 C-170.046
Z-1.1657 C-172.04
Z-1.1571 C-174.196
Z-1.1513 C-176.47
Z-1.1483 C-178.815
C-181.185
Z-1.1513 C-183.531
Z-1.1571 C-185.805
Z-1.1657 C-187.961
Z-1.1769 C-189.955
Z-1.1904 C-191.746
Z-1.8975 C-272.778
Z-1.9131 C-274.326 F1952.08
Z-1.9305 C-275.607 F1593.71
Z-1.9493 C-276.592 F1210.08
Z-1.9692 C-277.259 F813.26
Z-1.9897 C-277.597 F408.49
Z-2.0103 F25.
Z-2.0308 C-277.259 F408.49
Z-2.0507 C-276.592 F813.26
Z-2.0695 C-275.607 F1210.08
Z-2.0869 C-274.326 F1593.7
Z-2.1025 C-272.774 F1957.48
Z-2.8096 C-191.749 F2000.
Z-2.8231 C-189.955
Z-2.8343 C-187.961
Z-2.8429 C-185.805
Z-2.8487 C-183.531
Z-2.8517 C-181.185
C-178.815
Z-2.8487 C-176.47
Z-2.8429 C-174.196
Z-2.8343 C-172.04
Z-2.8231 C-170.046
Z-2.8096 C-168.255
Z-2.1025 C-87.222
Z-2.0869 C-85.675 F1951.42
Z-2.0695 C-84.394 F1593.71
Z-2.0507 C-83.409 F1210.08
Z-2.0308 C-82.742 F813.26
Z-2.0103 C-82.404 F408.49
Z-1.9897 F25.
Z-1.9692 C-82.742 F408.49
Z-1.9493 C-83.409 F813.26
Z-1.9305 C-84.394 F1210.08
Z-1.9131 C-85.675 F1593.7
Z-1.8975 C-87.227 F1957.48
Z-2.0035 C-75.068 F2000.
X1.15 F7.
X.85 Z-1.8975 C-87.222 F1432.39
Z-1.1904 C-168.251 F2000.
Z-1.1769 C-170.046
Z-1.1657 C-172.04
Z-1.1571 C-174.196
Z-1.1513 C-176.47
Z-1.1483 C-178.815
C-181.185
Z-1.1513 C-183.531
Z-1.1571 C-185.805
Z-1.1657 C-187.961
Z-1.1769 C-189.955
Z-1.1904 C-191.746
Z-1.8975 C-272.778
Z-1.9131 C-274.326 F1992.99
Z-1.9305 C-275.607 F1615.74
Z-1.9493 C-276.592 F1219.64
Z-1.9692 C-277.259 F816.14
Z-1.9897 C-277.597 F408.85
Z-2.0103 F25.
Z-2.0308 C-277.259 F408.85
Z-2.0507 C-276.592 F816.14
Z-2.0695 C-275.607 F1219.64
Z-2.0869 C-274.326 F1615.73
Z-2.1025 C-272.774 F1998.73
Z-2.8096 C-191.749 F2000.
Z-2.8231 C-189.955
Z-2.8343 C-187.961
Z-2.8429 C-185.805
Z-2.8487 C-183.531
Z-2.8517 C-181.185
C-178.815
Z-2.8487 C-176.47
Z-2.8429 C-174.196
Z-2.8343 C-172.04
Z-2.8231 C-170.046
Z-2.8096 C-168.255
Z-2.1025 C-87.222
Z-2.0869 C-85.675 F1992.28
Z-2.0695 C-84.394 F1615.74
Z-2.0507 C-83.409 F1219.64
Z-2.0308 C-82.742 F816.14
Z-2.0103 C-82.404 F408.85
Z-1.9897 F25.
Z-1.9692 C-82.742 F408.85
Z-1.9493 C-83.409 F816.14
Z-1.9305 C-84.394 F1219.64
Z-1.9131 C-85.675 F1615.73
Z-1.8975 C-87.227 F1998.73
Z-2.0035 C-75.068 F2000.
X1.1 F7.
X.8 Z-1.8975 C-87.222 F1450.18
Z-1.1904 C-168.251 F2000.
Z-1.1769 C-170.046
Z-1.1657 C-172.04
Z-1.1571 C-174.196
Z-1.1513 C-176.47
Z-1.1483 C-178.815
C-181.185
Z-1.1513 C-183.531
Z-1.1571 C-185.805
Z-1.1657 C-187.961
Z-1.1769 C-189.955
Z-1.1904 C-191.746
Z-1.8975 C-272.778
Z-1.9131 C-274.326
Z-1.9305 C-275.607 F1637.36
Z-1.9493 C-276.592 F1228.86
Z-1.9692 C-277.259 F818.89
Z-1.9897 C-277.597 F409.2
Z-2.0103 F25.
Z-2.0308 C-277.259 F409.2
Z-2.0507 C-276.592 F818.89
Z-2.0695 C-275.607 F1228.86
Z-2.0869 C-274.326 F1637.36
Z-2.1025 C-272.774 F2000.
Z-2.8096 C-191.749
Z-2.8231 C-189.955
Z-2.8343 C-187.961
Z-2.8429 C-185.805
Z-2.8487 C-183.531
Z-2.8517 C-181.185
C-178.815
Z-2.8487 C-176.47
Z-2.8429 C-174.196
Z-2.8343 C-172.04
Z-2.8231 C-170.046
Z-2.8096 C-168.255
Z-2.1025 C-87.222
Z-2.0869 C-85.675
Z-2.0695 C-84.394 F1637.36
Z-2.0507 C-83.409 F1228.86
Z-2.0308 C-82.742 F818.89
Z-2.0103 C-82.404 F409.2
Z-1.9897 F25.
Z-1.9692 C-82.742 F409.2
Z-1.9493 C-83.409 F818.89
Z-1.9305 C-84.394 F1228.86
Z-1.9131 C-85.675 F1637.36
Z-1.8975 C-87.227 F2000.
G0 X1.5 C-87.222
Z-2.3605 C-179.979
X1.2
G1 X.95 F7.
Z-2.0238 C-218.653 F2000.
Z-2.0004 C-221.408
Z-1.9998 C-221.482
Z-1.9816 C-219.525
Z-1.6411 C-180.293
Z-1.639 C-180.039

[cncsnw]

The C axis positions are positions, not incremental distances. If all of the work happens to be on the negative side of C0, then all of the C coordinates will be negative, even though the C axis does move in both directions.

This is for the same reason that all of the Z coordinates are negative, even though the Z axis moves in both directions.

The more relevant question you should ask, is how the feedrate values are derived. Z axis distances are in inches, and Z axis feedrates are inches per minute. C axis distances are in degrees, and C axis feedrates are in degrees per minute. The feedrate for an interpolated ZC move will be a combination of inches and degrees per minute, calculated so that the move takes the correct amount of time to cover whatever its distance across the part surface. See http://www.cncsnw.com/4thHowTo.htm for a discussion of this, and the math behind it. That page is aimed at mills with rotary tables, but the feedrate computation is the same for a C axis lathe.

[scatgo]

Thanks

[scatgo]

I still dont see how all z and c moves can be - when the spindle moves in clockwise and anticlockwise direction. If you watch the video of the part being made the z axis moves from left to right and right to left. How can that not be z+ and Z- moves in the program?

[tblough]

C-23 to C-60 would move CCW.
C-60 to C-23 would be CW.

Same thing happens on Z.

[scatgo]

C-23 to C-60 would move CCW.
C-60 to C-23 would be CW.

Same thing happens on Z.

For some reason iam not getting that. Can someone please elaborate??

[cncsnw]

If the C axis rotates from a position of C-23.0 degrees to a position of C-60.0 degrees, then it is moving in the negative C direction. Let's say that is CCW from your viewpoint.

Then when the C axis rotates from a position of C-60.0 degrees to a position of C-23.0 degrees, then it is moving in the positive C direction. That would be CW from your viewpoint.

So you will have seen it rotate in both directions, while always showing negative C coordinates.

[tblough]

Leave the negative numbers and the C-axis out for a moment and restate what Marc said.

If my X0 is in the center of the part, X-2.0 to X2.0 would be a 4" move to the right, while X2.0 to X-2.0 would be a 4" move to the left. I think this is what you are expecting:

G00 X-2.000
G01 X2.000
G01 X-2.000

If I set my WCS on the left side of the part, and I move from X2.000 to X6.000 that is a 4" move to the right. If I now move from my current X position back to X2.00 that is that is a 4" move to the left. In G-code:

G00 X2.000
G01 X6.000
G00 X2.000

If you set your Z0 to the right side of the part, all of your X coordinates are now negative. So, starting from X-2 moving to X-6 would a 4" move to the left. Going back to where i started would be a 4" move to the right to X-2.

G00 X-2.000
G01 X-6.000
G01 X-2.000

The numbers in the G-code all depend where the Zero point was set.

The C-axis is no different. Instead of moving right/left, it moves CW/CCW. Just replace X with C in the above.