Incorrect feed on C axis contour post

[Cjones]

Not sure why this is happening. When I post my C axis contour here is the code I get. Some of the feeds are way off. not sure why. Any ideas?

code:

---

G30 U0. V0. W0.

G00 T1200

T1212

G97 S5000 M33

G18 G98

M290

M90

C0.

G00 G56 X.975 Z-2.896

X.785

G01 X.755 F4.

Z-2.866 C2.946 F412.3

Z-2.896 C5.893

G00 X.785

Z-2.8832 C8.824

G01 X.755 F4.

Z-2.8719 C8.454 F159.92

Z-2.8602 C8.453 F.66 <---too slow

Z-2.8489 C8.823 F159.34

Z-2.8422 C9.361 F355.64

Z-2.8376 C10.259 F600.4

Z-2.836 C11.358 F740.57

Z-2.8376 C12.456

Z-2.8422 C13.353 F599.68

Z-2.8489 C13.885 F351.87

Z-2.8602 C14.268 F165.32

Z-2.8719 C14.267 F.66 <----too slow

Z-2.8832 C13.894 F160.62

Z-2.8899 C13.364 F349.12

Z-2.8945 C12.462 F599.68

Z-2.8962 C11.358 F740.31

Z-2.8946 C10.253

Z-2.89 C9.35 F600.4

Z-2.8832 C8.814 F352.89

G00 X.785

 

---

[Cjones]

Sorry let me add something. This code works. But the feed I pointed out will show up on a -Z move of like .1". Which is not the feed I entered and at the controller takes forever. Is this a machine definition for min feed or something. It only seems to happen in C axis contour paths.

Ty,

Chris

[robk]

Do a search on the forum for inverse feed rate.

.

.

.

Nevermind

[rdshear]

The main thing I noticed was that the rotation of the C-axis is only.001 degree on both of the moves you pointed out. With DPM feed, as the ratio between rotary and linear change so does your feed when both axis reach their destination at the same time. This provides a constant feed at the tool. You will notice in your code snippet, that your feed gets much higher as you approach the other end of the rotary/linear ratio.

 

I didn't do the math on your code, but I have seen very similar outputs that work fine. It really depends a lot on what your machine needs.

 

The settings for DPM, Inverse feed, ect.. are in the control definition of your machine in MasterCam. You need to make sure it is setup to output what your machine expects.

 

Your reseller could probably help if you aren't sure what to change.

 

Hope this helps some,

 

Rick

[Guest]

Have you actually tried to run the code?

 

Are you just "assuming" it's to slow? That is a very small move and that feedrate will be engaged for less than a second.

 

Has your machine rejected the code?

[Cjones]

Sorry,

No I didn't assume, I ran it. That's why I added my second post. "This code works fine..." It's the feeds I pointed out that are a problem. They work fine in what I wrote above. However, later in the code that feed .66 gets put with a z motion from lets say -1.1 to -1.2. The code is 40000k. I just grabbed the first few lines, and did not search for the exact line, but I can see it on the controller when its running and watch it inch along while running.

 

Rick what kind of feeds in the control defs. should I be looking at. Mine is set to feed in minutes not feed in seconds. Or am I in the wrong spot. It's a fanuc 18i controller.

Ty for any suggestions.

Chris

[crazy^millman]

Well I have a possible solution that will not be popular. You can set-up the post to do a Min feed rate amount. It now has a max feedrate amount and you can add logic to the post for the C axis that it will not do a min feed though I would look for others suggestion before doing it.

 

HTH

[rdshear]

quote:

---

Rick what kind of feeds in the control defs. should I be looking at. Mine is set to feed in minutes not feed in seconds. Or am I in the wrong spot. It's a fanuc 18i controller.

---

The setting in the control definition is the feed tab on the side and select mill. There is a rotary section there that will allow you to choose unit/min, deg/min, or inverse. You need to make sure that is set to what your control expects. The other thing to be sure of is that your post supports the output you choose. Your reseller, the provider of your post, or maybe someone else here should be able to help you with that.

 

[Stockley]

Could be your plunge feed rate or retract feed rate.