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Author Topic: Turn G3 feedrate problem  (Read 10453 times)

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Offline DAlgie

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Turn G3 feedrate problem
« on: May 04, 2009, 12:52:25 AM »
Melee and myself have been noticing a problem with turn in that the feedrate doubles when in G3. I thought it might just be that I'm too chicken to upgrade my old reliable version 1.84, but he is running version 3.4xx and the problem is identical. Even stranger is that when you use a G0 after the G3 the feedrate in the G3 goes to about 6 times the displayed amount! If there is a G1 after the G3 then it only goes to about double the displayed rate. We thought it might be something to do with Melee's new M71 roughing macro but it does the same thing with a simple G code run. Kind of interesting to watch if you're only taking light cuts in aluminium, but heavy cuts in stainless can be cause for concern!
   DaveA.

Offline Hood

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Re: Turn G3 feedrate problem
« Reply #1 on: May 04, 2009, 12:09:45 PM »
I have not noticed that on my lathe, was going to test out today to make sure but afraid my workshop got flooded from the office above so I had to switch the mains off. Hopefully I will get a chance tomorrow, that is if all the electrics have dried out.
Hood

Offline DAlgie

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Re: Turn G3 feedrate problem
« Reply #2 on: May 08, 2009, 12:48:36 AM »
That sucks Hood, hope nothing expensive got wet. Until Hood gets his stuff back running, anyone else ever program a G3 on turn and notice this?

melee

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Re: Turn G3 feedrate problem
« Reply #3 on: May 08, 2009, 03:31:53 AM »
Hi Hood

I started a thread here:-

http://www.machsupport.com/forum/index.php/topic,11420.0.html

not realising Dave was doing the same.

There are 2 simple .NC programs attached on that thread which demonstrate the problem.

Try them on your kit when it dries out and let us know

cheers

Melee

melee

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Re: Turn G3 feedrate problem
« Reply #4 on: May 08, 2009, 03:44:05 AM »
PS

I have effectively closed that thread now so as not to dilute any input

All replies to this thread please, the test .nc files are attached here

regards
Melee

Offline Hood

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Re: Turn G3 feedrate problem
« Reply #5 on: May 08, 2009, 06:01:05 AM »
Can you post a screenshot of the toolpath of these bits of code please.
Hood
Re: Turn G3 feedrate problem
« Reply #6 on: May 09, 2009, 05:48:52 AM »
Hi there,

I usually work in G95 mode (feed per rev) as I'm more used to that in the lathe, and I've not had this problem with G2 or G3. But I'm a bit paranoid and set the F on every non "G0" line as attached. Does this file show the feed problem on your setup?

One thing I did notice just once, Mach3 got the feedrate completely wrong on one line (G1) (much too fast, but not G0 fast), then the next line was extremely slow, after that it was OK. Code was fine as far as I could tell.

Do you still get the problem in G95 mode?  Also, I'm not sure how to get a feel for feed per min when turning. Why would you use that in the lathe? If no spindle speed feedback?

Regards,

Woody.

melee

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Re: Turn G3 feedrate problem
« Reply #7 on: May 09, 2009, 10:57:35 AM »
Hi Hood,

The tool path images are now attached below.

Hi Woody

I think G99 is the lathe equivalent of G95, which is milling G Code for feed per rev.

I use feed over time simply because I am used to it and have a pretty good off the top of my head idea of what ratios I need for different jobs and finishes.
 using higher spindle speed,  slower feed for finishing cuts etc. etc.
I don't tend to take heavy cuts and prefer to write programs that will just run unattended whilst I do something else, it doesn't matter how many loops it takes.
So I don't tend to suffer from spindle slow down and get away quite happily using feed over time

I will try using G99 and see what happens.

I have tried setting the feed rate specifically on the G3 line and it does not work, the rate still doubles.
This leaves open the temporary solution of setting half the feed rate you actually require and ending up just about right, but it is hardly satisfactory.

I will copy your file over to my Mach setup and let you know what happens.

regards

Melee
Re: Turn G3 feedrate problem
« Reply #8 on: May 09, 2009, 11:20:24 AM »
Hi Melee,

I think Mach3 may use G99 differently looking at the Mach3Turn manual, G95 is feed per rev and G99 is "R point level return after canned cycles" whatever that means! Page 10.10.

By the way, are you using Mach3 R3.042.027? Maybe worth trying because a number of turn related problems have been fixed, including a driver error in threading. I wonder if that also affected your issue?

Cheers,

Woody.

Offline Hood

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Re: Turn G3 feedrate problem
« Reply #9 on: May 09, 2009, 11:42:36 AM »
can you attach your xml as well please
Hood