Inverse Time problem

[Greg_J]

Hi Guys,

I'm having issues with using inverse time, the feeds are either too fast or too slow depending on what settings I use in my Control Def. (feed in minutes/seconds)

I'm using a Mazak Integrex J400 and I only use Inverse time when I'm using the C-axis (lathe chuck) so the program switches between inches/minute and inverse time.

I did some testing to see what exact time it's taking compared to what Mastercam says.

This is what I did:

I drew a Ø10.0 circle (circumference of the circle is 31.4159 = pi ) and made a rotary program for an endmill to cut on that circle at a feed rate of 31.4159 (pi) and it should take 1 minute to make the cut.

 My results:

Rotary test 1 time in Mastercam using the inverse time feed rate setting set to minutes: 1m 1.20s               -out put feed command has xxxx.xxx digits (ex. F6284.948)

Rotary test 2 time in Mastercam using the inverse time feed rate setting set to seconds: 1m 1.20s               -out put feed command has xxx.xxx digits (ex. F104.749)

Rotary test 1 time in the J400: 12s

Rotary test 2 time in the J400: 2m 52s

The second test I did is a linear move 10" long at 10 ipm should take 1 minute to cut. (my control def set to feed in minutes.)

That's exactly what it did, it took 1 minute to make the cut. It did what it was suppose to, so now I'm confused??? I expected the feed to be out by some factor so I could correct the rotary feed error.

Here is a sample code:
G68 X0. Y0. Z0. I0. J1. K0. R90.
G0 G17 X-10. Y-5.
G43 Z4.
G93 G1 Z2. F5.
Z1. F10.
Y5. F1.
Z2. F10.
Z4. F5.
G69
M05

I've used inverse time on a mill with a rotary axis and it worked flawlessly I would be cutting at 60 ipm from linear into a rotary cut and you could clearly see that cut was at the same feed. So now I have to reduce my feed values on a rotary cut so the tool will cut at the correct feed.

It seems like there is a issue cutting with the C-axis like it's using some constant surface feed numbers to adjust the feed.

I need to figure out if it's the machine or the code.

Has anyone dealt with this before or has some information for using inverse time that may help. 

 

TIA,

Greg

[Robert Ouellette]

So you drew a 10" circle and used an endmill to cut on center or outside compensation? If you were using left or right comp your actual cutting time will be off because of the radius of your tool makes your circle bigger. eg: 10 " circle cut with 1" endmill makes your actual cutting diameter 11". so 11" x pi = 34.55749" circumference = and would take 1.1 minutes to cut. and if you have a couple of thou cutter comp in control it will add to cutting time also. But if you programmed tool center then your cut time should be good.

Just something to look at before fooling with your machine.

[Greg_J]

I should have added I turned comp off so the tool starts on center of the line I used to draw the 10" circle.

Thanks for the reply.

The next thing I'm going to try is a 5" and 15" circle and see what times I get for the program and see it I get any changes the closer or further away I cut from zero.