4th Axis rotation angle limit problem

I have a 4 axis setup using a standard rotary table doing some work on continuous 4th axis milling.

During the finishing pass, I run a small ball nose end mill through the profile and it rotates many many many times around the A axis until the part is finished.

In step config I have the angle set to -9999 and 9999 but thats not even enough.

I find out recently in the middle of my run that the axis has hit the limit, which happened to be 6400 degrees even though I had set it to 9999 (which still isnt enough).

Is there a way to make EMC2 recognize that higher angle is an angle inside 0=<angle=<360 so that it never stops because it is 'out of limit'. Since my rotary table in reality has no angular limit.

How do I fix this? This is incredibly annoying. RIght now my temp fix is to split the gcode into small segments. So my finishing pass requires tens of files. I also have to re-zero the angle and run again.

Is there a solution to this?

E_M_C_user wrote:

Is there a solution to this?

Possibly "wrapped rotary" though I have never tried it.
www.linuxcnc.org/docview/html/config_ini...b:%5BAXIS%5D-section

What limits appear in the actual INI file? You ought to be able to go up to about 10^308. It may be that stepconf has sanity-checked the limit, too sanely.

I ran into the same problem yesterday.

My temporary solution was to comment out the MIN_LIMIT and MAX_LIMIT lines in the .ini file. This doesn't give an error message. Clearly, there is some default limit, but I don't know what that is. At least I was able to finish my run (which needed about 60 turns) without running into the 9999 limit.

I tried the WRAPPED_ROTARY option (which sounds like just the right thing). However, I had nothing but problems with that approach. The first thing I discovered was that G90.2 and G91.2 don't work like the wiki documentation says. Use of G90.2 or G91.2 gives an error message. The next thing I discovered was that you can't make a full turn or more. You can only turn something strictly less than 360 degrees. Then I discovered that going to a negative rotation gives you something other than what you would expect. For example C-90.0 goes 3/4 of a turn to the equivalent position of 270 degrees (but turns in the opposite direction). This is really counter-intuitive -- I'm thinking that C-90.0 should give only 1/4 of a turn. The real killer for me was that wrapped rotary options in EMC2 and MACH3 behave totally different. So developing software that generates g-code that will run the same on both EMC2 and MACH3 is impossible if you use wrapped rotary axes.

If there are any other solutions, I would be most happy to hear.

It's not possible to make one post processor work with more than one control system and even variations of that same control software will be different. That is why when you open up CAM software like Mastercam and Onecnc you find hundreds of post processors to pick from and then they may need to be configured to suit your machine in most cases.

To imply that LinuxCNC should behave the same a Mack is really funny...

John

Even after 40 years of engineering experience, I guess I'm still naive enough to expect standards (RS274D or ISO6983) to serve some useful purpose. I haven't shelled out the money to buy a copy of ISO6983 to see if it actually addresses the issue of wrapped rotary axis.

On a more practical note, the documentation on WRAPPED_ROTARY axis at wiki.linuxcnc.org/cgi-bin/wiki.pl?WrappedRotaryAxes is just plain wrong and needs to be updated. The use of G90.2 or G91.2 give errors.

Everything on the wiki is user contributions and the go to place for documentation is the manuals for the version your running. If you notice something is not correct on the wiki anyone can change them.

When the NIST released EMC to open source and the programmers took over and started to improve on the the implementation of RS274/NGC and things started to change from the original RS274/NGC. So a standard in that case is just a launching point. There is even a section in the manual that describes the differences from RS274/NGC and EMC/LinuxCNC. I don't think that is up to date anymore... a quick google show two versions of RS274NGC not to mention LinuxCNC's version.

I don't have a rotary axis but do understand there are some compromises to be made when using one.

LinuxCNC does not have G90.2 or G91.2 and that may be the source of your error.

John