Hello Guest it is September 16, 2019, 09:12:43 AM

Author Topic: A axis rotary problem, strange stalling issue  (Read 2058 times)

0 Members and 1 Guest are viewing this topic.

A axis rotary problem, strange stalling issue
« on: June 01, 2015, 02:54:53 PM »
I have a CNC router dedicated rotary machine recently installed running latest mach3. The A axis is the rotary and then the long axis is Y fixed on the centreline and Z is up and down. 8" cnc rotary table with nema 34 motor, its all pretty conventional stuff.

wrap programs are create programs in vectric

I am getting the rotary axis motor stalling at certain points in programs each and every time a program is run through, it ruins work. The other 2 axis are the same drives/motors so I have swapped the drive over and eliminated that, put a new nema34 motor on and eliminated that, unplugged the Y and Z and ran it through (still stalls), I also ran it with zero load on ie uncoupled from the rotary table and you can actually hear and feel it stall with absolutely nothing connected. I have come down to either the code or mach3 settings or a combination. It is nothing mechanical or electrical on the system.

The code is attached. On mach3 acceleration of A axis is set to 300 and velocity is 2000. Units are all in mm. In particular I get audible stalling at several points, one of the most obvious is at lines N1470 - N1480. Any help much appreciated.

« Last Edit: June 01, 2015, 02:56:49 PM by dougie329 »

Offline BR549

*
  •  6,887 6,887
    • View Profile
Re: A axis rotary problem, strange stalling issue
« Reply #1 on: June 01, 2015, 04:01:41 PM »
What is the reduction on your 4th axis drive? Is it 1:1 or other?. Sounds as if you are over speeding the A axis causing missed steps and stalling. Steppers need to run at low rpms to maintain enough torque to prevent stalling the motor. The faster you spin a stepper the less torque it produces.

Try reducing the vel and accel values on the A axis by 1/2 then retest.

Just a thought(;-) TP
Re: A axis rotary problem, strange stalling issue
« Reply #2 on: June 01, 2015, 07:02:22 PM »
It is 1:1 as it came from the manufacturer. From what I have found out the actual rotary table gear inside is 90:1. They come as kits with a tailstock etc exactly like the tormach units. It is well within the speed range I think, if I slow it down to 50% it still stalls at what seems to be the same points.

On the program there is no separate feed rate for the A rotary axis. I don't know where the a axis feed rate comes from, surely that should be in deg/min.  Could this be part of the problem?

Offline Greolt

*
  •  956 956
    • View Profile
Re: A axis rotary problem, strange stalling issue
« Reply #3 on: June 01, 2015, 07:35:37 PM »
This is a copy of something I posted on "Rotary Axis Feedrate Compensation" within Mach3.

It may be helpful in understanding the issue.

=========================================================================

All axis move in units per min. With a rotary axis those units are degrees.

So what is 120 ipm on the linear axis (desired speed of the tool in the work), is 120 degrees per min for the rotary.

That 120 degrees per min angular feedrate will make the tool move through the work at a speed dependant on the distance the tool is away from the centre of rotation. (in your case, very slowly)

So Mach has a feature to compensate the rotary axis feedrate, to accommodate differing radius that the tool is cutting at.

It is activated via the Toolpath Setup menu. Check "Use Radius for Feedrate" All the other settings in this box are to do with the toolpath display window.

On the Settings page there are three DROs labelled "Rotation Radius". IMO they would be better labelled "Origin Offset"

They are to tell Mach the distance that the relevant axis origin (Z in this case), is offset from the centre of rotation. (A axis in this case)

So if you are machining on the outer surface of a 10 unit diameter job and Z axis origin (zero) is set on that outer surface, then the correct value for the "Rotation Radius" DRO is 5. The distance that Z origin is OFFSET from centre of rotation.

If, on the other hand, the Z axis origin is at the centre of rotation (my preferred method for most jobs) then the correct value for "Rotation Radius" DRO is zero. The distance that Z origin is OFFSET from centre of rotation is zero.

Mach takes the Z axis DRO value and the "Rotation Radius" DRO value and adds them together to ascertain at what radius the tool is cutting at any one time. Then compensates the angular feedrate to have the tool move through the material at the desired speed.

Maximum velocity as set in motor tuning is honoured, so that will always be the upper feedrate limit.

Now there is one little "Gotcha". A zero value in the "Rotation Radius" DRO will automatically disable the entire feedrate compensation feature. This is a known bug and is being addressed by Artsoft at this time. Hopefully it will be fixed soon.

The workaround for this, is to use a very small value (eg. 0.001) in the "Rotation Radius" DRO when zero is the correct and desired value. Small enough to have no measurable effect on feedrate, but not zero.

Offline BR549

*
  •  6,887 6,887
    • View Profile
Re: A axis rotary problem, strange stalling issue
« Reply #4 on: June 01, 2015, 09:15:38 PM »
At  90:1 I almost can guarantee you are trying to overspeed the Stepper motor to get the feedrate. You are trying to drive the A at 2000 Dpm.

There are bascially 2 things that can cause stalling a stepper motor. Velocity too fast or accelleration to quick. Take your pick.

Most rotaries for 3d work have a max reduction of about 6:1

Just a  thought , (;-) TP
« Last Edit: June 01, 2015, 09:20:02 PM by BR549 »
Re: A axis rotary problem, strange stalling issue
« Reply #5 on: June 05, 2015, 11:38:56 AM »
I had a similar issue just yesterday, thought i could have been mechanical jamming, so stripped the pinions to rule out then went about testing each electrical component individually, anyway cut a long story short nothing seemed to be faulty so decided it must have been mach 3 that was corrupt. I reinstalled and bingo. Might not be the case for you but worth a go, especially if it was working correctly before.
Re: A axis rotary problem, strange stalling issue
« Reply #6 on: June 05, 2015, 11:43:19 AM »
If you do give this a go.. Make notes of all your settings and make sure to delete the mach 3 folder with all settings profiles before you reinstall. That is unless you have multiple profiles then if may we worth cutting these and pasting them to another folder elsewhere and re introducing and testing individually.