[LeeWay]

I don't understand why so many people seem to be having problems with Z axis shifts.

They don't seem to be having issues. They are. I used to be like you, Steve when I was the only one running my machine. Since I have operators now, one of the best moves I made was to fill out my tool table with correct offsets and have everything loaded in TTS holders. That and rigid tapping saves me a whole lotta time and wages.

[CadRhino]

Hi LeeWay,
If you don't mind me asking, how did you go about finding a good operator for your Tormach?
What machine are you doing rigid tapping on?
Best,
Nathan

They don't seem to be having issues. They are. I used to be like you, Steve when I was the only one running my machine. Since I have operators now, one of the best moves I made was to fill out my tool table with correct offsets and have everything loaded in TTS holders. That and rigid tapping saves me a whole lotta time and wages.

[LeeWay]

Only my tool holders are Tormach. My machine isn't. I call them operators, but they are Family. Son and his Fiance. That may be all coming to a close though, so I may be looking for an operator soon.

[CadRhino]

It is great when the family thing works out.
Good luck with finding another operator.
Nathan

Only my tool holders are Tormach. My machine isn't. I call them operators, but they are Family. Son and his Fiance. That may be all coming to a close though, so I may be looking for an operator soon.

[LeeWay]

I hired him on 09. Her about a year ago. I think it has run it's course. She got a cushy girly job and he is looking into something else. I am happy to be a stepping stone. They are trained well and at least one has good manners.

[nitewatchman]

My oldest son runs mine also. We get long sporadic runs of castings. so there are periods of a couple of weeks of a's and e's with slow spells in between. Works well for him as a part-time job.

Understand about the manner's, biggest problem with my son is him showing up when he is supposed to. Had to fire him once, he appealed to the HR Manager and my wife made me reinstate him.

In my day job I don't hire family and try to not to hire family and relatives of existing employees. Sometimes, can't be avoided. Several years ago hired man and wife and placed on separated shifts. Within six months both were involved with other coworkers. Came to a head with a four way fist and hair pulling fight at shift change in the break room. Lost four employees in one swat.

[DigDug]

I had the same exact problem as the OP. Using SolidWorks and HSMXpress and same Tormach_NexGenCAM_110911.cps post.
When doing pockets with helical entry it would loose Z height over several parts. Always getting lower and lower into the part on
each new pocket. The Z axis would kind of make a clunking sound when plunging and retracting to the feed height. I checked tightness
of the gib and also the motor connection to the ball screw and all was good.

The fix was to change the option in HSMXpress under "Linking" to "Always use high feed". This setting is in the far right tab
when you are editing a toolpath. I have also found that using "Preserve radial rapid movement" works also and lets X and Y rapid fast
but limits Z to the highest feedrate set for the tool and not a G0 speed.

Hope that helps,
P.S. This is my first post

PCNC 1100 (no ATC)
Standard Tormach issue Mach3

[kirk_wallace]

(Just thinking out loud)

It seems, from my brief reading of this thread, that the original problem was solved by upgrading (or downgrading) the machine software. But, from my limited experience, when I hear of Z axis creeping, it is due to steps being missed by the stepper motor due to being overloaded, or rather, the force required to move the axis was higher than the motor could provide. Common stepper systems have _no_ positional feedback, so the software has no idea that steps may have been missed. The software has to assume that every step called for is completed properly. The key is in configuring the software to never call for steps in a way that can not be met. Therefore, the system performance needs to be measured to find the safe operating envelope, such as maximum speed, acceleration and any resonance zones, then the software needs to be configured to stay within the limits. Usually a safety factor of 10 or 20 percent is applied to make sure that common performance variations are still within limits. An accurate performance model is key, and if done properly the software will never ask for steps that might be lost.

Further, it is up to the machine operator to make sure the machine's performance envelope is maintained so that the software model matches the current machine performance. If the machine changes, the original performance will need to be restored or a new software model will need to be created.

For the Z axis the model has to take into consideration that gravity on the spindle will load the up motion more than the down motion. The model has to assume the worst case, so the limits need to be set to the up motion parameters.

Another side of this is how well the model is applied. A perfect model can fail if the software cheats or is occasionally blind to the limits. This may be why some versions of software seem to be better than others.

Also, g-code can have a hand in it. Normal feed rates are usually well below the machine's rapid rate, but there is nothing to stop a feed rate beyond a limit from being entered. In this case, the software should at least detect that the feed rate is beyond the model limits and fault out with a following error. Since stepper systems don't have positional feedback, this is the normal source of following errors.

So, if one starts losing steps, check for (maybe in reverse order); a change in the machine configuration file (performance model), or a change in the software (model application), or a change in the machine's physical condition or motor driver defect (model mismatch). Being familiar with the configuration file and how it works can be handy.

[SCzEngrgGroup]

Load was not an issue in the OPs problem. He saw the same position loss when "air cutting". It is the controllers (i.e. - Mach 3s) responsibility to never command a move that violates the acceleration and velocity limits set in the Mach3 Motor Tuning dialog. In the OPs case, Mach3 WAS, due to a bug, commanding moves that violated those limits. That was a well-known, well-documented, long-standing bug in many versions of Mach3 that was finally fixed a few years ago. The bug was that under certain circumstances, when transitioning from a 2-axis (i.e. X/Y) move, to a 3-axis (i.e. X/Y/Z) helical move, the acceleration ramp on the Z axis was skipped, which commanded the Z axis to change instantly from a stop to moving at high speed, which the hardware cannot do.

Regards,
Ray L.

[Philbobb]

Ran into the same issue with my own code tonight. My Z was gaining height(too shallow cut) then gaining some back, then back to too shallow, by around 0.010". Using Fusion 360, essentially HSM works CAM, and the Tormach post. Tried changing to preserve high feed and still had issues. Had my first mill did what it wanted with the Z moment, went to -0.1" on a command of 0.92" before I hit E-Stop. Installed version 066 and Z height wasn't an issue. Same as the OP, Z was clunky with stock, quiet with 066, weird. Tried installing Mach on my laptop then copying the Mach3 exe to the controller, didn't work. It wouldn't get a link to the mill for some reason. Had to install it on the controller then copy from there.