This may not be a Mach4 issue and instead with either ESS (Smoothstepper) or PMDX but questions on the PMDX forum has been met with crickets so far so I’m going to try here.

We have ab AVID 4848STD CNC and upgraded from a router to a 220V water cooled spindle running off a Huanwang VFD. Also running a PMDX-126 BoB with a PMDX-107 spindle driver board. The conversion went reasonably well and the PMDX-107 calibration was spot on giving us just under maximum spindle speed (24000rpm) on the top end and just a bit over the minimum (8000rpm) on the low (30%) end. Spindle start, stop, reverse controls are working but our problem is with the speed settings. We can’t get the Mach4 speed settings to reasonably match the actual spindle speeds. With a tachometer we measured these discrepancies.

S23900  turns the spindle at 23961
S20000          "                    23961
S17500          "                    21420
S15000          "                    18365
S12000          "                    14665
S9000            "                    10970
S8000            "                      9740

I believe all our ESS,126,107and VFD settings are good as all else is working fine and the actual pin or jumper settings are consistent with documentation and settings noted in other threads in the PMDX forum.

Could this be a setting in Mach4 that we’re missing? I’m attaching both the Mach4 and ESS spindle control screens with our current settings for reference.

Thanks

Hi,
I'm not sure but what are you expecting?  You are using a PWM to analogue in the BoB, which may or may not be linear, certainly no better
than 5%, then the analogue voltage is applied to the VFD which will be linear to say 10%. Unless you have encoder (or some other pulse) feedback
and use the PID function of the ESS you'll get no better than 10%.

Alternately you need a Step/Dir type spindle, ie a servo driven spindle. I have a secondary spindle based on a 1.8kW Allen Bradley servo, and in Step/Dir mode
its speed accurate to within 0.1%, but I don't really care about that, what I care about is that it has low speed torque to drive tools in steel
and stainless. I spent the money so I had the torque to do the job in steel and stainless, I couldn't give a damn about ultra speed control.

Any way who cares? When you used a manual lathe or mill you got the closest speed  the gearbox/drive offered and then did the job. For example:
might have been nice to spin the lathe at 550 rpm, say, but the closest setting was 400rpm, and I could still turn up a nice part.
Just because the speed was off by 10 or 20% did not stop you from doing the job did it? Why get hung up on trying to get the speed spot on?

Craig

Hi,
by the way if you try to run your spindle lower than say 12000, or maybe at a stretch 9000, you risk blowing it up.
These high speed asynchronous spindles do not like low speeds, they overheat and blow up.

Craig

Your speed readings for each speed except the two highest are all close to 22% high.

The PMDX-107 used with most VFD's can normally achieve a speed setting accuracy of 5% or better over most of the range.

First, make sure that you have the default slot for pulley 0 configured in Mach4 to Min RPM of 0 and Maximum of 24000 (or 24001 if Mach complains when you select 24000). These numbers are used by Mach4 to calculate the PWM percentage. The case of protecting the spindle from cooling problems is normally covered by the motion controller plug-in overriding the minimum PWM. The PMDX motion controllers allow this, but I am not sure how this would work for a SmoothStepper based system.

I suspect that your VFD or its internal settings are scaling the input voltage by +22% and the two highest speeds are being limited by the maximum 400 Hz range of the VFD.

You could try using Mach to request some speed safely below the limit, say 18000 and then use the CAL pot on the PMDX-107 to get 18000 at the spindle. Not sure how this will affect the maximum speed you can reach, but it should cure the +22% over most of the range.

Alternatively you can dive into the gain or span settings in your VFD's parameters, but this can get complicated and confusing quickly. If you go this route be sure to document your VFD's parameters before changing them. It might also be informative to see if any of these parameters are not currently set to their factory defaults. Lastly if things are really messed up you can use the VFD's reset to factory defaults option.

averagejoe,

This is a machine in a maker space so many of the operators are new to this. As such we have them go through the fundamentals and safety practices on this cnc router. One of the fundamentals is to understand the relationship of feeds and speeds to their materials, tool life and quality of the project. I expect most of the members of this forum are experienced enough to know (hear) when the machine is not running properly but these new users typically don't. Part of the class we give them is to use feed and speed applications like GWizard and, at least for us, it's annoying when we know that they're using and adopting these variables, but their settings aren't matched by the machine operation. In the overall scheme of things is this a serious problem? No, but if something isn't working properly, we like to fix it.

Steve,

Thanks. We'll give the pot adjustment a try. We figured if the standard pot calibration was working then that was enough. Your explanation is very helpful.

Hi,

In the overall scheme of things is this a serious problem? No, but if something isn't working properly, we like to fix it.

Understood, and no issues with that. When I first started with CNC (Mach3 and parallel port) I shagged around for a long time trying to get the speed spot on
and in both directions....and what did I gain for all that effort....nothing. My regular 24000rpm spindle is within 10% or so from commanded speed and thats
entirely good enough. I could if I wished get it much closer but am I gong to make more or better parts as a result....no. Did I ever use a counter-rotating tool....no.

My current thing is adding a 4th axis, rotary at present but trunnion table in a month or two. I have just bought a years subscription to Fusion 360 Machining Extensions ($1200USD intro offer)
to take advantage of the fourth axis. What with the hardware Atlanta Drives low lash angle drive, Vexta stepper and Vertex chuck, the investment in dollars is well over $2500.
That's where I'm putting my time, effort and money which will help me make more and better parts.

Craig

Steve had the solution. I did use the 107 calibration routine but must not have found (heard) the maximum rpms in the soindle and over drove the pot. Once I set speed at 18000 in Mach4 and then use the pot and tach to match, all speeds up and down the spindle range were within 5% of settings!