For starters, when spindle load gets to be above .9 have mach feed hold and stop ( basically a brain that see's a certain parameter above a certain value and does a 1001).  This would save a lot of hassle down the road. When I get to .8 its time to resharpen and it will also tell me if my feed is too low or too high when I start out with a new end mill.    

You'd have to do a lot more than just read load to do that reliably, as you WILL see momentary loads that go well over 100% (for instance, when you enter a corner), and you don't want to trip on those.  Plus, the readings you get will typically be VERY noisy.  At a minimum, you'd need to do considerable digital filtering, just to get something stable enough to work with.  I don't see how you'd do that in a brain.  Possibly a macro-pump.

Regards,
Ray L.

How can a modbus packet be noisy?  OK, so there would have to be a rule about 100% spindle load for no more than .75 second or some other number.  why woudl I need a macro instead of a barin.  its a simple rule of if input> X and for longer than Y time period do 1001. 

What's digital filtering?   

The VFD may well be sending raw, instantaneous current readings.  If so, the readings you receive will not be steady, but will have quite a bit of variation from one reading to the next, and their values may well exceed 100% load at times, as most VFDs allow short-term overloads of as much as 200%.  To make them usable, it may be necessary to filter them using a digital filter, which is a software algorithm that that performs exactly the same function as an analog filter (resistors and capacitors), but all the processing is done on digital values, rather than analog voltages.

If I were doing it, Id make use of the current limit feature that is almost certainly built into the VFD, and take the VFD ERROR signal, and run that into Mach.  Then, when you over-load the machine the VFD will shut down, and you will simultaneously get an ERROR signal from the VFD you can use to shut down Mach3.  I think you'd find that would work much more reliably, with much less tweaking and tuning.

Regards,
Ray L.

OK, chalk one up for doing it the old fashioned way.  Do you know of a good analog or digital meter that I can hook up to the analog output of teh VFD to show me load?  Kinda like what tormach has.  I guess that acording to what you say, I shoudl just set a relay to go off at a prescribed limit and chain that to spindle fault input in my MACH. 

How about hooking uyp one of these to teh nalog output of the VFD? http://www.mpja.com/download/8054me.pdf  It's rated for 20VDC but, I can use a 5vdc power source to calibrate teh reading to show 50, put the decimal in teh 3rd position and that should be it.  I will have teh VFD output 10VDC on teh analog output and these is my load meter. 

Putting a voltmeter on the VFD will tell you nothing of value.  You need to be looking at current, which means putting an ammeter *in series* with one phase of the motor.  The Tormach load meter is nothing but an analog ammeter.  An analog ammeter contains a shunt, which is a very small, precisely known resistance.  When current passes through it, it creates a small voltage drop (typically 50mV at maximum allowed current), and the meter itself is a very sensitive voltmeter, connected across the shunt, that reads full-scale with 50mV across it.  Look at digikey, mouser, and other electroincs supply houses, and find one with a suitable full-scale reading.  But, a good analog ammeter will not be cheap.  However, a digital meter, in this application, would be completely useless.

Regards,
Ray L.

If the tormach load meter is just an ammeter, then why do the instructions for installation call for changing parameters in teh VFD? 

I am not sure about VFD's but servo drives often have an analogue output that you can set up to be used for different things. I have mine set up on the big lathe to look at spindle current and I have it scaled in the servo drives setup such that 10v is 150% of continuous rated current of the motor thus I have 0-150% load meter. I used an analogue ammeter with centre zero and made a scale up for it to represent 150% - 0 -150% and it works great, I used a fixed resistor and a trimpot to allow me to adjust it slightly to get true zero. I will take a pic later to show it. Oh and the reason I have the centre zero is the analogue out from my servo is +/- 10v rather than just 0-10v so if the spindle is M4 it will show deflection as the opposite way.

Hood

There are a number of reasons to present a spindle load signal to MACH.

I tend to agree that if the only use will be a readout, then it would be a lot easier to just put an ammeter on the motor (as already described) or use the remote VDF panel (also as already described). However, there are lots of reasons that it would be useful to have the spindle load presented to MACH (by whatever means the user chooses).

However, as can be seen from Hood's posting, the uses for having torque data are only limited by the users creativity and cleverness. 

I also have plans to rout the torque output analog signal on the spindle drive to MACH for the purpose of a read out certainly, but also to monitor loads as desribed ealier.

The momentary overloads are easily accomodated with a timer as descibed in a previous post. That is not really different from the normal faulting process in the drives from follow error, overload, overheat, or a host of other maladies.  However to take it a step further, you can have MACH slow the feedrate if the load exceeds a certain amount, or at least provoide a warning that something, a dull tool perhaps, needs operator attention.  If a user has industrial drives (like Hood is referring to) you can take the load info and feed back to the drive whatever corrective action you think is appropriate.

A project on my to-do list, just be way of example, it to limit the torque output of the spindle motor for hard (rigid) tapping operations. For example, if the machine is going to tap a bunch 1/4-20 holes, knowing when a 3.5Kw motor goes over 100% is not particularly useful information . . . equivalent to an indicator light that says 'your tap has shattered'. 

As part of my tapping macro, the drive will be set at some reasonable max torque for the size tap and material being cut. Monitoring this process would involve looking at values that are some fraction of 100% and could easily be less than 10%.