Reinhard,
On the Galil, you would use the TM command. TM is set to 1000 (approx 1ms) by default. That is the time base that everything uses. Increasing or decreasing the value of TM would be tantamount to feed rate override. The challenge then becomes to tie the value of TM to an analog input. This can be done in Galil DMC programming where a thread is dedicated to watching the analog and adjusting the values of TM (and possibly the PID values to if using servos. As I said, the Galil is a complex controller. They have good documentation, but it still takes years to master every facet. Meaning it is up to you to read the documentation and implement what you want to do. You will NEVER see a reference to feed rate override in their manuals. They give you the tools, you just have to figure out how to use them. However, if you buy a Galil, they do offer great support. They have good application engineers to help you get what you want out of the controller.
In order to run a Galil with Mach, you have to know how to run a Galil by itself first. I run a Galil on one of my machines. I consider it a viable hobby level controller IF you are willing to learn about it and IF you can/want to afford it. Budgets being what they are, everybody has their own levels to which they draw a line. Buying a Galil on eBay is not for the crowd that knows nothing about them. There are so many different models and a LOT of them on eBay were custom designs made for a particular purpose. And Galil offers no support for used controllers. So you better know exactly what you want to pull the trigger on an eBay Galil.
Multiple pass threading starts each thread pass on the index pulse on the encoder or the pulse per rev input. The infeed amount is already there. All that remains is synchronizing the Z feed rate with the actual spindle speed. Z always moves from the start point to the end point and never needs to be re-planned. It is NEVER as complicated as people make it. It is actually quite simple to produce a high quality thread with just a spindle pulse and a calculated trajectory. But it does take a real-time environment to implement the control loop.
There are real-time extensions for Windows. The problem is that all of them cost big bucks. It would more than double the price of Mach. There are two types for Windows, mainly; Hypervisor and HAL. A Hypervisor is running a RTOS on the hardware that then partitions a CPU core (or more) to runs Windows in a VM. The HAL method uses a custom Windows HAL. The HAL type turns Windows into a true RTOS and can be implemented with a single core processor. Of the two, I prefer the HAL type. Interval Zero
https://www.intervalzero.com/ is one that I like. In fact, they have a product called KingStar that implements a software EtherCAT controller. They are developing a plugin which is nearing completion. They demonstrated it running a machine at our shop a few weeks back. But this stuff, while cool, is way out of the realm of Hobby land.
Steve
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