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General Mach Discussion / Re: Losing Pulses at lower accelerations
« on: April 08, 2013, 11:41:41 AM »
Screw pitch on X and Y is 5 turns per inch.  Steppers are 2000 pulses per rev, so 5 x 2000 = 10,000 pulses per inch.

As I mentioned, I can get the X axis to at least 200ipm with no lost steps if it's running by itself.  The problem comes in when X and Y are running simultaneously, as happens for circles. 

Going from a 4A to a 15A power supply does not make any difference.

General Mach Discussion / Re: Losing Pulses at lower accelerations
« on: April 08, 2013, 08:20:39 AM »
As to what I want to do, I thought I said that in the first line of my first post.  I'm interested in high speed machining.  Now, whether my machine is capable of that or not, that's a different question.  Based on my testing, I'd say it's not.  I've already been through the testing you suggest, as detailed in my previous posts. 

There are two types of failures.  One is that a velocity or acceleration results in losing some relatively small amount of steps.  The second is that the velocity is high enough that the stepper locks up and misses a massive amount of steps.  The circle test I did resulted in this second type of failure.  For a given axis, a circle involves ramping speed up from zero to a maximum speed, then back to zero.  The second axis is the same, only 90 degrees out of phase. This ramp is far slower than the acceleration value.  The steppers are failing, or locking up, near the maximum speed, then restarting as the speed decreases.  I've found that the steppers quit working at about 50ipm. 

Since I've looked at the step pulse input to the Geccos, I know that it's being provided by the remainder of the system.  At the lowest kernel speed of 25k, the signal is stable and there's little jitter.  For 35k and above, there's jitter. However, I've tested at both values, and failure occurs at 50 ipm.

As for acceleration, most values up to 15 or 20 ips/s seem to work OK.  I've tried values from 1 to 50 at various speeds.  If the steppers didn't fail at higher speeds, then I could tweak these values.

So where I am is that my maximum reliable speeds are probably on the order of 10 or 20 ips.  This is far too slow for high speed machining.

Let's say that I am able to resolve this problem, and get reliable stepping up to 100ipm or so.  As you point out, I may run up against a second problem - lack of torque.  For the tests that I've done so far, I'm machining air.  I may find that when I'm cutting steel that I can't generate the necessary forces with the steppers to prevent loss of steps.

So that's where I am today.

General Mach Discussion / Re: Losing Pulses at lower accelerations
« on: April 07, 2013, 04:59:10 PM »
Thanks for the reply.  The effect of jitter on the stepper fits the symptoms.  I get lost steps, then at faster rates I get stalling.  If Mach3 is not that accurate in providing jitter free pulses, it makes sense that as it's trying to control two axes simultaneously that the jitter gets worse.

I have not yet tried cutting at these higher rates.  Do you think that loading the motors when cutting will make the lost steps worse, or about the same?  I'm thinking that maybe something like 40ipm is the fastest that I should go, but if I can't even cut at this speed, I need to look into something like the smooth stepper.

General Mach Discussion / Re: Losing Pulses at lower accelerations
« on: April 07, 2013, 03:00:38 PM »
More testing.

I put an oscilloscope on the Gecco step input.  It looks OK, although there is some timing variance from pulse to pulse when running at a steady speed.  I didn't see that the step pulse was doing anything strange when the motors made noise and stopped stepping.  I have to conclude that the problem is in the stepper/gecco part of the system.  The only thing that gives me pause is the jitter in the timing of the step signal.

I changed the kernel speed from 25k to 100k to see if that had any effect.  At the slowest kernel speed of 25k, the jitter went away.  Mach3 did warn me that the kernel speed was too slow for the 200 ipm max that I had in my motor tuning, but it was OK for the speed I was using in my G code.

I looked at the specs on the Gecco.  It's supposed to be rated at 200kHz maximum.  I have 10,000 steps/in, so that's a maximum of 20ips, or 1200ipm.  The speed should be OK.

So where I am now:
- the jitter I'm seeing could be bothering the Geccos at higher speeds
- the jitter could be a result of cross-talk in the system
- the jitter could be generated by small variances in Mach3s timing
- this is just as fast as the Geccos can run

General Mach Discussion / Re: Losing Pulses at lower accelerations
« on: April 07, 2013, 11:32:57 AM »
I did some additional testing.  I started thinking it might be a power supply problem.  I looked up my transformer, and it's rated at 4A.  I replaced it with a power supply rated at 15A.  I installed larger wires to the voltage inputs on the Geccos.

I wrote some G code to make a circle and have some simultaneous X and Y moves:

G00 X1. Y0.
G02 X-1. R1.
X1. R1.

This works at 50 ipm.  At 60 ipm, the Y motor makes odd noises at the middle of its traverse, and loses a lot of steps.  The X motor loses a few.

So, no change in problem.

Any ideas?  Could I be getting cross talk in the wires?  Is there an adjustment on the Geccos that I should make?  I thought about putting an oscilloscope on the Y step signal to see if it looks odd.  There are so many places that I could be having problems - Mach3, breakout board, wiring, power supply, Geccos, steppers, XY table.  I need some way to isolate the problem to just one of the systems!

General Mach Discussion / Losing Pulses at lower accelerations
« on: April 04, 2013, 02:17:56 PM »
I recently became interested in high speed machining.  My homebuilt CNC mill is several years old, and has always worked fine at the lower feed rates that I usually use (1-8 ipm).  I started testing what feed rates that I could get out of the system, and got some unusual results.

First, I ran a short program to run the mill back and forth on one axis:

G01 X2
G01 X1
G01 X2
G01 X1
G01 X1.5
G01 X.5
G01 X1
G01 X0

I ran the program using increasing feed rates.  I have a digital probe, and set X= zero before the run, then checked it after the run.  I was able to get up to 200 ipm with an acceleration of 25 ips/s with excellent repeatability.  I didn't go past 200 ipm in my tests.

I ran a similar test on the Y axis.  I could get 150 ipm using an acceleration of 10 ips/s before I started losing steps.  I found that holding this speed and increasing the acceleration made me lose steps.  This all made sense to me.

I then ran a program that moved the X and Y axis:

G01 X2
G01 Y2
G01 X1
G01 Y1
G01 X1.5
G01 Y1.5
G01 X.5
G01 Y.5
G01 X1
G01 Y1
G01 X0
G01 Y0

I found that using a feed rate of 150 ipm for X and Y that had worked OK on the single axis tests made me lose steps. (About 0.070 on both axes)  Then things started getting strange.  At a value of 50 ips/s, I got no lost steps.   I increased to 75 ipm, and started losing steps.  At this point, I held the feed rate at 75, and started playing with the acceleration.  I found that low accelerations, like 5 ips/s LOST a huge amount of steps.  Increasing the acceleration led to less lost steps.   At the low accelerations, the stepper motors sounded OK, but the deceleration noise was not a happy one.  The higher accelerations cause the stepper motors to stop dead nearly instantly, and really jerks the mill around (relatively - it's a big hunk of iron).

One of the things I thought might be happening is that the stepper voltage could be dropping when two motors are running simultaneously.  I monitored the supply voltage with an old analog voltmeter.  The voltage is only dropping briefly about 5V on the 70V supply during transitions.  I added about 1F of capacitance on the power supply.  It didn't change the testing results.

Any ideas?

Here's a newer version of the screen set.  I now show the midpoint after two probes, and I fixed a bug where the feed rate was not being reset.  I added a go to x0, Y0 button to the keypad.

Since my original post here, I posted my drawings on how to build a digitizing probe:

I use another probe to set the zero on the mill tool.  It's a piece of circuit board with a wire soldered to it.  When the tool touches the circuit board, it makes the circuit.  It works fine.

I have not gotten much feedback on this screenset, but I see that it's been downloaded nearly 100 times.  Is anyone using it?


Sorry you're having a problem.  The message is generated when the program thinks that Mach3 is not running maximized on the screen. That's necessary since the keypad generates absolute x,y screen coordinates to interact with Mach3.  If the screen is not where it thinks it is, it won't work correctly. 

The way that it checks is that it looks at the upper left corner of the screen and gets the name of the window that's there.  It compares it to "Mach3 CNC".  The message is generated when there's not an exact match.

It works on a computer with an 800 x 600 resolution, and also on another computer with a 1680 x 1050 resolution.  If you can provide additional insight or this gives you an idea why it's not working, I'll take a look at it.


The attached file contains a screen set (Probe.set) and other files that support use of a digital probe, plus a pop-up keyboard designed for use with a touch screen.

The screen set is based on the default Mach3 screen.  I took out the tool section on the first screen and replaced it with several buttons to support using a probe.  Other inclusions are pre-set spindle speed buttons and an MDI line on the first screen.  I made a few other minor modifications. 

I recently installed a touch screen monitor (from ELO) to display Mach3 on my mill, held by an adjustable arm (http://www.homemetalshopclub.org/news/11/presentation_monitor_arm.pdf).  It worked out of the box with all the screen sets I tried.  I loved it!  The only problem I ran in to was that I sometimes needed to use a keyboard to input data.  I thought about installing a keyboard, a mini keyboard, a numeric keypad, and a wireless micro keyboard.  All of these would work, but seemed inelegant.  I tried Mach 3s built in calculator (Operator - AutoCalculator). I installed Click-N-Type (http://cnt.lakefolks.com/), a pop-up keyboard, and this worked OK but was a bit kludgy.  I  tried the Plugin Virtual Keyboard (http://www.kd-dietz.com/klausphp/pages/eng/machscreen/description/ms_description.html), but again, it didn't do some of the things I wanted to do. I decided to write an application that had all the functionality I wanted.  I started trying to develop a keypad within Mach3.  This proved difficult, if not impossible.  I moved to a standalone program written in a language called Visual DialogScript, and eventually built just what I wanted.

Installation of the files is simple - just unzip the files and sub directories into your main Mach3 folder.  From Mach3, select View - Load Screens and point to Probe.set.  That's it!

Instruction for configuration of the keypad are included in the TouchKeypadReadMe.txt file.  If you want to use it with anything other than the screen set I built, it'll take some configuration of the TouchKeypad.ini file.  The configuration is described in comments inside the .ini file.

- 10k

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