Messages

1311

General Mach Discussion / Re: CNC Gear Cutting

« on: January 07, 2009, 08:45:10 AM »

Interestring thread. I just thought I'd add my 2 cents.

I"m new to home grown retrofitting and manually programmed CNC, but I have many years experience as an engineer and have done a lot of machining for prototypes of all sorts. My comment is that I have to agree with the folks who opined that this is really an academic discussion as the minute error at issue here is insignificant for almost any real world application.

The 'accuracy' of a gear from a 'timing' perspective is related only to the number of teeth. Any inaccuracy in individual tooth spacing would only effect that specific tiny portion of the trace and be completely gone by the time the gear moved to the next tooth. i.e. 32 teeth is 32 teeth and that is how many teeth will pass per revolution, no matter if a tooth or two are slightly off of their true theoretical azimuth or slightly over or under thickness.

Manufactured gears have a tolerance. Many are broached in a single pass. Like bearings, there are many different accuracies available with corresponding cost.  Gear tooth contour accuracy effects mostly the amount of sound (harmonics) produced and wear characteristics. No cut gears are really "accurate". The only applications that I know of requiring super accurate gears call for hardened and ground teeth and are for super precision, super smooth (quiet) or very high rpm service, none of which would apply to a clock, I would imagine.

Even in the most accurately produced gears, ultimately the 'final machining' is done by the gear mesh itself during break-in.

So, as has already been stated, use absolute angular positioning to eliminate a tolerance stack, rely on the accuracy of your setup (which from where I'm sitting looks more than adequate), machine and enjoy!

1312

General Mach Discussion / Re: The Need For Speed. . . . At least for rapids

« on: January 07, 2009, 07:27:27 AM »

As others have said, your speed is restricted by the kernel speed. I'm running 20,000 steps and the same total screw lead as you. With 25k and I max out at 75IPM, which is consistent with your results.

However, the stalling is a differnet problem. First off, you don't have enough voltage in your supply. Voltage should be many times the motors rating. I know it seems odd, but s that's the way it works. Probably why your motors don't get warm. Do some homework on steppers. www.geckodrives.com has a lot of good info and calcs. You can determine if your small steppers are up to the task. This is a somewhat complicated topic which requires some study (I'm still learning).

You need to look at the acceleration. If you have it set too high, the motors will stall trying to get the mass moving, which is especially demanding during a direction reversal. Raising the speed increases this problem.

Incidentally, your computer should be way more than enough for Mach 3. Currently I am using an old Intel P3 850mghz. It is a dual processor machine, but the CPU runing Mach never goes above 25% CPU utilization. On the other hand I was using a 1.2Ghz laptop wiuth a VIA processor and it was often pegged, so obviously processor brand type does have a lot to do with it.

You might want to confirm you are using the correct pulse width.

1313

General Mach Discussion / Re: Wireless network causes steppers to stall

« on: January 04, 2009, 12:53:51 PM »

D-Link USB wireless here also!


I also had a problem with the Xbox 360 wireless controller. I bought the PC adapter and installed the plug-in and it worked as advertised. It's really a slick way to control the machine, but not at the expense of reliability.

1314

General Mach Discussion / Re: Deeper into the 4th A Axis

« on: December 31, 2008, 09:47:18 AM »

docltf;

Being a total novice at this, I really had no idea that Mach was asking for.

As for the forum, I must say that this forum, unlike many, is very helpful and focused on the topics and not on flaming and personalities. A refreshing change from some.

Once I just went with observation instead of calculation, it only took a couple minutes to figure out what Mach wanted. It would have taken much longer to collect and post all of the specs and wait for an answer.

My 4th axis is actually just a stepper powered spin index, so it already had a degree wheel on it. I posted pics in the 'show and tell' section.

1315

General Mach Discussion / Re: Wireless network causes steppers to stall

« on: December 31, 2008, 09:33:12 AM »

I'm fairly certain that the problem is the radio waves emitted from the wireless adapter and not the CPU drain.

I'm now running a dual processor machine and I have biased one processor completely to Mach3 and it never goes above 25%.

The laptop would often peg at 100% and I mistakenly though that was the problem, but when the new machine had the same random bumping and stalling, I knew there was more to it.

1316

General Mach Discussion / Re: Motors stalling, losing steps

« on: December 30, 2008, 05:19:13 PM »

Unless i missed something, you did not say what you are driving the Kelings with.

If you are using Geckos, I can tell you that if you have the resistor set higher than the motor spec, the motor will stall randomly. I found this out by accident when I hooked a 4 amp stepper to a Gecko (203v) that still had a resistor for a 6 amp motor on it. Stall, stall, stall. Calculated and changed the resistor and all was well.

Just today I posted another accidental discovery. My wireless network adapter causes the steppers to behave exactly as you describe. I  don't know what part of the electronics it is effecting, but unplugging the wireless adapter cures the problem.

1317

General Mach Discussion / Wireless network causes steppers to stall

« on: December 30, 2008, 05:04:08 PM »

Just thought I would pass this along. I've been chasing a stubborn problem with the steppers stalling for no apparent reason. Finally I serendipitously discovered that it was the wireless network adapted causing the trouble. Plug it in .  steppers stall, unplug it, all is well.


Just another thing to add to the troubleshooting pool.

1318

General Mach Discussion / Re: Deeper into the 4th A Axis

« on: December 30, 2008, 04:55:59 PM »

If it helps, I gave up trying to calculate the steps per degree for my 4th axis. Nothing about the A axis was intuitive to me like the linear axis were, and anything I actually calulated was way off.

Ultimately, I just used the degree wheel and interated down till I got one degree of movement for one degree commanded.

So I would suggest you just command 45 degees and see what the result is and go biger or small on the count until you get close. At that point the number of steps per degree you are using will be some identifiable muliple of what you have step and gearing wise and you should be able at that point to get the exact number you want.

1319

General Mach Discussion / Re: New Cutter Comp code and Examples

« on: December 28, 2008, 08:33:02 AM »

G92 for the A axis is broken in the .43 development version.


Works fine in the lockdown version.

In .43, if you step thru one line at a time and it works OK, but run the code and the A axis does really strange things.

Gcode attached. (ignore note on depth of cut . . partial edit left over from earlier iteration)

Problem in at first G92 A0 when the program is RUN.

1320

General Mach Discussion / Re: New Cutter Comp code and Examples

« on: December 23, 2008, 11:05:42 AM »

First, let me say that I am glad to see work going forward on comp. That is what I have had the most problems with. It is useable for me, but only if I manually go into the gcode and add a custom lead-in for each circumstance. Also the comp would often do odd things where arcs came together without a straight section in between. If I added a tiny straight section, one problem (mismatched endpoint vectors) would go away and another (pausing at the tangent) would replace it.  I look forward to having the new code to play with!

I just want to weigh in on the cutter vs inside radius debate. As one who has written a fair amount of code with higher level math, I can tell you that a .5" cutter cannot cut a .25" inside radius as far as the computer is concerned if a check is first made using a "<" comparo.    i.e. the radius of .500000000000000000000000 is NOT LESS than .25000000000000000000000.

That being said, I don't see why "< -or- =" could not be used in comparing the cutter dia with the smallest inside radius. If there is some program reason that this is not possible, surely adding a 1 at the highest precision to the inside radius or subtracting it from the cutter would not result in any appreciable error. If internally, you are out 16 places (or more), methinks that this amount of error would be imperceptible except by a scanning electron microscope. This 'trick' could easily be done inside or outside of the comp processing, unless I am really missing something.  If inside, then a simple switch could turn it on or off so that people machining to a millionth of an inch would not suffer  

Seems moot now since I gather from reading the posts that something has been done to resolve this? As a matter of curiosity, I would be interested in what method was chosen.