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1

General Mach Discussion / Re: general problems with mach3

« on: May 24, 2008, 02:01:35 PM »

Well it wasn't the ball screw. And towards the end of the four hour procedure of taking the x and z axis sufficiently apart to disect the ball nut, sort the balls, and reinstall them, methodically sorting and spacing the 15 of 212 that are smaller, and then putting it all back together, I realized there was a much easier test. I should have simply decoupled the motor from the screw, and used a tick mark in the outboard motor shaft to see if it was still losing steps even without the motor connected to axis. This would have revealed to me ,as it did,that the problem was not the ball screw, or anything in the axis, but electronics or settings. So, wasted time, but knowledge gained.
And  the answer is : Motor Tuning, Step and Dir Pulses, If they're at 0 set them to 5. Thanks  Chip! It also smoothed things out a bit to enable "Sherline 1/2 pulse mode" in ports and pins.
I still have annoying resonance issues at mid speed, I guess the notorious "midband resonance." I'm using Keling drivers and steppers and BOB, the 640 OZ/inch motors and KL-6050 driver on x and y, with the KL-8078 on Z.
 It's not really a problem on Z, where it midband, expresses itself dramatically. With its 2 mm lead, it runs very smoothly from 1-38 IPM or so, and then stalls completely up to about 50, then smooth at higher speeds,  but I"d not want to go faster than 50 anyway on Z, and a reliable 35 IPM is actually fine speed, even for the joint cutting work with router horizontal I'll be doing.
On X, with its 20 mm lead, I get best results microstepping to 1/16 th, and then it runs smoothly up to about 60 inches minute, and smoothly again at about 90, and can go to 300 IPM fine, even at 1/16th mictrostep.
Y, with a .5 lead two start "no name" screw with a little roughness in the screw in a couple spots is good to about 18 IPM, and then bad to about 35 IPM, really atrocious in the middle of that range. Then it runs better, smoothing out beautifully at about 50, and can go to at least 120 IPM, far faster than I'd expect to use it. A little  more experimenting with settings, trying switching the drivers on Y and Z, to se if that helps quiet the Y at its resonant speeds. This is amzing stuff-- not exactly intuitive, is it?

2

General Mach Discussion / Re: general problems with mach3

« on: May 23, 2008, 07:33:12 AM »

Thanks, I'll try that when I get scew back together. I do have those set at 0 and noticed yestrday that might not be correct. A little paragraph in Mach set up I had overlooked. Tried a couple other settings to no avail, but not 5,5.

3

General Mach Discussion / Re: general problems with mach3

« on: May 22, 2008, 11:37:45 PM »

Thanks for all the suggestions. I think I have determined that my problem is mechanical, probably related to ball screw. The screw is driven by a direct Oldham style coupling. It's aligned well, and feels smooth by hand, but grumbles when stepper driven. I  did some manual screw mapping, with power off, turning the motor by hand, referencing to a mark in the motor shaft and "dial".   My lead is very close to its stated 20mm. Turning it 30 revolutions by hand and measuring the resulting 23.6 odd inches of travel with a steel rule gave me a number a few thousandths of an inch shy of 20 mm. So the step number I've been using to get very close to the travel I'm asking for is apparently inflated to compensate for the missing steps, which you all probably knew all along. I'm still learning here. I am amazed at the machines ability to miss steps in such a nearly consistant manner.
I then switched drivers on x and the perfectly performing z, which have different drivers. Same results though, making me think perhaps x stepper was the problem. I switched steppers, and same results. So I"m left to conclude that despite the smooth feel to me, the ball screw is causing missing steps.I should say that in motor tuning the axis sounds horrible, especially at very slow speeds. The smoothest travel came from using high microstep values, 1/25 or 1/32, but it's still usually a bit grumbly, and in consistant in its smoothness, which I guess is a clue. It's weird, because it feels smooth when turned by hand. 
I"m going to disassemble and clean the ball nut, and I might have some issues with its bearings...a long story.
As for accuracy of high lead screw, this machine is to be used for woodworking, so accuracy to within a couple thousandths would be fine.  The screw is a high quality THK four start, 20 mm diameter, 20 mm lead.Do I need to use a pulley and belt arrangement, gearing things down to achieve that?

4

General Mach Discussion / Re: general problems with mach3

« on: May 22, 2008, 01:38:33 PM »

Thanks Sid. I initially calibrated the screw by using the math method outlined in Mach setup, basing it on it being in THK catalog as 20 mm lead screw. I did same process for Z axis, a 2 mm lead, and it works fine. The x being "close" I didn't notice any problem until I ran a parts program. Then it seems like if I finish the parts program, leaving the part in place, and simply ran it again, it didn't line up perfectly. Close, but maybe 1/64 off, more at the end of the program than beginning. That presents a   big problem for running a second program with a finish pass.Using Vcarve Pro for CAM.
 So I rechecked, by zeroing the X axis, issuing G0X0, G0X24 commands, measuring and marking the results. That's when I saw I was way off, getting something like 23.32" of travel rather than 24. I did this several times with results identical to my steel ruler and 49 year old vision. So I did a math conversion based on the units I used for motor config, and reran it, doing this several times with smaller and smaller adjustments until I had what seemed like perfect repeatable 24" travel. But a day later, without having ran any more parts, it was different. Now if it were simply a problem of the wrong number of units for motor config, the axis would go precisely to a  specific spot for the G0x24 command, and precisely back to 0 for the G0X0 after, repeatably with perfect precision, if I wasn't losing steps, right? But what I"m seeing is it goes as close as I can measure to 24" of travel each time, but if I run it a dozen times (g0x0, G0X24) the points it goes to start to drift  a tiny bit, and then a larger bit,  in one direction, both points being off in the same direction, still very close to 24" apart. This means missed steps, right? I've checked the axis by decoupling the motor and it seems very smooth to me. Decoupled, you can actually push the whole router-Z -axis-assembly along the X axis rather easily, and if feels good. My machine is fixed gantry, moving Y axis  table.
 Since I used a different driver for the Z axis, maybe I should try attaching the z axis  that and see if I get similar problem. Or simply try different microstep settings. I"m running it at 1/25th.  I put it higher than I would have for my resolution needs (woodworking) because it (X axis) was very grumbly at lower microstep settings at lower speeds. Is this a clue to my problem?

5

General Mach Discussion / Re: general problems with mach3

« on: May 21, 2008, 11:19:28 PM »

My problem is best described by the inconsistant results I"m getting issuing jog commands. If I can't tell my x axis to travel a certain amount and get that amount, I"m nowhere. I'll be getting consistant results, and then check it awhile later (perhaps after simply restarting the PC) and the  results will be different. So I"m having trouble figuring out what's incorrect screw mapping, and what's missed steps. Can someone tell me  an ironclad test for this? My x axis seems well-aligned with smooth screw action. I"m microstepping 1/25th to make up for coarse screw, --  20mm lead. I think I really need someone knowledagable to take a look, because I"m running out of ideas.

6

General Mach Discussion / Re: general problems with mach3

« on: May 21, 2008, 07:50:51 PM »

I'm using Keling drivers and steppers and BOB (C-10), the 640 OZ/inch motors and KL-6050 driver on x and y, with the KL-8078 on Z. Mach has never crashed on me, although the software limits have seemed to go funky requiring a restart to clear once.
I guess it seems more likely to be electronic than mechanical. If it were mechanical, then somehow the effective lead of the screw was changing every so often, but was very stable until changed again, or at least stable for awhile. That doesn't seem possible.I'm running the axis way slower than its capable of, jogging it at around 100 IPM, when it runs smoothly at up to arround 300, at least -- (with a 31" travel there's not much use for high speeds). I am stepping at 1/25th microstep, because it's such a coarse lead (20 mm). Now noise, which I have no real understanding of, seems more likely. It's as if the pulse rate is slowly, or periodically changing by some definite percentage of the expected rate, around 2 or 3 percent. I did use sheilded cable for limit and home switches and for steppers though, and the x axis stepper doesn't run in a cable carrier at all. Any suggestions on how to diagnose "noise' issues? If it were lost steps, again, I don't see how I could get consistant results at times. Lost steps is more random, right? My profile tool paths meet up nicely, and I can send out a dozen sets of GOX0, GOX21, commands, and it gives perfect results on both ends. And then hours later, they're way off. I'll check my other axises. The Y has a funky used ball screw I'm replacing anyway, but Z is very nice fine pitch ball screw.
     


 

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7

General Mach Discussion / general problems with mach3

« on: May 21, 2008, 05:45:06 PM »

I"m having massive problems with my new shop built CNC. I'm getting inconsistant results from day to day, hour to hour. I "discoverered" yesterday that my x axis screw, (a THK 20 MM d. 20 MM lead, four start, bought used in apparently good shape) was apparently mapped incorrectly, as determined by measuring a 24" run called for in MIDI screen. I had assumed it was in fact a 20 mm lead, as labeled. It appeared to be off by alot --about 2.7 percent. I did the math, adjusted the steps in motor tuning, tested it a dozen times with good results, and figured I had solved some mysterious issues i was having. Ran my first set of parts, with lousy results. Tool paths seemed inconsistant -a second program for a finish pass calced from same drawing didn't match up, and I was left pretty confused. All individual tool paths were fine, producing the desired size pocket. The problem was in initial referencing. I rereferenced beween programs, which may have been a mistake, but I should be able to do that, right? Today I checked the x axis again, and results were again way off -this time in the other direction, and I got it back to going the distance asked for by undoing most , but not all ,of the change I made yesterday. So now it seems I've had three different values work, and I"m sure this will stop working as well.
Another issue is that the reff X axis behaviour changes radically with speed settings of the axis. At higher speeds (200 IPM) it doesn't do its return trip -just clicks off and stops, at what would be an obviously very different position than if it were traveling slower. This I"ve found to be related to trying a higher debounce setting, which I did because my limit switches were tripping at moments of high resistance to the cutter.
Could I have a corrupted version of MAch (it came on a refurbished PC sold by an Ebay CNC stuff vender). Could the PC itself be the problem? I'm so frustrated and confused, and I have no experience with this stuff beyond the misery I've put myself through these past couple months trying to build a functional machine.
If anyone who is expert in these issues lives near Greenfield , Massacusetts, (I"m actually a few minutes away from there, in Colrain, I"d be happy to pay for a consultation to try to figure out my problems. I'm a full time woodworker, and all other work has ceased as I"m consumed with getting this beast producing for me. Thanks!