z axis losing position and plows into fixture...help

[Runner4404spd]

i made most of the fixture this morning and everything worked just fine. i was able to rough at various levels and came back to do a finish pass and the part came out great but a little small on the diameter. so i decided to create a finishing cycle with my cam program (onecnc btw) and here is the code it spit out. as far as i can tell the code is fine. for some reason it will do the first rough at .250 deep, which is correct. then it decides to plow into the material at the bottom of the hole to .800 deep. well this just ruined the first hole in the fixture. when i back the tool up and out and retouch it off, the tool is .300 lower than expected. ok, no problem maybe the touch off was off, then i went and ran the first hole again. it again wanted to plow to .800 deep. pulled it out and retouched off the tool again...again .300 low. rehomed the machine and retouched off the tool. now its .600 high and retouched off to the exact first number i ahd before to within .0002.

any idea whats going on here? i find it strange that it ran everything else just fine and the first set of programs i ran on it. now one thing i didn't mention yet is that the initial roughing steps were .1 this last time the steps were .250 deep. also to if it was a feed back or noise issue then i would assume it would show up everywhere no just on the second move.


N90 G49
N100 G17 G40
N110 G49
N120 G17 G40
N130 G20
N140 G80
N150 G90
N160 G98
N170 (0.37INCH END MILL)
N180 T1 M06
N190 S950
N200 M08
N210 G43 H1 D1
N220 G00 X0.67 Y0.4875 Z0.5
N230 Z0.1
N240 G01 Z-0.25 F2.0 S950
N250 X0.867 Y0.4528 F4.0
N260 G03 X1.0987 Y0.615 R0.2
N270 X1.105 Y0.6875 R0.4175
N280 X0.27 Y0.6875 R0.4175
N290 X1.0987 Y0.615 R0.4175
N300 X1.1017 Y0.6497 R0.2
N310 X0.9364 Y0.8467 R0.2
N320 G01 X0.7395 Y0.8814
N330 Z0.1
N340 G00 Z0.5
N350 X0.67 Y0.4875
N360 Z-0.15
N370 G01 Z-0.5 F2.0
N380 X0.867 Y0.4528 F4.0
N390 G03 X1.0987 Y0.615 R0.2
N400 X1.105 Y0.6875 R0.4175
N410 X0.27 Y0.6875 R0.4175
N420 X1.0987 Y0.615 R0.4175
N430 X1.1017 Y0.6497 R0.2
N440 X0.9364 Y0.8467 R0.2
N450 G01 X0.7395 Y0.8814
N460 Z-0.15
N470 G00 Z0.5
N480 X0.67 Y0.4875
N490 Z-0.175
N500 G01 Z-0.525 F2.0
N510 X0.867 Y0.4528 F4.0
N520 G03 X1.0987 Y0.615 R0.2
N530 X1.105 Y0.6875 R0.4175
N540 X0.27 Y0.6875 R0.4175
N550 X1.0987 Y0.615 R0.4175
N560 X1.1017 Y0.6497 R0.2
N570 X0.9364 Y0.8467 R0.2
N580 G01 X0.7395 Y0.8814
N590 Z-0.175
N600 G00 Z0.5
N610 X0.6749 Y0.4866
N620 Z-0.175
N630 G01 Z-0.525 F2.0
N640 X0.8719 Y0.4519 F4.0
N650 G03 X1.1036 Y0.6141 R0.2
N660 X1.11 Y0.6875 R0.4225
N670 X0.265 Y0.6875 R0.4225
N680 X1.1036 Y0.6141 R0.4225
N690 X1.11 Y0.6875 R0.4225
N700 X0.4415 Y1.031 R0.4225
N710 X0.3579 Y0.8684 R0.2
N720 X0.3953 Y0.7519 R0.2
N730 G01 X0.5118 Y0.5893
N740 Z-0.175
N750 G00 Z0.5
N760 (END TOOL)
N770 M5
N780 M09
N790 M25
N800 M30
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[Cruiser]

First i'd suggest checking all the pertinant wire connectors that you can, then, I've found that the slide on connector blocks which slide onto the driver pins of the gecko can become troublesome if they have been R&R'd many times. I found out this one by changing the block as it was the only untested part of my system and found that the problem changed to another circuit. If this is it then it could be an easy fix. Another possibility would be if there is any way that coolant can get to your encoder, This ended up being my primary issue and till i found the leak it cost me three encoders. It could be as simple as over amping the drive on a bind which would cause a mommentary fault and mach keeps going but drive stops servo for a string of pulses then it goes again. I had this problem on my "Z" before i did my major re-do but you know that story. Another possibility would be some mechanical slippage somewhere in the mechanics. I would start by trying to induce the problem, and then do some simple mods like gib tension, another shot of oil, etc. to get an understanding of what and why ! If your using the servo from IH and the currant limiter on driver is reduced then it could be that simple. It could possibly be overtaxing the pc, i had that happen once too. But that ended up being more dramatic as the machine started traveling off to oblivion till i tapped the panic button. Make some simple changes to motor accel rate and test it to see if you can induce it and go from there. If you have the full kit from IH then give them a call this morn and I'm sure they will have more sugestions to check. My memmory isn't doing too well lately.

[Runner4404spd]

cruiser your right. the mill was losing position with an up rapid move in z, i changed this from a g) to a g01 and all is good. now in reality how do i prevent a similar thing from happening in the future. basically how do i idiot proof this so it never happens again. what worries me is that i bought a servo driven system so this kind of lost step wouldn't happen as i expected the drive to fault. any thoughts on this?

[SCzEngrgGroup]

cruiser your right. the mill was losing position with an up rapid move in z, i changed this from a g) to a g01 and all is good. now in reality how do i prevent a similar thing from happening in the future. basically how do i idiot proof this so it never happens again. what worries me is that i bought a servo driven system so this kind of lost step wouldn't happen as i expected the drive to fault. any thoughts on this?

That suggest perhaps you have the gibs too tight, or not enough lube on the Z ways? Have you checked your power supply voltage under load? Perhaps a faulty axis drive that is not reaching full current?

Regards,
Ray L.

[Cruiser]

Runner, I don't think of it as loosing steps, I think it is different ! Anyway, If you were able to watch the driver you would see the fault light go bright. Mine does it if I tune it too high in acceleration and velocity. It is the servo drawing too many amps for the driver so the driver faults out till the amps fall back. First, check that the current limiter is full right on the gecko & using the motor tuning settings, reduce velocity 5 points at a time till it will rapid at that rate without faulting, then consider, Is this going to be the limit or is something dragging to make the load higher than it needs to be. I don't know for sure if tuning in too tight will effect it or not, but gib too tight will. The servo is powerful but is limited to some extent by the drivers limit so you may need to just leave it at the reduced settings. I must reduce mine from 130 peak to about 110 or it will amp out and stall. My gib is just barely at zero lash but I don't rely on it now with the rail system. I have the biggest power supply that Aaron had with gecko 320 and that hefty custom servo IH still uses. But the gecko still only passes 20 amps max. The only fix I know of is to reduce velocity till it doesn't fault, keep the slide oily. OH, I did one other thing to help reduce friction. I rubbed Molly lube on slide and dove's till it was stained real good with the molly but didn't leave grease behind. Grease will hold grit and allow it to pull into friction zone. I still use lots of oil, but the molly stain / film helps ! I have two types of molly grease and the assembly lube is most content of molly i know of, I also have pure molybdenum disulfide (molly !) powder and it loves to work with cast iron, and it is really slick, and it likes to be rubbed into clean cast iron and other porous metals. I just checked my motor settings @ velocity 120 and acceleration 7 for "Z" and 9 for "X & Y" setting too high does no good what so ever ! Note ! most of the time when i talk of acceleration I am referring to velocity ! I have to go look to refresh my "OH YEA" I hope some of this helps ya out, now after all this rambling i need another cup o JO

[BobWarfield]

So the servo faults (e.g. the driver fault light goes bright) but Mach keeps going?

I assume the driver resets because you've tied Enc+ or similar to Err/Res? Because otherwise, it ought to just stop when it faults even if Mach keeps going, no?

You can set things up pretty easily to stop on a fault. That's the way I prefer it. There is a nice manual circuit in the G320 documentation that's easy to set up. Alternatively, you can buy the C17 "Master Control Board" from CNC4PC. The latter is what I'm using. It takes the servo Err/Res, E-Stop, and any limit switches (if you have them), as well as the Charge Pump and manages all of that. If any flips it stops the machine (actually it opens a really connected to your DC power supply and sends a signal to Mach 3 to stop it) and lights an LED telling you what happened.

Pretty cool little board.

With Err/Res tied to Enc+ and a long program, the servos are going to just wake up when the fault clears and the g-code will pick up wherever it happens to be. Scary!

Best,

BW

[Runner4404spd]

yeah, after seeing this i may have to rewire the err circuit and adapt to the board. i had a gerc (gecko error reset controller) board for one of my other projects so i will look into that one plus the one you mentioned bob.

this is something that definitely needs to be fixed. after looking over both boards i remember why i had left it out. neither board supports a shared switch for homing. i would need to add individual home switches i think and i didn't want to mess with the IH kit i bought. i guess i could hook one side up to this board and leave the other switches tied into the parallel card but that seems rather silly. ultimately i guess i would gain one input?

[Cruiser]

I've heard of the board and the way I see it is this. If you push the limits then the board is going to stop ya for as long as your trying to push the limits. If you set things up correctly or within the limits of the weakest link then you don't need the board ! I've got some cnc4pc boards that I'm going to off load if your interested. I have a combo board, power supply, and old style speed control board. Every time I try to incorporate the neat boards I end up with one more to off load ! Aaron told me time and time again that the kiss principal was the only way to go and All I have managed to do so far is to prove him right time after time after time ! So, What offers do I get for my collection of boards ?

[BobWarfield]

Cruiser, I'm an engineer, so my job is to over engineer!

Seriously though, it's a bad thing to have the servos fall out of fault and just keep going at some random g-code place. You gotta watch the mo-chine carefully if that's a possibility. I'd be off doing something else and then I'd hear that horrible noise and everything would start to move in slow motion like those Peter Sellers movies.

Nooooooooooooooooooooooooooooooooooooooooooooooooo oooooooo!!!!!!

Cheers,

BW

[Cruiser]

Bob, Doctors never treat themselvs and engineers Well you know ! I am a grease monkey, mechanic, & machinist and I have spent my life on the floor. First, You should know if a motor can draw in excess that it will, and if the adjustment creates the situation then the adjustments can prevent them ! So, Since the motor will over draw the limit of the driver, with incorrect adjustments, then, we set the adjustments up so it can't ! If you put in the board you STILL must make the proper adjustments or you won't get anywhere board or not ! Now if you want to invent another board to sense when the first one reads a fault and shuts down mach to re set the machine and then well maybe another board is needed to keep track of mach so it knows where it will need to restart from then hum, may need another board to keep track of all of them so ...... Bob, you better get busy, lots of boards needed here ! KISS stands for Keep It Simple Stupid !

[BobWarfield]

But Cruiser, you're a pro machinist: how come the pro machines have the boards to stop the controller on a servo fault?

Just so they can charge more? Maybe there are other reasons servos fault besides a too-small power supply. It isn't just about incorrect adjustments. Maybe something else unexpected happened. Whatever it was, I just don't like my machine jumping to some random spot in the g-code and heading out!

Being able to stop on a servo fault is a good thing, boards or not. Just like those little diodes in your limit switch wiring, they gotta be there if you want things to work right. KISS is great. Things should be as simple as possible to do the job--but no simpler!

BTW, what's the weather doing in Aspen these days? I bet it's nice.

Nice here in CA too, but boy you are right, I gotta get busy on a buncha stuff!

Cheers,

BW

[Cruiser]

Bob, I was trying my hand at funny, but I'm not a comedian ! And I'm tired and crazy with boards ! My biggest problem all along was trying to blend boards into the system to do a job. Yesterday I took off some boards and went back to basics. It seems that the inevitable ground loop or ground fault is always present. Its true the board may help. but its also true that with proper adjustment and tuning it is not needed. I was trying to think of what may cause a similar problem to occur but can't, not to say that it can't happen, so, the board may have credence after all. I won't have one tho !
Now to change the subject ! OK ? Bob is your machine about to make chips ? How did the stand end up looking ? I recall a pic of some welding going on but that was yrs ago and nothing since ! I'm tired of problem and trouble whacking and would rather enjoy a moment of leisure !
Runner, what does that bore look like now ? Is it round yet ? What ya using to measure it with, calipers, telescope & mic, bore gauge, ID mic ?

[Runner4404spd]

ok, well heres an update... my bores in the fixture are still not round. and i'm using a dial bore gauge to measure. also as the holes progress down the plate they get worse out of round. on the first few holes i get a bore thats 0.869 x 0.868 which is fine, i can deal with .001 tolerance on a hole in steel plate. i assume this should be tighter and i assume the mill is capable of better its just my lack of experience with tuning i'm guessing. what i don't get is why they get worse. and the bore get worse in the x. th final holes as 0.868 in the y and 0.864 in the x. this to me makes no sense unless my damping is set to high on the x axis drive. still looking for suggestions. i would like to get this working right but i do have another mill coming since i don't have the time to futz with this any longer. i bought a fadal 3016 at a going out of business sale for $10,500.

[oltimer]

runner
congrats on the new mill. just 1 suggestion after reading all your post, weld the control panel shut on all 4 sides. just kidding, time for little bit of humor, sometimes it helps.
oltimer

[BobWarfield]

Interesting.

FWIW, I have read several interesting tips to improve on this over on PM. For example, some folks grind a relief in the endmill so that it only cuts down at the bottom 1/2" or so of the cutter. This is useful for deeper holes. You say you are cutting plate, so I assume not too deep.

Of course, if you really need to be accurate, you interpolate and then clean up the hole with a boring head.

But when you say the error gets worse, are you saying it is worse as you move the x-axis making the same hole in a row? So that the first hole is good to a thou and each successive hole is a little worse?

That latter could be a few things. Perhaps the steps per inch is very slightly off and the further you move from the zero point the more it is felt. I suppose a worse case would be that the ballscrew is a tad off. Mach3 lets you remap the screw to improve that.

Congrats on the VMC!

Best,

BW

[Runner4404spd]

i got the screws in the IH kit i bought so i don't think its them. and yes the error gets bigger as the position moves further but only on the x. i have a plate with two rows of holes. i have drilled out the hole first with a .281 drill bit then a .625 drill bit and now i'm circular interpolating them to get an interference fit for a pin to fit in. the pins are .870 in diameter. so ultimately for what i'm doing right now being +/-.001 would be ok. the pins get pushed in then bolted in from the bottom.

my final step tonight is make a bunch of 2.00 inch blanks and then i will circular interpolate the hole in this until it cuts a true circle while adjusting my damp and gain. ultimately maybe i'm being too picky, has anyone else cut holes like this on their home made cnc with better results?

[SCzEngrgGroup]

i got the screws in the IH kit i bought so i don't think its them. and yes the error gets bigger as the position moves further but only on the x. i have a plate with two rows of holes. i have drilled out the hole first with a .281 drill bit then a .625 drill bit and now i'm circular interpolating them to get an interference fit for a pin to fit in. the pins are .870 in diameter. so ultimately for what i'm doing right now being +/-.001 would be ok. the pins get pushed in then bolted in from the bottom.

my final step tonight is make a bunch of 2.00 inch blanks and then i will circular interpolate the hole in this until it cuts a true circle while adjusting my damp and gain. ultimately maybe i'm being too picky, has anyone else cut holes like this on their home made cnc with better results?

How deep are these holes? How heavy a cut are you taking? Are you doing a couple of "spring passes" to finish up? What type of endmill (diameter, flutes, material, flute length, etc.)? Is your Z axis quill drive or head?

Regards,
Ray L.

[Runner4404spd]

holes are .525 deep. i am taking .125 deep cuts witha 1/2 inch end mill. i stepped this up once already from 3/8 and this time i predrilled the holes. i am taking a finish pass and it doesn't seem to help. these are the dimensions after the finish pass. so again this leads me to believe there is something wrong with the tuning of the servo drives or atleast the x axis isn't were it should be yet.

[SCzEngrgGroup]

holes are .525 deep. i am taking .125 deep cuts witha 1/2 inch end mill. i stepped this up once already from 3/8 and this time i predrilled the holes. i am taking a finish pass and it doesn't seem to help. these are the dimensions after the finish pass. so again this leads me to believe there is something wrong with the tuning of the servo drives or atleast the x axis isn't were it should be yet.

At low speed, the servo tuning shouldn't make much difference, unless the I term is not working. These are Geckos, right? If you do the finish pass 2-3 times does it get any better?

Regards,
Ray L.

[BobWarfield]

What you describe, where the error only affects X and is off by more the more you move in X, makes me think the steps per inch value is not quite right on Mach3.

I don't know what it is supposed to be on your machine, but you can check it pretty easily:

Put a precision pin in a collet chuck (or other holder) in your mill spindle. You could even use an endmill so long as the smooth part of the shank is available to you.

Clamp a similar pin vertically in your mill vise.

Jog the two pins fairly close together.

Measure the distance between them with a digital caliper or micrometer--whatever you are comfortable with that will register well enough accuracy wise.

Zero the X.

Jog the pins apart some distance, jogging only in X.

Compare the DRO on Mach3 with your measured distance between the pins.

Did the mill move the commanded distance or not?

If it did, this isn't your problem. If it didn't, you can calculate how much to change the steps per inch by based on how much things are off. Change it and recheck.

The larger the distance you jog between zeroing and measuring, the bigger the error should be if this is your problem.

This one is at least easy to check and fix. Hopefully this will take care of your problem.

Cheers,

BW