Messages

1351

General Mach Discussion / Re: Bugs in Mach 3.42.015

« on: November 15, 2008, 05:54:19 AM »

Hood,

Thanks for providing yet another excellent reason for using servo motors!  I am leaning that way for my next retrofit.

Ray,

Remeber that I am a newbee at this stuff, so I'm probably going to ask some stupid questions, and not understand some of the answers. Please don't take that as me being argumentitive. I appreciate your comments very much.

I dislike the homing operation. My modified Z axis is pretty tall (for a baby mill) and I almost never use the top of it, yet every home has to run the head all the way up while I wait impatiently. Same with the X axis. If the steppers loose steps for some reason, you go thru the whole process again.

Even though, as both myself and Hood pointed out, the OP has not explained his reasoning, I now have my own:

Yesterday I finished a preliminary run with my new 4th axis. It is a stepper powered spin index with a 5C 4" three jaw chuck. On the little baby X2, the rig takes up nearly half of the table. Yet to home, or re-home, I sit and wait for the whole rig to pass in front of me. It may be silly, but if I had to use that rig a lot, I would certainly consider setting up a set of limit switches that would eliminate the ride to the very end of the table, and only set zero at the beginning of the actual useable portion of the table.

I disabled my Z axis homing bacause I had to remove the limit switch to install my new Z axis ball screw. I probably won't reactivate it because  it is such a pain.

Incidentally, years ago I had a large Bridegport knee mill with a table that went on forever. That was not a CNC machine, but I can tell you that probably 90% of the time, I used only about 12 to 18" of the middle of the X travel. I can see an advantage to having homing based on that envelope and just turn off homing an reset manually on the rare occations when I needed the whole table.

1352

General Mach Discussion / Re: Bugs in Mach 3.42.015

« on: November 14, 2008, 08:00:40 AM »

1) You *can't* zero machine coordinates, other than through a homing operation. That's the whole crux of the issue.

2) You could do that, but it would be a little silly. That is exactly why we have work offsets. You tell the controller where machine zero is, and everything else is referenced to that. You don't *need* multiple machine zeros.

Regards,
Ray L.

Ray,

Am I missing something. Your first comment says you can't and then your second comment says you could.

That actually illuminates my point, which is as I said, I don't personally comprened the reason to do it, but if one wanted to do it, is it doable?

Personally, I have to agree with you on the logic of one master machine coordinate system and offsets, but the OP wasn't asking if his idea was a good one, he just wanted to know if it was doable.

My engineer brain just can't resist trying to solve a problem, even if the problem is hypothetical.

I was hoping for a comment on my macro idea. I don't know about MAch3's capabilities yet in that regard, but it certainly seems feasible to get rid of the .0013 error or whatever it was that was annoying the OP.

1353

General Mach Discussion / Re: random e stop error

« on: November 14, 2008, 07:45:41 AM »

Hood,

You didn't make that distinction in your post.

However, I mis-spoke. I didn't actually set the debouce up, I ran into the problem when I was playing around with MachTurn. The debounce was set to whatever the default is, I suppose, because I had never messed withit in MILL or in TURN.

I just noticed that the RPM would read to 350 and go no higher in TURN, yet it looked accurate in MILL, so I started comparing and experimenting. I just set both boxes to zero in TURN, and the RPM DRO started working right.

Thanks for the heads up, though. I'll see what I can find in the docs about the different debounce settings.

1354

General Mach Discussion / Re: Can someone explain the current draw of these stepper motors, please.

« on: November 14, 2008, 07:27:24 AM »

I read most of the stuff on the Gecko site. I am using 4 of the Gecko 203v drives.

Power is one consideration, certainly, but steppers cannot do tiny jogs accurately and I've been told on this forum that this is inherent in microstepping.

I have had problems with the steppers loosing steps. An interesting paradox of these el-cheapo asian machines (mine is the X2) is that the ways are so crappy and inaccurate that i find I have to run them fairly tight to have any chance of keeping some accuracy in the machine. Moving the tight tables, and especially the head, take more power than cutting the part.

The Y axis on this machine was a huge PIA to get working. If I set the gib for a nice sliding fit at one end of the travel, it would completely jam befor it could get toi the other end. If I set it for a sliding fit and the tight end, it would literally be clunking back and forth at the loose end.

I had a binding problem with the Y axis ball screw which turned out to also be caused by the bad machining on the X2.

You get what you pay for. I did not expect to get a fine accurate machine, and in manual use, it's actually an OK little brute. CNC really showcases the limitations though.


 

1355

General Mach Discussion / Re: random e stop error

« on: November 14, 2008, 07:12:53 AM »

FWIW, setting the debounce up makes my RPM reading completely inaccurate. I suppose the index signal has a problem with debounce.

I was getting random e-stops also and it drove me crazy for a while. It was metal chips getting on the exposed limit switch terminals. Covered them with heat shrink . . end of problem.

1356

General Mach Discussion / Re: Bugs in Mach 3.42.015

« on: November 12, 2008, 10:20:54 AM »

I had two thoughts about Swarf's issue.

Keep in mind, I am a newbee to CNC and also to MACH 3, so these may not be reasonable ideas . . .

First; my undestanding is that Swarf's button is running some sort of macro. If so, could not the macro reset the machine coords, then MOVE to zero and then reset again, all within the macro? It seems to me that would correct for the minute error in calculating the position and the second reset would be the true zero sought.

Second; is there any practical reason one could not have more than one set of limit swiitches? I do not comprehend the reason to re-zero the machine coordinates at different points, but assumming there is some usefull purpose to that, why could there not be additional limit switched installed for the different set-ups? So you would plug in set A for part A and when you were going to run part B, you just plug in (or switch to) limit switch set B and re-home the mill.

1357

General Mach Discussion / Re: Can someone explain the current draw of these stepper motors, please.

« on: November 12, 2008, 10:07:00 AM »

THX again, Ray

You have a way of using analogies to make things clear(er).

And thx for the link.

I did the retrofit on this little baby mill for a specific project. However, it turned out to be great fun. When that project is completed, I plan to sell the mill complete and go with a little larger mill (X3?) and do another retrofit using servo motors instead of steppers, so an in-depth study of steppers would probably not be benefitial other than as a point of interest.

Here again, I am no expert at this point, but servos seem to have a lot of advantages for not too much more money.

1358

General Mach Discussion / Re: Cannot do single point threading. What's wrong?

« on: November 11, 2008, 03:44:15 PM »

Joe,

Well, I see my use of the secret code word 'slot' successfully confused everyone . .LOL!!

I don't know what to call it, Joe and in my case it is actually a round hole in the disk,  . . . . BUT . . . , the Mach manual calls it a 'slot' so I assumed that was the convention.

 . . "When in Machville . . . ."

Interesting discussion, thanks all.

1359

General Mach Discussion / Re: Can someone explain the current draw of these stepper motors, please.

« on: November 11, 2008, 03:30:44 PM »

Lemo and Ray,

I am an ME and not relay good with electrons. I have some basic understanding of volt/amp/watt relationships and I understand how some common components; resistor, transistor, capacitor, diode, etc work.

One comment "the Gecko connects the motor to the power supply"  clicks. Would it be at all accurate to then consider a stepper controller as a 'smart relay' of sorts, or am I still in left field? I can see where a relay does not care what voltage is being passed thru it (so long as it is within the rating) as it s just a switch between the supply and the load.

I had it in mind that the Gecko itself was powering the stepper. Apparently this is not the case at all. I also get the pulsed DC effecting the ammeter.

Mysteriously, I also have an ammeter on the DC output of my PWM speed controller and it seems to read what I would expect. The controller is 5 amp continuous and has a limiter. The ammeter shows around 2 for normal operation and spikes to 6 when the motor is really stressing or is stalled. So . .  I'm still a little confused about that.

Why wouldn't the 120v DC PWM controller misread badly like the 36v DC Gecko input?  Output vs, input? Is it a frequency thing?

BTW, I have a little device called 'Kill-a-Watt' that measures AC draw, so I'll give that suggestion a try.

Thanks for the info and patience, guys. It's making more sense now . . . slowly.

1360

General Mach Discussion / Re: Cannot do single point threading. What's wrong?

« on: November 11, 2008, 02:50:44 PM »

Joe,

I don't have 'expectations' at this point. I'm just asking questions because I'm a newbee at this.

But I do my homework first. In my OP, I stated that the mill has an index on the spindle. That is what the software uses to determine the spindle speed and azimuth.

Ultimately, it turns out I was just chasing my tail as the feature is intentionally disabled.