Author Topic: Bugs in Mach 3.42.015  (Read 22137 times)

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Offline HimyKabibble

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Re: Bugs in Mach 3.42.015
« Reply #70 on: November 12, 2008, 11:02:57 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.







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.
Regards,
Ray L.

Offline RICH

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Re: Bugs in Mach 3.42.015
« Reply #71 on: November 12, 2008, 01:39:43 PM »
In latest developement version .018 /.017 something still seems wrong in the the extrema for the mill.
See swaftboy's  post "Program Calculation Extrema Error".
RICH

Offline simpson36

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Re: Bugs in Mach 3.42.015
« Reply #72 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.
Quote

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.

Offline HimyKabibble

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Re: Bugs in Mach 3.42.015
« Reply #73 on: November 14, 2008, 10:58:46 AM »
There is no contradiction.  AFAIK, the *only* way to zero machine coordinates is through a homing operation, which means switches that tell Mach where "home" is.  Your question was "why not have multiple sets of home switches", and I indicated that you could, but it would be silly.  The first statement still stands, AFAIK, and I think that has been confirmed by others on here already.

Regards,
Ray L.
Regards,
Ray L.

Offline Hood

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Re: Bugs in Mach 3.42.015
« Reply #74 on: November 14, 2008, 11:20:52 AM »
You can set the machine coords to zero if do NOT have home switches enabled, as said previously this is a handy thing for me as on the lathe I do the homing within the servo drives as it is deadly accurate, always exact, well as exact as I can measure (0,001mm).
 The OP has failed to say why he needs to set the machine coords to zero at positions other than machine  zero, also he has failed to say how he is doing it. Brian said that
Quote
there is NO SetMachZero()  call. in VB.. there is an OEM button
and as far as I see the OP is trying to do it via VB from within a button.
 If he wants to zero the machine coords at any point other than machine zero then the best thing to do is disable the home switches and then it can be done. I dont see why he doesnt want to do this as what is the point of having home switches if you deliberately set your machine coords to  zero other than at the machines actual zero position. There may be a good reason but after asking, and also someone else asking he has not said why.

Hood

Offline simpson36

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Re: Bugs in Mach 3.42.015
« Reply #75 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.




Offline Hood

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Re: Bugs in Mach 3.42.015
« Reply #76 on: November 15, 2008, 07:04:01 AM »
Simpson
 No need to home to the extent of your axis, you can have a home switch positioned at any location on an axis, you then set a Home Off distance in Homing and Limits which then tells Mach where the actual machine zero position is for that axis. As an example the X on my lathe is positioned so that both front post and rear turret are at an equal distance from the spindle centre, I have a home off distance set so that when I home with the master tool the X axis DRO is set to the distance it is away from spindle centre (X zero on a Lathe)

On the subject of servos and homing, you need to have servo drives that are capable of doing internal homing, drives like Geckos, Tek10's, Rutex etc dont have that functionality. Greg is considering making this a feature of the SmoothStepper but that will only be when he has time so may not be for a while.

Hood

Offline HimyKabibble

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Re: Bugs in Mach 3.42.015
« Reply #77 on: November 15, 2008, 10:10:07 AM »
Simpson,

    Having the home switches in the middle of travel is quite common - you can put them anywhere you like.  In fact, I'm adding optical limit switches to my machine, and may decide to put home in the middle of the table, for the reason you suggest (although Z pretty much HAS to have home in the full up position for, I think, obvious reasons....).  It was the idea of having multiple home switches that seemed a little silly to me, and suggested that the OP didn't understand the purpose of the home switches, nor the function of work offsets.  When you have multiple sets of home switches, they're really no long home switches.  And even on a large machine, I can't imagine the time saved to be worth the problems all the added switches and wiring will create.

Regards,
Ray L.
Regards,
Ray L.

Offline Hood

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Re: Bugs in Mach 3.42.015
« Reply #78 on: November 15, 2008, 10:43:37 AM »
Ray
 couple of things, first if your z is relatively out of the way such as on a manual  bridgeport you can use an optical without any coolant protection, I did that on my first conversion (manual bridgeport) What I did  was have the signal interupted by a piece of steel with two slots in it, one top other bottom. Now if you did that for a home switch then you could have it so that the slot is any desired location of the travel, in fact you could have it so that it is open from your desird position up the way (or down) and write a bit of VB to go in the Ref All button. It would look at the home input from the Z and see if its active or not, if its active then it would move off first so tht its inactive then reverse and start the homing procedure. That is the way my servo drives do their homing, its a great idea as it means you dont have to make sure you are at the correct side of the switch before you do the homing.

hood

Offline HimyKabibble

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Re: Bugs in Mach 3.42.015
« Reply #79 on: November 15, 2008, 11:17:09 AM »
Ray
 couple of things, first if your z is relatively out of the way such as on a manual  bridgeport you can use an optical without any coolant protection, I did that on my first conversion (manual bridgeport) What I did  was have the signal interupted by a piece of steel with two slots in it, one top other bottom. Now if you did that for a home switch then you could have it so that the slot is any desired location of the travel, in fact you could have it so that it is open from your desird position up the way (or down) and write a bit of VB to go in the Ref All button. It would look at the home input from the Z and see if its active or not, if its active then it would move off first so tht its inactive then reverse and start the homing procedure. That is the way my servo drives do their homing, its a great idea as it means you dont have to make sure you are at the correct side of the switch before you do the homing.

hood

Hood,

    That's a good idea!  BTW - On a (loosely) related topic - What precautions, if any, are normally taken to prevent machine damage in the case of a servo runaway.  I'm wondering if I should provide hard limit switches a bit inboard of the physical end of travel, to prevent the table from running full-speed into the end of travel.  (One of the places steppers have an edge - runaways can't happen....)

Regards,
Ray L.
Regards,
Ray L.