Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: FP on February 27, 2009, 03:51:54 PM

Title: table coordinates wrong
Post by: FP on February 27, 2009, 03:51:54 PM
Hi. I was just sitting through the first two mach video tutorials, and got to the point where I was ready to set up the Homing/Limits fields for our ROMAXX machine. We have mach in metric, and the bed is 289 x 610. We don't have limit or home switches, so I've linked the machine coordinates to the work coordinates -- I thought that then at the start of a session the machine could be zero'd to the corner, and an offset could be used to position the work piece. When I toggle display mode into table view, this gives an out line that looks more or less correct. However, when I began using the offsets to try to position a job, the units seem to be massively off: the coordinates to get the work piece up to the opposite corner are 7 000, 15 000!

Relevant screenshots are attached.

Any insight would be appreciated


ps -- sorry if this message showns up more than once in the forums. I'm having weird problems and can't tell if it's uploading or not.
Title: Re: table coordinates wrong
Post by: Hood on February 27, 2009, 04:11:37 PM
If you zero the X DRO and command a 100mm move does it move 100mm?
You seem to have your X as the shortest axis, is that correct? Normally you would have X as longest and Y as shortest but I suppose that will depend on your own personal taste and where your controls are positioned when using a router.
Title: Re: table coordinates wrong
Post by: jimpinder on February 28, 2009, 05:59:31 AM
Machine Co-ordinates are used by the machine to keep track or where it is. They are of little vlaue to we mere mortals, becasue they are just numbers. As the machine moves, it adds to these co-ordinates, offsets, tool lengths etc etc. It seems to know what it is doing - but not I.

If you say that you do not have homing switches, but you want to home, then, you have in fact home swithces. It is just that yours are manual, not automatic. I assume you must have some stop block or similar that you run up to, so that you know your position is correct. It you then "Ref All Home" because your switches are deactivated, the machine code readings will go to 0,0,0. This is "home"

Press the Machine Co-ords button, so the led goes out, and zero the axis. You are now zeroing the "Program Co-ordinates" This is the one by which we keep track of the program as it moves through.

I do not understand what you mean when you say that you have tied the machine coordinates to the Program Co-ordinates. They will not tie.You can, as just described, have them co-incidental, i.e. there is no offset between them, but they are not tied.

If you now jog your machine to the start position of your program, and type in the MDI line G54, and then zero your Program Co-ordinates display, then if you check the Machine Co-ordinates, this has not changed. If you check the fixtures list, you will find that G54 has changed to relect the new offset between the two sets of DRO's.

As far as I know, the tool display shows your program in  Program Co-ordinates, and if you are starting at 0,0,0 then the display will have the toolpath outlined round it.

The process of  writing a program is  such that you write the program from a 0.0.0 position convenient to the program, not the machine. If you write the program and run it into Mach 3, it will give you the maximum and minimum values of each axis, so you can check if it is too large for the table. If, for example, you then cut a square of paper to those maximum and minimum values , and lay it on your table in the most convenient position, with the 0.0.0 psoition clearly marked, all you have to do is home your machine (by whatever means), jog the machine to the 0.0.0 point of your program, and set an offset,

To do this , you simply type in the offset number you wish to use,e.g. G56 then zero the Program Co-ordinates DRO. If you check G56 fixture you will find it reflects the offset from your Machine 0.0.0 position.

If you add  G56 , followed by G0 X0 Y0 to the beginning of your program then :-

If you "home your machine" and run the program, the first thing it will do is move to the 0.0.0 position of the program.
Obviously, if you fit in a block or something to poisition your workpiece to, then, the program is repeatable and accurate.