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Author Topic: How do I tell Mach3 my CNC's table size?  (Read 19694 times)

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How do I tell Mach3 my CNC's table size?
« on: February 07, 2009, 08:56:23 PM »
Hi,

I have built my own CNC machine, and got it talking to mach3 ok. Now I need to figure out how to tell mach3 how big my cnc's table size is, and where 0,0 is?

I can import a file, but when I start the cycle the cnc is starting in a position where it will eventually hit the end stops during the cut.

Do I need to set limits or machine coords? Also I am exporting files from CorelDraw, so would that have an impact on the file exported. Probably a dumb question, but if I set the cnc table size in Corel, will mach 3 then use that as it's reference?

Thanks!

BTW here is the machine, as you can probably see, it's first output was the standard "Hello World". The LCD is a touch screen, and the controller boards are from http://www.routoutcnc.com/



Re: How do I tell Mach3 my CNC's table size?
« Reply #1 on: February 07, 2009, 09:09:26 PM »
All you need to do is position the machine where you want 0,0 to be, then clear the X and Y DROs by either typing in 0, or clicking on the Zero button next to each one.

Regards,
Ray L.
Regards,
Ray L.

Offline Hood

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Re: How do I tell Mach3 my CNC's table size?
« Reply #2 on: February 07, 2009, 09:12:45 PM »
If you dont have limits then just jog to a position on the table that would represent the X0Y0 and give you the largest cutting area then zero the DROS. What I mean by that is if you were cutting something and the X0Y0 in the code was slap bang in the middle then move your table to the middle and zero the DROs. If your code had the lower left corner as the X0Y0 then move the table to lower left and zero the DROs.
 If you wanted you could pretend you had Home switches and each time you started Mach you could jog to the lower left corner and press the RefAll button, that would set the machine coordinates as zero which in turn would mean you could set up softlimits which would allow you to see the table size on the toolpath display if you wished. You still need to set the offset position to zero to suit your code.

Hood
Re: How do I tell Mach3 my CNC's table size?
« Reply #3 on: February 07, 2009, 09:30:28 PM »
Thanks guys, that helps me out :-)

I do have home switches on all axis, but they need some tweeking as mach 3 can send the machine crashing past them! I have tested them in the diagnostics screen and they are triggering ok.

Ta.

Offline Hood

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Re: How do I tell Mach3 my CNC's table size?
« Reply #4 on: February 07, 2009, 09:34:04 PM »
Shouldnt do that, is it going past them on a Ref All move? If its just in a normal jog that Mach goes past them then that would be normal if you have them set as just home switches, if you had them set as limits as well then Mach should stop at them.
Hood
Re: How do I tell Mach3 my CNC's table size?
« Reply #5 on: February 07, 2009, 09:39:28 PM »
I will have another look at my home switch configs, and setup my soft limits.

Cheers.

Offline jimpinder

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Re: How do I tell Mach3 my CNC's table size?
« Reply #6 on: February 08, 2009, 05:21:00 AM »
I dont know whether it is time to go into the machine co-ordinates and program co-ordinates, but it ties in with your first question.

You have fitted switches - you don't say where - but I assume that these are combined limit and home switches. There is a difference. If they are acting as limit switches, then, once you have activated them, that should be that - the machine should go up to them and STOP (It has reached it's limit). So that is the first job. Get the switches active. Wire them up to LPTI (or your BOB) one at once, and configure them on Config/Ports and Pins/Inputs. When you have done this turn to the diagnostics page, and (leave the table out of the way) switch the switches manually. You should see the appropriate led light up. If it has already lit, then it is configuraed wrongly, and the active low/high needs changing. It you can't get it to light, then you must look to your BOB. I can't say any more, because a lot of Bobs invert the signal, and there are so many combinations, it is impossible to say, but the right combination of high or low common, low or hign input is there somewhere.

Once the limit switches are fitted, configured and working, then you should be able to jog round your table and when the switches are hit, the table will stop. If you tick Auto Limits on the settings page (or something like that - I am away from my machine at the moment so can't check the proper name) then this will allow you to back off the switch.

Home switches work differently, although they are (in many cases) the same switch. Here the machine will travel (at reduced speed) until it hits the switch. It will back off until the switch opens again, then stop again. The DROs will automatically set to 0 (if you have the homing page configured that way) - end of story - there is nothing else you can do with homing - and you will see from the page, the speed and directions can be specified, so you can home to the most convenient point for you. Mach 3 automatically alters the program when reading a switch as home or limit.

Here is the rub - because with homing you are joining the "big boys". Homing sets your machine co-ordinates to zero. Machine co-ordinates  are those by which the machine keeps track of its-self. You cannot alter them, other than to home the axis.

If you press the Machine Co-ordinates button, and the led is lit, then the DROs are displaying machine co-ordinates, if you press the button again and the light goes out, you are viewing program co-ordinates. Program co-ordinates are the method you use to keep track of the machine, because it refers to your program.

Home the machine and check the machine co-ordinates (0.0.0). Press the button and view the program co-ordinates. These may also be 0.0.0. If they are not, then zero them by pressing the zero buttons at the side of the display. Your two systems are now together.

If you now jog you table to where you want the 0.0.0 to be for the program you are running, and when you get there zero the program co-ordinates, then if you check, the machine co-ordinates have not changed. The values displayed on the machine coordinates DRO's are the offset of YOUR 0.0.0 position, to the MACHINE 0.0.0 position, and if you now look at "Config/Fixtures" you will see that G54 reflects this. There are 255 offset slots to use. G54 is the default. If you copy these to G55 or G56 then you have YOUR 0.0.0 referenced.

You can now try for real - home your machine - from anywhere. Type in G55, followed by G0 X0 Y0 Z0 and the machine should now go to where you wanted your 0.0.0 position to be.

If you include G55 at the beginning of any programs, if you "home" your machine, then run, it will always start from exactly the same place.You will see that with 255 slots to go at, your can start your programs from anywhere on your table.

Hood mentioned about telling Mach 3 the size of your table - yes you can set soft limits, which will prevent the machine exceeding these. However there is no way you can tell Mach3 you have a 10 x 12 table or whatever. Mach 3 reads your program, and draws the limits on your toolpath display from your program, therefore you need to keep your program inside the limits. I can see, from your picture that you obviously have limits, from theconstruction of your machine, I on the other hand, can overlap my table, therefore the size is irrelevant.

That seems enough diatribe for a Sunday morning.


 

 



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