Move Z

[john_l]

I was toying with the MZ command on my bot as a way to set Z height and got a response I didnt expect...

I turn on the control. I set a known .5" thick piece of wood block material on the material surface and manually Z zero to this block. I remove the block and type "MZ -.5" I expected the bit to lower the half inch to the cuttable material but instead it raised about 5/8-3/4" ?

[bill.young]

John,

Did you type "ZZ" when you had the bit at the top the block, to zero the Z axis at that location, before making the "MZ, -.5" move?

Bill

[mitch_prest]

are the move commands always absolute position as apposed to relative..

mitch

[bill.young]

Mitch

All ShopBot moves by default are in Absolute mode, unless you change it to Relative mode. And all part files automatically run in Absolute mode too, even if you've set your ShopBot to Relative mode before the file starts. If you have a file that was created in Relative mode (I'm not sure I've ever come across one), you'll have to add the SR command at the beginning to have it run in Relative mode.

Bill

[john_l]

I thought that I had ZZ'ed at the block height. I must have not done so because I tried several times after, making sure I typed ZZ and it has worked each time since.

So, please confirm that this is how it works... MZ will not work dependably unless you have ZZ'ed at some level. You cannot just MZ from where the bit happens to be when you start?

Thanks!

[mitch_prest]

just so I am clear.. if you ZZ.. you are then setting that as the absolute zero for the Z at the place where the bit is when you enter the command...

mitch

[bill.young]

Hey John,

I think you're thinking in "Relative" mode and the ShopBot is working in "Absolute" mode.

By default all the Move commands in a ShopBot like MZ are made in "Absolute" mode, meaning that they tell the tool to move to a specific location. For example, let's say that the Z axis was originally zeroed 1" above your wooden block...it's Z-axis location is at 0.0". When you moved down to the top of the blank, the Z axis would now be at -1.0". If you then make an "MZ, -0.5" move without zeroing the Z-axis first with a ZZ command, -0.5" is higher than -1.0" so the Z-axis will move up until it reaches the -0.5" location. The "MZ, -0.5" command told it to move TO that Z-axis location, not to MOVE -0.5" in the Z-axis.

If you were in "Relative" mode, any Move commands would act as though the current location is 0.0, no matter what it's "real" location is. So a negative move will always move in a negative direction and a positive move will always move in a positive direction. Some people like to work in Relative mode but it can be confusing sometimes. If you're in Absolute mode and give the tool a "J2,0,0" command it will move to the "real" 0,0 location which is usually at the corner of the table. If you're in Relative mode, though, and give it the same "J2,0,0" command, the tool won't move at all...you told it to move 0" in the X and Y direction from the current location.

Hope I haven't confused things (though I'm afraid I probably have). Look in the Command Reference in the Help menu for information on the "SR" command and the difference between Relative and Absolute modes.

Bill

[bill.young]

Hey Mitch,

That's correct..the ZZ command sets the current Z-axis location to 0.

Bill

[john_l]

Bill, You didn't confuse things at all. Thanks to your post, I finally understand. Sorry it took all that, but I thank you.

[bill.young]

Hi John,

Glad to hear it helped...sometimes too much explanation is worse than not enough!

Bill