Setup 2 Heads

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Setting up 2 cutting heads:

The easiest way to calculate the offset between the two z's is to use a hole centering routine. The file is installed with SB3 in your "C:\sbparts" folder and is named "S_Center_inHole.sbp". The idea is that it works just like a prox switch zero or something like that. Imagine a 1/4" aluminum plate with a perfect 2" diameter circle cut out of it. The plate is screwed to your table and has a lead back to one of the shopbot inputs, let's say input 1. You stick a piece of drill rod in your chuck, use K to move the rod into the hole and then initialize the hole centering routine. Basicallly it moves back and forth in X and Y until the switch trips, then it moves to the center of that travel. You do that 2 or 3 times and you get a real good center on the circle. Record those coordinates, move the drill rod to your other Z and repeat. Once you have the two XY coordinate sets you just subtract one from the other to get a precise measurement of offset.

A less easy way to do it is to draw two squares in Part Wizard or whatever. One square has to be bigger than the other, and they should be about the same centerpoint. Toolpath one with the Z, one with the A. Cut them with a ballpark offset value to get started, then measure across X and Y to see how much you need to adjust the offset. The fact that both are squares will give you a good measurement even if the alignment is pretty poor. Do that 3 or 4 times and you'll have it right.

Whichever way you do it, write the number down and put it in your safety deposit box or something so you'll always know what they are. Software has a funny way of eating little files like that and never hurts to have a hard copy. Back up the file called "my_variables.sbc" that's in the "C:/sbparts/custom" folder and maybe print it out too after you get prox, zzero, and head offset configured. custom writing service

Running the Z and A axis independently it's real simple. Draw and toolpath as you would ordinarily, but when you output the code you just choose the post for the second head for anything that should be run on A. As long as your offset is right it should be good to go. The only problem is that there is one or two moves to 0,0 in ArtCAM and Part Wizard that you can't get rid of and will be performed with the offset figured in, which means that the primary head will go X negative by whatever your offset value is. If you have enough table space for it to do that it's great, but if you don't the remedy is to use an X home position of 6 in ArtCAM / PartWizard. It's a rarely used box in the same territory as where you set safe Z. Setting home to be positive 6 inches will offset where the machine returns to home by positive 6 inches and negate what would otherwise have been a journey into negative X land for the primary Z. On a PRS you should have plenty of room if you set your table surface up with some sensitivity to range of travel so it's likely to be a non-issue for you, just rock 'n roll.

For running tandem there's a utility called the Axis Duplicator. Basically, once you create a file for one axis, you run it through this little program and it turns M3's into M5's and duplicates the coordinates provided for any axis that you choose for any axis that you choose. Essentially, you'd take a normal file created with the arcs-inch post, run it through this thing and tell it to duplicate Z for A. Then, you just run the new file and it tells both heads to do the same thing at the same time.

For zeroing A there's a file identical to the one for zeroing Z named A_zero.sbp that you can set up as a custom cut like C2 - I usually use C4 or C5, whatever you have open.

- Grant Bailey

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