Coordinate System Woes?

I have the Sparkfun version of the Shapeoko and am using the Universal Gcode Sender. I don't know if you can help, but I'm having issues with understanding the coordinate system. I see a Work Position and a Machine Position. Through trial and error, it is clear that the Work Position needs to be set so that the (0, 0, 0) is lined up with what I put in the CAM software as the origin.

My main issue is that if my Machine position is not also at (0, 0, 0), the end mill will just scrape through the piece before starting the cut (which will turn out as expected). To get the Machine position at (0, 0, 0), I have to disconnect and reconnect my computer while the end mill is in the (0, 0, 0) Work position--this seems like a workaround and not me using and understanding this properly! Any help?


JON-A-TRON3 months ago

Machine position refers to the absolute coordinates of the machine. Remember the right-hand rule. Your thumb is the X axis (the longest axis) your index finger is the Y, and your middle finger is the Z. If you're looking at your machine facing the short side, place your hand on the lower right corner of the machine and you'll see that it must be the 0,0,0.

Now, Work Position is the coordinate system that's specific to the job. So if your job is a 6" X 6" X 2" piece of stock you're cutting into, the work position can be anywhere on the bed that will fit that size stock. You could make the work position the same as the machine position, placing your stock on the lower right corner, but you might want to move it to another spot so that you can get proper work holding, for example.

If your tool path makes the tool scrape through the part, you might not have your heights set properly- your traverse / travel height might not be above the stock.

Another reason this might be happening is that you're not zeroing your tool off of the right spot. In Fusion, you can set the origin at the top or bottom of the stock (really you can set it anywhere), so be sure that if your Z-Zero is at the bottom of the stock in Fusion, that you zero the tool off of the bed when you're setting up the machine, and off of the top of the stock if that's where you had it in Fusion.

I hope this helps, let me know!

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kcastaneda (author)  JON-A-TRON3 months ago

It totally helps--thanks so much. I feel like I understand all of this is theory, but in reality a couple of things are happening that I'm not understanding. I think that with experience I'll get there...

I just ran into warped wood and the bit falling due to the collet not being tight enough, which both caused some of my scraping issue. I also moved the Work origin to the top, which seemed to help.

Regardless, we made our first finished project! Thanks to this class and your help!

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nicely done! That's a great subject for practice.