X and Y travel limits -Delta printer with Marlin firmware

These firmware values:

#define X_MAX_POS
#define X_MIN_POS
#define Y_MAX_POS
#define Y_MIN_POS

define limits on how far the printer can move along the X and Y axis.

But a delta has a circular XY printable area, not rectangular. This means if the printer tries to move to X_MAX and Y_MAX simultaneously the firmware will let it, even though this places the print head outside the bed (and in fact can run into a support tower sometimes).

Is there a way to deal with this besides shrinking the X and Y limits significantly smaller than the actual print bed?

Okay, I will try to answer your question by explaining the printer limits and firmware parameters that you mentioned above. I have a rostock delta printer, and although it is a delta my bed is still a square. Even if it was a circle, I would still think of my bed in the form of a square. My bed is 200mm wide. However, I have four bolts that I do not want the nozzle to hit, so my printable diameter is 180mm or -90 min 90 max in both the X and Y axes. In the firmware, as well as the printer host that you use (repetier, pronterface, etc.), you will define the mechanical dimensions of your machine. Your printable radius or diameter (depending on which firmware or host that you use) will define the machines travel. So X and Y max would not equal the extreme maximum that the machine can move, but will be limited by the limits that you set.

Your bed will be inside of your towers, so you would not be shrinking your bed significantly just to avoid hitting your towers. That's a conclusive statement and I'm sorry about that, but your horizontal smooth rod offset to the center of your printer (center of tower/rails or rods to the center of your printer) will always be larger than your bed. Since the machine moves in triangular movements, the print area will always be smaller than that distance. So for instance, my smooth rod offset is 177.6 mm (radius), so a total diameter of 355.2mm total, of which 200mm is usable as my printable area.

I hope that explanation answers your question.

Edited 1 time(s). Last edit at 08/29/2014 02:40AM by Wildcard.

The rostock mini kit I bought has a round bed with a 85mm radius / 170mm diameter. There are bolts outside that radius to attach the motors. My smooth rod offset is 142mm giving a total diameter of 284mm.

In order to prevent the printer from running off the edges I have to set the limits mentioned to that of a square inscribed in the circle which means dividing by sqrt(2), yielding 120mm or a 4.7 inch square. That is quite a bit smaller than the advertised printing area of the kit.

It would make more sense for the firmware to calculate the distance from the center rather than along an arbitrary X or Y axis within the printer's volume. It would allow significantly larger print volume. I take it from your response that it currently doesn't work that way. Seems like it would be a nice option to have.

Edited 3 time(s). Last edit at 08/29/2014 10:58AM by mk3a.