Are there any delta printers with non-circular print areas?

I am working on delta support for RepRapFirmware on the Duet electronics. The only delta printer I have experience of is the Mini Kossel. In order to avoid unduly restricting the applicability of the firmware, I have some questions relating to delta printers generally:

1. Are there any delta printers out there that do not have circular printing areas? I need to generalise the M208 command (see [reprap.org]) to support non-rectangular print areas, and I am wondering if just adding suipprot for circular printing areas is sufficient.

2. The Marlin firmware for the Mini Kossel homes the axis by driving all 3 motors simultaneously in the +Z direction to the tops of the towers, stopping them each when the appropriate endstop switch is triggered. It then performs a fine homing of one motor by driving it down a little, then slowly up until the endstop is triggered again. It repeats this for the other two motors. Do all delta printers use a similar arrangement, i.e. endstop switches at the top of the towers, and the 3 towers can normally only be homed together? This is obviously a good technique as it keeps the effector in the same XY position until the axes are homes, but I am wondering if any other techniques are ever used.

Thanks in advance!

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Repetier and Smoothieware both home the same way. If you do not know the location of the effector (as in when first powering up), the safest thing is to home all three towers at the same speed (to keep X and Y where they are) until you can determine each tower's location through hitting the upper endstop. Once all three hit the endstops, then Repetier and Smoothieware will drop all three towers at the same time and move them up slowly at the same time to re-trip the endstops for fine tuning.

Delta printers only use the max endstops, and do not have min endstops installed. We like living dangerous in that regard. Seriously though, the Z_min input is used by auto-calibration systems that use either a mechanical switch or an external digital FSR signal processor such as JohnSL's board or an Adafruit Trinket. I suggest following this standard of the Duet has 6 endstop inputs.

In terms of coordinates, X=0, Y=0, Z=0 is at the center of the bed with the nozzle on the glass. When you home a Delta, you need to set the coordinates to X=0, Y=0, Z=Z_max with the carriage at home.

Regarding bed shapes, many are round. Some people do use square/rectangular Mk2 beds. I seem to recall someone manufacturing a triangle-shaped bed, but can't find it at the moment.....

Technically, a delta bot using the maximum usable area it can does not print in a true full circle. At a point, you will reach an error high enough at extremes that you are actually bounded by a triangle with rounded corners.

Edited 1 time(s). Last edit at 12/28/2014 08:29PM by MrBaz.

Thanks for those responses, they have allowed me to make some decisions. Homing in RepRapFirmware is normally done using macro files homex.g, homey.g and homeall.g on the SD card. So I have defined homedelta.g as the file to be executed when any G28 command is executed and the printer is configured as a delta. This will make it easy for users to adjust the homing behaviour. For now, I will include support circular print areas only on delta printers.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I'll contribute, since it looks like you did not get the correct answer about built area (which I wanted to respond to but I was lazy to search for references).

The build area of a linear delta printer is closer to a hexagon than to a circle, but the exact shape can be much more complicated especially depending on the shape of the towers and carriages. I have seen square, circular and hexagonal (heat) beds. It also depends a lot on the relationship of delta radius and delta diagonal rod length.

A somewhat better approximation (for classic rostock) than a hexagon is here: [forums.reprap.org]
Still it would not be exact for deltas which can tilt diagonal arms a bit backward too. Anyway, a circle is a good enough approximation.

If a printer cannot print correctly outside a triangle (as MrBaz pointed out), then the problem is in printer calibration. One can calibrate a printer so that it prints well in the whole available print area. With a correct zprobe and a bit of math knowledge it is even easy to do: [github.com]

I agree with hercek. If the printer is calibrated then you can print anywhere on an enlarged bed.

In Slic3r you can provide an STL with the bed outline and it will use it. That makes it very handy for placing objects.

See this thread

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My printer: Raptosaur - Large Format Delta - [www.paulwanamaker.wordpress.com]
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