XY Scale/size error

Hello!

I've been fighting with my delta printer for like a year+ (surrended for months) with measurements on XY.
My problem is the larger is the piece, larger is the error, for example:

20x20 cube ---> 20,6x20,6
100x100 square ---> 140x140 WTF?

Looks like a Rod leght issue but it doesn't fix it. When I get the 20x20 right the larger one is still on error.

Any idea? My towers seem to be on the right spot.

Some photos of the printer. Sorry about the messy wiring.. It need some more work.

Here are some possible reasons:

1. A geometrical error in your build. In particular, check that the bearing spacing at the top of each pair of rods (on the carriage) is exactly the same as at the bottom end (on the effector). If they are different then the effector will tilt by varying amounts depending on XY position, which will cause print distortion.

2. The elastic bands you have between pairs of rods will distort the rods (i.e. cause them to bow in towards the centre), which changes their effective length a little. If the amount of distortion varies with XY position (because the bands get stretched more or less), then this will again result in the effector tilting. If you must use elastic bands to keep the joints tight, it is probably better to place them near the ends of the rods than in the middle.

3. You have the wrong tower steps/mm or wrong rod length configured in the firmware. Have you checked that the steps/mm is correct, for example by measuring the heights of your test prints?

4. You are exceeding the angular range that the joints can handle.

5. Is the firmware that you are using known to work on deltas as large as that? 8-bit firmwares in particular might be subject to overflow issues.

Causes #1, #2 and #3 will cause the distortion to appear gradually as the size of the printed part increases; whereas causes #4 and #5 are more likely to cause no distortion until the size exceeds a certain critical value.

Additional suggestions:

1. Print a test piece comprising a set of grid lines covering the whole printable area of the bed. I expect you will see that the spacing between pairs of lines widens at the edges. Is it gradual increase in spacing, or is there no increase until a certain distance from the centre is reached?

2. Mount a bulls-eye spirit level on the effector, so that you can see any tilt.

HTH David

Edited 2 time(s). Last edit at 11/13/2018 04:02AM by dc42.

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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].

Just switched back to my older arms (shorter). Calibrated it and everything is fine now, just lost a bit of YX size but win in Z.
The longer ones I made myself, they don't seem to be a difference in lenght so I don't really know what's wrong with them (too long maybe?)

I run the standar arduino+RAMPS with TMC 2130. really silence at -50mm/s but really at 50+ (hybrid mode ON) sounds like something is about to breack off.

Thanks DC42 for the help!