Required tolerances on frame alignment

OK

I am looking for guidance on what sort of tolerances I should be looking for in respect to the Angular measurements of the Tower's in relation to the bed.

I know they need to be as close to 90 degrees as possible but What sort of error would be deemed to be acceptable.

My build has come out with 2 towers within 0.25 degrees of error and the other is at 0.1 degrees of error, Do you think this is acceptable?

the towers are within 1mm of equilateral sides (1 leg is 1mm longer than the other 2.

Should I think about any sort of correction to allow for the tower positioning if so how do I do it in DC42's excellent Firmware (Dave think you may have to answer that for me)?

that's enough to be going on with for now.

Thanks for any comments good or bad.

Doug

I intend to look into a calibration mechanism for the tower positions in my fork of RepRapFirmware next week. This will comprise an extension to the M665 command to allow the individual tower positions to be defined, and a 7-point auto calibration procedure.

If the towers are leaning but parallel, to a first approximation I think this is equivalent to their not being at the corners of an equilateral triangle. It will also cause the print to lean, which can be countered by axis compensation.

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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].

Hi,

That's a very interesting question and I would really welcome some informed comments on that, since I am also putting together my Delta Steel prototype these days and facing the very same issues.

I believe column angle errors will become more significant the further you print from Z=0 which is the height for which you will calibrate your printer.

Correct me if I am wrong, but a quick calculation gives me sin(0.25) * 100 = 0.44mm is your error at a height of 100mm with an column angle error of 0.25 degrees.

While column position errors can be corrected by existing calibration procedures, column angle errors as far as I know can't (yet) (again, please correct me if I am wrong).

Quote
AndrewBCN
Hi,

That's a very interesting question and I would really welcome some informed comments on that, since I am also putting together my Delta Steel prototype these days and facing the very same issues.

I believe column angle errors will become more significant the further you print from Z=0 which is the height for which you will calibrate your printer.

Correct me if I am wrong, but a quick calculation gives me sin(0.25) * 100 = 0.44mm is your error at a height of 100mm with an column angle error of 0.25 degrees.

While column position errors can be corrected by existing calibration procedures, column angle errors as far as I know can't (yet) (again, please correct me if I am wrong).

You beat me to doing the maths um that gives me 4.5 mm out at the top of the towers will have to bring that in a bit I think some diagonal bracing is required (Good job I got some 20x20 extrusion for this eh)

now the question is do I fit them as I intended (Vertically just in front of the Towers) and then sheet it in Ally to form and enclosure and then use that to pull it all into line?

Doug