Rostock Mini Pro calibration problems with effector

Greetings
For a start I would like to say that its the second printer I've built, first one is Prusa on which I printed parts for my Rostock, there were lots of problems during my first build as I haven't ordered a full kit but bought all parts by myself, but there were no trouble that I couldn't find a solution on web or this forum, this is my first topic, as now I seriously have no clues what to do and sometimes think about sacrificing a goat to 3D printing gods.

I've been trying to calibrate my custom rostock for about 3 months now, wasted 1kg spool of PLA for calibration prints. currently there is +0.14 mm inaccuracy in x tower and +0.21 in y tower (relative to z tower). After checking pretty much everything, squareness of towers, rod lengths, eliminating backlash I've came to a few conclusions:

- Errors translate when I rotate my effector, they move with it. If for example i rotate whole effector 120 degrees, errors also translate by 120 degrees. I've printed another effector on my colleague printer, and it helped a bit, but the problem persists. Effector has tolerances about 0.02 mm in rod mounts.

- Squarness of towers seems to have no effect on the print, I've tried to shorten one tower by about 3 cm, then bedleveled and printed, errors were the same, which seems very strange to me, as they should change somehow, based on all opinions here.

I will now try to print a few new effectors whit different settings and see if it changes anything, do you, fellow reprapers, have any ideas on what else could affect the print?

It could be that the bearing spacings are not the same on each side of the effector. For each pair of parallel rods, the bearing spacing must be the same on the effector as it is on the carriage.

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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].

What do you mean exactly by:

• currently there is +0.14 mm inaccuracy in x tower and +0.21 in y tower (relative to z tower)
• squarness of towers

It looks to me like you are talking about tower heights. Really these do not have such a big impact on the quality of your prints because they are mostly compensated for by endstop adjustment. It is important but not critical to have your towers the same height. Differences in height will lead to some of your towers having a very tiny bit different angle to the bed because the derivative of function towerAngleError(towerHeightError) is zero when towerHeightError=0.

I would say what you are describing is impossible. Ad dc42 mentioned. It could be different spacing or asymmetrical effector. But I have hard time how you could achieve these errors in a rostock design. All the tower parts are exactly the same between towers. If you printed them on one printer there should be exactly the same. An asymmetrical effector would mean a very serious problems in the calibration of the printer on which you printed it. Or just plain wrong STL file or the original model of the effector. Make sure all your rods are the same length. If you rotated diagonal rods with your effector than different rod length could be a reason of the behavior you see. If you used the original plastics universal joints then you may need to replace them with angle ball joints. But the only problem with the old universal joints is that they wear out quickly and lead to backslash. They will not cause imprecise prints when they are new and tight (without play).

I'm talking about errors in print dimensions, when I print the test object mentioned in post [thingiverse] it has following dimensions:
X 60.14 mm
Y 60.21 mm
Z 60.00 mm
I rotated only effector, without rods.
I'll try to print another effector with best possible accuracy and update with results.
Effector model is in attachments if you want to take a look

Quote
dc42
It could be that the bearing spacings are not the same on each side of the effector. For each pair of parallel rods, the bearing spacing must be the same on the effector as it is on the carriage.

+1

The problem you're having is probably due to effector tilt.

As DC42 said, the distance between rod ends at the carriage must match exactly the distance between bearings at the effector. They can be different between towers, but the distances between bearings on one tower must match when comparing the carriage to the effector. This is the most likely cause of your issues.

I find it difficult to accurately measure the distance between bearings when installed on the printer, and you can't really measure them accurately when off the printer due to screw tension changing the distance between bearings (when using a printed effector). You can get a rough idea by measuring the distance between screw heads.

To adjust this, you can file the effector or carriage down to get it close, then use spring washers between the rod end and the effector / carriage. Then you tune the distance using screw tension. Be careful not to use large spring washers, as this can limit the angle of the diagonal rods.

Another thing that affects effector tilt is the angles of the effector, if the screw holes aren't at exactly 120 degrees from each other then you can run into problems. Likewise if your carriage screw holes aren't exactly level then this causes effector tilt as well. Yet another parameter to tune is that the screw holes on the carriage must be at exactly 120 degrees to each other (on the other towers). I designed a special tuning fork tool to measure and tune this.

Your effector model in the STEP file is correct. One of the poorer designs based on TES but it should do. I believe your print of the effector must be imprecise. Improving TES would also lower your printer sensitivity to the effector/carraiges geometry errors but it is hard to do anything with TES this far in the printer design. You would need to redo effector, carriages, and probably also smooth rod distance and therefore also top and bottom brackets and because of that possibly also bottom and top late. In the worst case you would need to redo almost everything

Thanks everyone for your help
I've printed a new set of carriages and effector, then finished them with file to have accurate dimensions, I've had to clean holes with a drill.
After mounting it, these are the results of test print:
X 60.10 mm
Y 59.97 mm
Z 59.98 mm
I think that screws are a little bit tilted because of the drilling, but for now this accuracy is enough for me, maybe later I'll try to print that again with bigger holes so they fit without problems.
Deltas need a whole new level of accuracy, if I had to chose a second time I would go with core xy or h-bot mechanism I think.

Quote
Sashir
Thanks everyone for your help
I've printed a new set of carriages and effector, then finished them with file to have accurate dimensions, I've had to clean holes with a drill.
After mounting it, these are the results of test print:
X 60.10 mm
Y 59.97 mm
Z 59.98 mm
I think that screws are a little bit tilted because of the drilling, but for now this accuracy is enough for me, maybe later I'll try to print that again with bigger holes so they fit without problems.
Deltas need a whole new level of accuracy, if I had to chose a second time I would go with core xy or h-bot mechanism I think.

That is excellent! What's that, something like 0.18% difference between axes? Nice work. It's not easy to get that level of consistency.