Prints are a little bit small

Discussions related to the Rostock MAX v2
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Joined: Wed Oct 22, 2014 11:54 am

Prints are a little bit small

Postby shentheory » Sun May 14, 2017 11:41 am

I've had my V2 for a couple years now, and so far havent printed many things that had to fit together or fit with something else. But I've being printing exactly that lately and found that even my PLA and PETG prints, are coming out small by more than a few millimeters in some cases.

I printed this calibration object, it's a mini version of a larger one linked in the description.

Each angle leg is suppose to measure 6cm. But I measure btwn 55-56mm pretty evenly on all 3 sides. Everything else like the angles and horizontal radius are on point for me. Most things print out well in general, but the XY dimensions are always short by some margin within 1-5mm. For smaller objects it's usually only a 1-1.5mm shortage.

I posted a comment because the calibration adjustments they give are for marlin, and there were many that used repetier commenting. I got replies back from someone with a repetier-host avatar named repetier. I'm not worried about the angles or the radius, again those are good for me. It's just the dimensions/print size I'm trying to fix :

Adaption to Repetier-Firmware

If you have eeprom enabled you can do all the calibration without recompiling or changing the code.

For the angles just change the Alpha A/B/C values like you would change the angle in Marlin formula.

For the diagonal rod length correction change the Corr. diagonal A/B/C values in EEPROM. Here you do not enter a factor like the instuctions computes but the difference between the target diagonal length and the one you have set. Just think that the value you enter gets added to the nominal diagonal length.

If all changes are in one direction, reduce them by the mean value and add that to the nominal value.

My Replies:
Shentheory - in reply to repetier

Shentheory - in reply to repetier
Here's a screenshot of my eeprom. After Delta Radius param it shows Z prob. Why am I missing corr. diagonal?

repetier - in reply to Shentheory
Ok, I see they are in deed missing in your case. Is this the original repetier-firmware or from a vendor where vendor has removed the output for these 3 values assuming he has no error? If I check this on my firmware it is between "delta radius C" and "z probe height".

Simple solution is to add the 3 lines for eeprom output to your firmware. See eeprom.cpp in you should find the first 3 lines with the next 3 lines missing:
writeFloat(EPR_DELTA_RADIUS_CORR_A, Com::tDeltaRadiusCorrectionA);
writeFloat(EPR_DELTA_RADIUS_CORR_B, Com::tDeltaRadiusCorrectionB);
writeFloat(EPR_DELTA_RADIUS_CORR_C, Com::tDeltaRadiusCorrectionC);
writeFloat(EPR_DELTA_DIAGONAL_CORRECTION_A, Com::tDeltaDiagonalCorrectionA);
writeFloat(EPR_DELTA_DIAGONAL_CORRECTION_B, Com::tDeltaDiagonalCorrectionB);
writeFloat(EPR_DELTA_DIAGONAL_CORRECTION_C, Com::tDeltaDiagonalCorrectionC);

I think this gives you the options back.
Harder method is to upgrade to current firmware which includes setting all parameter also you can find them in your configuration.h.

So would this be something I could add to the eeprom? Does it need to be added to fix my issue? I'm using 0.91ROSTOCK directly from the download page, is the new repo with all firmware the one I should use? I'm not really sure the best way to go forward fixing this issue. I tried playing around with the "diagonal rod length" in the eeprom with the idea that the shorter it is the more it has to move, hence larger. But that didnt seem to make an effect and i reset it to 290.8.

Any help/tips/advice on how I can fix these dimensional issues would be great! I've tried to check everything at this point, I'm use to it now. Belts are tight, enstops are secure, towers are level, things print well......just, a little too small.

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Location: Aberdeen, SD

Re: Prints are a little bit small

Postby Harblar » Fri May 19, 2017 12:36 pm

Use this guide right here:

You almost certainly need to adjust the length of the Diagonal rod in your eeprom settings if it is off by that much. I'd also suggest upgrading to the injection molded carriages and ball cup arms. They're nod needed but they'll definitely help with overall accuracy. :D

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