Zoffset needs to be adjusted after each full calibration

miglo
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Zoffset needs to be adjusted after each full calibration

Postby miglo » Wed Feb 17, 2016 5:25 pm

First of all, thank you 626pilot for an amazing firmware! I think I would have tossed my Rostock out the window by now if it was for it.

Not so much a bug but a quick question. After cleaning things and doing a total recalibration, I find I have to adjust my zoffset (.25 - 1.25mm), otherwise the head just grinds into the PEI layer and scars it. Is there anyway to alleviate this?

Mig

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mhackney
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Re: Zoffset needs to be adjusted after each full calibration

Postby mhackney » Wed Feb 17, 2016 5:51 pm

What you describe sounds like the inherent flex in an FSR probing system. Is that what you are using?

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miglo
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Re: Zoffset needs to be adjusted after each full calibration

Postby miglo » Thu Feb 18, 2016 5:35 am

mhackney wrote:What you describe sounds like the inherent flex in an FSR probing system. Is that what you are using?


Indeed I'm using the FSR system.

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Re: Zoffset needs to be adjusted after each full calibration

Postby mhackney » Thu Feb 18, 2016 9:40 am

Ok, then read the Commissioning section of this: http://sublimelayers.blogspot.com/2016/ ... -duet.html

Even though you are not running Duet, the principle is still the same - there is inherent flex in an FSR probing system. If you can press down on the glass surface anywhere on the bed and see it move a little, you have a problem that needs to be fixed or compensated for. You can minimize this flex in a lot of ways. The first is to use a stiff backing on the bed, the snowflake does a good job of this. But the way the glass is clipped can also introduce some potential for movement. The compressible pads you put on top of the FSRs also, but their very design, introduce some flex. Ideally, you would like the flex to be the same directly over all 3 FSRs. And my experience is that it is close enough not to be an issue - but this also depends on your mounting system and how carefully it was assembled. In this case, with a stiff bed, you simply need to adjust the Z height and it will be effective over the entire surface - see my post above. If, not, then you have several options. The first would be to figure out why all 3 FSRs are not triggering the same and fix that. Second is to individually adjust each probing point with an offset. The RepRapFirmware supports this, I don't know of any other firmware that does.

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