Intermittent homing/optoflag failure?

Has anyone experienced intermittent yet somewhat frequent opto-endstop failure? Did you solve it? Was it opto-flag placement, or a bad cable?

I had my first print last night:

[www.keegan.org]

and despite having homed Y many many times before, now several times during a 66-layer build it will go to home Y and not see the endflag, causing a loud grumbling sound as it rams into the back, and then causing that whole layer to be offset.

I tried turning off inter-layer cooling but it still homed multiple times during the build, so I have to address this now vs after my first water-tight minimug.

Anyone thinking "been there, done that" right now? Any ideas beyond the obvious?

The flag looks aligned.. It homes correctly most of the time. I don't remember if i've seen it fail while not during a print..

Thanks!

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--Jeff Keegan (Just Another RepRap blog)

What is your opto flag made out of?

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Tin can. Pretty stiff. Shiney though..

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--Jeff Keegan (Just Another RepRap blog)

When the opto flag is mechanically stable, i.e. stiff (doesn't bend easily) and always hits it's target then there should only be two other possibilities:

1. the opto flag is partially transparent (unlikely in your case)
2. the receiver is seeing light from somewhere else...

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Put some black tape or paint on it. The flag needs to be non reflective to IR as well as opaque. Otherwise stray IR from incandescent lighting can trigger it.

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[www.hydraraptor.blogspot.com]

Excellent.. I'll try putting some electrical tape on it and see if it's still thin enough to easily go through the sensor (otherwise I'll try some paint.)

What's weird is I can't remember a time recently when it failed to home when I did it by hand via the RepRap host control panel.. Maybe it's some light from one of the other stepper driver boards, reflecting off of the flag? Hmm..

Thanks.

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--Jeff Keegan (Just Another RepRap blog)

Hey thanks, I think that was it! I don't want to jinx myself and call it too early, but I was able to do a third minimug attempt that didn't miss Y's endstop once, whereas it was happening multiple times during the build before. Then again maybe I was printing during different lighting conditions or something, but I hope this fixed it.

I got lazy and instead of going downstairs for black electrical tape I just cut a small piece of blue painters masking tape (the same stuff I print on) and that did the trick.

Thanks again!

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--Jeff Keegan (Just Another RepRap blog)