Auto touch Z end-stop

Topics Related to the ORD Bot Printer

Re: Auto touch Z end-stop

Postby TLHarrell » Mon Mar 10, 2014 9:43 pm

orcinus wrote:Call me crazy, but i don't feel comfortable having the whole gantry weight rest on the nozzle tip in order to calibrate the Z.

If i understood the idea correctly, this actually rests the whole gantry weight on the nozzle tip EVERY TIME you calibrate.
Unless it's just meant as an emergency measure, but then - what's the point, it's as good as having it float mechanically when the nozzle hits the bed.


Best method for this, adapted from the CNC industry, would be to have a touchoff location with a spring mounted contact. The system would move over the plate, feed down at a moderate rate until contact is made, lift a short distance, then touch back off at a crawl. The plate would need to be mounted in a way to allow it to be adjusted to match the bed height.
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Re: Auto touch Z end-stop

Postby orcinus » Mon Mar 10, 2014 9:46 pm

I like that as an idea.
Although, if you implement that, you might go the whole 9 yards and add Z probing instead - no fuss with adjustments in that case (or, if there is a need, it's a matter of adjusting the Z offset of the probe in software).
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Re: Auto touch Z end-stop

Postby cvoinescu » Mon Mar 10, 2014 10:54 pm

TLHarrell wrote:Best method for this, adapted from the CNC industry, would be to have a touchoff location with a spring mounted contact. The system would move over the plate, feed down at a moderate rate until contact is made, lift a short distance, then touch back off at a crawl. The plate would need to be mounted in a way to allow it to be adjusted to match the bed height.

That works only if you assume the bed is level. If you want to use the auto-level feature of the firmware, where the software compensates for a bed that's slightly tilted, it doesn't work -- the probe needs to be on the carriage, not on the bed (unless you have one probe in each corner of the bed).
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Re: Auto touch Z end-stop

Postby Atreidae » Wed Mar 12, 2014 1:44 pm

I was toying with the Idea of using the alu bed as an earth with a +5v rail attached to the Merlin hotend.. the idea worked in theory but would only be good for a 4 point calibration.. Still thinking about it.
Robotronics were nice enough to point out another customer that got a Z-probe working.. I'd personally be doing more design work, but I have over 50 PC's in the garage that need to be wiped.

Anyway, check this out http://bjblaster.homedns.org/blog/?x=en ... 219-113423
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Re: Auto touch Z end-stop

Postby orcinus » Wed Mar 12, 2014 8:25 pm

Why would you need more than 4 points?
(In fact, why would you need more than 3?)
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Re: Auto touch Z end-stop

Postby Atreidae » Wed Mar 12, 2014 9:45 pm

3 points is fine if you know you have a totally level surface. But as I've recently discovered this isn't always the case.

a Glass plate would help.. but it wouldn't be perfectly level either, when we start pushing the boundaries of the printers (I'm currently printing at 160 micron as getting things level for much finer appears to be very difficult) it would be usful to know if the bed is flat the guys coding Marlin added in "Grid leveling" to test multiple points across the bed.. I assume for that reason.
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Re: Auto touch Z end-stop

Postby orcinus » Wed Mar 12, 2014 10:55 pm

I might just be lucky, but i've never had issues with bed flatness.
I used to print on a mirror, now i'm printing on borosilicate glass plate.

Can't really judge, but i think this obsession with bed leveling/compensation is about 15% real need and 85% inventing solutions for a problem that doesn't exist :)

I don't even home my bed automatically - my limit switch is at the top, i use it to get close to the bed (the range of motion from bed to the top is known) and then manually touch the nozzle in a spot or two, then set zero with G92 Z0. Before shutting down the printer, i issue G1 Z50 or G1 Z100 and it's usually good to go with just a G92 Z50 or G92 Z100 next 5-10 times i turn it on.
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Re: Auto touch Z end-stop

Postby secretgspot » Thu Mar 13, 2014 2:39 am

Image
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Re: Auto touch Z end-stop

Postby fma » Fri Mar 14, 2014 4:06 pm

Could you give us the reference of the proximity sensor you are using? How is the repeatability?
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Re: Auto touch Z end-stop

Postby TLHarrell » Fri Mar 14, 2014 5:37 pm

Looks like this one:
http://www.ebay.com/itm/LJ12A3-4-Z-BY-I ... 20e075eb8c

No word on repeatability in the specs. Says detection distance of 4mm. No +/-. And since it's inductive, it needs a ferrous metal surface to detect.
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