More accurate Z home sensor..?

I am having a nightmare with the Z axis home switch. It's just getting that first layer printed and once I got it right, the next print is out, not a lot but getting very annoying.

My Z home switch is well secured and have a screw adjuster that works fine, I just don't think the micro switch is that accurate and was wondering if there is anything better?

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This might be a good read for you
I´d like to implement an analog z-stop for my prusa i3. More like a potmeter. But I don´t know much about Marlin and RAMPS yet.
-Olaf

Optical endstop.

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DaveRC
I am having a nightmare with the Z axis home switch. It's just getting that first layer printed and once I got it right, the next print is out, not a lot but getting very annoying.

My Z home switch is well secured and have a screw adjuster that works fine, I just don't think the micro switch is that accurate and was wondering if there is anything better?

it's not so much accuracy but repeat-ability thats the problem with those switches, there is many better options like the the fsr ( force sensitive resistor ) which is probably the easiest to wire up and allows you to use your hotend touching the bed as the switching mechanism , there is also induction and capacitive sensors however these are a bit more of a pain to wireup

the easiest solution is to simply get rid of it and set your nozzle position manually before the start of every print, after a couple of prints you'll get used to it and you'll be able do it by eye very quickly

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+1 on the optical end switch. Very reliable and repeatable as there is no flexure or wear elements.

I installed a hall-effect sensor on my Prusa i2. Got it in a Ramps kit off of ebay. You can adjust the depth on them using a potentiometer on pcb which makes them very sensitive and precise.

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KDog
I installed a hall-effect sensor on my Prusa i2. Got it in a Ramps kit off of ebay. You can adjust the depth on them using a potentiometer on pcb which makes them very sensitive and precise.

Do you have a link?
THX
-Olaf

Here's a solution to the same problem, I've removed the end stop on the Z-axis completely.

1. Find your ideal z position using the paper method.
2. Send a G92 Z0
3. Lift the nozzle some known value after each print ends, I always lift mine 30mm (G1 Z30). You can do this on the end g-code part of your slicer program
4. Create 2 macro buttons "Set Z", "Home Z" in pronterface. Every time you turn your printer on press "Set Z" (G92 Z30). When you're ready to print use "Home Z" (G1 Z0). and your nozzle will be exactly where it was in step 1 every time.

I've used this method for about a year with very consistent results.

Here are the disadvantages-
-You can't use G28 to home everything at once, unless you want to mod marlin's G28 command to ignore Z
Both Sli3er and Cura automatically add a G28 command to their start G-code, you must remove these (its a one time operation).
A G28 using this method will send you nozzle through your heat bed.

-If you abort your print midway through, you must remember to lift your nozzle back to its start position (G92 Z30 in my case).

Im sure there's other disadvantages but those are the main ones I've encountered

Edited 1 time(s). Last edit at 05/12/2015 04:48AM by eci22.

G92 sets the position of the axis where it is, in other words G92 Z0. sets where the head is to Z0. If you use the method above and anything moves while the printer is off you have lost your position. It's generally a bad idea to rely on a printer holding position with power off, not to mention the issue of drivers only wanting to turn on with whole steps, so if your magic position is a few microsteps away from a full step, that can induce error as well.
To the OP what kind of homing speeds are you using? Too fast and you won't get good accuracy.

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Koko76
G92 sets the position of the axis where it is, in other words G92 Z0. sets where the head is to Z0. If you use the method above and anything moves while the printer is off you have lost your position. It's generally a bad idea to rely on a printer holding position with power off, not to mention the issue of drivers only wanting to turn on with whole steps, so if your magic position is a few microsteps away from a full step, that can induce error as well.
To the OP what kind of homing speeds are you using? Too fast and you won't get good accuracy.

You are quite right if anything moves it can potentially be a problem. But why would the printer move when it's off ? I've transported my printer in a car and moved it around a bit but the Z axis being on threaded rods don't move unless you want them to. From practical experience it has not been a problem. I'm not sure what the issue with drivers mean

A)Every printer isn't built like yours, some use different methods for the Z axis.
Things can and do move when you don't expect them to. See cats and children for examples of how (but neither one will admit it )
C)Stepper motor drivers won't simply pick up mid micro step. If you don't grok micro steps, might be time for some reading. When you restart a drive that's been off if the motor isn't on a whole step, it's not going to come back at the same place, it will likely snap to the nearest whole step. This may or may not mean anything depending on a variety of factors. If where you stop (in your case Z30. ) isn't a whole step it's going to snap to one when you restart.

It may work fine for you, but it's not a good practice in general to recommend. Too many variables. It's almost as quick to just set your zero with a piece of paper every time you turn the printer on. Then instead of assuming you are where you think you are, it will be known.

i second the idea of manual z at power on. The switches suck, and any time you change bed material it needs to be manually set at optimal zero. Also depends on how stable the bed is.

I've used a microswitch for a couple years and it has worked fine. What I don't do is use a leaf spring lever to operate the switch. A screw comes down and directly pushes on the little button on the switch. It has been very repeatable. All that said, I will be switching to an opto interruptor because I have had two occasions when the zero switch was ignored and the X axis came down and broke the zero switch off its mount. With an optical switch the opto interrupter will be out of the way and safe from harm.