Auto touch Z end-stop

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Re: Auto touch Z end-stop

Postby r691175002 » Fri Mar 14, 2014 5:43 pm

Inductive switches rarely include a specification for repeatability, and when they do it is generally +-5% of detection distance. In practice, even very cheap sensors are generally better than 0.001" and they are commonly used as homing switches on CNC builds. I use inductive switches on my own CNC but I have always been worried the sensors might drift over time, especially with temperature/voltage changes.

Inductive switches will work with non-ferrous metals but generally have a shorter detection distance. You can see a chart of the sensitivities for different metals here:
http://www.fargocontrols.com/sensors/inductive_op.html
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Re: Auto touch Z end-stop

Postby flickerfly » Fri Mar 14, 2014 5:55 pm

I saw one guy using something similar with very repeatable results on a PrintrBot Simple Metal. I wonder if the heated bed's copper traces are sufficient at the distance of the glass thickness plus a bit. This seems like a nice option since it's easy to implement and low impact on the mechanical operation of the bot.
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Re: Auto touch Z end-stop

Postby fma » Fri Mar 14, 2014 6:42 pm

Is the thickness of the plate important for inductive detection? I was thinking to add a very thin sheet of iron between the heat bed and the glass...
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Re: Auto touch Z end-stop

Postby r691175002 » Fri Mar 14, 2014 6:55 pm

fma wrote:Is the thickness of the plate important for inductive detection? I was thinking to add a very thin sheet of iron between the heat bed and the glass...


Most of the detection distances are based on approximately a 1" cube of iron (the datasheet should have details). In my experience, thinner sheets of ferrous metals do okay but non-ferrous metals become very hard to detect. No real way to know without trying it, but I have a feeling you can detect iron sheet from a few millimeters away.
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Re: Auto touch Z end-stop

Postby fma » Fri Mar 14, 2014 8:50 pm

Ok, I'll give it a try. Thanks!
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Re: Auto touch Z end-stop

Postby TLHarrell » Thu Mar 20, 2014 6:43 pm

Thought this would be relevant here. Cross post from HackaDay:
http://hackaday.com/2014/03/19/ask-hack ... resistors/
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