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View Full Version : Electronic edge finder: how do they work?



irving2008
21-08-2009, 11:26 PM
Been looking at electronic edge finders that light up when they touch the edge of the workpiece, but don't see how they work. Is it that touching the workpiece completes a circuit through the mill - this seems a tad tenuous, or does the contact close a switch in the finder.. in which case how sensitive is that if these are good to .02mm or better! Thoughts?

Lee Roberts
22-08-2009, 12:09 AM
Well have you seen the edge finder a guy posted on the zone ? i also read about a guy who took the mouse from an old laptop and turned it into a edge finder.

Is that the kind of thing you mean or ?

Lee Roberts
22-08-2009, 12:12 AM
These:

Center Finder (http://www.mycncuk.com/forums/video.php?do=viewdetails&videoid=22)

Mach3 CNC Probe Tool (http://www.mycncuk.com/forums/video.php?do=viewdetails&videoid=21)

irving2008
22-08-2009, 12:13 AM
Well have you seen the edge finder a guy posted on the zone ? i also read about a guy who took the mouse from an old laptop and turned it into a edge finder.

Is that the kind of thing you mean or ?I mean this sort of thing:

tumutbound
22-08-2009, 12:18 AM
The tip is insulated and when it touches the workpiece, the circuit is completed and the LED lights.
Too bad if you're machining plastic. :thumbdown:

irving2008
22-08-2009, 12:21 AM
The tip is insulated and when it touches the workpiece, the circuit is completed and the LED lights.
Too bad if you're machining plastic. :thumbdown:that means the circuit is tip, workpiece, table, column, head, chuck... surely not... a tad tenuous at best...

John S
22-08-2009, 12:26 AM
that means the circuit is tip, workpiece, table, column, head, chuck... surely not... a tad tenuous at best...

Only as tenious as power station, sub station, machine tool and neutral,
is 36,000 miles a second or whatever good enough ?

irving2008
22-08-2009, 12:42 AM
Only as tenious as power station, sub station, machine tool and neutral,
is 36,000 miles a second or whatever good enough ?
not speed John, connectivity... surely relying on all those having a good or any electrical connection to each other is tenuous?

Lee Roberts
22-08-2009, 12:48 AM
Especially if the spindle has ceramic bearings no ?

BillTodd
22-08-2009, 08:58 PM
that means the circuit is tip, workpiece, table, column, head, chuck... surely not... a tad tenuous at best...

Yep, that how those ones work (I have a Sony probe for my magnescale DRO that works exactly the same)

You can get touch probes that are effectively sensitive normally-closed switches (usually three switches in series at 120' to each other) relying on movement of the probe to open the switches and the closed position of the switch as a position reference.

Nice home-brew design here:
http://tmonnot.free.fr/Fraisage/Palpeur3D.htm

Lee Roberts
29-08-2009, 05:35 PM
Just found the pics i was looking for irving:

BillTodd
29-08-2009, 07:41 PM
Lee, is that an IBM 'niipple' (touch mouse) being used as a touch sensor?

Any idea how accurate it is? (ie. repeatability etc.)

irving2008
29-08-2009, 07:50 PM
Lee, is that an IBM 'niipple' (touch mouse) being used as a touch sensor?

Any idea how accurate it is? (ie. repeatability etc.)not huge I'd imagine..., although the long probe improves. my concern would be how consistent the 4 switches are relative to each other...

Lee Roberts
29-08-2009, 10:33 PM
Yes it is, ill need to have a dig on the zone to find the Thread the guy started about using it. Cant remember all the details but i think he did get it going and was using it..

Lee Roberts
29-08-2009, 11:25 PM
Hi guys, here is the link to the guys thread on the zone: http://www.cnczone.com/forums/showthread.php?t=51079

What i also liked about this setup was that you could use it on wood and so on, gaging on presure rather then a "completed cicuit".