Cheap, Super-sensitive Digitizing Probe for Cnc... Harkman's Probe





Introduction: Cheap, Super-sensitive Digitizing Probe for Cnc... Harkman's Probe

it's so simple, and sensitive... i named it after myself... harkman's probe

if you want to scan, or digitize a model in a cnc program, it requires a digitizer probe.. unfortunately they are expensive, or, hard to
make yourself..
lots of examples use ball bearings, 3 contacts, for sideway forces, a spring...
here is one solution i didn't find... an easy one..,
while looking for a cheap solution (DIY) i couldn't help thinking about a very sensitive device, the needle of a turntable..
or something equivalent..
the solution...

a nail soldered on a piezo buzzer,

with a microprocessor as a converter,
with adjusable threshold..
While it can be done cheaper, i think this is the easiest way...

it takes about 10 minutes to make one... and is very sensitive, adjusable, easy to use, or to custom, to your own needs
what you need

1 small piezo buzzer
1 film can
1 nail,
foam (mousepad or something softer) for mechanical vibration-insulation)
small wire
an arduino, or other micro processor
(or use electronics, like an op-amp etc)

If using an arduino, download the knock program from arduino..
and read up on piezo as a sensor
the led should light up, when just scratching the nail....
then connect the ground, and an output port (saay 13) to your input (parallel port) as an digitizer..

the rest is up to you... digitizer is connected to the limit switch of the z axis but there are to many programs and cnc machines to tell what step is next to take...

here it is in it's first test

and one to test it in digitizer probe style (apparently)

comming up... the results of a scan...with my cnc machine



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    13 Discussions


    2 years ago

    Well did it PIEZO out or just crash and burn? Its only been 5 yrs, 5 mo , & 16 days sense this instructable was posted! Looks like someone forgot about with the results of the scan. Mr Harkman did you not get it to work?


    What news about your probe ?

    best regards


    This looks like a great idea, are you going to continue working on the project until you get it connected with a cnc machine and input a file of what you are scanning to produce a copy? if so I would love to get the result to build my own, it seams like such a simple way of producing a digitising sensor.

    well done

    Regards Poppy Ann.

    This is a "v1.0" copy of how Roland scanners work.

    The "v2.0" evolution that you're going to *kick* yourself (so obvious) when you read about it is...

    "buzz" the piezo.

    First - don't use a nail - use a needle - and don't "solder" it perpendicular, superglue it parallel (so the whole finished unit looks like a lollypop).

    Next - send a high-frequency AC signal through the piezo; this will vibrate the needle. You may need to experiment with different frequencies (dependant on needle length - it's the harmonics you're looking for)

    Finally, measure the piezo feedback (in-between the AC signals): when the needle tip (or many places on the shank) comes close to an object, the object disturbs the harmonics, which can be measured at the piezo.

    This setup is so sensitive you can easily get micrometer resolution!


    1 reply

    Hi cndg, I'm very interested on your approximation, but I can't find any information to put in paper your solution. Can you post a more concrete way? Nothing found on arduino forums. Thanks


    3 years ago

    Would you share The code?

    This seems to be a good idea. I guess the hardess part would be to perfectly align the nail in the center when you mount it on the CNC. It would be interresting to see it in action !

    Great design! I am excited to see next steps, and I will try to make one!

    Hello did you make any progres with connecting it to real cnc machine ?

    I'm not skilled with electronics can you tell me what is "op-amp "

    I want give a try to make such digitise probe .

    This is only going to pick-up your edges, as the piezo generates on movement.
    How would you distinguish between up/down edges?
    Across a perfectly flat surface there's no signal.


    2 replies

    when scanning/probing with a cnc machine the probe normaly goes down, until the probe touches anything, then it goes up...then a step sideways, then down again, until it touch make a point cloud... the differences in height wil result in a curved surface, where a perfectly flat surface wil generate lots of the same heights...

    On a perfectly flat surface it doesn't need to pick up, as it is perfectly flat..

    OK I understand it, you weren't doing the up-down in the video, but then you ain't a machine.