Gallery, Projects and General > Neat Stuff

Micro DRO made from tyre tread depth gauge

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kd0afk:
my finger isn't made of magnascale, why does it work when I run my finger across the sensors?

BillTodd:
Magnascales use a magnetic sine wave signal recorded on to a steel tape or wire. The read heads use a magneto-resistive element (the elements electrical resistance drops in the presence of a magnetic field)

Newall Spherosyn devices use magnetic (not magnetised) precision balls in a tube. Sensing is done by inducing a magnetic field with one coil while sensing the strength of the induced field with two other coils (to give a quadrature sine output)

Those cheap digital caliper devices (including the tyre depth gauges and expensive Mitutoyo etc.) use an array of capacitive sensors, that detect gaps in a conductive layer within the sticky backed tape. They will happily detect the motion of anything conductive (including fingers) if close enough to the sensing array.

kd0afk:
I don't doubt you but it just seems a bit sophisticated for a device this cheaply made.

kd0afk:
Wixey sells these things as a "saw fence digital readout" and they sell the strips in 31-1/2" strips for $35 and you get two of them. Here is the link:
http://www.wixey.com/fence/spareparts/index.html#wr7003

75Plus:
Wixey resolution is .005" which is fine for wood but is a bit coarse for metal. Some of the depth gauges will register .0005".

http://www.wixey.com/fence/index.html  Scroll to bottom for specs.

Joe

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