Digitizer probe progress

Just a quick post to say that I have my digitizer probe working. It
is based on the one in the files section drawn by Carlos Guillermo.
The file is digitizer.pdf.

Based on this I built the digitizer out of Delrin on my little
Proxxon mill. I had been looking for 2mm ball bearings for the
pivots and eventually got these from smallparts.com (shame about the
$25 postage, grrr). The probe works really well although I am
disappointed that I did not manage to get the probe part concentric
with the shaft that is held by the mill collet. This means it is
only good for digitizing rather than edge finding etc. I may rectify
this in the future and it was a function of my workmanship rather
than the design.

The first test I did used just a 9v battery and a light bulb. The
probe was mounted in a Bridgeport fitted with DRO. The probe was
advanced sideways into the vice until the light went out and the DRO
zeroed. The probe was retracted and then moved to the vice again
till the light went out. The DRO generally read 0.00mm or 0.01mm.
the test was repeated in x and y and then z. All gave the same
repeatability. This does not mean that the probe triggered with the
same amount of movement for each axis but I was pretty pleased non
the less.

Next was a more acid test, some actual digitizing. I didn't have a
proper probe tip made up so I just ground a brocken 1mm end mill to a
point and mounted this in the hub. I used Turbo cnc to run the mill
and do the digitizing, it allows the use of a single Gcode command to
do the scan. G32 I think it was followed by x,y and z limits, the
increment and the feed rate. It does a bed of nails type scan. The
probe was connected to a limit switch input without any debouncing
circuit.

I tried scanning a coin, a difficult test but it did work and the
point cloud was imported into Rhino, the features could be made out
once a surface was built from the point cloud. this involved joining
the dots in rows with a curve before removing the points and lofting
between the curves.

I will try to do some better tests of the in the future and also post
pictures showing the construction.

Anyway I am pretty sure the probe is good enough for any arty work
and with a bit of care should make a pretty useful tool.

Cheers,

Graham Stabler

www.indoor.flyer.co.uk/millingmachine.htm