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Touch Probe
Written
03-31-10
Parts built
01-01-10
Youtube video
at www.youtube.com/johngrimsmo
I made a
touch probe and touch plate for my X2. One of the first cnc projects that I
did on my mill, so it was a great little learning experience. I'm getting
some interference and false trips even when using shielded wire the whole
way.
Were I to do it again (which I might) I would make it
wireless.
There is a
plugin for Mach3 to have a touch probe screen, but at the moment I can't
remember where to get it. I am using the "toolchanger" screen sold to
me in the X2 dvd by
www.Hossmachine.info.
Here you can
see the two seperate probes, the left one is the touch probe and the right
one is the plate. I made 3 different probe tips and 1 plate, all from
4140 steel (machines NICE) and I even hardened and nickel plated them all
(totally overkill except maybe for the point). Also the 1/4" ball tip
on the left is pretty huge, not necessary. I really like the 1/8" ball
though, very useful.
You can see here how I made those little steel pins then
pressed them into the plastic lower plate (was a nylon cutting board from
wallmart). Then I soldered wires to each one, well I soldered first,
then pressed them into the plastic. The resistor you see is for the
LED which is hiding just under that resistor. In the upper part of the
pic you can see the center part. I turned those 3 little "fingers"
which will rest on the balls. The bolt is just an M6 bolt that the
tips thread onto.
The LED lights
up when it trips, which makes it pretty handy for manually jogging to an
edge, the whole workpiece lights up. For some reason a few months
later the LED fried, it's a bummer cause I found it handy.
Inner guts.
4140 tips. Like I said the 1/4" is just too big to
be of much use. For those that are interested, when turning these on
my CNC lathe, especially the two thin ones, I did not want to do the whole
length in one pass for fear of bending it, so I turned the first half
(halfway up the shaft) and left maybe 0.010" left, then I turned the second
half, then did a finish pass. For the pointed one I actually did the
finish pass backwards, from left to right, because I didn't want to start at
the tip and cause it to deform. Worked great!
The spring
keeps the triangular piece down until movement on the tip causes one of the
tripod legs to move and break contact. It's brilliant in its
simplicity. The wiring basically just makes a loop, with the 3 legs
creating contact. Hence the use of plastic for the triangle, so that
the 3 legs could be separate. I've seen guys make this bottom piece
from a PCB and they solder ball bearings on instead of those rounded pins
that I made. I wish I had done it like that! Soldering to those
pins was a pain, and having the wiring harness coming out and just soldered
to those pins has caused problems down the road.
Here's the
adjustment. The ball bearing spaces out the two parts by about, ohh,
0.100" maybe. The three M6 bolt holes that you see let me cinch it
down in any direction.
Zeroing in the
touch probe tip. It needs to be absolutely centered or else it's
function is pretty pointless. The major flaw with my adjustment method
shown above is that once mounted into the chuck I can't access the bolts to
adjust it! So I'd have to remove it, loosen one and guess which one to
adjust next, rinse, repeat. Took me about an hour to get it dialed in.
I've since seen other guys put little screws under their PCB at the bottom,
so the screws will tilt the PCB every which way until the tip is centered.
Brilliant!
I've been
using it now and then for the past year, it's a wonderful device that
everyone with the means should make/buy. The wiring sticking out the
side is probably my biggest complaint, especially how it's delicate 22ga
wire that's soldered to tiny pins. Every time I put it in, take it
out, move it, rotate it, etc that solder joint gets stressed. A quick
fix might be to ziptie the wires to the case, that way the zip tie takes all
the movement, not the solder joint. But I didn't do that so the wires
did break off, but I just soldered them back on.
A few weeks
ago I put the probe into the machine, then opened Mach3 and turned the
machine on, and right when I turned off the reset button the spindle turned
on (why, I have no idea) and ripped the wires out of the other end of the
cable.
My next
incarnation of this probe will be completely wireless. Now THAT will
be cool.
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Here are some
links to other touch probe makers:
$120 touch
probe very similar to mine, this is a GREAT price. Considering the
time I spent making mine, if your time is at all valuable to you, this is a
steal.
Wildhorse Innovations - The DRO-350 Store - Econo-Probe 3D Probe & Tool
Height Setter
Mach3 support forums:
touch probetool height setting probe
Simiar to mine with great info on digitizing:
Arnie -
Touch Probe
Nice simple plastic probe with the PCB idea:
Homebrew
touch probe
Arie Kabaalstra, very cool guy from the Netherlands with
a long thread on CNCzone.com about his machine build and touch probe
project. His design is where I got most of my ideas from. He
made his 1.25" dia so I tried to copy that and make it 1.5", but it made
internal packaging really tight. There really isn't any point to going
that small. Make it 2" and have tons of room to play.
My First CNC, own design, buidling in progress - Page 2 - CNCzone.com-The
Largest Machinist Community on the net!
Overly complicated but very informative and has great
Mach3 digitizing info and plugins:
The One
Penny Touch Probe
Great long PDF file about touch probes and digitizing:
Intricad - The design principle for an ultra sensitive touch probe
Google touch probe to see how the big boys do it,
Renishaw is a good company.
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Here are random pictures I've found online. These
are NOT my pictures, I've just compiled them for reference.
These two are Arie's:
My First CNC, own design, buidling in progress - Page 2 - CNCzone.com-The
Largest Machinist Community on the net!
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