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Touch probe for measuring and digitizing
A probe to attach on a CNC. A cheap variant of the digitizing probes.3D printer parts and enhancements
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This is a sensor probe inspired by Bertho's work as well as other people's work, old patents and some original ideas.
It is used to measure and digitize / scan objects by detecting when and where the probe touches the object.
You will have to print 3 parts (could be made with a cnc mill or a lathe as well) and make 2 pcb plates. (could be done by hand if you are good at it).
It requires no soldering on the steel balls (it can be difficult)
This one is made to be used in a hobby CNC mill (43mm collet mount) but the concept can easily be adapted to any kind of CNC machine (3d printers, mounted in the spindle, measuring rig...)
The electrical contact is cut as soon as the probe touches something from any direction.
Here is how it works:
-The lower PCB hold the balls in place
-The upper PCB presses the balls and makes sure they go nowhere,
-The probe holder has 3 steel pins that rests each on a pair of steel balls. That way there is only one position where the 3 pins touches the steel balls.
-The balls form a loop that is electrically closed only in the situation above
This means that the circuit is opened as soon as the probe is moved in any direction, even the slightest distance. It also means that the circuit is closed as soon as the probe is not touching anything.
From what I can see you can reach a precision of 20 microns (0,02mm) which is the most accurate my CNC is. You might get even better accuracy with yours!
I use it with my Profiler CNC and Galaad to run it, Mach3 supports it as well.
It gives quite good results scanning at 0,1mm resolution (plunge probing).
Materials and methods
- Print the parts from the STL files (choose the holder you want: with holes to insert the pins snugly or without if you want to glue them (other than 3mm)
- Cut 3x 3mm drill bits to use the shanks as contact pins (length 13mm)
- Make the PCBs (I milled mine, but etching would be fine as well).
- Find some springs
- Find 6x 4mm steel balls (I got mine from Conrad Electronic)
- Solder two wires on the PCB (in the "C" areas is easier)
- Connect to your CNC input
- Enjoy !
-To adjust how vertical the probe is, slightly unlock the 3 nuts on top and turn the 3 screws until you get the right position. Then tighten the nuts again.
I use an old 3,2mm mill bit as stylus, it works quite well.
This design requires no soldering on the steel balls.
The parts are printed but can be done with conventional machining tools (lathe, drill press).
In the Zip file you will find all my source files (Solidworks) and also the Galaad files I used to mill the PCBs
The parts represented as small tubes are actually the springs.
Issues are used to track todos, bugs or requests. To get started, you could create an issue.
I guess in the end I'll simply buy a commercial one
160eur +tax is perfectly acceptable to get a better result then a DIY one.
I chose an old endmill as a stylus since I have a lot of broken/dull ones and they are stiff as hell...
My guess regarding accuracy would be to get some gold-plated steel balls and rods to improve electrical contact and also make the parts out of machined metal instead of flimsy printed plastic. As it is, the accuracy of the probe is at least as good as the one of my mill.
When it comes to fastening, this design is for machines with a 43mm spindle collet, so you put the probe instead of the spindle.
To put it in a regular collet (ER11 or whatever), I suggest this variant: http://www.thingiverse.com/thing:507156 (but I would definitely make the shank from metal if you want any kind of repeatability).
I very much apreciate the technical drawings. Great work!
Great idea on adusting the centricity of of the probe shaft with the 3 bolts.
I guess the accuracy could be improved by a larger diameter and longer probe shaft?
Do you have some photos of your finished design?
How do you attach it to the spindle? I see nothing that could be mounted into an ER11 collet.