A simple touch probe made with basic tools

Six contact points register any displacement.

LinuxCNC contributor and processing enthusiast [Andy Pugh] is certainly not afraid to try to make specialized tools to see how well they work, and this time he has been busy making a touch probe (video, embedded below) to check the accuracy of machining operations and general measurement applications.

These things are not cheap as they are basically ‘just’ a contact with a long probe, but as with anything that is specialized and machined with tight tolerances, you can understand why they cost what they do.

After inspecting and spending some time reversing the engineering of such a device, [Andy] then he continued to grab some PEEK bar he had lying around and threw it into the lathe (do you understand that?). He notes that Delrin would be more cost effective for those who want to reproduce this, but as long as you have the ability to process it and it is non-conductive, there are many other options you can try.

By using no special tools other than a collet block (like this one), all the angled holes and slots were made with ease using a special 3D-printed fitting for the vice. A nice, easy access, we think!

[Andy] tested the repeatability of the probe, mounted over his CNC-converted Holbrook lathe, and reported a value of 1 μm, which works quite well. The centering of the probe tip inside the probe body was a bit gone, as one would expect for something made practically by hand, but it is less of an issue as it appears as it results in a fixed offset, that can be compensated for in software. Maybe the next version will have some adjustability to dial it out manually?

The entire assembly is formed of two plastic parts, a handful of earth-treated hardened steel pins and a large spring. The only part that is extremely special is a shelf item tip. During the electrical connection, you may notice the use of a self-flowing verowire pen, which was something this writer did not know existed and has already placed an order for!

Reference The 3D model for the design is divided from [Andy]’s Autodesk Drive for your viewing pleasure.

Of course, this is not the first do-it-yourself touch probe we have seen, here is one for example, and here on Hackaday.IO here is an attempt to make one using a piezoelectric transducer.

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