Nikken BT40-UMT200 3D Touch Probe - BT40 to Kwik-Switch Conversion

One day while setting up for a job, I irreparably damaged my dollar-store electronic touch probe by cranking X with the wrong scale set. Instead of ten thousandths, it went tenths. Ouch. In the past, I've been able to bend it back into shape with the help of an indicator, but it was high time to get a real indicating tool anyway.

So, I went shopping and found a great deal on a Nikken BT40-UMT-200 3D Touch Probe. It's a 3D Electronic (LED + Tone) touch probe with at least 6mm Z and 13mm X/Y overtravel protection. Repeatable to a few tens of microns, not only will I get substantial extra accuracy due to the quality of the tool, but the overtravel protection is perfect for the occasional goof during setup.

Nikken BT40-UMT200 3D touch-probe with over-travel

I took a chance while staring at the photo on eBay - if I purchased it, could the probe be removed from the holder? Was it just like the straight-shank probe merely tucked inside a BT40 holder? Well, I reasoned that it probably wasn't directly cut from the toolholder, and went for it. When I got it apart, it was slightly different than I imagined; 9V instead of AA batteries, it had no shank, and the BT40 holder was tooled as the body to hold the battery and piezo transducer. Luckily, I had a 1.25" endmill holder exactly the same size and diameter, albeit with a slightly larger bore that would need sleeving.

I turned down the case-hardened endmill holder to accept the outer sleeve from the original, and turned a shoulder on the inside to seat the probe. I didn't want to introduce any error by turning the holder in the lathe, and it was particularly awkward to hold it at the ends and turn the inside shoulder, so I mounted a boring bar in a chuck on the mill table, put this new probe toolholder in the mill, and used the mill itself to turn the shoulder to keep runout to a minumum. Wouldn't you know it though, I grew impatient. And rather than buying a proper high-quality tap, I used some old home-hardware store over-hardened and brittle M4 taps and snapped one of the fuckers off in the very last hole to be tapped. I could swear. Again.

I made a few mistakes that I wish I hadn't made such as drilling through the old body after I had sleeved it. The case hardened inner surface caused compression to build up in the drill as I drilled through and when it popped through the inside surface, it pushed the sleeve too hard causing it to warp. In the end, I had to press-fit the probe even after grinding down some of the buldge. It worked out though since I lost one of the three tap holes. I might go back and drill three more, but I was in a hurry to try and use it :-)

The final product.

Word from the wise(er): Don't cheap out on taps.

It's all done with copious pictures to boot.