Modified (tungsten-carbide tipped) Fluke TL71 Probes

[eKretz]

Thought some others might be interested in my latest project. I've sharpened up my 87V's probe tips a few times now but they rapidly dull again, so I decided to change them to tungsten carbide tips.

I grabbed a couple replacement points for General brand carbide-tipped scribers (part number 88P) and chucked them in a drill, then ground the steel part of the shank down to the same diameter as the carbide points (in this case about .042") for a length of about ¼" from the point, then cut the tips off so I was left with small cylindrical carbide tipped steel rods of .042" diameter x ¼" length.

Next I flattened the points on the ends of the stock Fluke TL71 probes and center punched them as close to center as possible with magnification. I used a small toolmakers clamp to clamp the probe square to the flat surface of the clamp, then drilled .045" holes down into the probe tips to the proper depth on a drill press - with the probe handles extending through a hole in the table.

Last, I fluxed the tungsten-carbide tips and the probe tips with Stay-Silv silver soldering flux, assembled them, and placed the probe body into a container of water so that the probe handles were submerged about 1/8" in the water and then silver soldered the tips in with a MAPP torch.

Following that, I sharpened the tips with diamond hones until they were good and sharp. The following images show the finished product - the brass of the probe tip, the silver solder line and the tungsten-carbide are all visible in the close-up. These ought to last a good long while.

[FlyingHacker]

Looks pretty slick. Let us know how they hold up.

[eKretz]

They should be pretty well invincible now. I have one of these exact same scribers that I use on steel all the time and it has lasted years. Probing soft electronics metals will be child's play for these.

[eKretz]

Thought I'd update this. The brass part of the probe tip oxidized and began to look unsightly pretty rapidly, so I ended up nickel plating the probe tips. They are still dead sharp, haven't had to sharpen them since making them. The nickel plating has solved the oxidation problem.

[TimFox]

How much series resistance do you get with these probes and tips?

[eKretz]

Pretty much the same as original. I haven't actually checked individual probe/cable series resistance with a milliohmmeter, but with everything nice and clean and probes touched together in ohms mode on my 87V it's generally around 0.14-0.20 ohms.

[David Hess]

Music wire is hard enough to make good probe tips; do not try to cut it with your diagonal cutters.  Tungsten electrodes for MIG welding might be good.

[tautech]

Music wire is hard enough to make good probe tips; do not try to cut it with your diagonal cutters.  Tungsten electrodes for MIG TIG welding might be good.

Fixed that for you. 

MIG wire if thick enough might be fine too as it's high tensile however being steel it will rust.
IIRC some use sewing needles for tough sharp probe points.

[TimFox]

Years ago, when steel phonograph needles were used to play 78.26 rpm discs (0.003" nominal groove size), there were probes with a chuck to hold standard phono needles.

[eKretz]

Yeah for most softer materials found in electronics work hardened steel will do plenty fine. I occasionally get into crusty old steel terminals when working on cars, trucks, tractors etc. so I wanted something that would likely not need any maintenance. Ever. Tungsten carbide is waaay harder and more abrasion resistant than even the hardest steel. I'm guessing I'll scrap these probes before I'll need to sharpen them.

Oh, and no these would not work well for TIG welding. Generally those are almost pure tungsten with a very small alloying content of lanthanum or zirconium, etc. (Was a machinist, toolmaker and welder in a past life. Still have my own little shop with machining and welding equipment).

[TimFox]

Tungsten carbide is a decent conductor with excellent mechanical properties.  I did have a disappointment back in grad school, where I needed conductive precision balls that were not magnetic--WC seemed a good idea.  When I complained to the vendor that they were very magnetic, he admitted that they were alloyed with cobalt.