The making of a very sharp probe!

A dollar store “scrapbooking” purchase turns into an electronics tool.

Always on the lookout for something that can be used as it is not intended, I bought a “piercer” in the crafts aisle of my local dollar store some time ago. Actually I bought one of each size, three in total. They look like regular stick pens, but with sharp points instead of ballpoints [Photos 1 and 2]. They are even based around what appears to be an empty ink tube. The three sizes, aparently taking naming guidance from some coffee houses, are Needle, Fine and Medium. Truth be told, I must have bought a dozen by the time I was finished!

Photo 1. It looks like a pen!

The story...

Photo 2. The starting points. Sizes are Medium (black) which is the thickest one, blue is called Fine and the red, which is called Needle, is the sharpest.

So why did I buy them? Probes, circuit probes, my friends. I had this idea that their sharp points would be really good for piercing oxidization, conformal coating, or anything else that came beween me, my DMM and a circuit under test.

Photo 3. The cap end. It was easy to drill the proper size hole in the cap.

So I got some test lead cable out and started hacking. The outside diameter of the wire was such that it fitted nicely inside the tube that was there: it only remained to drill out the end cap with a similar sized hole ([Photo 3], a bit snug is good) and to drill a hole in the end of the tube near the business end for the conductor to exit, wrap the conductor around the metal and tighten down the end cap. Well not quite, since there are plastic (insulating) bits that get in the way, but you get the idea. I did have to solder the wire to the metal tips, [Photo 4]. Carefully—the plastic has a low melting point!

Photo 4. The sharp end. You can spot the slot in the flange, which was already there, that I used for the stranded wire to pass through. You can also see the hole I drilled in the tube for the stripped wire to exit from. Guess I should have cleaned off the flux!

The finished probes.

For some reason when I built these I made a blue one instead of a black one Photo 5. There were some problems found:

• The manufacturing quality control, as you might expect, is poor. Amongst other things, this is reflected in the lengths of the pins. Many of the pins are so long that if the caps are not put on just so the pins stick into the cap. I enlarged the holes the caps a few times to alleviate this problem. You can see a large difference in pin length in Photo 5.
• Although it seemed like the ferrules were sized to fit their pins there was not always conductive metal to metal contact. The soldering option became mandatory.

Photo 5. Two finished probes.

I did find that the points on finest (red) ones were too brittle to be useful. But of course I wanted the red units for their bodies! So a set of four is needed if you want to use the medium points in a red and a black body.

How'd they work?

I find I reach for these probes off of my probe hanger very, very often. They do the intended job very well! Obviously these should never be used on any live circuit where the voltages are higher than say 15 V! I guess the screw-on metal caps could be insulated for safety just in case, but so much of what we do is powered from 5 V or lower these days. Also, I use them frequently on un-powered circuits to check continuity or resistance, so no concern there. If I were to use them frequently for higher resistance measurements then insulation would become more important so that skin conduction didn't interfere with measurements.

And, though I was not thinking in these terms when I made them, they are good for insulation piercing as well as getting through any coating on soldered connections. They can also be used to connect right through solder mask to tracks!

Availability?

The original tools have gone from my local dollar store, perhaps because they might be dangerous? Either the sharp nature combined with kids or the fragility of the finest points might have caused them to be removed from the market, I don't know. There's an URL on the package and it still is alive (but has no details of products--you have to be a dealer to log on to the site) but I've sent a query to the email address (info@multicraftimports.com) that is supplied. An eBay search turns up none that look like this: there are some all-metal ones which might work, but the paper piercing sub-hobby seems to have gone towards rolled wheels with patterned piercers—not appropriate at all!