an unusual cutting tool

[Mark Kinsler]

https://youtube.com/shorts/EIJP44fKNeA?si=cxXryECMmWipiLp1

That might actually work. Spark plug ceramic is, if all the ads from the 1960's were true, extremely hard but resistant to any sort of stress. I will have to experiment.

[Paul Koning]

Sure, it's probably fairly hard and resistant enough to shock to deal with the pressure pulses in the engine.  Better than carbide tooling?  I very much doubt it.  Carbide inserts are cheap and do the job quite well.  For cases where they don't (severely interrupted cuts), the best answer is high speed steel, rather than any kind of carbide.

The obvious benefit of this trick is that it's cheap, especially if you use an old worn-out spark plug, and easily available in third world countries.

paul

On Jan 27, 2026, at 6:30 PM, Mark Kinsler <kins...@gmail.com> wrote:

https://youtube.com/shorts/EIJP44fKNeA?si=cxXryECMmWipiLp1

That might actually work. Spark plug ceramic is, if all the ads from the 1960's were true, extremely hard but resistant to any sort of stress. I will have to experiment.

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[Mike Schietinger]

Wear eye protection 

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[Dave Typinski]

For turning wood, I bet a broken plug would work a treat. The fractured corner
might not get hot enough to become dull too quickly.
--
Dave

On 1/27/26 21:07, Mike Schietinger wrote:
> Wear eye protection
>
> On Tue, Jan 27, 2026, 8:00 PM Paul Koning <pa0...@gmail.com
> <mailto:pa0...@gmail.com>> wrote:
>
> Sure, it's probably fairly hard and resistant enough to shock to deal with
> the pressure pulses in the engine. Better than carbide tooling? I very
> much doubt it. Carbide inserts are cheap and do the job quite well. For
> cases where they don't (severely interrupted cuts), the best answer is high
> speed steel, rather than any kind of carbide.
>
> The obvious benefit of this trick is that it's cheap, especially if you use
> an old worn-out spark plug, and easily available in third world countries.
>
> paul
>
>> On Jan 27, 2026, at 6:30 PM, Mark Kinsler <kins...@gmail.com

>> <mailto:kins...@gmail.com>> wrote:
>>
>> https://youtube.com/shorts/EIJP44fKNeA?si=cxXryECMmWipiLp1
>>
>> That might actually work. Spark plug ceramic is, if all the ads from the
>> 1960's were true, extremely hard but resistant to any sort of stress. I
>> will have to experiment.
>>
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>
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[Mark Kinsler]

I've always thought that used spark plugs somehow looked useful, but that's the first repurpose I have seen.  

There was a store in Pittsburgh that sold rebuilt spark plugs.  They had new electrodes welded on and didn't look so great, but I suppose they were a standard item of commerce.

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--

Mark Kinsler

512 East Mulberry Street
Lancaster, Ohio USA 43130
740-503-1973

[Paul Koning]

> On Jan 27, 2026, at 9:22 PM, Mark Kinsler <kins...@gmail.com> wrote:
>
> I've always thought that used spark plugs somehow looked useful, but that's the first repurpose I have seen.
> There was a store in Pittsburgh that sold rebuilt spark plugs. They had new electrodes welded on and didn't look so great, but I suppose they were a standard item of commerce.

Interesting!

There are obvious applications for spark plugs in ham radio, as feedthrough or stand-off insulators. Nowadays most antennas are dipoles and feedlines are coax, but for open-wire feedlines this would make a good feedthrough, and similarly if an insulator is needed to hold something in a high voltage circuit such as a power amplifier, this would work nicely. I had a case like that with an 807 transmitter, but it so happened I had a "real" insulator handy.

Aircraft sparkplugs would work particularly well since they (if I remember right) have a screw attachment at the top rather than a snap-on one.

paul

[joel.e...@gmail.com]

The interesting thing about this project is that it wasn’t so much cutting as spin forming the end of the tube into a closed hemisphere.  I’ve mostly seen this technique used to form disks of metal into bowls.  I’m fairly sure that bowls made this way are formed by tooling that is not necessarily hard but is generally lubricated.  The metal disks would  be annealed before forming.  This guy used the friction to heat the tube red hot and then form it.

On Jan 27, 2026, at 9:00 PM, Paul Koning <pa0...@gmail.com> wrote:

Sure, it's probably fairly hard and resistant enough to shock to deal with the pressure pulses in the engine.  Better than carbide tooling?  I very much doubt it.  Carbide inserts are cheap and do the job quite well.  For cases where they don't (severely interrupted cuts), the best answer is high speed steel, rather than any kind of carbide.

To view this discussion visit https://groups.google.com/d/msgid/howthingswork/4B482A9F-F092-43FD-91D6-813FB01A8ED8%40gmail.com.

[joel.e...@gmail.com]

The broken plug would certainly cut wood, but I’ve never seen a wood turning chisel with a cutting edge shaped like the edge of a broken plug.

> On Jan 27, 2026, at 9:14 PM, Dave Typinski <dav...@typnet.net> wrote:
>
> For turning wood, I bet a broken plug would work a treat. The fractured corner might not get hot enough to become dull too quickly.

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[joel.e...@gmail.com]

Did the store that sold those plugs have a sideline of reboring severely scored cylinders?

On Jan 27, 2026, at 9:22 PM, Mark Kinsler <kins...@gmail.com> wrote:



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[joel.e...@gmail.com]

Most of the plugs I have replaced had become ineffective due to various forms of fouling building up on the insulation around the center electrode.  I have seen Allan Millyard, who is a demi-god among engine builders, burn that away with an acetylene torch and the plug back into use.  

On Jan 27, 2026, at 9:22 PM, Mark Kinsler <kins...@gmail.com> wrote:



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[Dave Typinski]

Prior to the mid-1930s, aero engines used screw-post plugs, similar to those on a Ford Model T.

For the last 90 years or so, aero engines have been using the style of wires and plugs shown below -- primarily due to the RF shielding required to keep ignition noise out of the comms & radio navigation systems and second to provide a more secure harness-to-plug interface.
--
Dave

[Paul Koning]

> On Jan 27, 2026, at 9:43 PM, joel.e...@gmail.com wrote:
>
> Most of the plugs I have replaced had become ineffective due to various forms of fouling building up on the insulation around the center electrode. I have seen Allan Millyard, who is a demi-god among engine builders, burn that away with an acetylene torch and the plug back into use.

There used to be spark plug cleaners -- sand blaster attachments where you'd screw the plug into the cleaner and it would direct a blast at the fouled insulator. I remember a J.C. Whitney catalog that showed these.

paul

[Joel Phelps]

The subject of cleaning spark plugs reminds me of the last time I needed to make a roadside spark plug change. I was headed from Mass to Burlington, Vermont and I was on Rt 91. It was early spring of 1971 (probably) and I was riding my Suzuki T500 two stroke motorcycle. I had ignore weather reports that said it might be sort of cold. Not a good plan since I didn’t really own any motorcycle foul weather gear. The T500 suddenly went from a 500cc twin to a 250cc single. I pulled into a rest area figuring is was a lead whisker shorting on of the plugs. I whipped out my trusty Suzuki provided tool kit and had the steel rod that provided the handle for the spark plug wrench promptly bend into uselessness. It was depressing to find myself in nowhere VT watching clouds roll in and spit snow. Fortunately, the lead whisker fell off on its own and I was able to continue my ride. This wasn’t the best of ideas as the temperature continued to drop and by the time I got on Rt 89 it was colder, snowing harder and my hands were so cold I couldn’t bend my fingers. Fortunately my girlfriend (the motivation for this ill considered trip) had access to the family chalet in Stowe and I ended up sitting under the carport watching the snow pile up waiting for her to come rescue me.

When I got home, I swiped a piece of drill rod from shop I worked in and threw the Suzuki rod in the trash. I put that drill rod in every motorcycle tool kit I had until I bought my first BMW (in those days BMW gave you real tools sufficient for maintaining their motorcycles) in 1985. I think I still have it. The young lady ended up dumping me a couple of years later but it was fun while it lasted.

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