Problem- Making Spark Plugs

[bob2251]

I want to build a small radial engine , but the smallest plugs I have seen listed is 1/4 " And I will need smaller than that. What do you use as an insulator

[dynosor]

Don't know how to make a ceramic insulator, but how about these plugs?

http://sparkplugs.morrisonandmarvin.com/

[stevehuckss396]

Originally Posted by bob2251 I want to build a small radial engine , but the smallest plugs I have seen listed is 1/4 " And I will need smaller than that. What do you use as an insulator

I made a spark plug that had a 6-56 thread. The insulator was made from Corian counter top material. The electrode was .020 nichrome wire super glued thru the corian. I dont have it any more because i dropped it and it broke.

It worked!

[vlmarshall]

I've seen machinable ceramic... I think McMaster Carr sells it...
Here's a link.
http://www.mcmaster.com/#machinable-ceramics/=1zopf8

[stevehuckss396]

Originally Posted by vlmarshall I've seen machinable ceramic... I think McMaster Carr sells it... Here's a link. http://www.mcmaster.com/#machinable-ceramics/=1zopf8

Looks like it would be good stuff. At 7 bucks an inch for 1/8 inch rod, i think i would stick with the corian. I got a 20 pound box on ebay for 8 bucks including shipping.

[vlmarshall]

Originally Posted by stevehuckss396 I got a 20 pound box on ebay for 8 bucks including shipping.

Wow, I'll have to remember that one.

[LongRat]

If you can get it, you could try Macor. It is a machinable mica based ceramic and I can tell you from experience, machines very well with carbide tooling. It has the electrical resistance you'd need but also very good thermal insulation and low thermal expansion.

[stevehuckss396]

Originally Posted by LongRat If you can get it, you could try Macor. It is a machinable mica based ceramic and I can tell you from experience, machines very well with carbide tooling. It has the electrical resistance you'd need but also very good thermal insulation and low thermal expansion.

Again 7 bucks an inch for 1/8 inch. Corian is cheap and will live in a model engine for years.

[T.L.A.R. eng]

bob2251, can you tell us anymore about the radial engine you are building?

[One of Many]

I made about 10-15 a few years back. The trials were made of pink corian and stainless electrodes, which I gave away as trinkets to friends. The keepers were white with tungsten electrodes. Spark was decent!

Pink is nice on some things, but not my engine. LOL!

DC

[CarveOne]

Originally Posted by One of Many I made about 10-15 a few years back. The trials were made of pink corian and stainless electrodes, which I gave away as trinkets to friends. The keepers were white with tungsten electrodes. Spark was decent! Pink is nice on some things, but not my engine. LOL! DC

How do you attach the ground electrode? Arc weld it with a power supply of some sort using a fixture to hold the parts in place?

CarveOne

[One of Many]

Originally Posted by CarveOne How do you attach the ground electrode? Arc weld it with a power supply of some sort using a fixture to hold the parts in place? CarveOne

The insolator well is drilled to a depth that leaves a flat inner face cap on the ground electrode end. I then screwed the threaded steel body from the underside of a 1/4" plate of aluminum held in my vise. The cap, errrr soon-to-be ground electrode setting proud above the plate was then CNC'd by a U shaped path, profiling the tang in one pass. Unscrew that one, swap it for another and hit the go button again.

The upper wall of the steel body is thin enough to swedge over(with a custom tool) after locktiting the corian insolator into the body for a good leakproof seal. The spark electrode is sized for length to set the spark gap, then locktited or superglued into place.

DC