Home made sparkplugs

[Doug_C]

Here is a drawing of my spark plugs. These are 1/4-32 with a .04 tungston electrode. I have not had the chance to run them yet. Keep in mind that these were designed for my Morton M5 radial. The threaded end could be made longer to reach into the combustion chamber of other engines.

The insulators are from Corian counter top material. The stuff cuts like fiberglass and fine sand. Use carbide. I cheated and spun these on a CNC lathe.

DC

[Doug_C]

Here is a photo of the plugs. I hooked them up to a magneto assembly, just to seem them spark a few days ago.

DC

[Harold_V]

Doug,
Great looking plugs! Problem is, even though we know the size, there's nothing in the pic to give perspective. How do you feel about putting a dime in the pic with the plugs and reposting for us? That would be very impressive!

How did you get your blue color? They look prototypical as far as I'm concerned.

Harold

[Doug_C]

Thanks Harold,

The blue as in background must be from the camera. I took the picture upon white printer paper. I edited the PIC to include the dime this time. I guess I did not think of perspective reference. It does help a lot.


DC

[Harold_V]

Hey Doug,

Oh, yeah! They're way cool with the dime for perspective.

Sorry about my confusing statement. I guess you weren't reading my mind. I was referring to the bluing (or blackening when I think about it) of your plugs. That really looks good. What's your process?

Harold

[Doug_C]

Hi Harold,

These are natural steel color. I did not blue them. It must be the hue my camera puts on them.

I used mild steel hex material. Turned the threaded end complete then screwed them into a stub shaft for cutting the internal. That involved predrilling and boring with a 5/32 endmill to get the flat on the under side of the tang. The insulator bore and seat were cut with a standard 118deg drill point.

The tang was cut next by screwing them "tang end pointing up" into a 1/4" plate of aluminum held overhanging the vise jaws. I climb cut it all around in one pass as to prevent bending the tang during milling.

The insulator is slipped into position with a bit of high temp loctite and then set with the swedging tool. I did crack a few of the insulators from to much crimp, so that area could be made thinner to reduce the chance of fracturing.

The electrodes are cut long and ground square on one end. I placed a gap setting shim to bond into position. Once glued in place with the loctite, the brass connector end can be soldered to the extended piece of tungston. Then the tungston can be ground off to length.

Not to tough, but very tedious! [img]/ubb/images/graemlins/blush.gif"%20alt="[/img]


DC

[Michael_Az]

They look great. Good job.
Michael

[Harold_V]

Doug,
Yep, very tedious indeed! [img]/ubb/images/graemlins/smile.gif"%20alt="[/img]

I specialized in miniature work when I ran my shop, so making things of that nature is right down my alley. I have to confess that I like small work. [img]/ubb/images/graemlins/cool.gif"%20alt="[/img]

I've attached a pic of some parts that I made just before I closed the door on my shop back in '83. What you're looking at is a defense part called an antenna latch. There's one of the finished and assembled pieces in the picture, along with three other parts, all in different stages of completion, but each showing a different side of the latch.

The long spike is a common straight pin.

The finished latch is made up of four pieces, two .022" diameter stainless pins, the base piece, which is Armco iron (carbon free), and the latch itself, which is aluminum.

You can't see the one stainless pin, it is installed to hold the iron base piece to the latch. In the completed state these were anodized and also coated with a solid film lubricant. Fun job, took me two months to make 209 of them, all of which would fit in the palm of your hand.

Every operation on these parts was done on a Bridgeport, all manually. It took 26 different operations to make the parts. In general, tolerance on these was ± .003", with several ±.001" dimensions, including the two turns on each side of the large (.031") hole. The turns were done using a boring head and an indicator to control depth.

Imagine holding these things without crushing them! [img]/ubb/images/graemlins/shocked.gif"%20alt="[/img]

The pin shown in the assembled latch seems to have been sllightly bent at some point in time. It should be straight.

Harold

[Michael_Az]

Those are some pretty small parts Harold. I can imagine they would be hard to hold with anything. Also hard on the eyeballs by the end of the day.
Michael

[Doug_C]

For those of us that like the miniature side of mechanics, tolerances are scaled likewise.

Gluttons for punishment aren't we?

I made some parts in the early 80's that looked very similar to that. Only the hole you have at .031, on mine was .250. We turned the side bosses in the lathe on a mandrel. That would not work at .031 the same for some reason. [img]/ubb/images/graemlins/crazy.gif"%20alt="[/img]

DC

[Ken]

Doug:

Those are some great plugs! I have been thinking about making some of my own for a while, and your description was very helpful.

Questions:
You mentioned swaging the corian into the steel, along with using some hi-temp loctite. Just what do you do to swage the corian into the steel? Is it a press fit, tapered, or what?
Also, Do you turn the corian down further after it is swaged into the steel (the slight taper and rings), and then lastly drill the hole for the tungsten electrode?

Where does one obtain the tungsten electrode matrerial?

Ken aka Ozarks Hermit
Shell Knob, Mo.

[Ken]

Doug:

Whoops! I neglected to see your drawings of the plugs, including the swedging tool. Next time I should look befoe I ask.