Spark Plug constructlon revisited

[GailInNM]

Thanks for the comments. All are welcome. If you have a different way of doing things please post them.
I apologize for the time lapse in this thread. Life has a way of getting in the way of playing with toys.,

There are a couple of ways of cutting the OD of the washers. The first way that I will illustrate takes the least amount of tooling but is slow to make the washers. Still it OK for a dozen or washers. A mandrel is made from 1/4 diameter rod by turning the end down to a smooth sliding fit on the ID. Make spud about 1/2 inch long and keep the inside corner sharp. A clamping sleeve is made out of the same material. It is about a 1/4 inch longer than the spud, about 3/4 inch long. It is drilled through so it is a sliding fit on the spud. Face off both ends so they are square and sharp.

The washer blanks are rough cut out with metal snips and then the corners are nipped off.

Here is the rough cut washers but the corners have not been cut.

The blanks are loaded on the mandrel. Up to a dozen can be put on at once. I have put on 6 in the photos. As copper does not machine well so the blanks are filed to be sort of round and then turned to about .005 over size. The copper will have smeared enough that the washers will be stuck to each other. Removing the last 0.005 with a file will remove this smearing so the washers will separate.

Gail in NM

 

[GailInNM]

Another method of producing the OD is by punching with a setup similar to that done when punching the ID. The punch is made from 1/4 stock and has a pilot turned on it that is a close sliding fit in the ID of the washer. It would be possible to drill the rod and insert the pilot, securing it with Loctite. The taper on the piloot just makes it easier to get the punch started in the ID of the washer.

If the die has a flat top as shown in the lower left of the following sketch it will take a fairly large amount of pressure to punch the washer. out. It two or three strikes on my small mill, Thiss pressure can be reduced by producing a shearing angle on the die as shown in the lower right part of the sketch. Although it would be easy to put a shearing angle on the punch using an inserted pilot the washer produced would be neither round or flat. Also notice that increased the side clearance from 0.002 to 0.003 inches. This also reduces the pressure required. This is 12% of the material thickness so a small burr may be produced. This burr can be easily removed if desired but as it is outside of the pressure sealing area of the washer it will not hurt anything if it is left on.

Gail in NM

 

[GailInNM]

A third method of making the washers is really just a rehash of the punching of boh the ID and OD. The punches are the same but the die has a guide for the punches built in. This allows the punch/die set to be used in an arbor press or the the punches to be driven with a small hammer. The difficulty with this method is that the punches are difficult to remove after punching. A few ways of to remove the punches iare:
1. G grip the punch with pliers and twist while pulling.
2. Cut some shallow grooves in the punch body so a pry bar can give extra force.
3. Leave the ID punch flat and drive the punches out with a small brass punch.

The bottom of the die uses the same relief as before. The upper portion has holes that gives a smooth sliding fit on the punch body. A little side play is OK as the punches will try to center on the cutting part of the die as soon as the punch starts to enter of the stock.

Another advantage of this method is that no set up is required so you can punch out a few washers and store the tooling. Then you can pull out the tooling and punch out a few more if required at a later date.

No photos as I have not done this since I got my kick press 30 years ago, but I did use it prior to that.
Gail in NM

 

[GailInNM]

I have made many plugs using Corian and it works fine but is quite brittle. Also it is difficult to find in some overseas countries. I went searching for a replacement material and fount that pulltruded fiberglass epoxy rod has slightly better high voltage insulating qualities and better heat and flame resistance. It machines easily and the swarf is fine and does not pack up as bad in the flutes of small drill bits.
Best of all it is easy to find as it is used as the shaft for bicycle safety flags. Most of the time the flags are sold with the flag glued to the shaft so when the flag wears out the old shaft is thrown away. So if you ask around you may find one for free. But even if you have to buy one they can be found on Amazon or Ebay for $10-15 for a 6 foot one with bike mount and flag. And that i s several lifetimes supply. All that I have seen are 1/4 inch diameter and have come from China so should be available in most countries.
I have only made a few plugs with it so far. All have tested OK. I ran one of them in an engine for about 25 hours. Then, I inspected the plug under a microscope and could not see any depredation of the insulator.
GailInNM

 

[simonbirt]

I have made them using PTFE insulator, I know that it gives off nasty gases if it melts. I would not use it in a high performance application but recon it is OK in my hit and miss engine. The combustion temperature is clearly above the melting point of PTFE but the cylinder head is an effective heat sink. In fact the whole engine is made out of material with a lower melting point than the combustion temperature. The advantages of PTFE is that it is easy to machine and it seals easily arround the electrode.

 

[Steamchick]

I heard someone say they simply used fuses from the domestic plug. The insulator ceramic tube can be machined (carefully), but 2 of 3 made good plugs (or so I believe). But maybe different countries use different fuse bodies and different ceramics. If you can work glass, you may be able to glaze a wire core, then glue it into the steel body? Or use exhaust pipe sealant clay to seal a ceramic tube around the core wire and into the body?
Lots of options!
Let us know what is best?
K2

 

[Jasonb]

I've done them using glass tube as the insulator and a tungsten tig electrode down the middle all put together with Locktite "Black Max" as per Nick Roland's design.

 

[Steamchick]

Nice one Jason! Should work I think - and you can tune the mixture by flame colour with this one!
K2

 

[Steamchick]

Brilliant! Thanks for the explanation.
Considering using PTFE, I like your idea of the grooves so the epoxy forms a structure that resists the sheer from the internal engine pressure on the insulator. Have you considered making the assembly so the shoulder is on the inside part of the insulator, and assembly from the inside? - Of course, this means the side electrode must be bent after the insulator is installed. But obviously your method is successful, so no reason to change. What engine do they run in?
K2

 

[simonbirt]

Here are the drawings and construction notes.

The photo shows the tooling used. Left to right top to bottom:

Screw gauge for single point thread cutting
Swaging tool
Block to support insulator and electrode while punching over top
Gauge for body
Finished bodies
D bits for body and insulator
Punch to attach cap
Form tool for cap- radius, groove and parting
Mandrel to hold bodies
Prototype plug

 

[GailInNM]

Great ideas and methods Jason, Steamchick, Simon and others.
Very nice constructions plans Simon.

By sharing our ideas and methods novices builders can see that spark plugs are not really "spooky" and that as long as a few basic techniques such as spark gap, adequate electrical insulation and sound mechanical strength are met they will work. So designs can be mixed and matched to suit the builder's tools, tooling and material availability and with confidence that the plug will work. And experienced builders can also get new ideas to incorporate in their next build.

Thanks for sharing everyone.