Tech request. Plastic.

I want to build something that needs to be insulated.

( a distributor test rig )

I have an old distributor machine, probably from the '50s.

Id like to be able to hook up a dist, with its cap and wires, and go into fixture that would simulate the plugs.

Part of that needs to be plastic to be insulated.


What kind of plastic is easy to cut ( or machine ), drill & tap, etc?

And is easily avaiable?

 

how thick would you need? the reason i ask is i used to share a building with a sign shop and when they changed out a lighted sign face they would throw out the old face. it is a pretty industructable plastic that machines easy, but it is only 1/4 thick. check a sign shop near you the scraps or old faces should be free.

 

Thanks for the tip.

Maybe if can be glue'd I could build it up to the thickness I need?

 

how about...dare i say... wood?

 

Delrin can be cut,drilled and glued and is damn near indestructable? (White cutting board material)
I've seen it polish and wear down stainless when used as guides in track of water well-lift tracks.
Dunno the cost,but how much would you need?

 

mcmaster carr has lots of plastics, I've used uhmw polyethylene for some robot parts. It machines ok, although it doesn't cut as clean as you'd like. It's pretty inexpensive for a block, it comes in a wide variety of shapes and sizes.

They have a pretty good online catalog, search "plastics" and you can read all about the various kinds of plastics available.

 

I think 2 sticks of 1"X1" about 18" long would be plenty.

 

phenolic sheet maybe?

I rigged up a simple plug holder for my machine so I could safely spin magnetos but I did not need to insulate it, I needed it to be grounded to the machine

 

Easy-to-Machine Chemical-Resistant Polypropylene

two bucks a foot for a 1x1" bar

 

I am a fan of Delrin. I use it in cars and machines, all over the place.

 

I've had good luck in the past letting my fingers do the walking through my local yellow pages. I've found plastic dealers and have even been able to dig through the "drops" and scrap bins for freebies (especially if you buy the shop guys a coke)

Good luck
Bobby

 

Basically, what I want to do is make replacement plugs.

Spaced roughly the same distance as plugs are on the heads, so the plugwires will fit without too much trouble.

I dont want to use acctual plugs because I dont want anything with internal resistance ( and I believe most modern plugs have internal resistance )
And I want to be able to adjust the gap, so I can vary the length of the spark.
( because the internal pressure in the combustion chamber affects the spark too )

I'm thinking by measuring the distance a spark can go, I should be able to tell if there are any problems in that area.
Like a bad wire, a bad connection, or cap, etc.
And I should be able to tell right away which one was causing a problem, if there is one.

 

U.S.Plastics is a good source we like to use at work. I think their prices should be a little better than Mcmaster-Carr also. Check out this link for UHMW rounds.
http://www.usplastic.com/catalog/item.aspx?itemid=23155&catid=868
UHMW is another one that machines very well while I would stay away from gummy (doesn't machine clean) materials like polypro and such.

Smokey

 

ah, very interesting

I seem to remember a thread about just such a setup

wonder if it's still floating around somewhere..

 

To use real spark plugs, just check the center electrode with an ohmeter. Real plugs will show 0 ohms.

then you just have to remove the ground electrode and add the adjustable gap. Or remove the ground electrode and use body threads to adjust a gap to ground.

I think you would use the compression pressure to determine the gap, right?
So if you wanted to fire a plug at .035 in 150 psi chamber, you would have to jump a .350 gap in room air.

cool project.

Frank

 

I do not understand the goal of your creation but Delrin is a good material to work with.

 

found it:

http://www.jalopyjournal.com/forum/showthread.php?t=628039&showall=1

so you would substitute electrodes for the plugs to get what you are talking about right?

 

We had a Sun distributor test machine with the mechanism you described, two insulated blocks with opposing contact points. One of the blocks was on a hinge and the gap could be adjusted with a simple lever.

 

WOW!

That is great info.

Thank you Paul.

Edit.

I was thinking about using a 1/16 dremel tool collet with a piece of Tig welder tungsten in it screwed into the insulator.
With a brass screw into a brass or aluminum bar on the other side that is grounded back to the distributor housing.

But starting with a non resistor plug screwed onto the insulator would be a lot easier to do...

 

but not if it's mounted in plastic

 

Yeah, I realised that when I saw the pics in your link.


Major flaw in my thinking...

 

It looks like Delrin or Plexi is probably the way to go.

The hunt is on...

Thank you for all the Info guys.

 

Delrin! Need any let me know I have tons


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Cool!

Thanks, man.

I'll do some measuring, etc

And I'll let you know.