Little Demon V8 - helpful hints (hopefully)

[Carbuilder]

How to machine these tiny parts, especially the cross-hole?



Here's one way not to do it. I drilled holes in a plate the thickness of the length of the pins and put over-length ones in:



The idea was to mill them off to the correct length. But I made the fit of the pins too loose and they spun when the end mill hit them. Also chipped the teeth on the carbide end mill....another one bites the dust!

So I drilled new holes in the plate so the pins were a fairly tight press fit into the holes and that worked well to machine them off to the correct length:



The longer one is my indexing pin, for the next step. I had the spacing exactly .2" on centre for the pins, as well as the index pin. So with that known, I flipped it up on end, indexed off the longer pin, and accurately drilled the cross holes:



Then I just tapped the pins out with a pin-punch and job done!

Rick

 

[Eccentric]

Nicely done. I like to see how you are experimenting with ways to streamline the machining process when many copies of a part are required. "Mass production" really helps to produce a set of parts that are equivalent and not too time consuming.

 

[stanstocker]

It could be helpful to secure the pins in the fixture with superglue / CA / Krazy Glue as you prefer to know it. I use this frequently to make small parts. Gentle warming with a torch will allow the pins to be pressed out, or soaking overnight in a closed jar of acetone will dissolve the glue. This is particularly useful for light flat bits that are somewhat fragile, gluing a brass clock gear blank to an aluminum carrier makes life easy, trying to work with one unsupported is often frustrating.

 

[Carbuilder]

Spark plugs done.....hopefully/maybe...

I made one plug some time ago as a test. I couldn't find Corian anywhere, so I used PEEK. It is slightly flexible but should take the temperature OK.



Got back to making more plugs. Machined all the parts, except the insulators.



The parts certainly keep getting smaller and smaller!



Since I couldn't find Corian locally and didn't want to order a large piece, I bought the Corian insulators pre-made. I made 10 plugs and they all looked great.



BUT....

When I checked them all after swaging, 6 of them were cracked. The Corian was cracked right at the crimp. I thought maybe I went overboard with the crimping, but giving it more thought, I don't think so.

When I assembled them before crimping, the insulator was not protruding from the nose of the plug. I was pretty sure my machining was accurate. I measured the insulators and found that they were all about .020" too short; it was the part that goes into the plug that should have been .360" long and was slightly under .34". Since the electrodes were already bent, it was not possible to trim down that end of the plug. I figured there was no harm in making the hole in the other end of the plug a little deeper. Reworking them, I may have made the holes a touch too deep.

I think what might have happened is the extra length of the plug body material that is crimped inwards gets forced into the insulator and cracked it.

I put some thin CA glue into the crack and that seems to have bonded it nicely. Not sure how strong it is or how strong it has to be, but I'll try and be careful with them. I may put an extra fillet of thicker CA at that seam. Or maybe make a small tube that goes over that area, with a taper inside to match the crimp, and CA or JB weld it on to reinforce that area. Can't really fix it any other way without scrapping the 6 plugs. I should have measured the insulators before making the plug bodies.

Rick

 

[peterl95124]

wow, those look really great !

IIRC most CA glues have a max temp slightly below boiling (though there are some special ones that go slightly above), so perhaps HYSOL epoxy would fair better, probably even loctite would fair better.

I've made a fair number of Corian insulators, they work, but I recently bought some scrap Macor on eBay, its a machinable glass-mica composite that's even better than I thought it would be, I turned it with carbide because that's all I ever use, but drilled it with HSS, 1/16 and 1/32, and the drills weren't affected at all (in contrast to alumina which dulled a 1/16 carbide spade drill just to get 1 diameter in and caused it to wander all over the place, and then it shattered when I tried to part off the buggered end)

both of these substances are brittle, and while I have succeeded in using a roller ball bearing to "roll seal" the body around the end of the insulator (at least in theory, I can't really check for cracks after its sealed in there), I mostly use loctite, its simple, easy and high temp loctite grades are available for up to 650F.

 

[Carbuilder]

wow, those look really great !

IIRC most CA glues have a max temp slightly below boiling (though there are some special ones that go slightly above), so perhaps HYSOL epoxy would fair better, probably even loctite would fair better.

both of these substances are brittle, and while I have succeeded in using a roller ball bearing to "roll seal" the body around the end of the insulator ( I can't really check for cracks after its sealed in there)

Thank you very much.

Not sure how hot these will get at that location, but yes, maybe too hot. I should probably JB Weld a small reinforcing tube over that area. Checking for cracks with these isn't an issue, as just holding them they bend at that location so the they are cracked right through the insulator. If/when the engine runs I'll likely be so thrilled with it that I won't mind making some new spark plugs if I need to.

When I tried to find the max temperature that Corian can take, apparently 212F is it, so does that mean it doesn't get any hotter than that in these engines? Or maybe that is the max temperature before it discolours or looses some properties on a counter-top.

Rick

 

[Carbuilder]

A short video on machining the spark plug caps.