Ok, so on my homemade HCCT, I used a small brake drum for the spark ring. In the picture below, it looks like someone used a transmission drum, maybe reverse? Or if not, could you use a reverse drum (they are all cracked anyway… :-)
But my question is, how would you mark off the 16 segments to have the sparks fire in the middle of each like in the picture below?
Well, I know how I would do it, but I may have tools that some others do not have access to.
For myself, I would center the drum on a rotary table on the milling machine, center the table to the quill, and then using a small end mill, mill a groove every 22-1/2 degrees around the rim of the drum. Another method would be to take a piece of masking tape and apply it to the rim of the drum. Overlap the ends slightly, then take a sharp knife and cut through the tape and remove the overlap so you end up with the ends of the tape just touching each other. Now you have a piece of tape the exact length of the circumference of the outside of the drum. Carefully remove the tape and put it on a smooth surface from which it may be removed. Measure the exact length of the tape, divide by 16, and using that as your distance between segments make a mark with a pen or some other marker on the tape at each of the points. Then you can reapply the tape to the drum and make a file mark or something to correspond to each division point on the tape. Remove the tape and you're done.
Just a couple of ideas.
The markings are really not of much use when setting up coils. The firing occurs every 22.5 degrees because that is when the magnets pass the magneto coil. All you really need is the ability to see a time/space relationship between sparks. With just a brake drum as the ground path for the spark you will be able to see any double sparking or misfiring. Just make sure whatever you use is properly centered so that the spinning pointer will have a uniform gap at all points around the drum.
Or if you have access to a gear about the same diameter as your brake drum
and the tooth count on the gear is exactly divisible by multiples of 16, you can
use it as your degree wheel.
Or even easier may be downloading one from the internet.
Here is an example . . .
Even if it does not look perfectly round on your monitor, it will print out ok.
The HCCT flywheel is not keyed to the mounting shaft.
First decide if you want the sparks to aline with the marks or in between the marks.
Then loosen the flywheel attaching nut or the hand crank bolt and turn the flywheel on the shaft or the shaft and the flywheel.
Where the sparks happen is not important. Having 16 sparks is important.
On the home made units the flywheel is bolted to a transmission input shaft so there is no adjustment there.
If one were really concerned about the markings being where the sparks are I would install the ring / drum / whatever unmarked, then with a coil installed and sparking mark the ring.
As John R pointed out, the markings aren't of any real use. Many of the testers used a small emergency brake drum and others used the single gap deal that revolves. All your concerned about is if you have a double spark which is separated by about 3/16 inch. Of course your also concerned that it fires at all points consistently. If it isn't you'll see it even without marks on the drum.
Thanks for all the ideas. My crank (with the spark tip) to turn the flywheel is locked in place with a set screw. If I loosened that, I suppose I could turn the crank just a bit one way or the other to center the spark.
But no, I don't suppose the marks are really important, but it looks kind of nice to have them centered like that...and I gotta have some project to work on in the cold weather. I actually had to dig out my windbreaker this morning!
I agree that the marks are not necessary. But if you want them, just measure the cirmumference and divide by 16. Run the tester and make the first mark where a spark occurs, then make the rest evenly spaced at whatever measurement you came up with. Or maybe I misunderstood the original question?
The later Allen HCCT units and the one that Bob Scherzer copied and sells also had provisions for testing a coil ring or flywheel. The flywheel is attached by a large single nut with a lever attached to it that lets the flywheel be removed by just removing the one nut. Then the coil ring can be removed by just loosening two large wing nuts that clamp it in place.
I have never seen an original Allen Electric HCCT unit with the spark ring markings every 22.5 degrees apart.
Ron the Coilman
Well, I thought this was a copy of an original anyway.
Ron's correct about Allen testers not originally using a brass spark ring but rather they used an early T brake drum. I did a couple with brake drums but everyone looking for a HCCT wanted one with a brass ring. I guess more for the "Bench Art" then for just a tester itself. So I modified mine to use a brass ring since the mounting holes are the same as used to hold the mag coil ring on the other side of the cast base. Just needed to extend the threaded rod out the front to mount the Delrin insulators. Bob