After mulling things over while munching on a sandwich and sipping a coffee, I decided to hit the computer and read some of the past references on the project. It kept creeping up that Japanman had done such a good job on just a drill press, no lathe required. Yet using a drill press I got three duds in a row. And yet on the lathe, no problem. Then it dawned on me. The key was the Phillips bit that JMan used.
The first picture illustrates three that you get in the typical tool kit. At the very first attempt, I used the number 2 bit for no particular reason except that it seemed sized right for the job. It, along with the 13/32" bit for the tap was used but I got leakage so I went looking for a substitute for the Phillips bit and that's when I found the counterbore bit that had the correct taper, shown in the second picture.
By this time I decided that I'd better give myself the best chance possible to get a good result so I went to my lathe. And, I had good luck making all the turbo buttons I wanted, as shown in picture three.
But that doesn't help you guys and that's when I made the promise to reveal how YOU could do it with tools you'd likely have on hand. The trouble is, I made the promise without determining if I could deliver. Well, a promise made is a debt unpaid so I just HAD to figure this out. After all, if Japanman could do it,,,,
SO, as it turns out, bit number three is used to cut the taper AND the bore for the threaded portion all at the same time. Yes, it's not a cutting bit but here's the deal. Get yourself a brand new one, one that has never mated with a screw. Bad imagery, I know. Anyway, use a fine stone or a sanding block with 400 grit to dress all the cutting edges. You don't have to make them razor sharp, just take off any burrs or imperfections. Pay special attention to the taper portion. Get it nice and shiny. Try not to alter the taper. With care and a light touch it can be done.
Picture four shows all the tools you'll need. The number 3 Phillips bit, the tap (M8 X 0.75 bottoming) and a 3/16" drill bit. The latter is only used as a go, no go gauge.
Use the Phillips bit to drill the taper AND the bore for the threaded portion. This is the key. In the previous set of instructions, doing the bore for the threads separately on the drill press did not guarantee that it was on the same line as the taper seat. The accuracy of the lathe assured this,, not possible free hand with a drill press.
Picture 5 and 6 shows the Phillips bit cutting cleanly and effectively. The key here is to go slowly and to use the 3/16" bit as a go, no go gauge for the hole at the taper. Yes, this is tedious but the point here is to get a good result first. Once that's done, you can use the good piece as a gauge to apply the collar as a stop for the next batch you do as in picture 7 and 8. You ARE going to make a bunch of these aren't you? No sense letting the expense of that tap go to waste.
Once again, use a mounted stone to deburr the underside and from here follow the steps in the first set of instructions.
Success !!!
!!! What a delicious feeling having the prop snap over smartly indicating a perfect seal. Testing with a bit of oil at the plug interface shows no bubbles and gentlemen, finally, we HAVE it.
Continued,,,,,