My pleasure Dave. Thanks for the input and those are good points but,,,

The seat is actually OK and in perfect alignment. It's the threaded portion that can be off center. The stem of the counter sink bit is too small to bore a hole big enough to accept the tap. Therefore, you have to drill out that portion with a larger diameter drill. On the lathe, everything is held firmly in alignment. Doing it free hand, with the drill press, it's just too easy for the vise to wobble, walk, shift etc. Note that the final drill bit is not that much larger than the shank portion of the countersink bit. So there's not much material to force the drill bit to center properly. On the lathe, all is in much better alignment for the initial lead in of the drill bit. Also, the issue IS the tapped portion because the counter sink has a pilot tip that starts exactly on center and guides the taper to cut exactly square and in alignment.

Real machinists must be shuddering and tsk tsking at the use of the Phillips bit and maybe it shouldn't work but it does.

In any event, some corrections and additions need to be made.

Item one is that you should use a countersink bit just to get the initial cut started. Then switch to the Phillips bit. It's not such an issue with Norvel plugs, but is a little more critical with Cox units.

Item two is that you want to start the Phillips bit dry to get a feel for the way it cuts and to make it easier to clear chips. As you approach the end of the cut, DO apply some cutting oil to give the tapered seat a good finish.

Three, I ran across a Phillips bit of another brand that was quite dull in the "cutting" edges. Guess I got lucky with the brand I started with. If you have a dull one, get another or DO sharpen the appropriate edges taking care not to alter the taper. If you've worked at sharpening cutting tools you'll know the edge to work on and the edge to leave alone.

Item four is the go, no go gauge. The 3/16" was suggested to make sure that you don't go too far. Like a haircut, you can't put any back. The final cuts will have to be with oil and are incremental. You get a feel for it and you can feel the bit cut a bit and you back off, take it all out, wash it and then test fit your plug. Running the plug in by hand won't do, you have to tighten it up firmly to get a good, sealed fit. Use oil, see below. Once you've got it right, (and that turns out to be EXACTLY 4.8 millimetre) you can use your good piece to set the location of the cutting bit's stop collar for all future jobs. Even then, you may have to tweak and fine tune. DO have lots of dead plugs to fool with.

Item five is that you DO want to put some lube in the thread and on the taper when installing the plug. Remember, you washed out the piece and if you install it dry, there's a chance of getting some galling and bits of metal falling into your engine when you take the plug out. Ask me how I know. [:@] With lots of lube, tighten and loosen the plug a few times to help seat it for a perfect seal. Your final task will be to clean out the bit of black this creates on the tapered faces of both pieces. Once seated, this effect no longer occurs but do make sure you lube the plug JIC.

Finally, making a drill bit of the right diameter with the proper taper tip is kind of beyond my skills and the tools I have. And the point of this thread was so that anyone can make their own turbo adaptors. Myself, I only have a simple Taig lathe with attachments and some home made fixtures. It's really quite primitive. I would love to upgrade but I'm waiting for the Chinese to offer a complete CNC shop, You know, turning, milling, grinding etc with an accuracy of five ten thou. for 500 bucks. [X(] The way things are going, you never know.

Here, http://www.rcuniverse.com/forum/m_44..._2/key_/tm.htm classicalgas, (Bob) showed how he made adaptors to take Nelson plugs for Cox .020s. Thanks Bob, that gives me some ideas. Which will be the next item to tackle if I can get the proper die cheaply enough.

That may take care of the .020 but what concerns me a lot is a source of plugs for my precious TD .010s.

But now that we have silicone tubing in very small sizes that resists diesel fuel, I just may go all diesel and not ever have to worry about plugs again.

Nahh, no fun in that.