Reverse D-bit ?

I'm going to be installing bushings for the primary throttle shaft on my Quadrajet carb , and have been pondering on how to accurately ream the worn bores so there is no binding . I was thinking about lining it up and boring the holes on the mill . And then tonight I had a thought ... they sell a piloted reamer for this , so why not make a single flute piloted reamer like a d-bit drill ? I wouldn't even have to harden a piece of O1 drill rod to cut the aluminum alloy carb base . I like this idea enough that I ordered a piece of 3/8" O1 drill rod ...

-------------------------

I made one with the pilot half-round, but I think if I made more I'd leave the pilot full round and mill a narrow slot at the cutting step, with rounded edges if it would be hardened. It doesn't seem to matter if the cutting edge is slightly above or below center, and resharpening it will take the edge below center anyway. I'd test it on scrap the same thickness as the carb wall to see if it chatters or galls.

My first D bit opened up the U bolt hole in a truck leaf spring without any back relief, but in aluminum a little cutting edge and shank relief gave a smoother hole finish. A gear-shaped broach of unhardened O-1 drill rod was noticeably duller after broaching one hole in a zinc pulley. It bent when broaching a second pulley.

made a tapered venturi reamer as shown, with no back relief. While it didn't exactly cut freely in aluminum, it did the job.

Pulling the bushings in with nuts on threaded rod would help keep them straight. I'd use long shaft couplers with the ends faced true to the threads, and if necessary stepped to center the rod in the bushings. jsw

You "can" cut aluminum with some might soft steel, but I don't think you will be happy with the results. HSS drill blanks are available and inspite of the fact that I prefer carbide when possible HSS will work nicely.

You "can" cut aluminum with some might soft steel, but I don't think you will be happy with the results. HSS drill blanks are available and inspite of the fact that I prefer carbide when possible HSS will work nicely.

------------------------

If it doesn't cut the test sample smoothly he can harden and resharpen it. The finished hole size doesn't matter if he turns the bushings to fit.

I prefer to temper on the softer side initially so the tool is less damaged if it won't cut. Temper too hard and it may chip. I needed two tries to drill the neighbor's son's truck springs. The custom U bolts he ordered for a higher-than-Dad's lift kit came 5/8" instead of 1/2" diameter.

The funny thing is that when they need to haul something too long for their $$$ trucks they call on me and my 7' bed 1991 Ranger.

An empty tin can lying on its side with some charcoal in the bottom concentrates and retains the heat of a propane torch. I coat the tool with Ivory soap to reduce scaling. O-1 is hot enough to harden when a magnet doesn't stick to it.

Until I bought a Victor oxy-acetylene tote kit (for $50) the white-hot hardening temperature of HSS was beyond my reach. O-1 is relatively easy to work with. Keep its cutting speed in steel at 50 feet/min or less.