D-bit reamer question...

[alanganes]

Hi all,
I recently made myself a D-bit type reamer. I have made a few in the past for use on non-metal stuff (mostly thin fiberglass and plastics) that worked out fine. I recently needed to make some fairly accurate and consistent 0.50" dia holes in some aluminum parts. So I made myself a 0.500" D reamer out of some W1 steel rod, ground nice, accurate angles on it, hardened and honed it. Looks pretty good. I tried it on a few test parts in aluminum. I drilled a hole leaving about 0.006" to ream out. I used the D reamer in the mill, very low speed, backed out frequently, well lubed. On three (these are holes that go all the way through the part) holes I got consistent 0.501" dia holes. That is close enough for what I am doing, and I can adjust the size of the reamer if need be, so I am happy with that part, but the finish was not so great. For what I am doing with this finish is not really critical, but in other cases it would be, and besides, it sort of bugs me.

I am assuming (dangerous, I know...) that this is a shortcoming in my technique. Hoping to tap the group wisdom here. What is the best way to apply one of these reamers? Any guidelines on speed, feed, etc. in aluminum?

Thanks for any ideas.

-AL A.

[Rusty Marlin]

lubrication with Al is very important, a shot of WD-40 can take a part that flat will not run, do to chatter, finish galling, what have you... and just like magic turn the job into a absolute perfect jem.

So I guess my first question to you is, did you use lube on the cut?

[Paul F]

My limited experience with single-flute D-reamers is that you have to keep them CLEAN CLEAN CLEAN!
If you back out of the hole, STOP, and clean all the chips off the reamer, and out of the hole, before continueing.

You've got a large surface area that will be happy to "smear" chips around and around on the inside of the hole, and screw up your finish.

The context I've used them in is rifle barrel chambering reamers. They make great roughing reamers to move a lot of material, before using an expensive finishing reamer... but I've finished a couple chambers with them also.

Run slow rpm, lots of lube, keep it clean, and don't feed it too slow.

YMMV
Paul F.

[alanganes]

Thanks for the replies. I lubed with plain old cutting oil, the sort of stuff plumbers thread iron pipe with. I know that is not optimum, but it was at hand. I did not think of using WD40 for AL, I guess I knew that is supposed to work well, must have forgotten. I'll give that a try.

Rusty, I will try again, being sure that everything is clear of chips. Do you think that is even necessary to back the reamer out when reaming a through hole? Will the chips just push/fall out the bottom? Also, I was perhaps feeding a bit slow. I'll try being a bit more "assertive" with it.

Thanks again.

-AL A.

[gzig5]

If you think that the chips are causing a surface finish problem, use a "gentle" stream of air to continuously blow the chips out the bottom of the hole. Doing this should allow you to ream the hole in one pass without backing out. Re-apply the WD-40 as needed to replace that which gets blown out with the chips.

Greg