Weird drilling conundrum

[J Tiers]

How many posts before it becomes obvious that you need to buy or borrow a #4 or 0.209 chucking reamer?

Tge OP probably knew that when he used the drill and did not get the desired result. Especially considering that he mentions reamers first off.

[reggie_obe]

Tge OP probably knew that when he used the drill and did not get the desired result. Especially considering that he mentions reamers first off.

There is a difference between knowing the path and walking the path.

[Bented]

That whole deal of sneaking up on the size by increments of 1/64 (or even less 😶) is flawed and lousy practice.

Just do NOT put a drill down a pilot hole, UNLESS that pilot hole is just a bit bigger that (at most) the web of the following drill at the chisel end. Same size as web is good, under a little is OK, but NEVER so big it is just a little smaller than the drill itself.....

I'm gonna get all "Bented" here, and say that this is one of those things that for some reason hobbyists just love to do. There's no explaining it.... somewhere someone must have set this rule down in one of those "must-have" hobby machining references, and ever since lots of folks do it "because".

I tried it once, when I needed a tiny increase in hole size, and that was enough. The drill does everything except what you want it to do. Catches, jams, tries to screw right through on its helix, cuts off-center, cuts a three lobe hole, breaks the "corners" off the drill, whatever.

I made 204 of these parts this week, stainless 3/8 Sch. 80 pipe, the ID finishes at .478" +- .005".
The stock begins at .42" ID., removing .030" per side with a twist drill was AWFUL at best, tough on drills and very inconsistent during the entire run.

I would not even consider trying to remove .001" per side with a twist drill, this would lead to much pulling of hair and madness.

[garyhlucas]

That whole deal of sneaking up on the size by increments of 1/64 (or even less 😶) is flawed and lousy practice.

Just do NOT put a drill down a pilot hole, UNLESS that pilot hole is just a bit bigger that (at most) the web of the following drill at the chisel end. Same size as web is good, under a little is OK, but NEVER so big it is just a little smaller than the drill itself.....

I'm gonna get all "Bented" here, and say that this is one of those things that for some reason hobbyists just love to do. There's no explaining it.... somewhere someone must have set this rule down in one of those "must-have" hobby machining references, and ever since lots of folks do it "because".

I tried it once, when I needed a tiny increase in hole size, and that was enough. The drill does everything except what you want it to do. Catches, jams, tries to screw right through on its helix, cuts off-center, cuts a three lobe hole, breaks the "corners" off the drill, whatever.

Sometimes you have to put a very slightly larger drill into an existing hole. If you stone the 'hook' on the flutes parallel to the axis of the drill it won't grab and you will get a nice clean hole as it kind of acts as a reamer.

[J Tiers]

Sometimes you have to put a very slightly larger drill into an existing hole. If you stone the 'hook' on the flutes parallel to the axis of the drill it won't grab and you will get a nice clean hole as it kind of acts as a reamer.

Yeah, I have seen info on that deal, got it out of an old toolmaking book, where they suggested it for very small reamers, like 0.030 and 0.050". I just didn't want to mess up the drill I had.

They suggested both that and hitting the corners to round them a bit instead of the sharp corner.

Still got no clue about the fascination with step drilling those tiny steps.

[Bented]

Step drilling has advantages at times, I dislike drilling holes with a manual tail stock as it is labor intensive and hard physical work. If a 1.5 minimum hole is required I will often start at 3/8 or 1/2".

Cranking a tail stock wheel by hand grows old quickly.

[dian]

my experience:

1. a drill will produce a hole smaller than its tip diameter (makes sence)
2. a lousy drill or lousy setup will produce a larger hole
3. i often use a drill instead of reamer. mostly for press in situations. i have 5.95, 7.75, 9.95 etc drills for that.
4. procedure for exact reaming (short of boring) to h7 10mm: 9 mm drill. 9.5 mm drill, 9.7 mm drill (producing a very smooth 9.75 mm hole), h7 reamer
5. no idea how above would work in a lousy drill press.
6. i would never drill in 0.025 mm steps, also because i dont have such drills. they dont exist.

[754]

Most of the time...
won't drill on size if you want it to ..
won't drill over size if you want it to.. then it will drill on size..
they have a mind if their own... twisted mind... hence the name TWIST drills.