Drill Size For Metric Reamed Holes?

from the thumbnail i thought this was about thread depth and was about to rudely refer you back to your copy of machinery's, but there doesn't seem to be a table for reaming.

i guess as long as some but not all of the tapered tip of the reamer goes into the hole you're good to go.

>>1187185
Machinist fag here. Yes your logic itself is sound but how much stock you want to leave for the reamer depends on what you're cutting. Unless you've got a nice machine which I'm assuming you don't because lol /diy/, .018 seems like a lot for a reamer if you're doing steel or other hard materials.

>>1187185
Simple rule of thumb is around 5% of the finished hole size, but you can go a little under or a little over as long as you have enough flute or your drill doesn't go over/wander/oval/whatever.

You should be ok with a #2 drill or #1 drill. If you don't have numbered drills, I wouldn't suggest using a letter A drill because it's risky as drills can go oversized fairly easily, so the reamer might not clean up the hole. 7/32nd should work, you should have enough cutting flute, just be sure you can evacuate the chip. If it packs up at the bottom your reamer will go oversize, or if it packs up in the gullets it'll fuck surface finish/possibly go oversize.

19/64ths should be fine on the 8mm reamer, letter M or N would also work.

>>1187333
What this guy said.
Even on the machines at my job that cost as much as a house, the reamer is usually taking ~.015 iirc for steel plate.

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>>1187333
>>1187340
>>1187343

So for a 6mm (.236) ream hole = #1 Wire Gauge drill (.228) leaving .008 for the ream
and for a 8mm (.315) ream hole = N Letter Gauge drill (.302) leaving .013 for the ream

Yeah, that sounds better, as 6mm is pretty small while 8mm can take out a bit more material (steel, in this case).

>>1187357
Yeah those are more reasonable amounts. Remember, a reamer isn't meant to take off lots of material, it's just to make a very precise hole. Now, bigger reamers like if you're doing 1/2" plus can handle .020" or so but anything under than should be around ten at most.

>>1187357
>>1187360
>reamer isn't meat to take off lots of material
>Yeah, that sounds better, as 6mm is pretty small while 8mm can take out a bit more material (steel, in this case).
Keep in mind that the reamer flutes remove material radially, so you're really taking 0.004" per side and 0.0065" per side for 6 and 8 mm respectively. Of course reamers are indeed not meant for hogging, but drills can so easily go oversize/get weird in all sorts of ways that you should definitely do a test part in the same material before doing it for real.

If you're taking more material with a reamer (as long as you have cutting flute of course), drop the spindle speed but keep the same chip/tooth load. You can always go slower in SFM if you have more material to remove, this will keep the reamer from going oversize. Don't forget to clear chips.

>>1187364
>but drills can so easily go oversize/get weird in all sorts of ways
If your drill is off by four fucking thou in the diameter you need better drills or a better vice.

>>1187365
>If your drill is off by four fucking thou in the diameter you need better drills or a better vice.
You'd be surprised. If you haven't had a drill fuck off out of nowhere on you, you haven't drilled a lot of holes.

I had a job a few months ago, we drilled six hundred plates three feet square, 1 inch thick 416 stainless with 144 holes per plate. We ran through a few of our in-stock drills before ordering some for the job, tweaked feeds and speeds as the job ran between the normal 118 HSS, the cobalt HSS, then a carbide or two.

Doesn't matter what the machine, tool holder, clamping method, drills will do funny things.

Believe me, around drills the ice is thin.

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>>1187365
>f your drill is off by four fucking thou in the diameter you need better drills

That was my concern using fractional drills, as they tend to get a lot of use and might walk while letter and wire gauge drills are usually ignored and will thus cut truer.

>>1187365
>>1187368
-cont-
We had a new cobalt 135 for the job go sidewards, we had a 118 break by splitting in half along the spine, leaving half-helix curls in the last hole, we had holes go tapered, triangular, oversized, even a little undersized.

Worst I saw was a brand new Dormer drill that had a bad grind in another job. 7/8ths diameter, drilled nearly 3/16ths oversized. Sometimes all it takes is a change in coolant concentration and suddenly everything goes out to lunch.

If you have a critical hole and you're leaving it to lady luck and a fucking drill bit, you will one day regret it.

>>1187372
>triangular
I just had that happen yesterday. I do not understand it. That has gotta be a really specific wobble for it to be a triangle.

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>>1187368
>stainless

>>1187380
Probably the grind of the cutting edges that's a little off. Triangular holes is really common when drilling sheet metal with the rag trick as a fairly predictable result of the nature of a drill (being man-made and imperfect, even in the slightest) as it is both starting into the surface and exiting out the bottom without the cutting edge being completely in the work. Something like that, anyway.

>>1187384
At least 416 is free machining, it isn't as bad as 304 and 316.

>>1187394
>Triangular holes is really common when drilling sheet metal with the rag trick
without the rag trick*

If you're trying to drill sheet metal youtube/google rag trick so you get round holes.

>>1187395
>If you're trying to drill sheet metal youtube/google rag trick so you get round holes.

https://www.youtube.com/watch?v=4HOxfZKIZQk

>>1187404
Yep that's the one, thanks.

>>1187380
https://www.youtube.com/watch?v=QhpOg186fks

Go to 12:12 and there is some high speed showing how the cutting edges walk

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I fixed your picture :D

I would go for:
O5,8mm for O6mm
O9,7mm for O10mm
O19,5mm for O20mm

If I work on single parts I always pre-drill, because the drill could be fucked up and the diameter gets bigger.
This means:
O5mm
O5,8mm
O6mm reamer

There are 3 main reasons why holes are getting bigger as you want:

- (By far the most reason) Someone (maybe you ^^ ) fucked up the drill by resharpening it. If the main cutting edges are not exactly of the same lengh the dead center is out of center.
The dead center is leading the drill in the hole. If you pre-drill you can avoid the negative effect of a bad sharpened drill.

- A build-up edge. Material is sticking on the cutting edges and do part of the cutting work. what leads to a bad surface, more heat and a change in the drill geometry.

- The feed rate is to high and the drill rip off the metal instead of cutting it.


I have a personal hate when working on single workpieces and have to reame a hole.
There are soooo many factors influencing the result...
- How good is the spindel of the machine
- How good is the reamer itself
those are the static factors

What each hole affect is the concurrence of:
- The feed rate
- rpm
- what kind of lubricant you use
( hole gets
saliva = smaler
cooling water = ok to smaler
oil = ok to larger
)
- how much lubricant you use

.......


thats the reason I like to use an end mill on a cnc.

>>1187185

When reaming, you take your finish size, and then subtract 3% of that to get your final drill size. So (for the sake of easy math), if you wanted a reamed hole of 0.100", you would use a drill size of 0.097", then use your 0.100" reamer after the drill.

According to a recent machining class I took, it was called the "3% rule".

>>1187426
That's apropiate, only that metric drills are more common in 0,25mm steps
So, it would be 5,75mm for 6mm and 9,75mm for 10mm
19.5 or 3/4" would work for 20mm

i AGree on the reasons for bigger holes
resharpening drills is not as easy as it looks when you want presicion.

>>1187370
this logic is wonderful

>>1187370
Interesting workplace for sure...

BTW it's a wise habit not to trust metal drill indexes in a shared workshop because some pudstrangler always puts smaller bits back in the wrong spot. (They are the same shitbirds who don't sharpen or replace dull bits but leave it for you instead.) I learned early on to measure shanks instead of AssUming.

The Malmstrom torrent of Machinery's Handbook is good if OP doesn't have a copy. It answers many questions.