metric drill swap

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SteveM
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Joined: Mon Jun 27, 2005 6:18 pm
Location: Connecticut

metric drill swap

Post by SteveM » Tue Dec 10, 2019 6:22 pm

I picked up an auction lot that came with some metric drills, which I have little use for.

They are all sizes in 10ths of a millimeter (e.g. 8.9 mm) and none are whole or half millimeter. They range from about 4mm to 10mm

There are about three dozen drills and all appear to be either new or little used.

I have a drill index for metric drills that takes whole and half sizes and I'm missing a bunch, so I would be willing to trade the entire lot of my drills for a bunch of whole and half size metric drills to fill out my set. I need 1.0 thru 5.5 by 0.5 mm and 8.0-9.5 by 0.5 mm.

While getting every size I need would be cool, I'll take what I can get and will trade the lot of 36 even if you can get me most of the way there. I just don't like the idea of perfectly good tools going in the scrap bin.

Steve

leeko
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Joined: Wed Jan 25, 2017 10:11 pm

Re: metric drill swap

Post by leeko » Tue Dec 10, 2019 6:50 pm

Tap drills?

I would suggest keeping them. Drills don't take much space!

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SteveM
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Re: metric drill swap

Post by SteveM » Tue Dec 10, 2019 9:58 pm

leeko wrote:
Tue Dec 10, 2019 6:50 pm
Drills don't take much space!
You haven't seen my shop.

Steve

leeko
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Re: metric drill swap

Post by leeko » Tue Dec 10, 2019 10:38 pm

Hah, man after my own heart

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tornitore45
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Re: metric drill swap

Post by tornitore45 » Thu Dec 12, 2019 10:07 pm

metric drills, which I have little use for.
A metric drill is nothing but a filler for spaces between imperial sizes.

Integer number infinitely many
Rational number infinitely many
Real Numbers infinitely many

One could not possibly have all the sizes
Mauro Gaetano
in Austin TX

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SteveM
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Location: Connecticut

Re: metric drill swap

Post by SteveM » Thu Dec 12, 2019 10:33 pm

tornitore45 wrote:
Thu Dec 12, 2019 10:07 pm
A metric drill is nothing but a filler for spaces between imperial sizes.
I made up a tap / drill chart that looked at all possible drill sizes for a tap from 50% to 100% thread, and there are some options using metric drills that are better than imperial ones, but those are mostly in the very small sizes and where you can get drills by the 1/10 mm. I might pick up a small-diameter set by 10ths for that reason.

For 0-80, the typical drill chart shows 3/64" tap drill which gives you 81% depth.

Don't know about you, but I'm not comfortable with a tap that small with that kind of engagement.

Using a metric drill, you can get a lower depth of thread. I can't run the spreadsheet on this computer, so I can't tell you what that is off the top of my head, but I think you can get in the 50%-70% range.

When you are at things like 1/4-20, it doesn't make much difference.

Steve

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tornitore45
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Re: metric drill swap

Post by tornitore45 » Fri Dec 13, 2019 10:12 am

Re-reading my post it may be interpreted as negative. I am all for having as many drill sizes. Sometime is a good idea to double drill to avoid going oversize. A drill shaving a few thousands is not going to improve location or straightness but it will improve roundness and size.
Mauro Gaetano
in Austin TX

Harold_V
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Location: Onalaska, WA USA

Re: metric drill swap

Post by Harold_V » Fri Dec 13, 2019 4:25 pm

tornitore45 wrote:
Fri Dec 13, 2019 10:12 am
<snip> Sometime is a good idea to double drill to avoid going oversize. A drill shaving a few thousands is not going to improve location or straightness but it will improve roundness and size.
Yep! And this bit of information is something that all machinist types should understand. Double drilling doesn't rival a reaming operation, but it goes a long way towards ensuring hole size when it's critical. Even poorly sharpened drills will drill size when they're forced to center on their margins instead of being guided by the web. Eliminates any potential to wing.

When we were in the R&D stage of the development of the Sergeant Missile, all holes were drilled on vertical mills, manually. We were required to double drill, to avoid oversized holes. Every feature of every part was 100% inspected, so holding size was critical to part acceptance.

On that subject, it stands to reason that each hole required three changes of cutting tool. To aid in that endeavor, the shop had some Wahlstrom quick change drill chucks. They are an absolute marvel, as cutting tools can be changed with the spindle running.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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