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Thread: How to size used drills
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8th July 2015, 05:41 PM #1
How to size used drills
I have all these bits with scored ends, so they have no sizes legible. They are P&N. and Suttons some have a bit of rust others are like new. Some have the ends reduced and like new.
So how do I identify the imperial & metric from number drills? I have only found 1 letter F.
Also some of the metrics are in odd sizes like 6.3, 4.1, so I'm guessing there is a part set in 0.1 increments rather than the usual 0.5
I tried using a vernier but even marked drills seems to be nominal size. The two drill stands I have, Tudor & AF, have different size hold and I have a frost 9/32 that is too fat to fit in either.
At this stage I think I keep the marked ones for accurate work and use UN marked ones for near enough or further boring out.
Open to other ideas? Are the old metal drill guage going to help or again are they nominal.…..Live a Quiet Life & Work with your Hands
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8th July 2015, 05:57 PM #2GOLD MEMBER
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Try the gauge or as already done use the Vernier or Mic.
For accurate either bore or ream.
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8th July 2015, 06:01 PM #3
The other idea I had is to drill a hole … measure that, but there is too many drills.
…..Live a Quiet Life & Work with your Hands
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8th July 2015, 06:03 PM #4GOLD MEMBER
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Hi Dale,
Its not the size of the drill you're interested in, its the size of the hole .
BTW if you're measuring near the end of the flutes at the shank end, then you'll be reading a little small.
I'd put them in size order then fill your metric and imp stands with the closest drill you have.
Stuart
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8th July 2015, 06:08 PM #5GOLD MEMBER
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Unless the drill that you use for drilling the holes is spot on the chances of the holes being over size is excellent,same goes with the twist drill you use to drill the hole,unless the flute length is the same the hole will be oversize.
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8th July 2015, 06:12 PM #6GOLD MEMBER
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I use drill gauges like the pair below with their oily papers sleeves. I have a letter one too but couldn't lay my hands on it for the picture.
Pete
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8th July 2015, 06:22 PM #7
I keep tellin my missus something similar to that.
pipeclay
Unless the drill that you use for drilling the holes is spot on the chances of the holes being over size is excellent,same goes with the twist drill you use to drill the hole,unless the flute length is the same the hole will be oversize.
Are you saying if the tip has been reground and tip slightly off centre it will bore oversize? I don't see the flute length running up the bit making a difference??
PMQC Inspector
I use drill gauges like the pair below with their oily papers sleeves. I have a letter one too but couldn't lay my hands on it for the picture.
Pete…..Live a Quiet Life & Work with your Hands
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8th July 2015, 06:31 PM #8GOLD MEMBER
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Change it to cutting edge/ lip.
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8th July 2015, 06:57 PM #9
Measure with vernier, refer here http://www.csgnetwork.com/drillsizeconvert.html
Job done.Those were the droids I was looking for.
https://autoblastgates.com.au
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8th July 2015, 07:00 PM #10GOLD MEMBER
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"How tight do the drills fit the holes in the gauges? Also have you ever measured the holes to see how exact they are or what tolerance?"
If the flutes don't go in back up one and then compare to one of the other gauges if you think it is a number or letter. I haven't ever measured the holes but the gauge is hardened steel and there is no mistaking a size except the one fraction and letter that are the same. I don't know if they come in metric but expect they do. Any bit I have tried in the gauge tells me the size and when I put on reading specs the marked size on the bit matches the size from the gauge. If it is a messed up bit then the hole it drills won't be correct no matter what the bit size is.
Read what General says about it an decide for yourself.
Pete
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8th July 2015, 07:42 PM #11.
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What you need is a vernier caliber that has fractional read outs.
This save constantly referring to a conversion chart.
Unless you have 0.1mm variants in your stash then they will either be imperial (64ths) or metric (0.5 mm) increments.
I Measure with the vernier and unless the flutes are badly damaged it usually is very close or integer or half integer mm if it's metric otherwise it will be an imperial so I flip the scale on the vernier to imperial (64ths) and it will tell me what it is.
There are a few that are close. e.g. 5/16 is 7.94 mm and 19/64 is 7.54 mm but most are really easy to distinguish by this method.
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9th July 2015, 09:11 AM #12SENIOR MEMBER
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Dont get too concerned here mate. Drills are not that accurate. Thats why reamers are made.
As the other gents have said, just measure with whatever means you have. Vernier, mics, drill guage. I measure the shank just below the flutes. Again as the others have said, Unless its a number or letter drill, it will be close to a std size.
Do you have a chart showing the sizes of number and letter drills?
bollie7
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9th July 2015, 11:05 AM #13
I don't have a fancy digital vernier that shows fractions.
Which ones do that?
I don't have a drill chart either, but NCArcher did post a link to one.…..Live a Quiet Life & Work with your Hands
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9th July 2015, 11:17 AM #14.
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9th July 2015, 12:47 PM #15Senior Member
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If you suspect you are measuring a non-metric drill, multiplying the millimetre size by 2.52 will give you the imperial size in 64ths. Not much help for letter size drills though.
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