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  #21  
Old 01-31-2019, 08:32 AM
Lew Hartswick Lew Hartswick is offline
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Quote:
Originally Posted by terry lingle View Post
Drill bits make holes that are not round straight or accurately sized they are fine for putting a bolt through and often good enough for most other purposes.
If you need better accuracy you move to more accurate finishing tools.
By definition a 5/16 drill bit must make a hole at least 5/16 in diameter but which may be larger than 5/16. If you want to see how much oversized a drilled hole can get just sharpen a bit so that the point is almost at one edge.
Reamers allow very accurate holes but work best when the drilled hole you are reaming is as close as possible to the desired finished size. while the standard drill index has 29 bits between 1/16" and 1/2" nominal there are actually about 150 drill sizes available in that range when you add up all the different sets available.
standard 29
number 60
letter 26
metric drills 25
quick total 140 different drill sizes in specific indexes.
A few of these bits are the exact same specification 1/4 inch and "F" letter drill come to mind.
With this many increments available selecting the proper pilot drill for a reamer is pretty easy.
This leaves the whole drill range above 1/2 inch not covered.

Note that I am only detailing drill bits for use on metal here.

My own drill collection goes to 1 7/16 and above that i can bore to about 15 3/4 on my lathe.

Reamers are only used where very close tolerances are needed and are relatively expensive so while I own all of the above drill sets I only own reamers that I have needed or those I have acquired as part of bulk purchases.
JFG :-)
Right off an E is exactly the same as 1/4 but just for something to do one of these days when I have nothing else to do I'll go through those sets and see how many "duplicates" I can find. :-) But we have to agree on a tolerance first. Since "drills only drill an approximate diameter" in spite of the numbers to 4 decimal places on the indexes. :-) Oh, Metric drill bits come in tenth mm but lets not take those into account, just .5 mm set. :-)
...lew...
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  #22  
Old 01-31-2019, 12:22 PM
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terry lingle terry lingle is offline
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Actually if you want to put your money in foolish places you can get custom drills in any size you specify out to 4 digits or more to drill holes approximately the size specified
That is pointless as the current off the shelf drills cover every possible drilled hole call out on any drawing when correct + - tolerances are specified.
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  #23  
Old 01-31-2019, 12:42 PM
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MetalWolf MetalWolf is offline
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Quote:
Originally Posted by terry lingle View Post
Actually if you want to put your money in foolish places you can get custom drills in any size you specify out to 4 digits or more to drill holes approximately the size specified
That is pointless as the current off the shelf drills cover every possible drilled hole call out on any drawing when correct + - tolerances are specified.
I have 4 or 5 complete sets of drill bits I take good care of and keep in order
so I can see spending any more money on drill bits... didn't mean to start a huge debate with this by asking if there was a chart for DBto reamer sizes...
I get the gist of it and can figure it out when I need to now with the info you guys have given... as I understand it needs to be undersized just enough but not so much it will damage the reamer or the piece I'm working on...
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