Drill bit conversion/confusion

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kooster

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Can someone please clarify/explain the correct usage of bits that are sized in mm and those sized in fractional measurements. For example, a 9mm bit does not have an exact fractional/decimal equivalent and visa versa for fractional bits to mm. Does this depend on the manufacturer or is there a standard of sorts. I am looking to purchase a Colt 9 mm pen bit but do not see any fractional/decimal equivalent. It seems somewhat confusing to me.
 
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There are many ways to "standardize" measurements between MM and Inches.

I choose to use the decimal equivalent in inches (thousandths) because those measurements are readily available.

9 mm=.3543"
11/32"=.3438
23/64"-=.3594

The difference from .3438 to .3594=.0156 which very closely approximates the compressed dimension of 5 pieces of 20# looseleaf paper. Remember that this dimension is the DIAMETER, so the distance from the "tube" to the wall of the hole is one HALF the .0156, or about two and a half sheets of paper----THIN!

Ed
 
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I usually grab a calculator and do the conversion.
9mm/25.4mm = 0.35433"
0.35433" x 64 = 22.677
So either 22/64 (11/32) or 23/64

I'd pick 23/64 as the glue can fill the gap between the tube and blank. 0.0025" or 0.064mm

But I like the data sheet that Frank has. I think I'll be using that from now on.

Be aware that a drill bit may be slightly smaller or larger than it's stated size due to manufacturing tolerences. Also the hole size may vary due to the material you're drilling and your drilling setup. I swear that in some woods the hole gets smaller after drilling.

Tony O
 
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There are some kit instructions that I find ask for too large a drill bit. I now measure my tubes and ref. the chart to pick my drill bits.
 
Even more good stuff. This site is like a "easy access encyclopedia" (for all you young uns, that was a set of reference books covering every subject known to man at the time). Now it's called the internet !!!
Anyhow, thanks again.
 
I had a lot of issues by following the kits instructions. I now measure the tube OD with a caliper and add 0,3mm (or 0,012") to find the appropriate bit. Maybe a bit more, that is 0,4mm (0,016") when reverse painting before gluing PR or Acrylics blanks.
 
Perhaps the attached PDF file will help - I keep it posted by my lathe and drill press.

kooster said:
Can someone please clarify/explain the correct usage of bits that are sized in mm and those sized in fractional measurements. For example, a 9mm bit does not have an exact fractional/decimal equivalent and visa versa for fractional bits to mm. Does this depend on the manufacturer or is there a standard of sorts. I am looking to purchase a Colt 9 mm pen bit but do not see any fractional/decimal equivalent. It seems somewhat confusing to me.
Click to expand...
 

Attachments

with ca glue it need to be close , with expoxy and poly - expanding glues they will fill in the extra space if needed. ( if drilled a little to big but smaller than the bushings )
David
 
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