Drill size alternatives?

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Chasboy1

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Jan 11, 2019
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Hi Folks, now with more 'indoor weather' coming I will returning to the pen workshop. I have 2 new kits I want to make.
One requires a 10.5 mm drill and the other a 'penmakers drill letter size "O"...
Are there any close, more common sizes that I could make work? Is the letter size the same as the more common letter sized drills?
Thanks all!
 
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Chippa

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O twist drills are slightly smaller than a 21/64 And a 10.5 is slightly smaller than a 27/64

You can get HSS letter and mms pretty cheap though, I would honestly just buy the recommended.
 

magpens

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@Chasboy1

I agree that it is best to go with the recommended drill size.
If you try to go a little smaller you run the risk of splitting the blank when you insert the tube (if you have to force the tube in).
In addition, if you make the hole smaller, there will be less glue between the tube and the blank ... a problem if you make the hole TOO small.
If you go larger then you run the risk of the brass tube not being properly aligned with the axis of the blank.
It is sometimes possible to get a "better" fit of the tube in the blank by playing around with alternative size drills, but it's risky.
The thing is that the final fit of the tube into the blank depends slightly on the blank material (e.g. wood or "acrylic") no matter what drill you use.
That's because all materials have elasticity; they do expand when the drill goes in; they shrink back a little when the drill comes out.
To some extent, the recommended drill size is a compromise because the "recommender" does not know the material you want to use.
If you want to play around with the hole size then you really need to buy a range of drill sizes to try out; and that's going to cost you more.

With regard to the 'penmakers drill letter size "O"' (quoted from your post) .... there are so-called penmakers drills on the market, but don't buy them.
When I began turning pens I bought a few. . They have a slightly different spiral twist pattern, and may be a bit longer than standard machine drills.
But I did not find that they made any real difference to the drilling process .... in my opinion.

So I would just buy "jobber" drills from a machine tool store in the specified sizes. . Drills from Walmart, Home Depot, etc., are also OK.
But machine tool stores will stock a greater range of sizes and get you exactly the recommended size.

An "O-size" drill will be of the right diameter whatever type of drill you buy .... jobber or penturners or stubby or whatever.
To answer your question .... "Is the letter size the same as the more common letter sized drills?" .... the answer is YES.

Here is a link to help you compare drill sizes among the standard SAE, metric, and letter sizes ..... just for your reference, nothing else :-


As I said, I recommend that you just go with the recommended sizes to keep life simple and avoid unnecessary costs.
 
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bmachin

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I have an iPhone app that shows all US drills (number, fractional and letter) in order of diameter in one column. The adjacent column shows the decimal diameter in inches. The third column shows the diameter in mm and the fourth column shows available metric drills. I picked mine up in the App Store. If memory serves, the app was free. I'm sure there must be an equivalent for Android as well. Quite Handy.

Starrett offers a free wall chart with the same info, as well as (I think) a wallet sized card. Go to starred.com.

Bill
 

leehljp

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You are looking for other bit sizes to possibly work with. . . Are you familiar with Harbor Freight's drill bits? They are not the top of the line but they have a good price on a huge set:

115 piece Letter, Number and fractions. Covers most.

There is a cobalt set - more expensive too but has been worth it to me for the number of years I have used them.
 

walshjp17

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I have an iPhone app that shows all US drills (number, fractional and letter) in order of diameter in one column. The adjacent column shows the decimal diameter in inches. The third column shows the diameter in mm and the fourth column shows available metric drills. I picked mine up in the App Store. If memory serves, the app was free. I'm sure there must be an equivalent for Android as well. Quite Handy.

Starrett offers a free wall chart with the same info, as well as (I think) a wallet sized card. Go to starred.com.

Bill
What is the name of the app? There are several in the app store but I don't see any as you describe.
 

Paul in OKC

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The "O" bit is .316, 5/16 is .312 so could work. A little tougher on the 10.5 (.4134). Letter "Z" is .413, 27/64 is .4219, and 13/32 is .4062 so a bit more difference in that one.
 

Chasboy1

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Thank you to all who responded. All of the info was valuable. I felt like I was talking to my Dad. He was a machinist for Norden during WW2. He had letter drills also, but they are long gone. I downloaded the app mentioned, it cost $.99 and was well worth it.
I do have 2 Starrett Charts, the small card and the larger one mounted to my toolbox!
What a great forum!!
 

howsitwork

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Well younhave an answer to the size question on drills. Just an observation as Mal said it's worth getting the correct size drills but it's also worth having one 0.1mm bigger to hand as well.

Reason - as Mal mentioned there is some degree of "shrink back" after drilling and with challenging woods ( Lignum vitae comes to mind) you may need to go a smidgen larger to get the tube to actually fit without raising your blood pressure in a big way ! You can get metric drills in 0.1mm increments upto about 12 mm fairly easily. So. 10.6 in the tool box might be worth having?
 
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