Letter sized bits.

I

Ian Fifelski

Joined
Oct 4, 2017
Messages
528
Morning all again,

Looking for another chart:D. I can't find it anywhere. What letter sizes should be used with which fractional size?

Thank you.
 
Thanks A.McPherson A.McPherson
So there are no letter sizes for under 15/64?

And on the chart, would it be the fractional size under the letter size is the one to use? So for 1/4 - letter D and 5/16 - letter N?
 
You're talking about holes for pins right?
Generally you want the hole to be a couple thousandths bigger than the pin.
So if you look at the chart, the next larger size from 1/4 is 6.4mm, then 6.5, then "f". I use "F" bits for my pins though handle materials if I'm going to peen (pien? Pein? is that how you spell this word?) the pin. I use bigger drills to go through the steel so there is less chance of binding and have a bit of wiggle room with scale placement.
 
Yes, I am talking for pin holes.

Interesting, The holes I have drilled with 1/4 bit are too large for my 1/4 pins. The pin slides easily through them. So I assumed letter bits were used to fix this by being a little smaller.
 
That's one problem with pin stock. It's rarely the dimension that it is sold as. Probably the best way to deal with the problem is to measure the stock with calipers, then use the drill that is the most appropriate.
 
No problem.
Other, more experienced makers might have better solutions, so if they chime in...
 
The barefoot boy said:
Yes, I am talking for pin holes.
Interesting, The holes I have drilled with 1/4 bit are too large for my 1/4 pins. The pin slides easily through them. So I assumed letter bits were used to fix this by being a little smaller.
Click to expand...
A standard twistdrill will always bore slightly larger than its diameter. Its just the nature of two cutting edges & flutes weeblewobbling their way thru.
Drilling slightly smaller bit than the target size is one way to ’get it closer’ but truly accurate holes need to be bored small & reamed to final size.
 
I have found little pin variation over the years but it has occurred. How are you drilling your holes would be a bigger question to me and does the press have any runout (wobble) to it. A more likely reason for your 1/4" holes to be oversized. Years ago I use to use all kinds of different sizes and have now (probably 10 years ago) standardized on two sizes 1/8" pins and 1/4" pins and thong tubes. I use a #30 for the 1/8th" hole and a F for the 1/4".
 
Thanks for chiming in guys! To be fair about the "pin stock" size comment, I'd do often buy lengths of brass and steel round stock and use them for pins, so that may be where I'm getting the variations from too.

I've also found that holes in wood tend to shrink too, so that might be an issue as well...
 
Horsewright said:
I have found little pin variation over the years but it has occurred. How are you drilling your holes would be a bigger question to me and does the press have any runout (wobble) to it. A more likely reason for your 1/4" holes to be oversized. Years ago I use to use all kinds of different sizes and have now (probably 10 years ago) standardized on two sizes 1/8" pins and 1/4" pins and thong tubes. I use a #30 for the 1/8th" hole and a F for the 1/4".
Click to expand...
I am drilling with my old delta 12" drill press. It seems very steady and I just got a new chuck on it.

I just drilled a hole in some wood and the pins are perfectly snug, so its fine if I have some movement in the tang holes (better for the epoxy actually) as long as there are no gaps between the pins and the wood. So it will be fine. Thanks all!
 
My advice of drilling pin holes is:
1) The tang should be drilled 25% to 50% larger than the pin. This assures no binding or alignment issues. The epoxy will fill the gap and make the handle slightly more shock resistant. The extra room is especially important if the pins are being peined/peened. It is also important with Corby bolts.
2) The handle material should be drilled about .003" to .005" larger than the pin. The fit is called a slip fit. The pin should easily insert without forcing, but not slide right through. The pin should broughened on 100 grit paper, and coated with epoxy. Putting epoxy in the holes is also a very good idea. This assures the pin has an epoxy bond all the way through the handle.
3) On brittle materials like ivory and MOP, the hole should be a loose slip fit. Any binding or unwanted expansion during peining will surely chip or crack the material. Glue in the pin hole is very important here, as the pins are often not peined.
4) Coloring the epoxy to match the wood makes the tang/handle jpoint as well as the pin/hole transition invisible.

Note - a drill bit won't necessarily drill a hole the size of the bit. Due to the material being drilled and the inherent run-out and wobble of bits and mthe drilling machine, the hole may be much larger ... or even smaller on woods and materials that are very elastic. Drilling a pilot hole about 90% of the desired size, and then re-drilling is a good idea. Having reamers for your most used sizes is an even better idea. On places like ebay you can get bags of used reamers for $10-20. They are worn to be a tad off specs for a high-tech machine shop dealing on .0001", but fine for our purposes.
 
If you're in the USA, Starrett will send you posters and pocket charts free. If you're outside usa, somebody sells them on ebay

As mentioned, dial calipers are handy for measuring
The cheap chinese ones are pretty good.
 
You must log in or register to reply here.
Back
Top