How to get a drill bit to enter and exit at exactly where you want it to go

[danmart77]

I like to build longrifles and chairs for myself these days. One question that comes up often in workshops is how do you get the drill to enter and exit where you want it to be?

Top photo is the entry and the bottom is the tooling idea. You simply line the bit up with the point of the cone or nail or screw where you want it to finish the hole being bored.

 

[tvrgeek]

The rest of us just use a center punch. Start with a very small split point drill, then finalize.

 

[zapdafish]

whats the official googlable name for that cone? lol

 

[mquan01]

how do you keep it straight over 12 inches? that is always the issue I had...

 

[bobsmodels]

Just a couple of things that help. First and foremost the drill bit must be sharpened correctly, both lips exact. If they are not one side of the bit takes off material at a different rate than the other and the bit will go off center. You want the drill to enter where you want it. Using a center drill has the wrong geometry. It is designed for a 60 degree center and your bit is going to be 118 or 135 and is not going to match. Either use a 118 spotting drill with a 118 drill bit, etc. Another trick is to use a a ball endmill to center the hole for the bit, works best for me. This may be obvious but the material must be clamped to the table so it cannot move, you cannot just hold it even in a vise.

As for 12" - the drill press must have a heck of a throw. Only way I can do deep long accurate holes is in a lathe.

Bob

 

[tvrgeek]

And a drill press is pretty flexible. If you want real precision, you need a big mill.

 

[mpeele]

how do you keep it straight over 12 inches? that is always the issue I had...

To drill a 12" hole accurately you need a Gun Drill. When using a gun drill you have to drill a pilot hole 3 times the diameter of the hole deep and 3 or 4 thousand larger that your gun drill. They are a single flute drill bit with no twist. I have made them for wood out of mild steel and O-1 drill rod. For wood you don't need to harden them if you don't want to. They go straight because there is no side clearence like a twist bit. They are actually more a reamer that a drill bit. Drilling with one is fairly slow because you have to back it out to clear chips/dust every inch or so depending how long you cut the flute. To make the flute you grind out a 45 degree slice along the length. Tip angle is fairly flat about 15 to 20 degrees with enough rake to allow the bit to advance. You goal is produce more dust than chip. They work better with point off center.

Gun Drills are actually a metal thing but the concept works well with wood. Metal Gun drills have coolant and chip clearing holes drilled along there length that are drilled with Gun Drills. They can drill holes 80 time their diameter where normal twist bits are about 8 times their diameter. Twist bits are not real precision tools. If you want a precision hole you drill with a twist bit and then ream it in several steps to final diameter.

I have 3/8" and 1/2" 12" twist bit that I have welded a 2' 1/4 extension on that I used for drilling lamps. They only have flutes which extend 8 time the diameter and will drill somewhat straight. I dill 3 or 4 inches from the top and bottom with my drill press and then remount in lathe and drill through my tail stock from the bottom to connect the holes. Not always perfect but close enough to get lamp cord through.

 

[Hmerkle]

anyone who has blown out the side of a pen blank </= 4 inches understands a twist drill does not drill a strait hole!

 

[tvrgeek]

It would look like Dan is only trying to drill a couple of inches, but needs it in exactly the right place and needs it at the correct angle. So again, I suggest a mill, not a drill press, and split point bits as chisel points will migrate more. Buy proper bits for a mill in the right length so you don't have excess flexibility.

You can make a drill press much more steady by putting an adjustable post under the table. It was enough to use my DB to rough out mortices with a forsner bit. Not sure it is precise enough for installing a lock but it helped.

 

[Hmerkle]

I respectfully disagree that drilling on the mill will have vastly different results than with a drill press. While the mechanics of the mill are built with tolerances. What I have experienced is "drill drift" not quill-induced wander. Obviously, this assuming you have sufficiently clamped the work piece.

 

[tvrgeek]

I totally agree with the drill drift, especially with chisel point bits, but the tables of drill presses are just not much better than a wet noodle.

 

[Hmerkle]

I totally agree with the drill drift, especially with chisel point bits, but the tables of drill presses are just not much better than a wet noodle.

good point - "well-clamped" to a noodle = not clamped! I have always had "old 'arn" because I woldnt waste money on "cheap alternatives." But I would turn "getting a new tool" into a project spending my time rather than money!

 

[Graywolf]

I don’t know, I’ve always done a careful layout and drilled from both sides. That way if there is any drift or just poor aim, it’s in the middle. Just my two cents.

 

[Hmerkle]

I don’t know, I’ve always done a careful layout and drilled from both sides. That way if there is any drift or just poor aim, it’s in the middle. Just my two cents.

That is a VRERY effective way to avoid drill drift. I don't make a lot of pens, but that (and lamps) is where I have heard a lot of people have problems... So that is typically end-grain drilling and especially in hard (dense)woods the drill can drift... I an guessing speed is the reason a pen turner doesn't drill from both ends, but I encourage Adm (@allisnut) or bruce (@sawman101) or any other pen turners or flute makers to chime in...

 

[tvrgeek]

Not the OP's question but is seems instrument makers use spoon bits. There is also something called a "pen makers flute bit" for use in a lathe. They seem to be a brad point. There are many many drill geometries. Each will have it's use. I have almost quit using standard chisel points. Even thinking about the fancier DrillDoctor so I can sharpen all my chisels into splits. It seems their only attribute is they are cheaper to make.

 

[tvrgeek]

This thread made me think. I wonder of one put a shock absorber on the idler shaft on a typical DB, would that damp some of the vibrations? Probably need a lever several inches to get enough movement to dampen. A V-belt is going to vibrate, but maybe we can make it better.

 

[danmart77]

I don’t know, I’ve always done a careful layout and drilled from both sides. That way if there is any drift or just poor aim, it’s in the middle. Just my two cents.

whats the official googlable name for that cone? lol

Thats the dead end of a lathe. Nothing fancy I don't use it so it is REPURposed.

 

[danmart77]

The rest of us just use a center punch. Start with a very small split point drill, then finalize.

Well that's fine for what you might be doing but as you can see in the top photo, I have 20 hours cutting the barrel channel and some stock shaping done. If you drill the angled hole crooked you are not happy.

If you care to see the steps involved in building one of these you can look at a video on youtube

 

[tvrgeek]

Well that's fine for what you might be doing but as you can see in the top photo, I have 20 hours cutting the barrel channel and some stock shaping done. If you drill the angled hole crooked you are not happy.

View attachment 199402
If you care to see the steps involved in building one of these you can look at a video on youtube

For the simple question of getting it in the right place, a punch and small bit is still more than precise enough even for precision machine work. But if you have a secondary need for no wandering, dead strait etc., then my suggestion of a milling machine or in the least, a support post to reduce the flex in the drill press table. You also may look into short drill bits. Look at machine suppliers like MSC, REX etc. Jobbers are pretty long and flexible.
Just an example:

https://www.mscdirect.com/browse/tn/Holemaking/Screw-Machine-Length-Drill-Bits?searchterm=dril+bit&navid=4287924421

Of course, 200 years ago, it was done by hand with a brace and spoon bit.

 

[danmart77]

The rest of us just use a center punch. Start with a very small split point drill, then finalize.

that will not ensure the bit comes out where you need it to come out.