[Amps] Want to use a knob with a 3/8" opening on a 1/4" shaft.

[Will Matney]

George,

Well the barell - rod is supported not only in a chuck but has a steady rest at the end to be drilled supporting it on both ends and centering it. Just where the bit meets the work, the bit passes through a support with a guide bearing and the other end in the moving tailstock. That way both ends of the drill are supportted so it cant flex. As the tailstock moves to the spinning rod, the drill slides through the support bearing on the other end then into the rod. That stops any flex or deflection between the drill guide and the rod being drilled. Once the drill has went in so deep, the drill shank is the same size as the hole and keeps it along a straight path. There are a few instances where you could run into a hard spot and the drill can vear off center but that is rare. Another thing that helps is the drill rod has an oil tube in it which delivers cutting oil at the tip and forces the chips back out the straight flute to the rear.

Rifling is done on a rifling machine or a forge. On a rifling machine, a hooked cutter is pulled through the barrel and rotated so many degrees as to how many lands are in the rifling. The twist is made buy gearing in the machine slowly turning the hooked cutter pulling through something like 10 - 16 inches per foot. Winchester uses a forge which you put in a drilled rod. You slide a carbide form in the middle which has the chamber, bore, and rifling on it. Then the forge hammers the barrell down on this inside die to create the rifling and bore at one time. After, you pull out the die and the barrell is done besides threading it and bluing. They used to use this but may be using rifling machines now, I'm not sure. Another way uses a chemical and electro etching of the lands in the rifling.

Best,

Will


*********** REPLY SEPARATOR  ***********

On 12/24/05 at 11:45 AM gdaught6 at stanford.edu wrote:

>Hi Will,
>
>> Well it will center it up, but if the tailstock is still offset, and
>> not on center, the pressure on the side of the hole from the bit will
>> cause the hole to be larger in diameter than the drill (wallow it
>> out). So, the bit needs to be true on center. Even at that, a bit is
>> not accurate for a finished hole even in a lathe. The only way to
>> finish the hole off so it's true, and the correct diameter is to ream
>> it, or bore it with a boring bar. 
>
>Also, the drill can wander off center, can't it?  That is, a really 
>deep hole (like a rifle barrel) can be curved instead of dead 
>straight.  
>
>Then, with a satisfactory hole, how do you put in the rifling???  
>I've always wondered about that.
>
>73,
>
> George T. Daughters, K6GT