[TheForge] shrink fit techniques

[theforge@mailman.qth.net]

>On Fri, 1 Feb 2002 11:38:42 -0500, RW wrote:
>
>>Bob, sounds good.  How does one find drill bits that are , for  example,
>>.001 smaller than the hole?
____________ 
>
>	One sends the bits or mills to a sharpening shop and
>specifies the cutter diameter one wants them reduced to.
>
>	One could also put existing bits in a micrometer and see
>what size they REALLY are.  You'd be surprised.

>Roy Wilson
____________

the size of the drill is only a part of what size the hole will turn out to be. if the drill has not been sharpened perfectly, that is with the cutting edges (lips) of the drill exactly the same length, the hole size will be off by twice the amount the edges are off.

drills are considered a roughing tool. in everyday work this doesn't matter. machinerys handbook has a chart of "probable hole sizes" for various drills.

if a precise hole size is wanted use a reamer. reamers can be bought +/-.001 on most fractional drill sizes (1/2-3/4" etc.)

you can get pretty close with drills if you start small and work up. if you want a .750 (3/4") hole drill first with 1/4" then 11/16" then 3/4".

bob s.