On Tue, 21 Feb 2012 19:10:34 -0600, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Karl Townsend fired this volley in
:

have you heard of the Devlieg microbore line?
http://tinyurl.com/79g7e25

Karl,

I can't even imagine how an adjustable boring bar would help in this
case. I have an adjustable boring head of the off-set slide type.

But insert-style (indexable carbide, and not) internal threading tools
are a LOT cheaper, and in this case, more flexible than that... those
cartridges are outrageously expensive.

The grinding of a healthy relief on the bottom is important, but more
important would be grinding the angle to less than 60-degrees to make up
for cutting on the lag and lead.

A single-point threading mill would give its best profile when as small a
cutter radius as possible, commensurate with enough stiffness and thread
depth.

LLoyd

ya, you want about 1/2 or at most 2/3 diameter from single point tool
to bore on thread mill. I scored a whole set of micro bores real
cheap, also drawers and drawers of inserts. I like to grind the form
on just the brazed insert with the baldor and then put it on the
optical comparator. I've done threads, timing pulleys, and gears this
way. Works a treat.

Probably a case of use what you have.

karl