On 21 March 2018 at 14:47, Ken Strauss <[email protected]> wrote:
> I need to thread mill some tapered threads (similar to normal pipe threads --
> NPT). I am considering using polar coordinates in incremental mode to
> approximate a tapered helix. Is that reasonable? Is there a better way? Will
> cumulative errors bite me after hundreds of incremental moves?
Why use incremental mode? It is probably just as easy to use variables
and a loop
Polar coordinates ought to work, but you can approximate a spiral with
arcs too. (I would guess that 8 per rev would be better than 4 per
rev)
In polar, and not using incremental, something like this, assuming you
are already at X0 Y0
#<Z> = -1
#<pitch> = [1 / 13] ; 13TPI
#<minor> = [1 / 2] ; radius of 1" thread
F10
G0 Z #<Z>
G1 ^0 @#<minor>
O100 DO
G1 ^90 @[#<minor> + #<pitch> /64] Z[#<Z> + #<pitch> * 0.25]
G1 ^180 @[#<minor> + #<pitch> / 32] Z[#<Z> + #<pitch> * 0.5]
G1 ^ 270 @[#<minor> + #<pitch> / 21.33] Z[#<Z> + #<pitch> * 0.75]
G1 ^ 360 @[#<minor> + #<pitch> / 16] Z[#<Z> + #<pitch> * 1.0]
#<Z> = [#<Z> + #<pitch>]
O100 WHILE [#<Z> LT #<pitch>]
This uses 4 arcs. It could be done exactly the same with more, for a
closer approximation to a true spiral.
--
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916
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