BillM wrote:
I've got a passage in a die head that I need to smooth up.
Looks like it was drilled
and nothing further was done to it. Material is hardened
P20. Hole is 18mm straight
with a through length of 12-13 inches. I need to get the
inside smooth/polished with
no visible surface pits. scratches, drill marks etc.
Estimate I'll have to open it up
10-15 thousandths to get below the worst of the grooves.

Hole goes through, but I only have 1 1/2" clearance on the
back end, so everything has to be done from one end. Final
diameter, concentricity, straightness and taper aren't
important. I would actually like it to finish with a slight
taper, smaller at the rear.

Mounted points, followed by Cratex and then polishing
compound on a felt bob?
Expanding carbide reamer first to get it smoothed up a bit?
Flex-Hone and a brass lap?

Thanks,

Bill



Ream as smooth as you can then go at it with on of those hone brushes
(looks like a bottle brush but with small abrasive balls on each
bristle) powered by an air drill or equivalent. For final finish use a
'butterfly rod' which is nothing more than a 1/4 rod with a saw kerf
splitting the end for an inch or so, into that slit place a length of
folded length wise abrasive cloth, power the 'butterfly rod with a die
grinder for higher RPM. Use progressively fine grades of abrasive cloth
to desired finish.

At least that's what I'd try....

Regards
Paul


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