"DeepDiver" wrote in message
...
"Terry" wrote in message
ps.com...
Taking off that small amount will be interesting. Just hope I don't go
to much and scrap my backing plate. If I keep my gibs tight I think I
can do it ok.


Ok, I might get chastised for this by the more experienced machinists in
this group, but here's something I've done when I need to squeak off a
tiny
little extra amount of metal in my lathe: I take a piece of fine emery
cloth
and back it with something rigid, like a piece of flat metal stock and
then
apply it evenly to the workpiece. Basically, it's like combining the
simplicity of a file, with the finer and smoother cut of toolpost
grinding.
And by selecting the correct width of emery (and backing piece), you can
hit
the entire area at one time so you're less likely to get steps, gouges, or
helical patterns. The key is keeping your backplate pressed lightly and
evenly across the surface of the work. If your shoulder is critical (as it
is on your lathe chuck, you want to make sure the emery does not extend
past
the side edge of the backing piece and that your backing has a smoothly
polished edge so it won't cut the shoulder.

Often, all that's needed is to remove any high-ridges that were created by
the single-point cutting tool and the fine emery does an exceptional job
at
producing an almost mirror finish. But like filing, don't get carried away
and take off too much.

- Michael


Chuckle!

You won't get chastised by me, but I sure as hell have plenty to say to
those that use files for such operations. That's nothing short of insanity,
and is very poor practice.

Your points about leveling the highs with abrasive cloth or paper are right
on, as is your method of applying them. It would be very difficult to lose
center, or create steps by your method, due in part to the relatively slow
cutting process, although you do run a slight risk of rounding edges.
Beyond that, it's very best way to go, short of grinding, or *turning*, my
preferred method, considering the part is already in the lathe.

I would assume that in this instance, the material in question is cast gray
iron. Unlike mild steel, it will gladly allow a cut of a few tenths, with
excellent results. That would be my choice of methods to reduce a diameter
by a small amount. You risk nothing by this method, unlike all others.
Putting a file to a surface that should be considered precision isn't a
great way to go.

Harold