Re: [CAD_CAM_EDM_DRO] final finishing of steel bed

Graham Stabler wrote:

>I have just finished doing the final pass of my egg-box style steel
>bed plate. It is 730mm X 730mm in size and I have finished it with
>a shell mill with carbide inserts (only two inserted so it acts like
>a fly cutter). If the overlap between the passes is small a very
>slight lip is seen, this I think is due to the head of the mill not
>being spot on vertical. To avoid this I have made the step over
>half the diameter of the shell mill. However the fact it is carbide
>means that it doesn't really like taking off tiny amounts. I have
>ended up with a flat bed but the machining marks are unusual to say
>the least, you cannot feel them but you can see patches near the
>overlaps.
>
>I would like to polish out the machining marks on the bed either
>manually or using the big mill it is still mounted to. I don't want
>to mess up the flatness so I am looking for ideas of what to do.
>Could I for example just use a largeish fine oil stone?
>
>

I used a combination of bench stones to finish the bed on my Sheldon lathe
rebuild. I had some "air tool oil" from Sears in a black rectangular can,
that made a wonderful lapping oil. Does anyone know what this stuff is?
It was red like transmission fluid, smelled like WD-40 or LPS-1, and was
pretty thin, maybe around SAE-10. I would rub two bench stones together
with oil liberally spread on them, and it would very quickly make them both
flat. (You have to apply the rubbing with some care to improve flatness of
two surfaces if you do it this way, inspecting with a straightedge.)
Then, I
could apply the stones to the surface to be polished. I was hand-grinding
the bed with Cratex rubberized and cotton-bonded wheels, which left a dull
and rippled finish, on the micro-scale. So, I then rubbed
longitudinally with
the bench stones to improve the surface finish and make very slight
adjustments
to the flatness. Without another tool to check flatness, you are
working blind.
Also, just because you milled it on a milling machine does not, in any way,
mean it is flat! it may very well have +/- .001" or more waves in it,
especially
since your spindle is not perpendicular to the table movement.

Jon