Re: final finishing of steel bed

--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers <rogersmach@y...>
wrote:

> Surf it for flatness. "Seeing" these marks is irrelevant. They way

to surf it is first obviously with a surf gage which few people have
although, one can be made with a block with one ground flat surface
and attach an interapid or other dial indicator along its side. Then
just move it around the block and it will show variances is surfaces.
Or put the plate on a surface plate and attach a dial indicator on
your height gage and surf it that way. A fine grit boatstone or
diestone with oil will work out all the maching marks. Will make a
good flat surface for a router. Tram the mill head in with an
indicator and resurface if there are lips that you can feel. Use new
inserts in the cutter or keenly sharpened cobalt or at least high
speed steel to cut down on deflection. If a fly-cutter is used dont
swing it to wide.

>
> Ron
>

interapid ? Isn't that a brand name like the Starrett LAST WORD ? I
think the generic name is test indicator....

The machine lines are just that. the cutter has to be a little
deeper in one area than another so will cut a radius.

Also, when it does not cut, it will push or burnish the metal, also
making a mark.

You are exactly correct that carbide is better utilized with a deep
cut and not a small dusting. They do make cobalt and HSS inserts
for most of the most common sizes so, that might be one solution.

you could use some jewelers rouge or some grit and a flat block to
lightly skim the surface. the higher side will be indicated by that
ridge grinding off leaving that polished look.

On one hand some would warn against hand lapping, but if you
considder that your tooling marks are deeper and a light grit and few
strokes will not effect the surface to any measurable degree, it is a
valid test for ridges.

A warning about lapping, if you take two equal sized plates and slide
them over each other with grit, the centers will see every part of
every stroke and the edges that hang over will only see half of every
stroke. This results in the center being worn/polished more than the
edges.

But, the question is about the need for ultimate flatness. If you
have the gantry, you can put on your dial indicator on it and run it
around the table to see how perpendicular they are.

And, taking a note from the making of the Hubble Lense, you can map
your table, put in a small 'thing' and grit and lap the table with
your software, in only the high places.

As I understand, the Hubble mirror was flat with a Capitol F.

In scale, it was flatter than the thickness of a dime as compared to
the Gulf of Mexico.

Dave