Re: Digest Number 4217

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Ron Ginger <ronginger@a...>
wrote:

> Lapping, by putting a compound between the sliding parts and moving

them

> back and forth is nothing less that accelerating the wear on the
> machine. You improve nothing, you just wear it out, exactly as is

going

> to happen over its life.
>
> Lapping (or scraping) the parts with respect to some master surface
> known to be flat and true could make an improvement.
>
> Why do people continue to refer to using lapping compound to

accelerate

> the wear as lapping?
>
> ron ginger

I submit that a milling cutter, hand scraper, and surface grinder are
also excessive and premature 'wear' of parts.

One laps parts to remove surface irregularities and to obtain
a 'better' fit.

Some reading into scraping details the need for oil spaces. Lapping
should NOT result in a mirror smooth or even completely even
surfaces. It is HIGHLY RECOMENDED you read up on hand scraping to
get an idea what an end result should be.

There has been much talk by people who do lap the mini-lathe and mini-
mill to remove the excessive high spots on some surfaces.

The reports are routinely entheuastic. Smoother movement, less
chatter, better feel.

The things I have lapped were very poorly machined and required
something to remove the high spots.

Dye-Chem revealed high spots that only allowed about 10% of the
surface to contact. That meant the when the axis moved away from
that spot, the carriage loosened up. and when it approached that
spot, it got tight.

I agree lapping is not for all machines, but I do submit it is a
candidate for machines that have the ways but with a flycutter and
are very rough.

Machines that have scraped or ground surfaces are NOT candidates for
lapping.

Look at this link
http://www.mini-lathe.com/Lapping/mt_lap.htm
The bottom picture shows flycut surface and you can still clearly see
the roughness. what was removed was the excessive high spots.

The surface in question is the one that has the countersunk screw,
NOT the upper surface with the half moon relief.

Dave