Re: [CAD_CAM_EDM_DRO] scraping beds for long tables

> When my father initialized me in scraping and later in a practice
> I was told that for a bed of a long travelling table (example x table of
> a Bridgeport that has a short bed) you should scrape into the bed
> a curve so that the curve counter arrests the weight of the table
> when it travels far out.

Sven;

This is an accepted practice. Both Edward Connally (Machine Tool
Rebuilding) and Wayne Moore (Foundations of Mechanical Accuracy) explain
the process in their books. What is required is either lots of experience
with what does or doesn't work, or extensive finite element analysis
followed by lots of experience with what does or doesn't work.

The ways of a gantry are arched to account for deflection from the weight of
the head. The column of a vertical machining center is tilted back to
account for the weight of the head. The angle between the column and saddle
surfaces of a mill knee is slightly obtuse to account for sag due to the
weight of the knee.

Sometimes, however, it's just the result of sloppy workmanship. Even
Bridgeport has had quality problems at times.

Doug