Re: [CAD_CAM_EDM_DRO] Binding Table - How do I regrind/Lap the ways ? ?

Mark Thompson wrote:

>Hi All
>
>I have a Old Bridge Port that was used for
>cutting silicon mirrors and table has been
>worn in the center. They only moved the table
>about 10" in the X axis for it life.
>
>I have removed all the silicon build up on the
>ways and knee.
>
>My homebuilt CNC system can only operate on 12"
>of X travel before it binds. It's a 12"X44" Table.
>
>When I tighten the gibs the table binds at the
>ends. Is there a good way to manually LAP the
>table ways ??
>
>

Yes. Assuming the ways are not Chromed, the cast
iron is pretty soft. You need to take the table off.
the best way is to remove the left end leadscrew bracket
and screw the table most of the way to the right. Then
remove the right bracket and screw the leadscrew right
out of the nut. Prepare a table, bench or whatever to
receive the machine table, loosen the gibs and slide the
table all the way off to the right. (It can't come off to
the left due to the heavier flange at the right end for the
power feed unit.) You should be able to set the knee at
such a height that the table can be cleanly slid off onto
the thing that will hold it. I don't know how much a
Bridgeport table weighs, but expect it to be up to 300
Lbs or so. (OOps, you have a 12 x 44 table, that will be
more!) Now, you need a hoist or engine crane to pick
it up and turn it over. You want to support it on 3
adjustable supports (machinist's jacks) so you can level
it, and so no twist is imparted by an uneven surface.

Now, you need a straightedge designed for hand scraping.
You apply a spotting dye to the straightedge and wipe it
over the bed ways, and remove metal where a print of dye
is left. As you bring down the high spots, you will see the
area marked by the dye expand. In your case, the scraping
will start at the ends and work inward as you go.

It may be much easier to have the table ground on a big
surface grinder, or even have it milled or Blanchard
ground first. Also, without a 44" straightedge, it will be
hard to keep it straight by spotting and hand scraping.
Spotting it on a 36 x 48" granite surface plate would be much
better, but that is a BEAR to move around. Rolling the table
over, then lifting it onto the surface plate, spotting it, then
torning it over and back onto the bench every 15 minutes or so
will be a big pain in the rear, after the 3rd time, too. that's
why professional scrapers have those fancy straightedges,
that are light enough to handle.

Jon