Re: [CAD_CAM_EDM_DRO] Levelling large table

At 02:41 PM 12/22/00 -0500, you wrote:

>We are starting to draw up our router table and need a way to get the top

dead-nuts level. The plan is to use 60"X120"X.5" cast aluminum tool plate
for the table and a square tubing steel weldment for the base.

The normal way to level a rigid or short flexible machine uses a machinists
level. It uses a cylinder square and dial indicator for forcing the
spindle orthagonal. I wouldn't trust it for this span, but a transit or a
dumpy level has built in optics and could work quite well.

I've leveled a lot of flexible and three point machines, but nothing that
big. I would probably make some square tube leg pairs of the appropriate
height and bolt those pairs to the table. I'd probably put the leg pairs
on two foot centers or less. A half inch thick table between supports
probably needs a shorter span between leg pairs than two feet. You might
get away with a larger span if you welded longerons between the leg pairs
after you level it, but my welding always warps everything. Maybe a good
welder with a Tig could weld without warping. Don't weld to the tooling
plate, just bolt it to the legs.

Then, using long taper wedges under the legs, I'd sight over every support
under the table. An ordinary piece of stock with a flat bottom and a
scribed line will work as your sighting target. You can see a couple of
thousandths with that method with luck. You can't see a thousandth or tenths.

Then I'd grout under the legs. It might even be worth drilling and
epoxying bolts, or drilling and cementing in J bolts to bolt through each
foot.

The result would be a flat table, but it depends in the long run (30 to 90
days) on the concrete slab under the table. If you want permanent then
make sure that the slab is one piece under the machine, at least 6 inches
deep, and full of rebar and maybe mesh too. If you want movable on a two
inch floor, then check level every two or three months, depending on the
floor, what's under it, and the accuracy you are trying to hold. I'd level
and fasten the legs to the floor first, then mount the tooling plate to
avoid bending it while you are putting it in position.

Make your moves slowly and think about the whole process. I've dumped a
couple of machines, and nothing gives you the "Oh, S !" feeling quite as
well, knowing that if you had thought it through it wouldn't have happened.

Having said all this, I'd still check with Smoke and the guys he debates
with on this list first. They have probably handled many machines this big
before. They probably have much better ways to do it.