Hi Jim
OK if your lathe is cutting smaller at the head stock than it is out
in space your bed has a twist in it. Now this is figuring that the
head stock is in correct alignment and or your spindle bearings are
not shifted in the head stock.
I kind of think its not the bearings and this is why. First you say
the taper is .005 in 4 inches. Now the distance between bearings is
about seven inches. This would mean that your spindle would have to
be out of alignment with the head stock casting about .010 This I
find hard to believe though it could be.
First I would loosen all the bed mounting bolts were it is mounted
to the table or bench. I would let is sit for one week. Now I
would snug down the head stock end of the bed leaving the tail stock
end lose. Now take another sample cut and see what you get.
Remember these things are made from hard rubber and will move all
over the place.
If you find after a week of rest and relaxation your lathe is still
cutting a taper lets try shimming the bed and get the twist out of
it. You will have to put a shim under the front bed mount at the
tail stock end. You could also put a shim under the rear mount on
the head stock end. I am talking a shim of .015 or so. Now bolt
the bed back down and let it sit for a week and then check things
again to see if things are moving yet.
You all will be surprised at just how little it takes to get a lathe
out of whack. Also just how little it takes with patients to get it
back cutting nice and strait.
It took Dave Kirk several weeks to get his bed moved around to were
he was cutting no more than .0005 in a few inches. Don't remember
just what Dave came up with but I am sure he is going to let us
know. :-()
We have a lathe at work that is a 14 by 40 and we do a job that
requires us to check the alignment at the begging of the day and
after lunch. This job we are using a fixture in the head stock that
we machine the face each time we put it in the spindle. Then we
mount a custom made mandrel to this that is hardened and ground. On
this mandrel we mount the lens mount for an electron microscope that
has a bore of 1.120 +.0002 - .0000. This lens mount is 14 inches
long and has an outside diameter of 2 inches. Now we have to face
each end perpendicular to the bore to a tolerance of + or - .000050
and at the same time hold an overall length of .0001. Now we do this
on a TWS Taiwanese lathe that now has over 17000 hours on the run
meter. Dam fine machine but we are asking it to do something very
much out of the ordinary. So you say how do we do this. Well ever
time we set the job up we have to align the bed with the fixture in
place. We do this by traversing the mandrel with a .000050
electronic indicator. We need to have the mandrel aligned to .0001
in 14 inches. The lathe is fitted with four bed feet at each end of
the machine. This makes for real fun moving things. With this
setup we can actually hump the bed in the middle or belly it down as
well as twisting it. This lathe weights 3200 pounds so is no light
weight. I give this example just so you can see what can be done
with a lathe.
Turk
--- In daltonlathes@..., "Jim Bonner" <bogyjim@...>
wrote:
Hi all,
I'm wondering if someone could give me some advice on getting my
lathe to cut straight. The lathe is a Dalton B6. When I cut a
test
bar,(without a center in the tailstock) I get about .005 taper in
6
inches. The smaller diameter is at the headstock end. I would
think
that if it was a matter of normal bed wear, the smaller diameter
would be at the tailstock end. I have checked for bed wear by
mounting a travel indicator on the carriage and indicating off the
tailstock flat way. It doesn't indicate any wear that way.
I'm thinking that the spindle bearings aren't aligned with the
bed.
As I recall there is about .004 shim under the large spindle
bearing
halves to take up for wear in the bearing.
Any suggestions?
thanks, Jim Bonner
