I just checked my tailstock alignment with my headstock and to my amazement,
it is .006 to high. I could see it being a little low from wear but how do
you adjust one that is already to high? Must I take the headstock loose and
shim it or is there an easier way? I would hate fighting trying to get the
headstock aligned again with the bed.
Scrape it! :-)
Before you start, double check!
Is there some dirt on the contact surface to the bed?
Is there dirt where the tailstock is separated for taper turning adjustment?
How does the reading change when you clamp the tailstock a bit/normal/a lot?
How does the reading change with the quill retracted/out to the max?
A tailstock a few 1/100 mm (max. 0.04mm; *not* inches) too high is
What I did was to chuck up a .750 reamer, mounted a dial indicator on to it
at the end nearest the tail stock, and then tightening the live center into
the hole in the end of the reamer. I tried this with tailstock near the
reamer and again with the tailstock extended. I also revolved the live
center to different positions to see if it made a difference, it didn't. I
then moved the dial indicator along the length of the reamer, (about 8
inch) and the indicator held steady. I also revolved the headstock and the
end of the reamer ran within a .001 or so.
I just went back and disassembled the tailstock. Although it was a little
dirty between the upper and lower halves, there were no shims or any thing
like that. I cleaned it up and tried all of my tests again but to no avail.
All of the readings are the same..006 high and all else true.
I do a lot of deep hole drilling, .250 and .312 and this affects the
straightness of the bores. I also use a steady rest quite a bit and I have a
1.375 roller bearing mounted and a number of collets made to run different
tapered spindles for facing and drilling. Last week I trued up the bearing
with the tailstock and noticed that the bearing was a little low so I raised
it to be true with the tailstock. Since then, I have been getting a little
chatter when trying to spot drill and the facings have not been dead nuts
true. That is the reason that I got to checking the tailstock and found this
According to Dick :
You know that many lathe manufacturers make tailstocks a little
high from the factory -- on the theory that the lathe will improve
accuracy with wear for quite a while before it starts getting worse.
And for normal turning between centers, a height error of 0.006"
should not make a perceptible difference in final diameter for anything
large enough in diameter to make turning between centers practical
As for your deep hole drilling mentioned below (and snipped),
you may need to start with the drills slightly under size -- and ideally
finish with boring to final size.
If you *really* want to zero that offset, take the tailstock
apart at the line where it spits to adjust for taper turning. Find
which side is flat, and which has projections, and set the flat side up
on a surface grinder and take off 0.005" or so (to leave it still a
little bit high, so it does not immediately go into the "wear makes it
worse" mode. :-)
High tailstocks are more common then one would think. An old time
machine rebuilder told me that it was fairly common, as it was a
response to wear on the tailstock ways, over time.
Doesnt help the owner of a new machine much though..shrug
Ive seen em as high as .01 on Chinese machines. The owners wound up
fixturing them on a surface grinder and setting them to rights.
"Abortion is self defense"