Leveling is the normal way (pun) that larger lathes are set up but the
minilathe is relatively stiffer due to its small size. Although the
castings aren't "aged", they are generally ground accurately so there
isn't any twist in the typical minilathe. Unless it is firmly bolted
down -- this can induce a twist, especially if bolted to something
that changes with humidity (wood) or temperature (metal) at a rate
different from the lathe bed itself. The simple rubber feet work well
because the lathe is light enough so it doesn't twist under its own
weight (as large machines may). (Hardinge made a large "portable"
lathe with wheels that was quite accurate so there is some precedence
for lathes not being bolted down.)
More commonly, tapers occurring in work held in the chuck (not between
centers) arise from poor alignment between the spindle and the ways.
This can be corrected by the owner with simple techniques but takes
several hours: Once
aligned the machine seems to remain aligned so this is a one-time
effort, i.e. the castings don't seem to "age" and twist.
John
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--- In 7x12minilathe@..., "Ed Boysun" <boysungran@...> wrote:
Guys that should know, tell me that a lathe bed has almost no resistance
to twist. You need to beg, borrow, or steal a machinist's precision
level and check the bed, both at the headstock and near the tailstock to
make sure that the level reads exactly the same in both places. If your
bench is solid, you may need to add shims beneath the legs on the lathe,
then clamp it back to the bench. If your table is not completely rigid,
you can adjust the feet of the table to impart some twist to the table,
and thus to the lathe bed. It surprised me; just how much a small shim
will de-twist the bed. A twisted bed will exhibit exactly the symptoms
you describe.
Ed B
--- In 7x12minilathe@..., "wrlabs" <wrlabs@> wrote:
Hi Folks,
If I can poll the collective wisdom on this I'd appreciate it.
I'm not sure I have a problem, but I think so.
Turning down a rod I get a 0.015" difference over 5.5", please see:
I would guess that would turn into 0.030" over 11"?
If I turn a cone in the chuck and pull up the tailstock, they appear
to match up as near as I can tell.
My failed laser edge finder drew a circle around the the tailstock
center that looked centered to me.
I get this just turning a reasonably robust rod just clamped in the
chuck too (measurable difference between ends, forget what the value
is now).
I'm really lost on this, only thing I can think of (SWAG) is (horrors)
that the bed is crooked or perhaps the saddle is crooked?!???
I'm really out of ideas, am I expecting too much of the 7x12?
Thanks & take care, Vikki.
GadgetBuilder