lathe cutting

[tbody321]

trying to turn a psiece of steel stock, mild carbon, and the round stock kept jumping. i tried to center the bit best i can but doesnt seem to change anything. im using an indexiable cutter and it does it with a hss steel bit. the lathe also has some side movement in the spindle? whats exxcessive? its a sb hvy 10. im hopinh the serpintine belt convertion did not mess with the thrust washer in the spindle or something like that.
any suggestions help is appreciated
tony

 

[xalky]

How long is the piece of stock? Diameter? How much of it is into the chuck? How much is sticking out of the chuck.? Is the piece of stock bent? Have you used this lathe before?

 

[tbody321]

short piece about 1.25 diameter. chuck is clamped tightly . never real had this issue before. but im no expert
ive been using lathe on and off for years. just cant seem to figure out why it jumps. is the tool better slightly higher or lower than cnter

 

[Thomas Paine]

sb heavy 10 has what bearings?

take off the chuck, put a test indicator on the spindle, put a broomstick or something in the thru hole, push up and down, pull back and forth. Measure your runout.

in a babbit or bronze bearing lathe, it should be .003"-.005"-ish to make room for 10 weight oil.

 

[xalky]

Ok, so your not a total newbie! ) You know how a lathe usually works, sorry, I was'nt sure. Your tool post is clamped down nice and tight? Tool stick out is too far?

Maybe a cheap insert or the wrong insert for steel? Some of the cheap chinese inserts need a little touch up on a diamond wheel to get them sharper. How does the edge look on your insert? do you have some sharper inserts?

Try cutting it with a HSS bit to see if it's better. If it is, then blame the insert. Sometimes they'll work a little better if they're dropped ever so slightly below center, .010-.020 below center. If the cutting edge is crap, you get crap.

 

[12bolts]

Tony check your cross and compound gibs for looseness.
Discernable movement, (by hand/eye) in your spindle is probably excessive. Even 3-5 thou sounds too much. Most plain bearing lathes recommend .001" of lateral spindle movement measured with a DTI.
Is this something you just noticed on this one job? Or have you noticed it before, even to a lesser degree? Are you sure of the stock material?

Cheers Phil

 

[GK1918]

Have you physically tried lifting the whole cross slide up and down, you just may be amazed... I'm not talking about gibs talking about the whole saddle.

 

[Thomas Paine]

i don't have a heavy 10 in front of me, but there should be a nut (maybe spanner) on the left end of the spindle to adjust end-play.



- - - Updated - - -

Most plain bearing lathes recommend .001" of lateral spindle movement measured with a DTI.

Cheers Phil

sorry! yes, phil is correct, word on the street is SB recommends .0007"-.0012". I said .003", not sure what i was drinking last night.

 

[mkeller]

3 jaw self centering chuck or 4 jaw chuck?