SB C9-10JR cutting a taper

[Jim F]

I finally got to use the lathe, have been holding off using it much, lack of lubes,
Tried to turn a piece of brass rod to .125.
1.5 " from chuck.
I had .002 taper.
Live center end was .125, chuck end was .123.
can adjusting the tail stock fix this ?

 

[benmychree]

likely adjustment would cure the difference.

 

[Larry$]

Maybe! First do the easy thing. Mount a dial indicator so you can see how much you are moving the tailstock. Move the tailstock .001" toward you and lock it. I'd use a heavier piece of stock for my test setup. Use a sharp tool so you aren't putting much side force on the work. For better accuracy turning a bar that is 10"+- long so it has larger areas turned near each end will allow you to get closer to parallel. To eliminate other possible things: retract the compound and lock it. Lock the cross slide, use a dead center and a bit of moly grease (or what ever you've got) and don't put a lot of pressure on it. Use the carriage feed rather than hand feeding. Watch

or

 

[benmychree]

The only thing using such a test bar neglects is that after aligning by that method, And then moving the tailstock to another working location, the alignment may well be off due to wear and alignment of the machine. Differences in center height of head and tailstocks will also effect differences in diameter.

 

[mikey]

I finally got to use the lathe, have been holding off using it much, lack of lubes,
Tried to turn a piece of brass rod to .125.
1.5 " from chuck.
I had .002 taper.
Live center end was .125, chuck end was .123.
can adjusting the tail stock fix this ?

Jim, clear something up for us. You were turning a brass rod sticking out 1.5" from the chuck so ... no live center was used, right? You had a 0.002" taper over that 1.5" length, right?

Okay, so the first thing that comes to mind is deflection. What was the OD of the rod? What kind of turning tool were you using and how was that tool oriented to the work? The fact that the OD was larger on the unsupported end makes this a real possibility because it suggests the tool is pushing the work away on the end but is able to cut as it approaches the chuck end that is more rigidly supported.

Next possibility is that the headstock may not be aligned with the ways. When a lathe cuts a taper in a work piece, the knee jerk response is that the lathe is not properly leveled. However, when the work piece is really short and tailstock support is not used, the headstock is the more likely culprit.

It is also possible that something is loose - a gib in the cross slide or compound - or there may be excessive wear somewhere in the structures supporting the tool post that allows the tool to move.

I would have a look at all these things.

 

[Jimsehr]

Mikey is right. Deflection. Put a 1 inch bar in lathe and turn it down about .01 then check for taper.

Jim Sehr

 

[Jim F]

Jim, clear something up for us. You were turning a brass rod sticking out 1.5" from the chuck so ... no live center was used, right? You had a 0.002" taper over that 1.5" length, right?

Okay, so the first thing that comes to mind is deflection. What was the OD of the rod? What kind of turning tool were you using and how was that tool oriented to the work? The fact that the OD was larger on the unsupported end makes this a real possibility because it suggests the tool is pushing the work away on the end but is able to cut as it approaches the chuck end that is more rigidly supported.

Next possibility is that the headstock may not be aligned with the ways. When a lathe cuts a taper in a work piece, the knee jerk response is that the lathe is not properly leveled. However, when the work piece is really short and tailstock support is not used, the headstock is the more likely culprit.

It is also possible that something is loose - a gib in the cross slide or compound - or there may be excessive wear somewhere in the structures supporting the tool post that allows the tool to move.

I would have a look at all these things.

I only cut 1.5" and I was using a live center.
After refering to the SB book, I moved the tail stock and it cuts true now.

 

[mikey]

Okay, you used a live center so now it makes sense that moving the tailstock influenced the cut.

 

[Larry$]

My first live center was OK but I wanted an extended nose. Bought one from a company that specialized in centers. Relatively cheap, Chinese. Way too much play to be of any use.