How to fix taper

nathanhouse · Feb 17, 2017

i have a SB 9". I'm assuming there is either an adjustment that is out of whack or I'm just missing something. I'm turning a short piece between centers and the stock started with about .002" runout. I made two small passes (total of .005") which obviously cleaned up the runout BUT now I have almost .004" taper. what am I missing? Kinda new to this machine so go easy...

AA+ · Feb 17, 2017

Recommend that one shift the tailstock over to eliminate the taper.

Best wishes --- Allen

nathanhouse · Feb 17, 2017

adjusted tail stock. It has zero runout, the work piece has .0005" runout and less than a thou taper end to end before I make a cut. Make a small pass of about .002" and I end up with .0015" taper end to end. It's round just not straight. Can I make any adjustments to the apron itself? I know I can tighten the gibs on the cross feeds and those are snug. What about the whole carrier?

v8packard · Feb 17, 2017

If the tail stock is true to the spindle center, and there is nothing else obviously wrong, you need to level your bed and then adjust it to eliminate taper. The procedure is listed in many posts, online videos, and also in the book How To Run A Lathe. If need be I (and others) can walk you through it, you will just need some 2 inch or so scrap bar to turn, some free time, and a way to adjust your lathe bed (adjustable mounting feet, or shims, etc.). It will produce very accurate results if done carefully.

Best of luck to you.

Marc

michiganbuck · Feb 17, 2017

A long part can have all kinds of problems. A thin part is more affected by the condition of the bed with the tool bit going high or low to center. Once you take a cut the head end should run zero run out. Likely you need to move the tail stock about half the .004 in the direction needed.

Truing the tail with a 12" master bar (or whatever) might make a brand new machine good at any length.. an older machine may need consideration for the part length and diameter.
On a grinder you measure the part then come in to hand rub the wheel to the part head end an tail, and adjust to get close to zero. then you fire up and see that you tickle first on the measured high side.

Also indicating a round part with the head and tail not being the same height can muck up test bar test with the indicator point going above or below center.

MaxPrairie · Feb 17, 2017

Search Keith Fenner on youtube.

kitno455 · Feb 18, 2017

The tailstock casting is split into two parts. The top moves laterally on the base using two adjuster screws, one on the front, one on the back. Adjust it after making a cut, then make another cut. Continue that process until there is no taper. This can somewhat counteract a twisted bed, but you should check for that too.

allan

jim rozen · Feb 18, 2017

kitno455 said:
The tailstock casting is split into two parts. The top moves laterally on the base using two adjuster screws, one on the front, one on the back. Adjust it after making a cut, then make another cut. Continue that process until there is no taper. This can somewhat counteract a twisted bed, but you should check for that too.
allan

Turning between centers, the bed condition won't be a big issue.

Just remember to slack the clamp that holds the tailstock to the bed before using the side-to-side adjusting screws.

Illinoyance · Feb 18, 2017

To align the tailstock you need to do a two collar test. Adjust the tailstock until the two collars are the same diameter.

Derek Smalls · Feb 18, 2017

Illinoyance said:
To align the tailstock you need to do a two collar test. Adjust the tailstock until the two collars are the same diameter.

Why not just use the part you are turning? After all,isn't that what you want to be straight at the end of the day? What better test can possibly exist?

Rudd · Feb 19, 2017

tailstock can also "droop" vertically with wear. Since we tend to pull the TS toward the headstock, the front wears faster than the rear.
I had this condition and shimmed the TS (between the upper and lower parts) to correct.

You are locking the TS, right? - i.e., not depending on screw to keep it tight.
Maybe not an issue with short parts, but have you leveled the bed?

Steven-Canada · Feb 19, 2017

The abundance of Southbend literature on the internet is huge..HUGE

Search for your manuals, parts list, "how to run a lathe"

Lots of info for free

nathanhouse · Feb 22, 2017

Thanks guys for all the info and input. I haven't gotten back to the project just yet since I've been doing a ton of other stuff but I'll put some of your suggestions to work when I do and let you know the outcome. Thanks

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