Removing a taper

[rscott9399]

So I am a hobbyist machinist. I have a piece of stock that I’ve been trying to “fix“ because it has a significant taper to it unfortunately the taper is the entire piece. The workpiece itself the taper is only about 15 or 20 thousands .
I was trying to put it in a four jaw And straighten it that way however all I seem to be doing is exacerbating the taper and making the workpiece worse.

how do I straighten this thing out?

Would a three jaw work better?
I feel like the problem is that when I hold the work ce in the four jaw chuck the work piece although it runs true close to the truck there is a bunch of run out towards the end of that I just can’t get rid of with a center or without a center it doesn’t seem to make a difference.

Any suggestions much appreciated.

 

[52 Ford]

I feel like the problem is that when I hold the work ce in the four jaw chuck the work piece although it runs true close to the truck there is a bunch of run out towards the end of that I just can’t get rid of with a center or without a center it doesn’t seem to make a difference.

Any suggestions much appreciated.

Not sure how the location of your truck is effecting runout. Maybe try parking your truck in a different spot? Maybe having it closer to the lathe will reduce the runout.

Serious, though. Take the part off the lathe, put it in a vise and find the center, center punch it, THEN put it in the lathe, put the point of the tailstock center in the divet from the center punch, while the tailstock center is keeping the part lined up, dial in the truck - I mean CHUCK side.

 

[MaxPrairie]

Once you get a good center in the part you need to adjust the tailstock in order to remove the taper. Don't know what your lathe is. 3 or 4 jaw doesn't matter. Use an indicator when moving the tailstock and should be within 1 or 2 thou on your first try.

 

[crazygoat]

Are you confusing taper to a bent shaft? You can have a tapered shaft without run out in it. It sounds to me like you have bent shaft.

 

[tdmidget]

Also, you might want to give Forum list | The Hobby-Machinist a try.

Why? The owner of that forum tried to destroy this one. Just because you weren't here at the time or have a short memory is no reason to endorse the asshole and his sycophants.

 

[52 Ford]

Didn't know that. I was suggesting it because he mentioned he is a hobbyist.

 

[michiganbuck]

Taper?
Holding the chuck end in a chuck the chuck can have stress to the part because of wobble in the chuck.
Set on a live center whatever error in an indicator reading of the point can be double on the part.
Set on a dead head and tail center is likely best.
A thin part may deflect from tool cutting forces at the midsection so hindering getting the tail end true.
Sometimes one may need to get the ends zero/zero..and crocus cloth the midsection to size.

Best to tell the part. Length, width, material, hardness, cutter type, set up.

and the condition of the lathe..It may be dead straight at 20" long part, and not that straight at a 6" part.

One quick straightening test is to first measure the part at two ends. Then when in the machine touch the part with an indicator or a tool bit to see how straight it is in the lathe. Then move the part center at the tail 1/2 the error you found.
I used to do this with a tool bit, and use my cross dial number for the move to get most all parts to .001 or so.. the tool bit is quicker than fooling with setting up an indicator.

Good to have a flat something at hand. It could be your lathe bed after you check it, a place to lay a part to see if it is bent...yes a small surface plate is bettter.

 

[michiganbuck]

If you can find a precision straight round something try putting it in each of your chucks and turn at a slow RPM (perhaps just by hand) to visualize how straight the chuck makes the part turn. Wobble is common in some chucks and it is good to know what the chuck and do.

One solution to wobble is to wrap a wire around the part chuck end, and put the out end on a dead tail center.

Still, long thin parts can be a bugger..super sharp bits, with proper rake angles can help with thins.

A following steady can help with thins.

 

[steve-l]

You are not clear on the taper description. Is it being created while you turn the bar? Or is it tapered before you start? It is very common that the source of your taper is internal stresses in the bar due to its manufacture and even when using a follower rest, you will be changing the stresses within the bar and causing even more warpage.This is very common in Europe. Much of the cheap steel is so mill stressed, it is not machinable.

 

[rogertoolmaker]

So I am a hobbyist machinist. I have a piece of stock that I’ve been trying to “fix“ because it has a significant taper to it unfortunately the taper is the entire piece. The workpiece itself the taper is only about 15 or 20 thousands .
I was trying to put it in a four jaw And straighten it that way however all I seem to be doing is exacerbating the taper and making the workpiece worse.

how do I straighten this thing out?

Would a three jaw work better?
I feel like the problem is that when I hold the work ce in the four jaw chuck the work piece although it runs true close to the truck there is a bunch of run out towards the end of that I just can’t get rid of with a center or without a center it doesn’t seem to make a difference.

Any suggestions much appreciated.

Mount a 12" Scrap bar in the three jaw chuck. Center drill; turn the bar around and repeat the process. Install the faceplate and centerers.
Place the Scrap bar on the Centers. Take a light cut at each end of the bar with the same settings. measure each end with a micrometer. Is the lathe true on centers. If not, adjust the tailstock. Repeating until it is true. Now that the lathe is true, mount your "Tapered Workpiece" on centers. Run the indicator along the length of the bar. Is it Tapered or Bent?

Roger

 

[tylersteez]

Why? The owner of that forum tried to destroy this one. Just because you weren't here at the time or have a short memory is no reason to endorse the asshole and his sycophants.

also wasn't aware of that and it's not like that story is advertised for every member to see before making a post. How is any newer member supposed to know that

 

[Illinoyance]

If you are turning the work in a chuck with no tailstock support there are two causes of taper: Part deflection under cutting forces, or the headstock is not aligned with the bed possibly due to a warped bed.
If you are turning between centers the taper is likely due to a misaligned tailstock.

 

[jim rozen]

Next up is a discussion of precision starrett levels and super-duper test bars.

 

[CarbideBob]

Next up is a discussion of precision starrett levels and super-duper test bars.

That is so old school.
Alignment lasers and interferometers are the only way to do to it right. .........Not

Unsure why the use of a four jaw here if the part is round.
Taper is uniform meaning constant or is it okay near the chuck and then gets out of control?
Size grows or shrinks to the tail?
Bob

 

[Lewie]

If you can't describe the problem , you won't recognize the answer. :-)
...lewie...

 

[crazygoat]

Since the OP hasn't bothered to come back, I don't reckon we will be able to figure out his problem without some answers to the questions raised.

 

[DDoug]

Why? The owner of that forum tried to destroy this one. Just because you weren't here at the time or have a short memory is no reason to endorse the asshole and his sycophants.

...and this is a problem-o how ?