# Boring an Accurate Internal Taper



## Antman (Mar 17, 2011)

Hi Guys,
  I'm trying to make a spindle for a rotab. I want to turn it between centres to achieve squareness of the shaft and 2 faces, and as an exercise, my first workpiece between centres. Also I want a taper, in the end of the spindle to locate a centre pin. The bottom of the taper to be tapped M6 x 1. The biggest centre drill I have is 8mm, but I want the taper to be about 12mm diameter at the outer end. First is a 60deg taper too shallow to locate a tapered pin?

  Trying out my taper idea on a piece of stock, I drilled 5mm and then using a tool ground from 4mm round HSS and 30deg on the compound, achieved an ok taper as far as finish goes but I don't know how close to 60deg it is. Certainly a lathe centre held in this taper seems wobbly.

  So 2 more questions: How to achieve accuracy in the angle, or is it so neccessary to be spot on 60deg for a centre for turning? I can turn the male taper at one setting of the compound?

  Thanks,
   Ant


----------



## kvom (Mar 17, 2011)

My .02 FWIW:

For machining the internal taper with the compound, I would use it to machine an external taper adjusting until the angle is as accurate as you can get or want. Then use the same setting for the internal. It will be easier to measure the external, but the method needed will depend on the geometry of your lathe.

Unless your tailstock is exactly aligned with the spindle center, turning between centers will not result in a non-tapered shaft. You'll need to measure afterwards. Assuming your rotab has a non-tapered center hole, squareness of both ends may be irrelevant.


----------



## Antman (Mar 17, 2011)

Thanks Kvom,
  My tailstock is quite nicely alligned (I think). I haven't attempted turning between centres yet but turning a 20cm testpiece between the chuck and the tailstock centre gives me less taper than I can measure.

  Measuring an external taper? The only way I can think is with a clock on the cross slide, advancing it with a number of turns of the feedscrew.


----------



## MachineTom (Mar 17, 2011)

You measure the internal taper, same as an external taper.

If you have a carriage stop, clamp a gage block say 1.000" between the carriage and stop. set an indicator to read the taper, remove gage block, move carriage to stop, read indicator, double that number if using inches per foot taper, or trig it out, then double for included angle.

Morse tapers are listed as inches/foot, Jarno, B&S are formula based.


----------



## Antman (Mar 17, 2011)

Thanx also MT, I think I can do that, except I suppose accuracy depends on getting the clock plunger square to the centre line of the workpiece.

Ant


----------



## kvom (Mar 17, 2011)

Tom's method is easy to understand, but the indicator needs to be exactly at the height of the spindle centerline to work. If not centered, the indicator tip will trace a hyperbola on the taper (remember your conic sections?) and give inaccurate readings. One way to verify that you're on center is to measure the taper across two different sections and ensure that the readings are equal.

Measuring and setting the taper are two different things. If the sides of the cross slide and compound are straight, then you can use angle bars to align the compound more accurately than with just the degree dial..


----------

