Making a Poor-Man's Taper Attachment

Tooling for my Taig lathe

Part of the Making Stuff collection
by Douglas W. Jones
THE UNIVERSITY OF IOWA Department of Computer Science

Copyright © 2018. This work may be transmitted or stored in electronic form on any computer attached to the Internet or World Wide Web so long as this notice is included in the copy. Individuals may make single copies for their own use. All other rights are reserved.

Mounting Bars
the bars for the taper attachment
A classic taper attachment for a lathe involves a rail mounted behind the lathe bed. To turn a taper, the cross-slide is disengaged from its lead screw and connected to a shoe that rides the rail on the taper attachment. This rail is angled to the lathe bed at the desired taper angle, the tool is adjusted to meet the workpiece at one end of the taper, and then the carriage is driven along the length of the taper.

To make my taper attachment, I first built a pair of bars that could clamp to the lathe bed. I used 1/2" square aluminum bars, with clamp shoes made from 3/4" extruded aluminum channel that was a snug fit on the bars. The shoe that rides on the rear of the lathe bed is fixed permanently to the bar by a press-fit pin and a screw. That clamp is held parallel to the bar by a 1/8" spacer.

The front clamp is free to pivot on its mounting pin, but it has a captive nut (a swage nut) driven into it that mates with a cap screw through a hole in the bar. To mount the clamp bar on the lathe bed, the rear shoe is engaged, then the front shoe it pivoted into position before the mounting screw is inserted and tightened.

After the bars were completed, I mounted both of them on the lathe and scribed a reference line on the bar tops parallel to the lathe bed.

Setting up to turn a taper
arrangement of taper attachment before starting to turn
I decided to dispense with the complexity of disengaging the cross-slide lead screw. The Taig cross-slide can be disengaged from the screw, but it isn't easy. Instead, I opted to make taper-turning rely on two-handed lathe operation, using one hand to drive the carriage down the ways while using the other hand to back off the cross slide. This means that the taper attachment simply blocks any motion of the carriage that would tend to cut too far into the workpiece.

To cut a taper, I clamp the two mounting bars to the lathe bed as far apart as I can and then use C-clamps to clamp the ruler from my combination square to the bars. To set the angle, I measure the distance between the bars and then multiply this by the tangent of the desired angle. One end of the ruler is set on my scribed reference line. The other end is offset from the scribed line by the tangent times the distance between the bars.

I made a follower for the carriage out of two pieces of hot-rolled steel bar. The bottom piece fits in the T-slot, while the top piece clamps down over it. At the far end, a 1/4" steel pin through both bars rides against the ruler. To set up for turning a taper, I do the following:

A finished taper
after the final pass of taper cutting
To turn the taper, proceed as follows:

The photo shows the 15°taper I was cutting, immediately after the final cutting pass. I'm cutting fairly hard steel, so I'm using a brazed carbide cutter. All of the swarf from the final pass is balanced on the cutter in this photo — it's a mixture of cutting oil and very fine gritty bits of steel because I made the final pass very slowly in order to get a nice finish to mate with the lathe spindle taper.

This setup has worked very well. So far, the primary use I've had for it is to turn 15° tapers on tooling that fits the lathe's spindle taper, but I've used it three times:

All of this tooling has seen significant use I am confident that I can use this method to accurately turn just about any taper shallower than about 30°. My experience with turning the 30° taper on the spindle center convinced me that that was close to the limit for tapers I could turn with this setup.

I described most of the material here in an May 31, 2017 posting on Nick Carter's Taig Lathe and Milling Machine Blog