Taper cutting on a lathe with a compound rest

[Idz]

A case profile or chamber reamer usually requires multiple tapered sections. Here is how I set up my cheap import lathe to use the compound rest to cut the tapers (the angle scale on the rest is useless) without having to un-chuck the work or resort to the elaborate techniques shown on the internet.

1) Zero the compound rest: Chuck a dial indicator into the tailstock and index the tip on the ground surface of the compound rest dovetail slide. Then crank the long feed so the indicator travels from one end to the other on the ground surface. Rotate the rest until you can move the rest back and forth with changing the indicator reading.


2) Set the taper: Mount 2 dial indicators on the cross slide touching the ground surface and measure the distance between where the tips touch the slide. Rotate the rest until the difference in dial reading divided by the distance equals the desired taper. Example: distance between tips = 3.00", both dials start at zero, rest is rotated so dial 1 = -.050 and dial 2 = .040 therefore taper = (.050+.040)/3.00 = 0.030 inches per inch


Here's the sophisticated tooling used to attach the indicators to the the cross slide. A little filing on a 1/4-20 bolt head and it fits the t-slot perfectly.

[C. Latch]

I need either a dictionary or more pictures. You're way over my head, and I mean that as a compliment.

[Red River Rick]

One dial indicator, mounted on the cross slide, and some simple trig works as well.

RRR

[bangerjim]

I use a taper attachment on the compound rest, but that method works great for short quick work. And you do not have to take the rest apart! Using 2 dials is nice, as they are dirt cheap these days.

More chips.......less math!

banger

[CastingFool]

I used to run a manual lathe at work, but never had to turn tapers. Someone else ran the machine that had a taper attachment, so he got to run all the tapers. I got all straight work, and did a lot of external threading using die heads.

[KCSO]

Thanks a neat tip!

[country gent]

Dang and all these years id did it with a sine bar and indicator.

[oldred]

some simple trig works as well.

RRR

Trig don't come in SIMPLE,

[yovinny]

Good on you
Anything that makes a job easier is worth it.

I reverse that first step and work off the chuck rather than the tail stock for my initial cross slide alignment. Then I can rotate the chuck and sweep the rod to start with, to make sure it's good before I begin. Tail stocks are notorious for being out of proper alignment, with lots being offset to compensate for being low.
Everything ends up concentric with the chuck in the end anyway.
Cheers, YV

[Idz]

The suggestion of using one indicator takes several iterations cranking back and forth to get things set. I use two dials since they are so cheap.
I set my dial for zeroing in the tailstock because its a convenient holder and it doesn't matter how far out of line the tailstock is. Using the tailstock means your work doesn't have to be removed from the chuck. I've used a trammel bar in the chuck to set the angle but that method means un-chucking your work each time you have to change things.
For those really picky folks I do have to point out that this method assumes the long feed is parallel to the chuck axis and that the ground edge of the compound rest is parallel to its dovetail slot. Both of these seem to be within a few mils even on my Chinese lathe and I would expect to be even better on a more expensive one. The only other trick is to make sure your two dials are reasonably perpendicular to the ground surface so you are measuring distances perpendicular to the chuck axis.

[Red River Rick]

Actually, I smartened up a few years ago and invested in B/N equipment, CNC..............and all those problems went away!

Life is Good!