Taper Method?

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MattM

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I have to turn a very precise angle (5.895 degrees) three inches in length. I will use my Leblond Regal lathe that has a good working taper attachment. Should I use that or the cross slide/compound method? Which would be the most accurate or are they about the same. I will use a sine bar to set the angle.
 
I would use the taper attach. That way you can cut under power feed. Accuracy should be same same. I assume your compound has more than 3 inches of travel.
 
I'd say the taper attachment, I suspect that using it may be the best method of using the sine bar to set the taper, besides that, tapers cut with the compound usually end up looking wavy. Yes, power feed is definitely an advantage to attain a smooth continuous cut.
 
Thank you. I do have more than 3" of travel on the compound.

I like the power feed idea and have used the taper attachment in the past to taper rifle barrels but there the angle was not super critical.
 
Once the first operation machining is done, one can use dykem, a file and a diamond hone to fine tune out any
irregularities in the part. I use old machines so am used to this procedure to get better accuracy on a
taper. This works especially well for stuff like Morse tapers when one has the female taper to gauge against.
If you don't have the luxury of a female taper, one is down to having to do a lot of measuring. Another help
is to make the taper slightly oversize so you have enough material to fine tune.
Fit and finish is what I use at the end of a lot of machining operations.
 
I would expect that the most accurate way to cut a small taper angle would be to turn on centers with an offset tail stock. Accurately cutting a taper requires a smooth cutting motion and the ability to accurately set the angle. The most accurate way to set a taper angle is using a sine bar. The sin(5.895º) x 3" is .3081" while the sin(5.890º) x 3" is .3079". Reading the offset to +/- .0001" resilts in a possible error of +/- .005º.

Turning on centers has limitations though. The angle is limited due to the ability of the center to engage the center drilled socket. The part also has to be accurately center drilled on both ends which is not always possible

A second choice would be using a taper attachment. There will be some potential added error due to the slip fit of the taper attachment. Also, any stiction in the cross slide could cause some local variation in the cut This is due to the offset nature of the hand crank biasing the compound slide first to on side and then the orher.

Last would be using the compound. Limited movement requires more precise measurements and any slop in the compound ways creates the cyclic pattern that benmychree described. That said, I recently had the need to cut an MT2 taper and used the compound. It was a PITA to set the angle properly but eventually, I got it right. The finish was excellent, actually surprising for a hand turned crank and checking with bluing, the angle was dead on. I wouldn't guarantee that it was +/- .005º though. I run my compound ways fairly tight which I attribute to the excellent finish. Also, the stock, although of unknown alloy, was most likely a free machining steel.

Tom Lipton, OxTools, did a YouTube video on turning and measuring tapers. In it, he discusses various means of measuring a finished taper.
Keith Fenner also did a recent You Tube video where he cut a tapered socket using his compound.
 
RJSakowski said:
I would expect that the most accurate way to cut a small taper angle would be to turn on centers with an offset tail stock. Accurately cutting a taper requires a smooth cutting motion and the ability to accurately set the angle. The most accurate way to set a taper angle is using a sine bar. The sin(5.895º) x 3" is .3081" while the sin(5.890º) x 3" is .3079". Reading the offset to +/- .0001" resilts in a possible error of +/- .005º.

Turning on centers has limitations though. The angle is limited due to the ability of the center to engage the center drilled socket. The part also has to be accurately center drilled on both ends which is not always possible

A second choice would be using a taper attachment. There will be some potential added error due to the slip fit of the taper attachment. Also, any stiction in the cross slide could cause some local variation in the cut This is due to the offset nature of the hand crank biasing the compound slide first to on side and then the orher.

Last would be using the compound. Limited movement requires more precise measurements and any slop in the compound ways creates the cyclic pattern that benmychree described. That said, I recently had the need to cut an MT2 taper and used the compound. It was a PITA to set the angle properly but eventually, I got it right. The finish was excellent, actually surprising for a hand turned crank and checking with bluing, the angle was dead on. I wouldn't guarantee that it was +/- .005º though. I run my compound ways fairly tight which I attribute to the excellent finish. Also, the stock, although of unknown alloy, was most likely a free machining steel.
Click to expand...

Since neither of my lathes has a taper attachment I use methods 1 and 3. Between centers has always worked well. the only downside is it takes time to reposition the tailstock once the taper is cut. Sometimes it took more time to reposition the tailstock than it did to cut the taper. A few years ago I purchased an Edge Technology alignment bar to speed up the process.

As for the compound I've used it to cut several #1 Morse tapers for tooling on an older (1936) Craftsman lathe. Fortunately I had 1 to copy so setting it up was relatively simple. Maybe I just got lucky, but the angle and finish worked out fine.
 
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