Taper

[junk iron]

I was turning some 1.750 long brass bushing on my old Clausing 1500,when I ckecked them I have .003 taper in that short of distance,is there anything to correcet this?
Thanks

 

[RJSakowski]

I was turning some 1.750 long brass bushing on my old Clausing 1500,when I ckecked them I have .003 taper in that short of distance,is there anything to correcet this?
Thanks

Yes There is. This is a fairly common problem , usually associated with twist in the lathe bed due to uneven leveling. Properly leveling the lathe, using a machinist's level can help. There is also a two collar test where a section of a stout bar is turned close to the chuck and some distance from the chuck and the turned diameters measured. There is another test which accomplishes the same thing without a need for turning. Unfortunately, I have been searching for it abut can't find it .
Another reason for turning a taper is a misaligned head. Some lathe heads are adjustable so the spindle axis orientation can be rotated relative to the lathe ways. Another reason for turning a taper is a misaligned tailstock. This is actually used to intentionally turn tapers where stock is turned between centers, being driven by a lathe dog engaging a faceplate. Since you are turning a relatively short bushing, I would assume that you are not using a tailstock center.
Finally,a taper can be turned due to deflection of the workpiece. All turning develops cutting pressure which deflects the workpiece. It is worse when turning long slender pieces and is aggravated by dull or improper tooling. The far end will always be larger than the end near the chuck in this case. Making one or more light "spring" cuts can help to reduce this as can using a follower or steady rest. Using a tailstock center can also help. There are many discussions on this website regarding the subject, one as recent as yesterday, A little searching should uncover them.

Bob

 

[JR49]

Bob
I simply had to respond even though I actually (thanks to this forum) knew the answer to this question. Your answer was so spot on, including every possible cause of the problem. Junk iron, I hope you know how lucky we, and many others are, to have such generous "pros" on here to teach us there craft. Whenever I thank a "pro" in a situation like this, I am tempted to make a list of all the great "pros" who give their time to help us, however I'm afraid I would exclude someone, so I don't do it. SO, To all the "Pros" who make this forum the incredible source of information that it is, THANK YOU, and HAPPY MACHINING. JR49

 

[wa5cab]

There are two additional possible reasons. One is the chuck, IF you were using one. The other is differential bed wear. You didn't give the diameter of the bushings, material or DOC,which can affect the probably of either bed wear or some of the possible causes that Bob listed being a possible culprit.

 

[junk iron]

Heres how I made the bushings,I used a 3 jaw and bored brass to .997 x 1.750 long,then used a Sunnen pin honing machine to finish to 1",then I put 1.250 bar in 3 jaw turned it so the busshing had a nice slip fit ,taped the shaft to secure bushing and turned o.d and came out with the taper.I have never leveled lathe but now is on my to do list.

 

[wa5cab]

If the lathe isn't properly leveled and anchored, all bets are off.

Note that it's true that a lathe doesn't have to be level in order to work correctly. Otherwise you could never operate one on a moving ship. It's just a truism that the only cheap way to ensure that the bed is not twisted is to level it