How to Turn OFF Center

oskar

oskar

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The attached image shows a 1/2” OD aluminum rod 1.5” long. I want to turn the center part which is 1/2” long to a 4-7/8” diameter. How do I mount this rod off center to my chuck? Perhaps put a 1/16" spacer in one of the jaws?

I have a 4 jaws self adjusting chuck and another one which is 4 jaws independent adjustable chuck.

Thanks

Off Center.JPG
 
I do not know how to turn a 0.5” OD rod to get a 4-7/8” OD on any part of it. Perhaps you meant something else?
 
oops my mistake, sorry about it. It should have been 3/8" as per attached.

Off Center1.JPG
 
I'm assuming you want the center portion that is 0.5" wide to be on a different center than the ends. Couple of ways to do it come to mind.

1) Put the work in your 4-jaw and use an indicator to dial in jaws 1 & 3 so they offset each other by the difference in centers. Your 4 7/8" dimension is off, I'll say it's 3/8" for the example. Zero out on jaws 2 & 4, but adjust 1/3 so they read off from each other by 0.125". Center drill the end and turn down the middle section.

2) You could put the 1/2" round in a V-block and use a surface gauge or better yet a height gauge to scribe a line on both ends in the middle of the round. Then turn the round 90 deg. in the V-block and scribe a cross line at 3/16" above or below the top or bottom edge of the part on both ends. Then center punch both ends. Use your 4-jaw and a wiggler with a braille point in the tail stock. Put an indicator on the edge of the wiggler and adjust the 4-jaw so the needle doesn't move as the chuck is rotated. Remove the wiggler and center drill. Repeat on the opposite side and mount the part on the lathe between centers and use a dog to drive it.

Guess an alternative to 2) would be to mark just one end with the offset center/ center punched hole. Use the wiggler in that hole and zero out the 4-jaw with the indicator on the wiggler. Your part is only 1.5" long, so not too much sticking out of the chuck.

Hope this makes sense.

Bruce
 
Is this what you have in mind? A half inch pin with a notch having a 2.4375 radius base. Edit didn't see the correction posted above during page refresh.
Off Center2.JPG
 
Use the 4 jaw independent.

First set it dead true with a dial indicator in tool post.

Next rotate Chuck so one jaw straight up.

Loosen back jaw then front (on horizontal plane) the same amount to move the stock over the desired amount.

Rotate Chuck to verify proper offset.

Now carefully tighten the two jaws that you used for offset and verify still correct.

Now very carefully tighten the other 2 making sure both are fully touching before making tight.

Slide dial indicator length of work to make sure it is straight.

Now center drill end so tail stock can support work.

Good luck.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 
Easy way to make this would be to drill and ream a .501 hole .0625 off center in a 1" round piece and tap a thread for a set screw in it . Put that in your 3 jaw , insert and lock your part down , and turn it . If you had lots of parts to do , this would save you indicator time . :)
 
Off set the part from the lathe center line, you are on the right track so far.
Like so
5" OD bar offset by 1 1/2" from the bearing journals on each end to make a cam for a steel manufacturing furnace, it is 91" long.
2 lathe centers were drilled in each end 3/4" apart, the square saddles are used to drill the centers in the ends in the same relationship on a milling machine using a right angle spindle attachment. This part took well over 30 hours to complete, it also has keyways and holes aligned to the cam. As long as you do not remove the bolt on saddles you always have a flat reference surface (one has to be removed to finish the other end) There is a good deal of set up work involved here. You can do virtually anything that you require if you are willing to spend the time setting it up, if it is profitable all the better. I have made 3 of these parts in three years, it never seems to get faster (-:
1045 HR steel gives an excellent finish if turned fast enough. I would not go much faster with such an unbalanced part even in a 24" X 110" machine.
 
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