Trueing Spindle Bore

Would it be possible to mount a pilot bushing on the outside end of the headstock to guide the boring bar, then make a boring bar with the cutting tool in the center of the boring bar, similar to what they used to use to bore steam engine cylinders. Then you would have to loosen the cutting tool and move it by hand a small amount to take each small cut. since you are just truing the bore and not going for an exact diameter that should work. Possibly use a bronze bushing in the pilot bushing and grease it well.
 
I would glue an 1/8 or even less tube inside and then machine that to be concentric.
 
Machinist18, I like someone who listens.
I believe some others have tried an approach like you mentioned, maybe it is called line boring.
That approach is my Plan B.
 
john.oliver35 said:
Oh my Ken - go to a race for the crashed, but leave the poor lathe alone!
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Always willing to give advice, good or bad-----Borrow a true shaft,anything will do.
Check female taper for dirt, bumps,scratches, etc.get a tenths indicator, install the the test taper, check it out. If it's OK, forget the through - bore ; nothing should be attached to, or measured from it........BLJHB.
 
OH! MY
If the bore is trued the spindle will warp...... Will Warp!
The question is, How Much?
It could be ruined by a very small amount of warp and isn't worth the risk, in my humble opinion.
A few tenths of warp and perhaps less would throw the 60 deg taper out and could cause serious vibration problems.
If you can afford to purchase a new spindle and just can't stand it, then get all the machining steps and equipment lined up and have fun.
 
How will you describe this improvement when you sell the machine?
 
Since the spindle bore is off center, I would guess that your spindle was machined from a casting, and not very well centered during rough turning. I would check both ends of the tapered section for runout, and if ok leave the rest of the bore alone. As others have pointed out, machining to achieve bore concentricity may result in a ruined spindle. I would be more concerned with the spindle's balance due to more weight on the thicker side. Do you have a vibration at higher spindle speeds? If you do, balancing the spindle may be the more prudent endeavor.
 
Dave 41 said:
Since the spindle bore is off center, I would guess that your spindle was machined from a casting, and not very well centered during rough turning.
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Or drilled from both ends and the holes didn't meet perfectly.
 
Why is the spindle bore off axis to start with?

It looks to me like the D1-4 head and the spindle blank were manufactured separately and then welded together. If that is the case the final OD of the spindle logically would be turned after welding so the critical alignment of bearings to spindle head would be assured. Any misalignment of the spindle with the D1-4 head resulting from the welding operation would therefore be corrected where it counts. Why would the manufacturer of a hobby lathe bother to true up the inside of the spindle where alignment doesn’t count?

So if I true up the spindle how much will it warp?
My other therapy group agrees with you folks that any amount would be too much. :)

Where do I go from here?

If my objective was to enlarge an already concentric bore in order to handle larger work then the risk of warp would probably be less and might even be worth taking. However my objective to remove metal from only one side of the spindle just for the exercise is a different kettle of fish (or wormsJ). Speaking of opening a can of worms, maybe I should go fishing instead of wrecking my lathe.
 
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Now you're starting to make sense, Mike.
 
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