# Trueing Spindle Bore



## Tozguy (Sep 7, 2015)

Ever since I discovered that the spindle bore on my lathe is eccentric I can't sleep.
I want to turn it true but was wondering if it might change the stress in the spindle and warp it (or produce some other unwanted result).
Leaving it alone is not an option unless the guys in white coats get me first.


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## Tony Wells (Sep 7, 2015)

Likely as hard as a landlord's heart.....so you probably need a grinder. If is a small machine, that would be most difficult. Best learn to live with it, I think.


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## Tozguy (Sep 7, 2015)

Tony, haven't had a landlord in a long time. The current boss around here has a kind heart so maybe there's a chance.
Seriously, I managed to drill and tap the outboard end of the spindle with no issues. If worse comes to worse it will cost me a $2 brazed carbide tool to find out the hard way.
My main concern is about how the spindle will like having some metal removed from one side only.


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## Tony Wells (Sep 7, 2015)

I would suspect that like most heat treated hollow rounds, it will move some. Whether enough to cause problems is a guess. But if it's that small, boring the full length of it may be problematic.


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## Tozguy (Sep 7, 2015)

The bore is 1.490'' in diameter. From the spindle nose to the other end it measures 14.5'' long. I am making a boring set up with a 1.25'' dia. bar that is 36'' long. You are right, it remains to be seen if I can get things ridgid enough to bore all the way through.


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## dfletch (Sep 7, 2015)

Wait a minute! Most spindle bores I'm familiar with have a taper for the first few inches for holding centers, collet holders, etc. Why bore it all the way through?


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## Dan_S (Sep 7, 2015)

I don't want this to come off the wrong way, but why do you think it needs to be perfectly concentric? also how much is it off by?


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## Tozguy (Sep 7, 2015)

Fletch, you are right, there is a MT5 taper for the first 5 inches in from the spindle nose. The spindle bore starts to be restricted at the 5.5'' mark. The MT5 taper is concentric to the spindle axis  so it won't get cut.
After that the bore is 1.490'' but not concentric with the spindle axis, by how much is a good question, maybe in the neighbourhood of .025''.
Dan, you are right too, for a normal person this is a perfect case of  'if it ain't broke don't fix'.
But I have a few ideas about how to go about boring the spindle that I am itching to try. Wish me luck, it might take a boatload of it to pull this off.


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## Brain Coral (Sep 7, 2015)

Hello Toz 

To each his own, but why on earth would it be necessary for the spindle bore to be perfectly concentric? It's job is merely to allow work, of up to a certain size, to pass through the headstock and present itself to the chuck. I am quite certain, that if you go ahead with the boring procedure, you will alter the spindle enough to render the bearing surfaces out of line with the spindle.

You seem determined to go through with it, so.... good luck.... by the boatload.... 

Brian


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## Tozguy (Sep 7, 2015)

Here is a pic of the shoulder beyond the MT5 taper. The taper is covered with a plastic sleeve to protect it when not in use. You can see how far off the bore is to the concentric section.



Brian, you may be right, I will look a bit further into the possible side effects. I am sure others have gone before me so maybe I can turn up some evidence one way or another.


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## JimDawson (Sep 7, 2015)

I'm with the rest of the bunch here, WHY?  BUT......I would make up a line boring bar.  A bushing for each end and the tool bit in the center, Feed with the drill chuck in the tail stock.


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## Tony Wells (Sep 7, 2015)

Frankly, I wouldn't do it. If it interfered with work, maybe.....but not likely.Too much at stake and too many places for things to go wrong. It's your lathe, so you do what you will. But I wouldn't.


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## Andre (Sep 7, 2015)

Unless you have 1.3" material through the headstock your probably not going to have a problem, HOWEVER.....make sure that MT5 taper wasn't machined crooked! If that is the case, contact your manufacturer. If it's behind the taper thats off, you could machine it but be careful.


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## chips&more (Sep 8, 2015)

What kind of a lathe is it? Who made it? If an Import, the steel they use is iffy at best. Probably full of internall stresses.  And you will weaken it a little. I think you will open up a can of worms. Use the lathe as it should be used, have some fun with it. In a few weeks you will have forgotten all about it.  Some collet drawbars do reference the ID of the spindle, but usually only at the last 1” or so at the back. You could clean up that portion of the ID I guess for a draw bar and other accessory items that would reference the spindle ID. Other than that, just don’t look at it, use it and have fun!


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## Dave 41 (Sep 8, 2015)

And I thought I had trouble keeping the worms in the can


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## Cobra (Sep 8, 2015)

I would be with the others.  If the MT5 taper is fine, leave the rest of the bore alone.


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## larryr (Sep 8, 2015)

Tozguy said:


> Fletch, you are right, there is a MT5 taper for the first 5 inches in from the spindle nose. The spindle bore starts to be restricted at the 5.5'' mark. The MT5 taper is concentric to the spindle axis  so it won't get cut.
> After that the bore is 1.490'' but not concentric with the spindle axis, by how much is a good question, maybe in the neighbourhood of .025''.
> Dan, you are right too, for a normal person this is a perfect case of  'if it ain't broke don't fix'.
> But I have a few ideas about how to go about boring the spindle that I am itching to try. Wish me luck, it might take a boatload of it to pull this off.


its not broke now but it sure might be when you get thru. leave it alone!!!


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## ken4570 (Sep 8, 2015)

Do it! I want to seehow this plays out!!


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## john.oliver35 (Sep 8, 2015)

Oh my Ken - go to a race for the crashed, but leave the poor lathe alone!


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## machinist18 (Sep 9, 2015)

Tozguy said:


> Ever since I discovered that the spindle bore on my lathe is eccentric I can't sleep.
> I want to turn it true but was wondering if it might change the stress in the spindle and warp it (or produce some other unwanted result).
> Leaving it alone is not an option unless the guys in white coats get me first.


 


Tozguy said:


> Ever since I discovered that the spindle bore on my lathe is eccentric I can't sleep.
> I want to turn it true but was wondering if it might change the stress in the spindle and warp it (or produce some other unwanted result).
> Leaving it alone is not an option unless the guys in white coats get me first.


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## machinist18 (Sep 9, 2015)

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.


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## Dadels2010 (Sep 9, 2015)

I would glue an 1/8 or even less tube inside and then machine that to be concentric.


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## Tozguy (Sep 9, 2015)

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.


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## The Liberal Arts Garage (Sep 9, 2015)

john.oliver35 said:


> Oh my Ken - go to a race for the crashed, but leave the poor lathe alone!


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.


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## tertiaryjim (Sep 10, 2015)

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.


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## eeler1 (Sep 10, 2015)

How will you describe this improvement when you sell the machine?


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## Dave 41 (Sep 10, 2015)

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.


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## John Hasler (Sep 10, 2015)

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.


Or drilled from both ends and the holes didn't meet perfectly.


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## Tozguy (Sep 10, 2015)

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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## mikey (Sep 10, 2015)

Now you're starting to make sense, Mike.


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## epanzella (Sep 12, 2015)

If you can't sleep now, what do you think will happen if you screw up your spindle doing a job that didn't need to be done. The factory didn't make the bore perfect because they didn't need to. If the 5MT is concentric that's all that matters.


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## higgite (Sep 12, 2015)

Tozguy said:


> Speaking of opening a can of worms, maybe I should go fishing instead of wrecking my lathe.


To butcher Thoreau’s quote a little bit, “Everyone should believe in something…. I believe you should go fishing.”

Tom


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## Tozguy (Sep 12, 2015)

*I’m all dressed up with no place to go.*

That Thoreau fella sounds pretty smart. I believe it is Gene Fowler who is credited with saying “I am glad that I paid so little attention to good advice; had I abided by it I might have been saved from some of my most valuable mistakes.”

It would certainly be a mistake to true the spindle bore on my lathe; one that even Gene would not want to make  . Total run out of the bore at the front is .090” and since spindle i.d. is 1.490” and o.d. is 2.145”, that is a relatively huge amount to take off of one side of the bore. If I persisted in wanting to true the bore it would only prove that I have a bad case of ‘tunnel vision’.

The fish weren’t biting so I went back to the lathe and decided to take just a token cut somewhere that would not hurt anything. It looked like the entrance to the bore could use a bit of chamfer so I started putting the boring set up together. 

Cutting the chamfer at the entrance to the bore allowed me to confirm that the boring approach I used can actually work even if it looks like a pipe dream. It was a boring afternoon but I have never had so much fun.

Here are some pictures in case anyone is interested.


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## Tozguy (Sep 12, 2015)

Here is the chamfer and proof of chips.


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## 4GSR (Sep 19, 2015)

Did you measure any of the OD's of the spindle to make sure you have meat to work with?


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## Tozguy (Sep 19, 2015)

Ken, yes, dimensions are given above. I only chamfered the entrance to the bore that is 5.5" in from the nose (pic above). It was a very light cut just to prove the boring set up. I did not attempt to true the bore as originally planned.
Since the run out of the MT5 taper at the front of the spindle is less than .0001" it would have been ridiculously reckless to do more than I did.


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