# Making a lathe test bar



## tjb (Nov 18, 2019)

If I turn a long piece of stock (aluminum or mild steel) using the three-jaw chuck and the tail stock, I get a slight but consistent taper, so I'm pretty confident my lathe needs to be aligned.  I have a 36" by 1 1/4" piece of tool steel that I want to use to make a test bar, but before butchering anything, I have a few questions:

1.  I'm assuming I should align between the three-jaw chuck and the tail stock.  Right/wrong?  (The chuck is a Bison that I bought new.  It's in very good condition.)
2.  My lathe is an OTMT 13 x 40 (looks almost identical to the PM1236 but larger capacity).  How long should I make the test bar?
3.  What's the best way to cut it?
     a.  Lathe?  I have an Aloris BXA tool post with a Kennemetal 'EVSCTR120326C' cutoff toolholder that can easily handle the diameter but I am uncertain about the hardness.
     b.  Band saw?  I have a horizontal band saw.  Same issue regarding hardness.
     c.  A better way?
3.  Is it necessary to cut it at all?  36" is pretty long.  Should I be nervous about trying to face and center drill with that much length hanging out the back - even if supported?  It'd be nice to keep it intact, but I don't mind cutting it if necessary.
4.  Any other tips I should know before wrecking a nice piece of tool steel?

Thanks for any advice.

Regards,
Terry


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## graham-xrf (Nov 18, 2019)

Hi tjb

First let me say that I have not done this yet for myself, because I am still in the middle of restoring my South Bend, but I know it is something I will ultimately have to do, so I have been researching.  I believe that using a test bar has to be done between centres (I think).

Certainly a test bar I bought for headstock alignment came with a MT3 taper to fit up the spindle without chuck, and a MT2 on the other end to fit up the tailstock. This, of course, is a different kind of measurement, done with a dial gauge onto the bar, instead of micrometer measurements of the diameter at each end of the test bar.

I have seen a test bar belonging to a friend who is into model engines. He made his from a piece of  40mm (about 1.57 inch) aluminum pipe which had "end bungs" welded into them, and faced off. He tried a few "centres" by hand using only a punch mark until he got least run-out, then committed to  proper centres. He said the tedious bit was to cut a relief out of the middle of the pipe length, to leave the slightly raised dumbell end bits for the proper measure cut. It looked about 400mm (about 15 or 16 inches) long.

If you do want to use the chuck, maybe true it up first. Check out YouTube for what to do to grind the chuck jaws. One guy used a Dremmel clamped down onto the compound. Tubalcain also has a video.


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## tjb (Nov 18, 2019)

graham-xrf said:


> Hi tjb
> 
> First let me say that I have not done this yet for myself, because I am still in the middle of restoring my South Bend, but I know it is something I will ultimately have to do, so I have been researching.  I believe that using a test bar has to be done between centres (I think).
> 
> ...


Thanks, Graham.

Sounds like I will certainly need to cut this piece of tool steel.  Thanks for the information, I'll definitely want to study it before proceeding.

Regards,
Terry


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## benmychree (Nov 18, 2019)

I would just find a piece of soft steel, perhaps about 1- 1/4" diameter and 9" long, turn one end down to a bit over 1" diameter and 2- 1/2 long to chuck onto, then relieve the remaining length down to about the same diameter, leaving a collar about 3/8" wide at each end; chuck it up and take very light cuts on each collar, and adjust leveling until the cut the same size.
Trying to make a fancy test bar run true enough to be useful for alignment purposes is an exercise in futility.


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## graham-xrf (Nov 18, 2019)

benmychree said:


> I would just find a piece of soft steel, perhaps about 1- 1/4" diameter and 9" long, turn one end down to a bit over 1" diameter and 2- 1/2 long to chuck onto, then relieve the remaining length down to about the same diameter, leaving a collar about 3/8" wide at each end; chuck it up and take very light cuts on each collar, and adjust leveling until the cut the same size.
> Trying to make a fancy test bar run true enough to be useful for alignment purposes is an exercise in futility.


John is right, and you can even do it in aluminum. Tweaking the tailstock to get it to run true to the point you get a near-the-same measurement on each end of the bar removes the "turning tapers" symptom. The guys who take this to an art form will tell you that there needs to be a slight offset to account for tool pressure, and that some lathes were made that way so that over their working life the "taper" would wear off, and then swing the "other" way. I don't know how true this notion is, but is was certainly believed by enough folk.

The levelling of the lathe is one cause, by introducing twist between the ways, and this does account for some of the cause of getting unequal diameters on the test bar, after the light cut. One tip I have seen is that one should not trust the setting that advances the tool. You take the light cut on one end, then move keep moving carriage to the other end, and continue the cut. Get the levelling right first, to remove twist stresses. This game can somewhat compensate for wear anyway. You do not have to knock yourself out getting absolute about it when a homebrew test bar can let you set up and get going, working around the effects of wear and age.


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## tjb (Nov 18, 2019)

benmychree said:


> I would just find a piece of soft steel, perhaps about 1- 1/4" diameter and 9" long, turn one end down to a bit over 1" diameter and 2- 1/2 long to chuck onto, then relieve the remaining length down to about the same diameter, leaving a collar about 3/8" wide at each end; chuck it up and take very light cuts on each collar, and adjust leveling until the cut the same size.
> Trying to make a fancy test bar run true enough to be useful for alignment purposes is an exercise in futility.


Questions:
1.  The way I'm reading your approach is about 2-1/2" is turned to @1" and chucked, so the other 6-1/2" sticks out.  Should it be faced and center drilled for tail stock?

2.  On the 6-1/2" length, leave a collar @ 3/8" wide on the 'chuck' end, another @3/8" wide on the 'tail stock' end, and turn the center down to something approximating the 2-1/2" section in the chuck.  Right/wrong?

3.  Adjust 'leveling' or 'alignment'?  My understanding is that they are two different things.  I suppose it could be a leveling issue, but I've been assuming it's an alignment issue.  Is there a way to identify which it is before proceeding?

Thanks for responding.

Regards,
Terry


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## Cadillac (Nov 18, 2019)

I wouldn’t waste your length on a test bar. 16” bar would be fine 1 1/4” something cheap. Chuck close to chuck and cut centers in both ends. Make or get yourself some aluminum donuts 1.250 I.d. Maybe 2” o.d. About .750 wide. You could set screw or press these onto your bar about 2-3” from the ends. This will be the test bar, chuck one end and use a good center in the tailstock. Take a light cut on both donuts with a sharp tool without moving the cross slide. measure and adjust tailstock half the amount.


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## Cadillac (Nov 18, 2019)

Even though leveled one would still have to perform this test to align the tailstock to the chuck. Perfect level technically means nothing in this case cutting cylindrical parts is the goal


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## tjb (Nov 18, 2019)

Cadillac said:


> I wouldn’t waste your length on a test bar. 16” bar would be fine 1 1/4” something cheap. Chuck close to chuck and cut centers in both ends. Make or get yourself some aluminum donuts 1.250 I.d. Maybe 2” o.d. About .750 wide. You could set screw or press these onto your bar about 2-3” from the ends. This will be the test bar, chuck one end and use a good center in the tailstock. Take a light cut on both donuts with a sharp tool without moving the cross slide. measure and adjust tailstock half the amount.


Okay, got it.  That makes sense.  Thanks for responding with this and your second post.

Regards,
Terry


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## graham-xrf (Nov 18, 2019)

There are two ways to use test bars. One type of test bar is a precision ground bar, with ready-made centers, and perhaps also, precision ground Morse taper ends. You only ever measure up to it, relatve to parts of your lathe, and you take care of it. The other is a test bar you repeatedly cut on the lathe itself, and you use a micrometer on it.

The alignments they make possible are different. the reference test bar is used for very fundamental stuff, like aligning the headstock to the ways. Other kind of test bar, the kind you make and repeatedly use for test cuts is the other sort, used for tailstock alignment, aligning centers, and the like. It reveals the "taper turning" tendency.

You have a cylindrical bit at each end, wide enough to comfortably use a micrometer on, and a void bit between that is cut deeper, so that you can move the tool between the end cylinder parts that you will measure. If the tail end ends up a smaller diameter, then it may be the tailstock is misaligned closer to the tool side than it should be. It can also mean that the headstock is pointing slightly towards the tool side.

If  you start by putting a center in the chuck, and also the tailstock, and push them together. Hold a steel rule or metal strip between the points, and gently press the points together. The metal will madly tip if there is the slightest mis-alignment, and the direction will be obvious. If things need a shim, this is where you see it.

Even though you get the centers together at the chuck end, it does not mean they will still be so when the tailstock is moved back. If the ways are not parallel to the headstock spindle, it may not matter how much you adjust the tailstock. It will drive you mad!

Assuming such fundamental stuff is not what ails it, and all it needs is the taper effect taken out, you can go ahead and align the tailstock.

There is a variation to this. One measure is to mount up an indicator to measure up to the cylinders. The other measure is to use a micrometer on the diameter of the trial cut cylinders. This trick takes time, but is superbly accurate.

Tubalcain, in detail, explains how, and he shows both measures being done.





There are LOTS of videos on this kind of alignment, as well as using a precision bar, which is agreed to be the faster method, though it does involve the purchase of a test bar you do _not_ cut on. I found a 16mm solid carbide rod about 300mm (about a foot) long for £13 (about $17)  that would be good for this - if I could figure out how to get some centers drilled into it!

"Rollies Dad's Method". I don't know who Rollie's Dad was, but after you read it, you can quickly start inventing your own test variations. I think, on this forum, there has to quite extensive discussions already, maybe in older threads.


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## Joeman77 (Nov 18, 2019)

Well there seems to be many trains of thought along this line. I can only tell you what worked for me.

 Number ONE! Get it level. With a good level, your 6" torpedo won't do it this time, spend a few bucks or borrow one. No Twist, no Cant. Full length check along and across the ways, as many directions as you can figure a way to check it. And make notes, gives you something to look at to see if you're making a difference, I tend to forget, notes and sketches are easy. Take your time, let it settle for a few days between leveling sessions, mine took 2 months to get & keep level. Cast iron doesn't move easy or fast.
 I wouldn't cut that piece of rod. Just face it off & center drill both ends, that way you can check alignment at several points along the travel of the tail stock. After you face & center drill it mark it lengthways with something to align with a chuck jaw with something semi-permanent, that way it'll be semi-repeatable and you can move it (longer or shorter). You don't need to make any cuts on the rod, a couple of dial indicators (tenths if you've got them), one for a top reading, one for the front, set up on the Tool-post with a couple of Mag-bases. Just keep running the carriage back & forth and making adjustments on the Tailstock until it's Dead-Nuts. And remember vertical alignment will cut a taper as well as side to side.
I know it sounds like a pain but, I've got my tailstock to less than a tenth front to back all along it's 36" of travel, I'm still off a touch in height, I'll get that straight as soon as I can get the tailstock split & shimmed.
 Before you start, be warned, this Rabbit hole goes deep, there's no sense stirring a pot of worms if you're happy with things as they are! Why spend months chasing 0.002" of taper along 3' of travel when most of your work is only 10 to 12" long?


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## Dan_S (Nov 18, 2019)

Several things can cause taper.


The bed can be warn, and thus will lead to differing amounts of taper depending on the position of the tailstock and carriage.
The bed could have twist, bow, etc and that will lead to a taper.
With unsupported work you can get tapper if the head stock isn't horizontally and vertically aligned to the bed. If the lathe is rigid enough, this can even cause issues with supported work, as the lathe will just make the work piece flex.
You can get taper if the tailstock is offset.
You can get taper if the tailstock ram isn't horizontally and vertically aligned to the bed.
You can get taper if the tailstock ram doesn't lock down consistently and securely.
Depending on how your tailstock is built, you can get taper when locking the tailstock down because the two parts of the tailstock shift in relation to each other.
tool pressure can of course all cause taper.

#'s 5,6,7 are what will usually get you on smaller or cheaper lathes. #1 & #2 can get you on heavily used lathes, or larger lathes that haven't been properly "leveled".


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## tjb (Nov 18, 2019)

Joeman77 said:


> Well there seems to be many trains of thought along this line. I can only tell you what worked for me.
> 
> Number ONE! Get it level. With a good level, your 6" torpedo won't do it this time, spend a few bucks or borrow one. No Twist, no Cant. Full length check along and across the ways, as many directions as you can figure a way to check it. And make notes, gives you something to look at to see if you're making a difference, I tend to forget, notes and sketches are easy. Take your time, let it settle for a few days between leveling sessions, mine took 2 months to get & keep level. Cast iron doesn't move easy or fast.
> I wouldn't cut that piece of rod. Just face it off & center drill both ends, that way you can check alignment at several points along the travel of the tail stock. After you face & center drill it mark it lengthways with something to align with a chuck jaw with something semi-permanent, that way it'll be semi-repeatable and you can move it (longer or shorter). You don't need to make any cuts on the rod, a couple of dial indicators (tenths if you've got them), one for a top reading, one for the front, set up on the Tool-post with a couple of Mag-bases. Just keep running the carriage back & forth and making adjustments on the Tailstock until it's Dead-Nuts. And remember vertical alignment will cut a taper as well as side to side.
> ...


Thanks, Graham.

I'm getting quite an education.


Dan_S said:


> Several things can cause taper.
> 
> 
> The bed can be warn, and thus will lead to differing amounts of taper depending on the position of the tailstock and carriage.
> ...


Thanks, Dan.

Keep it coming, guys!  I'm learning a lot!

Regards,
Terry


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## Joeman77 (Nov 18, 2019)

Dan_S said:


> Several things can cause taper.
> 
> 
> The bed can be warn, and thus will lead to differing amounts of taper depending on the position of the tailstock and carriage.
> ...



And remember.
 Everything moves, Benches, Cast iron, Concrete, even the very Earth under you feet!


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## graham-xrf (Nov 18, 2019)

Joe is right! Come to that maybe settle for a fifths indicator. If you get down to tenths, and start using levels of 4 arc-seconds sensitivity, (0.0002" in 10 "), you realize that everything is a bit squishy, and you can hardly ever measure the same thing twice and get the same reading. You can see a granite surface plate "deflect", and "level" even down to the concrete floor seems to move a bit.

The taper turning is effect is enough to be obvious. You can make the work turn parallel to the ways by adjusting so that the taper, over the lengths you mostly work, is too small to matter. It may get to be less than you are able cut and show it up in a measurement.


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## Dan_S (Nov 18, 2019)

Joeman77 said:


> And remember.
> Everything moves, Benches, Cast iron, Concrete, even the very Earth under you feet!



Even heat can cause issues if you are hogging of material and the part starts getting hot.


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## graham-xrf (Nov 18, 2019)

Joeman77 said:


> Take your time, let it settle for a few days between leveling sessions, mine took 2 months to get & keep level. Cast iron doesn't move easy or fast.


Joe - that is something I have wondered about. Suppose you have a lathe bed just plonked down on a bench, not necessarily level, or there is a bit of junk under one corner, or something. That iron is eventually going to settle a bit "twisted".

Can you measure any "bends or twists" coming out immediately? If it has "settled" into that state, and you take out the cause? Does it really take a couple of weeks relax out? Can you "force it" in any way?

I read that the guys who scrape on camel-back cast iron (semi-steel?) straight edges hang them up from one end and smack them with a mallet to make them "ring", to relieve internal stresses. Apparently done in a few minutes.

If a lathe bed has been set non-level, or worse, hard bolted down so that it "distorts over time", then making it level on the top will only work for a while, until some of the distortion works out. You have to level again, and again, approaching the desired end with ever lower forces, and doomed never to quite get there. Dang - but I can so dream up some dark stuff!


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## Joeman77 (Nov 18, 2019)

graham-xrf said:


> Joe - that is something I have wondered about. Suppose you have a lathe bed just plonked down on a bench, not necessarily level, or there is a bit of junk under one corner, or something. That iron is eventually going to settle a bit "twisted".
> 
> Can you measure any "bends or twists" coming out immediately? If it has "settled" into that state, and you take out the cause? Does it really take a couple of weeks relax out? Can you "force it" in any way?
> 
> ...


I'm not sure you can force cast iron to do anything fast without lots of heat & pressure, it moves slow and at it's own pace, usually a plus for us! I believe if it started out flat & true you can bring it back, except for wear or extenuating circumstances, it'll just take time.
 Movement is always measurable, just not always the direction we want! And everything moves! 
 I don't know about ringing it back, anything is possible though. In the case of Camel-back straight edges I guess I always thought those things were about one step short of granite when it came to stability.
 And sometimes dark is the stuff dreams are made of. Coal, Iron, Smoke & Fire!!


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## rwm (Nov 18, 2019)

Please look at post #13 here:









						Test bar
					

Hello. I recently-ish ordered a mt2 test bar, along with some other stuff. Unfortunately the test bar went out of stock before my order was packed. The company offers another test bar that is a combination mt2/mt3, and I told them they could send me that one instead. I had considered that one...




					www.hobby-machinist.com
				




Bob Korves gives an excellent approach.

Robert


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## Dan_S (Nov 18, 2019)

Joeman77 said:


> I'm not sure you can force cast iron to do anything fast without lots of heat & pressure, it moves slow and at it's own pace, usually a plus for us! I believe if it started out flat & true you can bring it back, except for wear or extenuating circumstances, it'll just take time.
> Movement is always measurable, just not always the direction we want! And everything moves!
> I don't know about ringing it back, anything is possible though. In the case of Camel-back straight edges I guess I always thought those things were about one step short of granite when it came to stability.
> And sometimes dark is the stuff dreams are made of. Coal, Iron, Smoke & Fire!!



You'd be amazed at what gravity will do with just a little bit of help.


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## graham-xrf (Nov 19, 2019)

Dan_S said:


> You'd be amazed at what gravity will do with just a little bit of help.


Though I was taught about stress vs strain diagrams, yield point, plastic deformation, etc. roughly at a time when when gasoline was $0.40/gallon, it seems the same stuff is still the prevailing wisdom.

Pure cast iron has no plastic deformation, and come to that, not much stretch either. It is brittle, and weak in tension, and just breaks. Lathe beds like mine (South Bend circa 1942) are made of "semi-steel", a loose term which can cover many grades, but apparently heavy duty, durable, and lower cost.

If it is stressed from being "un-level", so OK, it will deform. Take the stress off, and it should return back to where it started.  Provided the yield point was not reached, that should happen right away. If it did yield, but not break, then it will return to a new place, permanently deformed. I did not know there was a "get there slowly" time delay thing involved.


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## graham-xrf (Nov 19, 2019)

rwm said:


> Please look at post #13 here:
> 
> 
> 
> ...


Not only the (very detailed) explanation from Bob Korves, but the whole thread even. It is all excellent!

They make the point point that the lathe must first be aligned to not turn a taper _even without_ the tailstock.
This could be done either with a ready-made test bar, or any old bar (Rollies Dad), or by the two-collar cut.
Otherwise, you have to make allowances if you then use a tailstock. If the bed has a twist, the tailstock alignment would only be good at the tailstock position where the alignment was done. Even then, a perfect 2-collar test bar at that position becomes not-so-good if the tailstock is in any way turned so the quill is not extending parallel to the ways.

It seems to me that step #1 is to check the headstock end with a known test bar, or use any old bar, and get up the Rollies Dad Method. Likely it will be OK, but you at least have to look.

Step #2 is to make sure the tailstock is at least at the right place. The center's points should touch exactly. If the tailstock is already aligned, the centers should stay on the line as the tailstock is moved. You use the two-collar-cut test bar to reveal what is happening. Maybe a good thing would be to put a ground test bar on the tailstock, and use a dial indicator to become sure of what happens that end first, even checking extending the quill. Then finally, a two-collar cut should confirm things. A contrary measurement here would be a disappointment, but also a huge diagnostic!


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## nnam (Nov 19, 2019)

There are lots of good info.
If I may add, is this a question of making a test bar, or how to test the set up with a test bar?

With a good test bar, it can tell if a lathe has issue.  Making one to check a lathe is more about check anything that is wrong as pointed out already, meaning it is hard to know from the cut to know which caused the issue.

I saw Adom on YouTube (abom79), created a bar so he can align the tailstock.  He was making a same diameter with the tail, then trace with an indicator between the two to see any offset.

I wonder why he didn't just put the indicator on the chuck and rotate to indicate around the tail.

Also, 1.25" sags greatly.  So a good tailstock center position needs to support it, or using a lathe rest.

Once that is done, the carriage can be dragged left/right on the rod to check the bed for twist/wear.

A machinist level would be used to check for twist.

Head and tail can also need check for alignment.


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## graham-xrf (Nov 19, 2019)

nnam said:


> There are lots of good info.
> If I may add, is this a question of making a test bar, or how to test the set up with a test bar?


Hi nnam
Definitely it is about both kinds of test bar, and making clear the differences between them.
We throw in Rollie's Dad's Method, which uses any old bar as a circular cam, and uses the averages of the highs and lows as it wobbles it's end. Spectacularly accurate outcome, just by being clever - but time consuming.

With the right amount of thought, and making test cuts on just about anything, one can figure out what to adjust to make it straight. These methods are a more focused set of steps to check, confirm, and diagnose.

At some points, they do overlap. You could argue that with full application of (say) a ground reference test bar, you don't need to ever make and try a two-collar test bar. Conversely, making a test bar and measuring it, is what you do to check you are not turning a taper. This is instead of discovering the taper is on your favorite project!  From what you find, you can infer things about the lathe alignment, and figure out what to adjust. All these methods compliment each other.


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## lagweezle (Dec 23, 2019)

graham-xrf said:


> The guys who take this to an art form will tell you that there needs to be a slight offset to account for tool pressure, and that some lathes were made that way so that over their working life the "taper" would wear off, and then swing the "other" way. I don't know how true this notion is, but is was certainly believed by enough folk.



To be clear, I'm incredibly inexperienced. With that out of the way, I thought the entire point of doing one or more "spring pass" cuts was to mitigate the effect of tool pressure deflecting the work surface. Also, given that the cut, speed, and materials in use change how much deflection there is of the work surface, I don't see how an intentional offset of the tailstock makes sense. I'm inclined to consider this one of the many, many bits of knowledge that are passed around as true but ... really aren't. There is likely some truth to it, but the original truth, etc. has been lost to time and only if we're lucky can we find it again.


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## Dan_S (Dec 23, 2019)

lagweezle said:


> To be clear, I'm incredibly inexperienced. With that out of the way, I thought the entire point of doing one or more "spring pass" cuts was to mitigate the effect of tool pressure deflecting the work surface. Also, given that the cut, speed, and materials in use change how much deflection there is of the work surface, I don't see how an intentional offset of the tailstock makes sense. I'm inclined to consider this one of the many, many bits of knowledge that are passed around as true but ... really aren't. There is likely some truth to it, but the original truth, etc. has been lost to time and only if we're lucky can we find it again.



He isn't talking about the tailstock. back in the day when manual machines were still used in a production environment, the head stock would have an ever so slight angular offset for Chucked work. Time is money, so you don't want to make extra finishing passes when you're making hundreds or thousands of parts.


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