# A head scratcher here …



## poorboy (Jul 7, 2022)

I have an interesting issue with my PM-1340GT that I am trying to figure out.

I put a 2”x12" bar in the chuck and performed a collar alignment test  (with no tailstock). Took light cuts (.002") -- I then put a .0001" indicator on the carriage and ran the indicator over both collars  -- I am off by .0003" over 10 inches. Everything looks great - but ...

If I use a micrometer to measure the collar closest to the chuck and then measure the collar farthest from the chuck and the difference is .010". There seems to be a  taper in the bar. How can I have a taper and not have the indicator on the carriage show that there is a taper ?

Any ideas ?


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## Shotgun (Jul 7, 2022)

The bed is twisted.  As the carriage moves down, it move in or out .010" over that ten inches.  The indicator riding on the carriage doesn't see anything move.


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## poorboy (Jul 7, 2022)

I still dont understand. I just removed .002 from the collars using the same carriage - i dont understand how there can be a taper and an indicator not show that


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## woodchucker (Jul 7, 2022)

poorboy said:


> I still dont understand. I just removed .002 from the collars using the same carriage.


you need to put a precision level on the bed ways and get them level (from twist).
if your ways are twisted (not level) you carriage is not going to run straight. if your ways are lifted at the tailstock on your side, then you will cut closer at the tailstock end, if your ways are lifted at the tailstock on the back end, you will cut farther and it will look like the reverse of a taper, more like a trumpet.


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## Shotgun (Jul 7, 2022)

poorboy said:


> I still dont understand. I just removed .002 from the collars using the same carriage.


The same carriage that you mounted the indicator to?  What you proved there is that the tool did not move relative to the carriage as you made the cut.

The micrometer on each end was independent of the carriage.  It showed that the carriage does not maintain a specific distance from the workpiece as it moves down.  The carriage's distance from the workpiece is controlled by the ways.  The ways are twisted.  You generally take that twist out by adjusting leveling feet.  Several videos online demonstrating the phenomena with lathe mockups.


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## poorboy (Jul 7, 2022)

I have leveled my ways using a precision level (6 months ago). Let me take another look at things again. Thanks


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## Shotgun (Jul 7, 2022)

Things can move a lot in 6mos, especially when we consider .010" to be a lot.  Even with a precision level, the true test is still going to be the test you just did.


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## benmychree (Jul 7, 2022)

What order of precision is the level?  .005" is not accurate enough for finish leveling of a machine tool, I.E. a Starrett #98 is not accurate enough.  If you cut the 2 collars to the same diameter as evidenced by a micrometer reading and then used the indicator on the carriage, you should see evidence of the probable twist in the bedways.


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## mksj (Jul 7, 2022)

The bed would be a pretzel if it had that much twist, seems like it would more likely be a headstock alignment.  Just about every 1340GT I have encountered needed hedstock alignment, might be due to its size and light weight. I would check the bed is level, I use Rolle's Dad's Method for headstock alignment and then I do the 2 ring test. The headstock needs very small adjustments of the alignment screws where the motor is located, after you lightly loosen the headstock bolts.








						Rolle's Dad's Method
					

Rolle's Dad's Method (RDM) is a brilliant way to accurately measure the alignment of a spindle to the bed/column, and is extremely useful fo...




					benchtopmachineshop.blogspot.com


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## Shotgun (Jul 7, 2022)

mksj said:


> The bed would be a pretzel if it had that much twist, seems like it would more likely be a headstock alignment.  Just about every 1340GT I have encountered needed hedstock alignment, might be due to its size and light weight. I would check the bed is level, I use Rolle's Dad's Method for headstock alignment and then I do the 2 ring test. The headstock needs very small adjustments of the alignment screws where the motor is located, after you lightly loosen the headstock bolts.
> 
> 
> 
> ...


How do you distinquish headstock alignment from bed twist?  If the bed were twisted such that the carriage moved .010" away from the work, but the head was nodded down such that the work move .010" toward the cutter, could you detect a taper?  How does RDM know the difference?

Not an academic question.  I'm working on setting up a 80yr old lathe, and I think I've come to the conclusion that it doesn't matter as long as it cuts straight.


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## mksj (Jul 7, 2022)

You use bed twist to compensate to some degree for bed wear, on a new machine you should not have bed wear and it should cut straight if the head is aligned properly. Beds do settle, but I would not use bed twist on a new machine to compensate for poor head alignment. The head alignment is fairly straight forward, I use a 1" ground rod, or one can get a test bar. Using Rolle's method it also compensates for the chuck not holding the stock straight.


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## poorboy (Jul 7, 2022)

Just aligned my lathe again and will do some test cuts shortly. The level should be accurate to .0002"/10". I am guessing that Mark is correct and my headstock will need to be adjusted.  I am kind of worried about doing that though.


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## Christianstark (Jul 7, 2022)

Have you swept the indicator on the top or bottom of the work to check for nod? Which side of the taper is narrow?


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## poorboy (Jul 7, 2022)

Okay re leveled the lathe - so the ways should be aligned to within .0005. Inserted a 16" ground test bar into my spindle and ran a .0001 indicator on the side of the bar and also another .0001 indicator on top of the bar.

indicator on the bar's side:   looks like the head is off by around .0007 over 12". 
indicator on the bar's top:  looks like the spindle is nodding - that was off .003


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## Christianstark (Jul 7, 2022)

I assume the narrower side was at the Chuck side? Edit, I guess tool height would have more to do with that. Disregard this post I think



poorboy said:


> Okay re leveled the lathe - so the ways should be aligned to within .0005. Inserted a 16" ground test bar into my spindle and ran a .0001 indicator on the side of the bar and also another .0001 indicator on top of the bar.
> 
> indicator on the bar's side:   looks like the head is off by around .0007 over 12".
> indicator on the bar's top:  looks like the spindle is nodding - that was off .003


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## poorboy (Jul 7, 2022)

I just ran the two collar test - here are the final numbers:

1.60005" collar closest to to the chuck
1.59725" collar closest to the tail stock

It seems that i still have a .0028 taper (which is much better than before). i am taking .003 cuts - so there might be some deflection in the rod as well.

I also ran a .0001 indicator from my tool post - that sees an approximate difference of .0007 between the two collars.


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## mksj (Jul 7, 2022)

Headstock is out of alignment. It is not a big deal to align it, and as I mentioned it is frequently needed with the 1340GT. Please note that it can also be that the chuck is not holding the stock true, thus checking with Rolle's method, all you are looking at is that the swing in the +/- direction is the same.


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## RJSakowski (Jul 7, 2022)

poorboy said:


> I have an interesting issue with my PM-1340GT that I am trying to figure out.
> 
> I put a 2”x12" bar in the chuck and performed a collar alignment test  (with no tailstock). Took light cuts (.002") -- I then put a .0001" indicator on the carriage and ran the indicator over both collars  -- I am off by .0003" over 10 inches. Everything looks great - but ...
> 
> ...


When you cut the collars, the cut is referenced to the carriage.  Replacing the tool with a dial indicator, you are again referencing to the carriage.  The dial indicator should read the same in both positions.  A small difference could be caused by deflection due to tool pressure.  

This doesn't mean the two diameters will be the same.  Head misalignment, bed twist, or wear in the ways will cause a difference in the diameters. 

Note that what you did is essentially the opposite of what the RDM method does.  It measures the difference in indicator reading for two positions on a bar of uniform diameter.

Before attempting to adjust the head, check for alignment on a facing cut. A facing cut is minimally affected by bed twist.  If a facing cut produces neither a domed or dished  surface, more than likely, your head is aligned.  Rather than cutting a face, I use a dial indicator to measure the relative displacement of a boss on my faceplate when in a front vs. rear position.  Details are here. https://www.hobby-machinist.com/threads/on-the-level-further-adventures-with-the-g0602.72338/


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## poorboy (Jul 8, 2022)

RJSakowski said:


> When you cut the collars, the cut is referenced to the carriage.  Replacing the tool with a dial indicator, you are again referencing to the carriage.  The dial indicator should read the same in both positions.  A small difference could be caused by deflection due to tool pressure.
> 
> This doesn't mean the two diameters will be the same.  Head misalignment, bed twist, or wear in the ways will cause a difference in the diameters.
> 
> ...


Thank you - i will go ahead and perform a facing cut and see how that looks.


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## projectnut (Jul 8, 2022)

Keep in mind that the bar you're cutting the collars on shouldn't extend more than 4 times it's diameter without support from the tailstock.  Any longer extension will result in some deflection of the bar.  It could be due to the strength of the material or the quality (or preload) of the bearings used in the headstock.


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## davidpbest (Jul 8, 2022)

I invested in one of these -  makes aligning the headstock very easy.  Once the headstock is aligned you can adjust out any twist in the lathe bed.  









						Lathe Alignment Test Bar Shank Size 1MT, 2MT, 3MT, 4MT, 5MT, 6MT Hawk  | eBay
					

2MT 283mm (11-1/8”) 0.0002”. 3MT 335mm (13-3/16”) 0.0002”. 4MT 386mm (15-1/4”) 0.0002”. 6MT 507mm (19-7/8") 0.0002". 1MT 151mm (5-15/16”) 0.0002”. 5MT 400mm (15-3/4") 0.0002”. Hawk Werkzeuge comprises of a dedicated and skilled team of engineers with an aim of providing you tools of highest...



					www.ebay.com


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## pacifica (Jul 8, 2022)

poorboy said:


> I just ran the two collar test - here are the final numbers:
> 
> 1.60005" collar closest to to the chuck
> 1.59725" collar closest to the tail stock
> ...


When I first received my 1340 gt 3 years ago it cut a taper. Headstock was out of alignment from factory. Took less than 2 hours to re-align and have had no taper since. I considered it a plus that the lathe had the ability to adjust the alignment.


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## Shotgun (Jul 8, 2022)

davidpbest said:


> I invested in one of these -  makes aligning the headstock very easy.  Once the headstock is aligned you can adjust out any twist in the lathe bed.


I feel as confused as the original poster.
Doesn't a headstock misalignment and a twisted bed produce the same error?  A tapered cut?
How do you distinguish one from the other?

I like the post from RJSakowski.  It seemed to cut through the ambiguity.  Use a level to fix any bed twist, then what is left must be headstock misalignment.  But, without the use of a level first, is it possible to know which condition is causing the taper?  Could you "fix" a head misalignment by twisting the bed?


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## RJSakowski (Jul 8, 2022)

Shotgun said:


> I feel as confused as the original poster.
> Doesn't a headstock misalignment and a twisted bed produce the same error?  A tapered cut?
> How do you distinguish one from the other?
> 
> I like the post from RJSakowski.  It seemed to cut through the ambiguity.  Use a level to fix any bed twist, then what is left must be headstock misalignment.  But, without the use of a level first, is it possible to know which condition is causing the taper?  Could you "fix" a head misalignment by twisting the bed?


When I first got my lathe (G0602), I corrected the taper by aligning the headstock.  There was bed twist which was most likely due to bolting the lathe to a non flat surface.  I didn't have a precision level then. This was a big mistake because I was no longer turning a taper, facing cuts were now cutting a dish.  

The headstock alignment and bed twist work together in cutting a taper.  Two wrongs can make a right.  By contrast, facing cuts  are only slightly affected by bed twist.  

IMO, the correct sequence of alignment is to 1. Level the lathe; 2. Check headstock alignment by means of a facing cut close to the headstock and correct , if necessary.  A skim cut on the faceplate will do nicely or indicate on a boss in forward and rear  positions;  3. Check bed alignment by either two collar test or RDM method and adjust bed twist to correct. 4. Check tailstock alignment by modified two collar test or modified RDM method and adjust tailstock to correct.


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## poorboy (Jul 8, 2022)

pacifica said:


> When I first received my 1340 gt 3 years ago it cut a taper. Headstock was out of alignment from factory. Took less than 2 hours to re-align and have had no taper since. I considered it a plus that the lathe had the ability to adjust the alignment.



I haven't tried adjusting the headstock yet - for the headstock attachment screws (8mm) all you had to do was loosen them (both the top and bottom) correct ? Did you use a test rod to check for mis-alignment ?


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## Firstram (Jul 9, 2022)

poorboy said:


> I still dont understand. I just removed .002 from the collars using the same carriage - i dont understand how there can be a taper and an indicator not show that


Run the indicator on the backside of the collars if you want to see the difference.


projectnut said:


> Keep in mind that the bar you're cutting the collars on shouldn't extend more than 4 times it's diameter without support from the tailstock.  Any longer extension will result in some deflection of the bar.  It could be due to the strength of the material or the quality (or preload) of the bearings used in the headstock.


I use a foot of 3" aluminum tubing and a sharp HSS tool for the 2 collar test. Not 100% sure but it seems a large, lightweight, hollow tube would be a lot more rigid than a solid bar.


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## Parlo (Jul 9, 2022)

I would not bother checking any nod on the headstock. There will be no wear between the two mating faces so should be left as it was new.
However if the results infer that there is nod and the taper is assumed to be generated by the tool cutting over / under center remember this theoretical example.
A 2" diameter bar is turned 12" long on a lathe where the headstock sits on an angle of 0.010" over 12" the included taper will be 0.0001" included due to the 0.010" centre height difference in the tool over 12".
So basically, if your headstock is badly vertically out of true it will still only cut very tiny taper. Look elsewhere for errors that will make a much greater difference and don't start shimming the headstock.


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## pacifica (Jul 9, 2022)

Parlo said:


> I would not bother checking any nod on the headstock. There will be no wear between the two mating faces so should be left as it was new.
> However if the results infer that there is nod and the taper is assumed to be generated by the tool cutting over / under center remember this theoretical example.
> A 2" diameter bar is turned 12" long on a lathe where the headstock sits on an angle of 0.010" over 12" the included taper will be 0.0001" included due to the 0.010" centre height difference in the tool over 12".
> So basically, if your headstock is badly vertically out of true it will still only cut very tiny taper. Look elsewhere for errors that will make a much greater difference and don't start shimming the headstock.


I wasn't talking about "headstock nod" or doing any shimming. In the manual the 1340gt shows how to align the headstock and this is a sideways(horizontal) operation.


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## Firebrick43 (Jul 9, 2022)

Shotgun said:


> I feel as confused as the original poster.
> Doesn't a headstock misalignment and a twisted bed produce the same error?  A tapered cut?
> How do you distinguish one from the other?
> 
> I like the post from RJSakowski.  It seemed to cut through the ambiguity.  Use a level to fix any bed twist, then what is left must be headstock misalignment.  But, without the use of a level first, is it possible to know which condition is causing the taper?  Could you "fix" a head misalignment by twisting the bed?


Possibly, but not always.  

Head stock alignment is a function of exactly where its pointing.   You really need a ground rod, or better yet an alignment bar that David listed above.  

You check for twist first, setting a precision level front to back across the ways.  Once twist is out you sweep the test bar in the headstock to check its alignment.  Then you turn two a bar with two collars between centers to check/adjust tailstock alignment to the headstock.  A two collar test will show error in with all three issues and you cant tell what is causing it without certainty.


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## parshal (Jul 9, 2022)

Perfect timing for this thread.  It's been quite a while since I checked level.  I'd been planning to do it for a while and, boy, was it out of level.  I got it level with the machinist level front to back and checked the headstock using the bar that David listed.  It's been quite some time since I aligned the headstock.  I had it perfect with the bar over the entire rod with an Interapid.  I got it all tightened and verified alignment again.  I faced a 3" aluminum cutoff and had a difference of .001" from center to edge.  I did not expect that.


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## Christianstark (Jul 9, 2022)

parshal said:


> Perfect timing for this thread.  It's been quite a while since I checked level.  I'd been planning to do it for a while and, boy, was it out of level.  I got it level with the machinist level front to back and checked the headstock using the bar that David listed.  It's been quite some time since I aligned the headstock.  I had it perfect with the bar over the entire rod with an Interapid.  I got it all tightened and verified alignment again.  I faced a 3" aluminum cutoff and had a difference of .001" from center to edge.  I did not expect that.



Did you continue to the other edge to see if you got back the .001 and are in fact machining a dish?


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## parshal (Jul 9, 2022)

You mean put it in reverse and cut the other side*?*


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## Christianstark (Jul 9, 2022)

parshal said:


> You mean put it in reverse and cut the other side*?*



No, just indicate it from front to center to back. If front to center changes .001, it should change back to match the front measurement. The only reason I might suggest this is I have seen some recent postings on the castings on some mills not being dead square. Granted the thread I am recalling was for a milling machine, and I’m sur I am wrong, but if you indicated front to middle to back, and the indicator does not return to the same indicated value, then the cross slide/ casting may have an issue.


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## RJSakowski (Jul 10, 2022)

Christianstark said:


> No, just indicate it from front to center to back. If front to center changes .001, it should change back to match the front measurement. The only reason I might suggest this is I have seen some recent postings on the castings on some mills not being dead square. Granted the thread I am recalling was for a milling machine, and I’m sur I am wrong, but if you indicated front to middle to back, and the indicator does not return to the same indicated value, then the cross slide/ casting may have an issue.


The headstock out of alignment will also cause that problem.  I mount a boss on my faceplate and rotate the faceplate so the boss in near the front of the lathe.  I retract the cross slide and zero a dial indicator on the boss.  Then I rotate the faceplate so the boss is at the rear of the lathe and advance the cross slide until the indicator is in contact with the boss.  If the indicator reads zero, the headstock is aligned to the cross slide.  If the reading is less, the headstock is rotated counterclockwise to the cross slide when viewed from above.  If the reading increases, the headstock is rotated clockwise to the cross slide.  If the cross slide is perpendicular to the ways, the former case will result in turning a taper which is larger on the tailstock end while the latter case will result in a turning a taper which is smaller at the tailstock end.

On my lathe, I have no means of correcting a dished or domed facing cut aside from rotating the headstock.  With that alignment made, I can turn my attention to correcting any taper due to bed twist.


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## Christianstark (Jul 10, 2022)

RJSakowski said:


> The headstock out of alignment will also cause that problem.  I mount a boss on my faceplate and rotate the faceplate so the boss in near the front of the lathe.  I retract the cross slide and zero a dial indicator on the boss.  Then I rotate the faceplate so the boss is at the rear of the lathe and advance the cross slide until the indicator is in contact with the boss.  If the indicator reads zero, the headstock is aligned to the cross slide.  If the reading is less, the headstock is rotated counterclockwise to the cross slide when viewed from above.  If the reading increases, the headstock is rotated clockwise to the cross slide.  If the cross slide is perpendicular to the ways, the former case will result in turning a taper which is larger on the tailstock end while the latter case will result in a turning a taper which is smaller at the tailstock end.
> 
> On my lathe, I have no means of correcting a dished or domed facing cut aside from rotating the headstock.  With that alignment made, I can turn my attention to correcting any taper due to bed twist.



Agreed. But a cross slide out of square would double the error from front to back. A dished or domed face would read the same measurement recorded at the front, and the back.


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## Parlo (Jul 10, 2022)

RJSakowski said:


> The headstock out of alignment will also cause that problem.  I mount a boss on my faceplate and rotate the faceplate so the boss in near the front of the lathe.  I retract the cross slide and zero a dial indicator on the boss.  Then I rotate the faceplate so the boss is at the rear of the lathe and advance the cross slide until the indicator is in contact with the boss.  If the indicator reads zero, the headstock is aligned to the cross slide.  If the reading is less, the headstock is rotated counterclockwise to the cross slide when viewed from above.  If the reading increases, the headstock is rotated clockwise to the cross slide.  If the cross slide is perpendicular to the ways, the former case will result in turning a taper which is larger on the tailstock end while the latter case will result in a turning a taper which is smaller at the tailstock end.
> 
> On my lathe, I have no means of correcting a dished or domed facing cut aside from rotating the headstock.  With that alignment made, I can turn my attention to correcting any taper due to bed twist.


Are you setting the indicator on the face of the boss? Would setting the indicator directly on the faceplate give the same result?
I guess it's a choice between aligning the headstock parallel to the spindle axis or square to the cross slide.


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## ddickey (Jul 10, 2022)

Shotgun said:


> I feel as confused as the original poster.
> Doesn't a headstock misalignment and a twisted bed produce the same error?  A tapered cut?
> How do you distinguish one from the other?


For a new lathe, place a precision level on the cross slide and adjust the stand feet or lathe feet so that there is no movement of the bubble.
Then you take a test cut 5"-6" and measure both ends of the bar. Type and size of material for the bar, tool to use, spring passes & DOC's are very important.
After you get zero taper you're done.


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## ddickey (Jul 10, 2022)

davidpbest said:


> I invested in one of these -  makes aligning the headstock very easy.  Once the headstock is aligned you can adjust out any twist in the lathe bed.
> 
> 
> 
> ...


I've bought two of these both out of spec. In fact the last one I bought had .003" TIR. However, I was refunded the total amount I paid without needing to send back to India (2nd one).


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## RJSakowski (Jul 10, 2022)

Parlo said:


> Are you setting the indicator on the face of the boss? Would setting the indicator directly on the faceplate give the same result?
> I guess it's a choice between aligning the headstock parallel to the spindle axis or square to the cross slide.


You can run on the face of the faceplate.  I chose to add a boss because my faceplate has radial slots and concentric grooves and the indicator would drop into the slot and/or groove as I was changing positions.  The boss is domed slightly so there is no abrupt jump when making contact again.  I made it from a hex bolt and it is easily removed when I need to use the faceplate.  A Sharpie cross on the face of the boss ensures that I measure on exactly the same point front and back.

I chose to align the headstock square to the headstock because I had no other easy way to make  that alignment.  Once the headstock was aligned, I could then correct any taper turning issues by controlling bed twist.


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## parshal (Jul 10, 2022)

I took the chuck off and ensured there was no swarf and lightly stoned it and the lathe's boss, reassembled and made another cut.  It's close to .001" across a 3" aluminum cutoff.  The dish/dome measures the same all the way across.  I moved my Interapid a bit above center to avoid the very center of the cut and, of course, it read just a little less.  As much time as I spent yesterday getting the headstock aligned with the test bar I decided not to go after it given I'm in an uninsulated barn at it's near 100 outside and in.

I cut a two bar test over 12-15" and it cut perfectly so I'm leaving it alone.


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## Christianstark (Jul 10, 2022)

Looks like I am cutting a 1.5 thou taper over 6”.  Let the fun begin


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## poorboy (Jul 10, 2022)

Just did a facing cut .. almost no difference from to back (.0001-.0002 over 3") - so I am guessing that my gear head alignment is fine. Even though I used a precision level - doing the two collar test - I still have a .002 taper (the largest is towards the chuck).  Im guessing that my ways are still slightly twisted.

What a pain in the ...


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## Parlo (Jul 10, 2022)

poorboy said:


> Just did a facing cut .. almost no difference from to back (.0001-.0002 over 3") - so I am guessing that my gear head alignment is fine. Even though I used a precision level - doing the two collar test - I still have a .002 taper (the largest is towards the chuck).  Im guessing that my ways are still slightly twisted.
> 
> What a pain in the ...


Try locking the compound slide and leaning lightly on the toolpost pushing the tool into the bar when taking a cut. This will take out some slack in the setup, if this cuts without a taper then it is slack in the lathe ways. If it still has a taper then you can disregard this. It is a quick test to eliminate one potential issue.


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## Just for fun (Jul 10, 2022)

I adjusted my lathe with a precision level, without changing anything the next morning it was off a little bit.   Readjusted it,  tightened the lock nuts and it's off again, only just a tad so I called it good.


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## projectnut (Jul 11, 2022)

The attached document may help you find your problem.  It's a copy of the inspection sheet that came with each Sheldon lathe.  The graphics show what instruments were used and where they were placed for each measurement.  The text describes the acceptable range for each measurement.  The right column is for recording the actual measurements on each machine.


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## riveter (Sep 8, 2022)

davidpbest said:


> I invested in one of these -  makes aligning the headstock very easy.  Once the headstock is aligned you can adjust out any twist in the lathe bed.
> 
> 
> 
> ...


I had been looking at these but when I saw they were made in 1ndia I retreated. I have gotten some of the worst quality junk from there. But I did just order the MT5 test bar stated to have a max runout of 0.0002”. Thanks for the recommendation David.


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## riveter (Sep 8, 2022)

ddickey said:


> I've bought two of these both out of spec. In fact the last one I bought had .003" TIR. However, I was refunded the total amount I paid without needing to send back to India (2nd one).


I have ordered one. I will inspect it and report my results here. Advertised TIR is 0.0002”.


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## riveter (Sep 8, 2022)

poorboy said:


> Just did a facing cut .. almost no difference from to back (.0001-.0002 over 3") - so I am guessing that my gear head alignment is fine. Even though I used a precision level - doing the two collar test - I still have a .002 taper (the largest is towards the chuck).  Im guessing that my ways are still slightly twisted.
> 
> What a pain in the ...


I feel your pain. My lathe is cutting tapers too. And I thought I was going to spend my retirement making little steam engines.


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## davidpbest (Sep 8, 2022)

riveter said:


> I had been looking at these but when I saw they were made in 1ndia I retreated. I have gotten some of the worst quality junk from there. But I did just order the MT5 test bar stated to have a max runout of 0.0002”. Thanks for the recommendation David.


These photos and the descriptions that accompany each image might be helpful.  I'll be interested to hear your measured run-out on the test bar.  I spent $120 for mine hoping  that would be an indication of quality, and was rewarded with a very accurate test bar - or perhaps I just got lucky.









						Aligning the Headstock of PM-1340GT Lathe
					

Click the image to see the text description below the photo.




					www.flickr.com


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## JMBrewer (Sep 8, 2022)

Question for everyone, once you go through the headstock/tailstock alignment processes is this something you repeat yearly, etc.? Same with tramming a mill, once it's dialed in, do you need to go back and recheck that periodically or only once you've moved the head, etc..? Wasn't whether this could change over time with using the machine, I'd think over time things can loosen


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## Shotgun (Sep 8, 2022)

What I've learned is that everything is made of rubbery marshmallows.
You think that the 3" of cast iron your lathe bed is built from would be solid.  It ain't.  It dances like a lady of the night on meth.
At least with a mill, you can see the tram getting off when the herring bone pattern goes away when using the flycutter.


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## Firstram (Sep 8, 2022)

I've had great results using Rollies Dad's Method. Everyone should at least learn and try it before spending money on a test bar that will rarely be needed. I just had the headstock off of my lathe for some work, paint and some of mksj's magic. A quick test cut showed .003" taper in 2.5" after bolting everything back together.

I used a random piece of 3/4" cold rolled (in a 3 jaw) that was 18" long to align the spindle. The near end was +/- .004" and the far end showed +/-.015" of runout. After adjusting the headstock, I did a quick 2 collar test with a piece of 2.5"aluminum pipe 12" long, 9" from collar to collar and the difference is within .0005". Takes less than an hour, it's free and it's more accurate than I need to be for most of the work I turn out.

The most difficult thing about aligning the headstock is getting back to where you were before turning the wrong bolt the right way or, was that the right bolt the wrong way?


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## ddickey (Sep 8, 2022)

I agree that buying a test bar is not necessary for a head stock alignment.


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## davidpbest (Sep 8, 2022)

ddickey said:


> I agree that buying a test bar is not necessary for a head stock alignment.


It's not necessary, but it sure is convenient.


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## Parlo (Sep 9, 2022)

Firstram said:


> I've had great results using Rollies Dad's Method. Everyone should at least learn and try it before spending money on a test bar that will rarely be needed. I just had the headstock off of my lathe for some work, paint and some of mksj's magic. A quick test cut showed .003" taper in 2.5" after bolting everything back together.
> 
> I used a random piece of 3/4" cold rolled (in a 3 jaw) that was 18" long to align the spindle. The near end was +/- .004" and the far end showed +/-.015" of runout. After adjusting the headstock, I did a quick 2 collar test with a piece of 2.5"aluminum pipe 12" long, 9" from collar to collar and the difference is within .0005". Takes less than an hour, it's free and it's more accurate than I need to be for most of the work I turn out.
> 
> The most difficult thing about aligning the headstock is getting back to where you were before turning the wrong bolt the right way or, was that the right bolt the wrong way?


I agree, this method relies on first principles, not on a mandrel that you hope is accurate.


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## Shotgun (Sep 9, 2022)

I've been doing a lot of study on this, and my conclusion (yours may differ), is that RDM gets the bed to align with the spindle, no matter what else is screwed up.  

Your spindle could be pointing at the back wall, and RDM will try to bring the bed into alignment with it so that you get a straight cut.  If the spindle isn't too far off, ie a few thou, RDM will be successful at that.  But, take a facing cut across a 6" plate, and you'll be able to serve the first course of dinner out of it.  Assuming the first course is still soup, of course.  If you never do large facing cuts, and you need good tools to tell if you're lathe was out of line to begin with, then RDM was all you were ever going to need.

I have a 16" lathe, that I know I'm going to want to push to its dimensional limits in the near future.  After doing RDM, I'm still detecting several thou of dishing.  So, I gotta spend more money on tools that will be rarely used.  :-(


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