A head scratcher here …

[davidpbest]

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.

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[pacifica]

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.

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.

 

[Shotgun]

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?

 

[RJSakowski]

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.

 

[poorboy]

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 ?

 

[Firstram]

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.

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.

 

[Parlo]

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.

 

[pacifica]

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.

 

[Firebrick43]

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.

 

[parshal]

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.