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A Head Alignment Process for a PM1340GT

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Alan H

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#1
I moved my PM1340GT to its permanent position and leveled it. The PM1340GT is meant to be leveled and then the headstock aligned using its adjustable mount.

This post is about the head and tailstock alignment methods I used. I recognize that this is not the only way to do it nor have I invented anything new. I am just trying to share the process I used for others who might find it helpful. Key to the process I settled on are a good four jaw chuck, a 1” precision ground steel test bar, and a 2”diameter aluminum bar for test cuts.

The sequence I used:
  1. Aligned the tailstock using the “quick method”.
  2. Aligned the head using my four jaw chuck, a 1” round precision ground bar, and the Rollie’s Dad Method. (Note: if you aren’t familiar with the RDM, google it and you will find lots of info)
  3. Realigned the tailstock using the quick method.
  4. Turned a 2” diameter aluminum test bar with two collars using 4 jaw chuck and between centers.
  5. I did test cuts with the 2” two collar bar to confirm head alignment (w/o tailstock)
  6. I made a test bar out of 1” precision ground bar and confirmed tailstock alignment with it.
I aligned the tailstock to the head using the “quick method” as described in the PM manual (page 30). Works extremely well if you have two pristine centers and a single edge razor blade for a test plane. The blade is held between centers and the tailstock alignment adjusted until the test plane is perpendicular to the centerline of the spindle.

quick ts align.jpg

I used an 18” long 1” diameter precision ground bar that I bought from McMaster mounted and trued/indicated in my 4 jaw chuck. I then used the Rollie’s Dad Method (RDM) to confirm and correct a misalignment of about .0035” at 12” from the 4 jaw chuck. I loosened the 4 head mounting socket head screws and then snugged them back down but not full torque. I used the two adjustment screws on the side of the headstock to tune the bar to zero runout using a 0.0005” indicator. To say the head alignment is sensitive to the adjustment screws and the mounting screws tightening would be an understatement. I discovered if I pivoted the head on a fully tightened right front head mounting screw, I could then use a tightening sequence that maintained the runout. I tightened the right front mounting screw fully, then front left and then two rear bringing them all down partially and evenly a little at a time. When finished, the RDM was showing the zero runout that I was after.

RDM 1.jpg

With the head now aligned using the RDM, I realigned the tailstock to the head using the quick method. I turned a 12” long 2” diameter two collar aluminum test bar between centers using the 4 jaw chuck (test bar trued in chuck). Here's the test bar with two collars ready to go:

Bar ready to go.jpg

With live center support removed, I did test cuts on the two collars (one with a HSS tool and one with a CCMT insert). Using a micrometer to the tenths, this confirmed the headstock was aligned. To my surprise the RDM for the initial alignment was quite accurate and no adjustment was needed. Here are the test cuts:

1.980 w hss cut.jpg 1.9696 wInsert.jpg

I chucked the 18” long steel test bar in the four jaw. I center drilled the ends and confirmed concentricity of the center drilling both ends. By the way, my test bar has a surface hardness of RC60 and the center of the bar ain't soft.

center drill confirmed.jpg

Then using the center drilled test bar between fixed centers, I confirmed the tailstock alignment. This confirmed the “quick method” for tailstock alignment works well.

TS align test bar.jpg .

In summary:
  • I am glad to have my lathe in its final location and leveled on it six footed stand. I will use my leveling method in the future as needed. (thread on leveling)
  • The Rollie's Dad Method (RDM) of alignment with my 4 jaw and precision ground test bar will be my go-to method for rechecking head alignment from time to time. A good precision ground test bar is critical and I have preserved mine for next time. With the test bar trued up in the 4 jaw chuck, the RDM is easy to use. I did preserve my two collar test piece for future use if needed but I bet it gathers dust.
  • I trust the “quick method” for tailstock alignment. I have also put my centers in a safe place to preserve their "as new" condition for use next time.
Sorry for the long post but I hope this helps someone figure out how they want to work through this on their machine.
 

MonkMan

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#5
Thanks So Much. I will follow your procedure as outlined.
 

ddickey

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#6
Question about run-out of the ground test bar.
After your adjustments you have zero run-out or equal movement both sides of zero?
 

Alan H

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#7
Question about run-out of the ground test bar.
After your adjustments you have zero run-out or equal movement both sides of zero?
Correct - on my setup, I had equal movement on both sides of zero after alignment.

I will add a little to the explanation for others.

The precision ground test bar is trued up with no runout at the 4 jaw chuck. Without disturbing the indicator mounted on the carriage, you move the carriage down the bar and check the runout at the far end. If it's in alignment, any move off zero is exactly the same on both sides of zero. Any bend in the bar is irrelevant when using the RDM. However the bar should be precision ground and must be the same diameter end to end.

This is the beauty of the RDM technique. Your bar doesn't have to be perfectly straight. A tight tolerance on the bar's diameter is what counts.
 

Alan H

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#9
I really don't remember - I think it was on the order of .002". It really is irrelevant though.

Edit: what's important is that it is the same on both sides of zero.
 
Last edited:

ddickey

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#10
Well not really though because it shows some skew in the chuck, no?
Mine is ~ .005"
 

Alan H

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#11
Could be, but the tolerance on my ground bar is +/-.002" per foot.

Have you checked the diameter of your bar and the point of dialing it in at the chuck and then at the outboard point to make sure it is the same diameter?

If you bar is the same diameter, how about playing with rotating your bar in your chuck by 90 and 180 degrees and see what happens? May tell a story.
 

mksj

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#12
Every chuck has some degree of skew, even try to rechuck a rod and see what happens. A precision ground rod it less likely to have surface defects that could alter this. If a scroll chuck, you are scrolling over a distance of a couple of inches so what is accurate at one diameter most likely will not hold at another. If you hand turn the chuck you will find that you can change the readings at 12" easily 0.001 or more. The whole idea of looking at the swing and getting it the same in both directions is a quick indication of headstock alignment. You can then tweak it every so slightly to get the two ring to be dialed in. Personally it is a bit of chasing your tail, as a piece held 12" out would be supported at the other end with a center. I believe the unsupported distance for turning is something like 5X the diameter of the work. Even when the alignment is dialed in, many other factors will determine the diameter cut along a piece. Even though everything checks out in one condition, different material, different cut, etc., I find I need to tweak the tailstock alignment so the cut is the same diameter over the length of the cut.

If you have a lot of skew or high TIR, then of course that will cause other problems. So you try to decrease the inaccuracies and determine if your problems is the chuck or alignment, or both.
 

Alan H

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#15
Sorry, I do not recognize that chuck. What kind of mount is it and what lathe is it on?
 

ddickey

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#16
It's a D1-5. Not direct mount, has a back plate.
 
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