Looking for a recommendation on PM1340gt alignment

The headstock is not high, the tailstock is low. All depends on how you look at it. The tailstock is easily made taller by placing shims between the upper and lower portions. You can scrape in the headstock if it is not level, which makes sense (if you are skilled at scraping and diagnosing lathes), and you can also scrape the tailstock to make it level and pointing in the correct direction. Been there, done that, needed to shim it up after getting the geometry correct. There is no magic height dimension stated for the headstock beyond "13" swing."
 
Bob Korves said:
The headstock is not high, the tailstock is low. All depends on how you look at it. The tailstock is easily made taller by placing shims between the upper and lower portions. You can scrape in the headstock if it is not level, which makes sense (if you are skilled at scraping and diagnosing lathes), and you can also scrape the tailstock to make it level and pointing in the correct direction. Been there, done that, needed to shim it up after getting the geometry correct. There is no magic height dimension stated for the headstock beyond "13" swing."
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I'm referring to side to side(horizontal) movement, not vertical .No shimming or scraping involved.
 
Dabbler said:
Here's a funny but very informative video on leveling a lathe that was cutting a .002 taper in 8 inches. Enjoy!


(he is trying to talk to all levels here - but he does a great job!
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A concern that I have with the video is the use of the tailstock. Using it assumes that is perfectly aligned with the headstock spindle axis. A .001" offset would have created the difference in diameters that were observed. Twisting the bed to compensate for that offset just introduces a second error and like they say, "two wrongs don't make a right".

If the tailstock is aligned visually by bringing the center to close proximity to the a center in the headstock, it would be difficult to hit within .001". A thin shim placed between the two points can indicate alignment fairly accurately. The angle between a shim and a perpendicular to the spindle axis is arcsin(offset/shim thickness). A .020"thick shim would have a 3º angle for a .001" offset. However, if one was trying to dial in a lathe to less than .001"/over the length of the bar, you would probably want that offset to be about 1/10th that which would require eyeballing a .3º difference which would be much more difficult.

Another fly in the ointment is that either of the point to point alignment or the trapped shim methods require a sharp point on both the centers. A flat on either will created a circle of uncertainty where the opposing center falling anywhere within the circle will show the same deflection. Finally, there us an assumption that the tailstock axis is parallel to the spindle axis so the tailstock center would be unaffected by the tailstock quill extension and that the tailstock ways are true to the main ways of the lathe. That an awful lot of assuming.

My preferrence would be to run the two collar test without bringing the tailstock into play. Once I had my lathe running true to the ways, I would rerun the two collar test between centers to adjust the tailstock offset.
 
Sounds good RJ. Im hoping to finish the process the way your are suggesting. The test bar I turned was not turned between centers. It was held by the 4 jaw chuck unsupported. I was a little concerned that the bar I turned was out .0025 and the ground bar from the spindle was only out .0003 at a further distance. It may have been the micrometer I was using to measure the cut test bar. I did center the tailstock to the spindle (and will do so again) using a ground bar but have not adjusted for height yet. I just wanted to get it close in the event that I need the tailstock as I work through the process. So my plan is to indicate off the MT5 test bar for any upward bias in the headstock/spindle so I can take this into account as I adjust the headstock closer in alignment with the ways. Then measure the test bar with my new mic and confirm the taper tomorrow. I then hope to loosen the headstock bolts and adjust it to run parallel to the ways. If I can source some new bolts as PACIFICA recommended I will. I really appreciate any and all feedback. I have a lot to learn and Im trying to think this through. If Im doing something ass backwards please let me know. And Bob... I can wait to scrape the tailstock in!

Jeff

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The most accurate method I know of to centre the tailstock is to directly indicate it in at two depths using a tenths indicator. The tailstock is then brought in to alignment with the centre of rotation.

A sacrificial centre is held in a chuck and cut to a new taper.

Only then do you cut a bar between centres. Holding in any chuck, 4 jaw or not, is not nearly as accurate as this process,

As I said before, to be within 3 tenths at approx 9 inches is better than you can expect on a hobbyist lathe. The LeBlond I work on from time to time is a much heavier lathe and has been set up to be within 2 tenths along the entire length. it took my toolmaker friend abut 9 months of off and on work to achieve this.
 
GunMonkey said:
Sounds good RJ. Im hoping to finish the process the way your are suggesting. The test bar I turned was not turned between centers. It was held by the 4 jaw chuck unsupported. I was a little concerned that the bar I turned was out .0025 and the ground bar from the spindle was only out .0003 at a further distance. It may have been the micrometer I was using to measure the cut test bar. I did center the tailstock to the spindle (and will do so again) using a ground bar but have not adjusted for height yet. I just wanted to get it close in the event that I need the tailstock as I work through the process. So my plan is to indicate off the MT5 test bar for any upward bias in the headstock/spindle so I can take this into account as I adjust the headstock closer in alignment with the ways. Then measure the test bar with my new mic and confirm the taper tomorrow. I then hope to loosen the headstock bolts and adjust it to run parallel to the ways. If I can source some new bolts as PACIFICA recommended I will. I really appreciate any and all feedback. I have a lot to learn and Im trying to think this through. If Im doing something ass backwards please let me know. And Bob... I can wait to scrape the tailstock in!

Jeff
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On my 1340 gt everything was in alignment and ridgid --except the headstock needed to be moved sideways(horizontal) about 6 hundredths.
I'm pretty sure it came from the factory that way because once I aligned the headstock then the tailstock (which previously was centered)needed to be moved to align it , but the marks on the tailstock were now shifted 6 hundredths from the center mark. In a perfect world the tailstock would be centered on the marks(not shifted sideways) and the headstock would also be centered.Hopefully this makes sense.

tailstck.jpg
 
Thanks folks for the help.. I worked on the alignment this morning and Im pretty happy with the way it turned out. I couldn't source new screws in time so I reused the factory screws and they worked out fine. I made a very slight adjustment on the headstock. It took about 45 mins of loosening and tightening and the result was just under .0001 over 12 inches measure with my DTI on the ground bar. I then confirmed the adjustments by taking a skim cut on my test bar and tweaked the right front leveling foot about 10 degrees moving the bed upward. I'll check the lathe in a week or so and see where it is at. Im just thankful all went well and things moved in the right direction. I could barely measure a difference between the two ends of the barbell. I then recentered the tailstock using my ground test bar. It was about half a tenth off front to back. I know for a hobby lathe as Dabbler said this effort may be futile but the process has also helped me get to know the machine a little better.56071262098__9511E8C9-0C43-4318-84E0-2B0E601543D4.jpg
 
Congrats on your achievement! I truly hope it holds. You managed to get a fantastic result! Just to clarify: I intended to convey that most hobby lathes, light as they are, normally don't achieve much better than 3 tenths per foot.
 
Very similar to results on my 1340gt, I was under a ten-thousandths on 8" length with a 2 " steel rod. This has held for over 6 months.Shows the gt series of lathe by PM are great quality.
 
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