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Looking for a recommendation on PM1340gt alignment

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GunMonkey

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#1
Im setting up my new lathe and working through bed leveling and headstock/tailstock alignment. I have a MT5 ground test bar that reads with no movement/runout at the headstock. At 11.5" down the bar it reads with .0003 showing a slight bias toward the rear of the lathe. I moved on and aligned the tailstock between centers with a straight ground test bar. I then mounted a Bison 4 jaw direct mount D1-4 chuck and put a 3" aluminum round stock 14" long in and turned a barbell. I am getting a taper of about .0025 over 9" smaller at the headstock and larger at the tailstock.

Now for the question.

Am I better off adjusting the headstock or adjusting the feet on the lathe? or both? or is this as close as I will get it? My Starrett 98 shows the bed to be level front to back. Im hoping someone familiar with the lathe can give me some pointers before i loosen the headstock bolts.

Thanks, Jeff
 

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Dabbler

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#2
First it is important to get the bed ways level front to back AND headstock to tailstock at the same time. this is before you try to align the headstock.

Then you need to align the tailstock side to side and up/down.

Next, depending on the provenance of the MT5 test bar, it could be out. Usually you check with a parallel test bar between centres in addition, just to be sure...

Because your tailstock is in alignment cuts between centres can be made to get the head into perfect alignment. I haven't done this in 30 years, but those are the basic steps.
 

GunMonkey

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Thanks for your reply Dabbler.

The ground rod came from India and has a listed tolerance of .0002. It reads consistently as I rotate the spindle and increases gradually as it is moved from the headstock so I believe it is ground pretty true.

I did check with a parallel test bar next after seeing the slight offset of the headstock. I adjusted the tailstock about .0007 forward into alignment using the rod. The rod is being held by new carbide Bison MT5 and MT3 centers.

My last lathe was a South Bend heavy 10 and the bed would flex enough that adjustments could be made in the bed that would effect taper. Is this the case with a PM1340GT? I watched Tom Liptons video where he could not adjust taper from the bed of his Yam lathe and had to adjust the headstock.

I believe the headstock is slightly out of axis with the ways. Im not sure how difficult it would be to control the movement after loosening the bolts to improve the way that it rests on the bed casting. The .0003 is being read probably 15" from the first set of bolts so the movement required in the headstock would be a fraction of that I believe and could be hard to control and lock down.
 

Dabbler

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If you are out of parallel 3 tenths at 15" from the bolts - you are in. That is better than a Hardinge I worked on once. It takes a very experienced machinist to turn all but the most basic shapes to those kind of tolerances. I wouldn't mess with it. You could easily mess it up.

Your next step is to turn a bar between centres, say, 12" long, and measure the diameter at each end There a great videos on this on youtube, but essentially you first relieve the middle so the only heat you generate is at the ends. You also lock your cross slide so the tool remains true to the V ways. If your two diameters are within .0003 then your lathe bed and ways are a close as you can make them.

If I remember the video correctly, Tom Lipton was a little surprised about the bed thing, but his lathe is very heavy - I vaguely remember a very large number, could it have been 5000 pounds? This is a very unusual situation. Almost any lathe I've heard of, except the very heavy toolroom lathes and a few CNC lathes need their beds adjusted so they are flat. This should apply to your PM1340GT. My lathe is a 12X37 and weighs almost 1000 lbs, but it needs careful alignment whenever I move it.

My friend bought an 18" X 60" Mazak lathe, 6000 lbs. Very strong an heavy base. It took >2 hours to get the lathe bed flat in both directions after it had settled on his garage floor for a week.

Your rod may well be in line. I was being cautious, because I had a bad experience with an American made alignment bar.
 

Bob Korves

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#5
Dabbler, nice job on helping Jeff with this. Good advice.

Jeff, happy to see you found a lathe in better condition. Looks like you will get it dialed in accurately.
 

pacifica

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Im setting up my new lathe and working through bed leveling and headstock/tailstock alignment. I have a MT5 ground test bar that reads with no movement/runout at the headstock. At 11.5" down the bar it reads with .0003 showing a slight bias toward the rear of the lathe. I moved on and aligned the tailstock between centers with a straight ground test bar. I then mounted a Bison 4 jaw direct mount D1-4 chuck and put a 3" aluminum round stock 14" long in and turned a barbell. I am getting a taper of about .0025 over 9" smaller at the headstock and larger at the tailstock.

Now for the question.

Am I better off adjusting the headstock or adjusting the feet on the lathe? or both? or is this as close as I will get it? My Starrett 98 shows the bed to be level front to back. Im hoping someone familiar with the lathe can give me some pointers before i loosen the headstock bolts.

Thanks, Jeff
When my 1340gt was new(this year) I had almost the exact same issue as you did. I contacted Matt and he said probably I need to adjust headstock.Unfortunately you cannot expect the headstock to be dialed in.Also my tailstock is about 4 thousanths " high(was told by PM that this is standard for this lathe:confusion:), not anything you can do except scrape the bottom of tailstock(I left it alone)
It's not too difficult to adjust the bolts but can take several hours.
Basically use 2" steel about 8" long , no tailstock.Make cuts ,adjust, check--and so on.This has been covered in previous posts. Eventually it will go to 1 or 2 ten-thousandths of taper mover the 8".
 

Dabbler

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Also my tailstock is about 4 thousandths " high(was told by PM that this is standard for this lathe:confusion:), not anything you can do except scrape the bottom of tailstock
The LeBlond 15" toolroom lathe always came shipped with the tailstock .003 high. This is to allow for wear from sliding on the slantway (sort of an asymmetrical Vee way) and the flatway. You can scrape yours in or use a boring bar holder to hold a dead centre .003 below centre in the tailstock.
 

Dabbler

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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!
 

GunMonkey

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Thanks. I will be back at it tomorrow. The test bar I made is from 3" stock and I don't have 2-3" micrometers that will read tenths. I decided I should have some and they arrive tomorrow. I dont have any other scraps of stock long enough to use to make something in a smaller size that I could measure so it was buy material or a new tool.
 

pacifica

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This is the set-up I used when actually moving the headstock. Just tightening the cap screws can give a movement of .01". I tighten 2/3 rds of the way and then tap with a rubber hammer for incrementel movement, watching the movement on the indicator. That way you can gauge how much you moved the headstock.
If available you can replace the stock cap screws with USA made holo-krome or unbrako.A poor quality cap screw can cause unexpected jumps in movement.
 

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Bob Korves

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#11
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."
 

pacifica

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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."
I'm referring to side to side(horizontal) movement, not vertical .No shimming or scraping involved.
 

Bob Korves

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I'm referring to side to side(horizontal) movement, not vertical .No shimming or scraping involved.
Sorry, Pacifica. I think I am responding to a different thread... Senior moment.
 

RJSakowski

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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!
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.
 

GunMonkey

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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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Dabbler

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#16
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.
 

pacifica

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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
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.
 

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GunMonkey

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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
 

Dabbler

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#19
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.
 

pacifica

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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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