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PM 1236 Headstock alignment

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Bob S

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#1
I determined that the headstock on my PM-1236 is badly out of alignment so I have been attempting to perform the alignment per the manual. I obtained a 1.5 inch precision ground 12 inch bar that was mounted in the 4 jaw chuck and centered. Moving the dial indicator from the chuck to the end of the rod (about 5 inches) shows the head is out by 18 thousands over that run. Looking at the manual, on page 30, Figure A4 shows 2 6MM keys that pass through the headstock tab rail into the lathe bed. I was using a 6MM hex key and wasn't getting any resistance. So I looked closer and realized that both these bolts are missing, no sign of the expected thread showing for the bolt. Needless to say this is making the alignment difficult. Any advice?

Bob
 

machPete99

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#2
Not the answer to your original question, but be sure to check for runout on both ends of the bar. If you find some rotate to the midway position before checking the alignment. Often chucks won't hold things perfectly straight.
 

fradish

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#3
Have you contacted Matt for the replacement parts? He's always been very quick to respond when I send him emails...
 

mksj

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#4
In addition to contacting Matt at QMT you might also try to PM Darkzero or Ray C both who have had PM-1236 lathes for many years, and both are very experienced machinists. Some photos of your lathe would also help. It looks like the two 6mm screws retain the head in position against the 14mm head hex screws. when doing the head alignment, you need very small adjustments to align the head. There are several approaches to doing the headstock alignment, but using a test bar in the chuck and just running an indicator along the test bar, does not take into account the skew in the chuck. Some people use a MT test bar, but an additional cost that I do not think is needed. What I recommend is putting the headstock in neutral (gears not engaged), run your dial/test gauge against the bar and rotate the spindle so that the needle swing is the same (equal) in both +/- directions on the diameter measurement, recheck midway and at the end of the bar (about 12" out), the swing around zero should be the same +/-, but the actual number value doesn't matter. Therefore if the rod is not perfectly straight or held slightly skewed you can still align the head. It also gives you an idea of your chuck's performance, some people do a two collar test to look at the cutting diameter at two points or along a shaft, but this assumes that their is no chuck skew which is often not the case. In addition the lathe must be leveled first with a precision level. Two collar test is sometimes used for bed twist.
 

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Weldit

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#5
Since when is aligning the headstock on a new lathe part of the procedure. I thought this was all done at the factory and QC checked.
Am I wrong?
 

wrmiller

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#6
Unless your headstock, bed, and ways are one piece, anything can and will move. I always check every machine I buy. Who knows what bumps and bruises happened on it's way here.
 

Alan H

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I determined that the headstock on my PM-1236 is badly out of alignment so I have been attempting to perform the alignment per the manual. I obtained a 1.5 inch precision ground 12 inch bar that was mounted in the 4 jaw chuck and centered. Moving the dial indicator from the chuck to the end of the rod (about 5 inches) shows the head is out by 18 thousands over that run. Looking at the manual, on page 30, Figure A4 shows 2 6MM keys that pass through the headstock tab rail into the lathe bed. I was using a 6MM hex key and wasn't getting any resistance. So I looked closer and realized that both these bolts are missing, no sign of the expected thread showing for the bolt. Needless to say this is making the alignment difficult. Any advice?

Bob
Bob, sorry you're having trouble. Mark (mksj) has given you some really solid advice.

To repeat some of his advice, level the lathe first, assure your chuck isn't out, and then use the Rollie's Dad Method (RDM) to check alignment.

A precision ground bar has a tight tolerance on diameter but isn't necessarily straight and the RDM takes that into account. It works.
 

Bob S

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#9
I’ve had the lathe for a few years and had to disassemble it to get it into my basement shop. I knew it was out after re-assembly but not so much that it impacted the type of projects I was doing. I came across a need to take a cut in bronze over a 4 inch span when I found it was cutting too much taper for the length. Attempts to adjust the head have been sporadic as I have a good, straight precision bar that is centered in the 4 jaw but it is difficult to get adjustments right. All the methods suggested are for determining how far out the lathe is, I know that answer, I’m having difficulty with reducing these values to something reasonable. The best I’ve gotten is around 10 thou over 5 inches, would really like to do better than that. Part of my question is whether or not those bolts are required and could not having them be part of my problem. I wasn’t sure that since both were missing was this a design mod that didn’t make it into the manual?
 

Alan H

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#10
Actually the RDM is also for adjusting - unfortunately it is a trial and error process. Without photos or the manual, it's hard to give you any better advice. Please forgive me for repeating that the chances of the bar being perfectly straight are limited. I bought two from McMaster (12" and 18" lengths) and both are great diameter wise and both were out over the length.

Mark's advice to contact @darkzero and @Ray C is still one of your best bets for help since no other PM1236 owners have picked up on the thread thus far. I believe Will and Ray get a "notice of mention" since I used the "@" in front of their user names and perhaps will pick up here. But a p.m. from you would be more certain.
 

Ray C

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#11
Actually the RDM is also for adjusting - unfortunately it is a trial and error process. Without photos or the manual, it's hard to give you any better advice. Please forgive me for repeating that the chances of the bar being perfectly straight are limited. I bought two from McMaster (12" and 18" lengths) and both are great diameter wise and both were out over the length.

Mark's advice to contact @darkzero and @Ray C is still one of your best bets for help since no other PM1236 owners have picked up on the thread thus far. I believe Will and Ray get a "notice of mention" since I used the "@" in front of their user names and perhaps will pick up here. But a p.m. from you would be more certain.
First things first... Matt and I are friends and I still think the world of him, his business and the equipment he sells but, be apprised, I do not represent his company nor, do I provide warranty work for his fielded equipment. I'm purely a customer and matter of fact, need to give him a call to order another big heavy box. Anyhow, due to the difficulties in working commercially in the "hobbyist" arena, I no longer conduct business transactions in that area. After 3-4 years away from this web site, I'm back only to show shop and fabrication techniques purely to help keep the trades alive -and do it in a friendly forum.

Alignment:

In general, this style of lathe has (as I recall) 4 main bolts that keep the headstock on. I'm pointing at two of them and the other two are back by motor. I cannot take pictures because of the way the shop is currently laid out. Those bolts back by the motor had a a couple push-pull screws associated with them and that is how the head is moved precisely. All 4 bolts have to be loosened to utilize the push-pull bolts.

If a lathe has been assembled properly at the factory, it should survive shipping and only need leg/bench adjustment to make it cut straight. However, rough shipping can bump things out of whack. If it's been disassembled, alignment goes out the window. I'm not sure what bolts the OP believes are missing but, it sounds like he's talking about the alignment pin holes for the lower gearbox. Without pictures, it's hard to say.

Even after 4 years, Matt has supported many customers with issues that cropped-up down the road -and for a variety of reasons. Strongly advise that Matt be consulted. As far as I know, that lathe is still the same pattern as they have always been and he knows every nut, bolt and screw in them.
IMG_20180112_135232.jpg
Regards

Ray
 

Bob S

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#12
I sent an email to Matt, now awaiting a reply. Thank you to everyone that has responded so far!
 

SSage

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#13
I find pictures get things resolved much quicker. Get a browser plug in for the picture mark ups, the screen grab plug ins have drawing and text ability usually.
 

qualitymachinetools

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#14
You are right, pictures are the best. He did send one, and I knew what they were right away. Those screws would have had to be removed to take the headstock off when it was taken apart.
Its just something you can pick up at a hardware store for about a buck, just a pair of 8mmx1.25 socket head cap screws. He sent me a pic, they are the adjustment screws that are above the motor, that are talked about on the top of page 30 in the manual.
http://www.precisionmatthews.com/wp-content/uploads/2017/02/PM-1236-v4-1-2017-indd.pdf
It will be a whole new machine with those back in and it adjusted right, you can adjust that in as close as you want now, I would shoot for about .0005 over 6" or even better, the closer you have it the better, but it may take some time to get it that close!

Hey Ray, great to see you on here!
 
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Bob S

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#15
I picked up the recommended bolts from the hardware store but ended up having issues getting them started in the holes. Since the back of the lathe is fairly close to the wall it was difficult to align the head so I could get the bolts started. I dropped one of the new bolts and it fell into the cabinet, when I got in the cabinet I found 2 bolts still in a sealed plastic wrapping that were the same size as the ones I had just bought except they were slightly longer. I was able to get these started in the holes much more easily!
After a couple of hours of tinkering I got the head aligned better than it was before but still not as close as I would like. Since I needed the lathe to do some work on a project that a slight taper isn't an issue, I tightened everything down and put the lathe back to work. I'll re-visit the alignment process later, hopefully it will go much more easily next time.
Thank you to everyone that offered advise and suggestions to help get me up and running again!
 

Sleddog

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#16
I received my PM-1236 in the spring of 2017. I've been impressed by how straight it cuts. Absolute confidence that when I turn the cross feed to take a cut that's what it does & without taper.
A few weeks ago that changed. I started getting .002 taper over a couple inches. (I'm sure I know what caused it) Yesterday, I put a piece of 2" diameter material (cast) in the lathe. Sticking out about 2 3/4" Took a clean up cut to get rid of the "crust" then took a .015 doc & check with a mic & had .003 taper.
Out came the cast, I put a piece of 1 1/4" tool steel in & started to adjust the headstock. I got it adjusted to no taper over about 5". I put the cast back in & was disappointed when I still had 3-4 thousands taper! I spent the afternoon adjusting, taking .010 doc's, adjusting, more cuts more adjusting until I had less than a few tenths difference. I made sure everything was tight, covers replaced & buttoned up. Took a deep breath & took another cut......perfect:)
I sure hope this was the correct procedure. I don't want to go through it again. I'm getting too old for all the kneeling/squatting/deep knee bends associated with getting it squared away.
 

JCByrd24

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#17
Just to be clear the two collar test cut method does eliminate any issues with chuck, whereas the OPs method clearly does not. As I've recently learned even 4 jaw chucks dialed in at the chuck will almost always be out a little a few inches down the bed. RDM can be used but is not as fool proof as the two collar method, and to me is more work. Both are impacted by bed wear and twist.

A method that can be used to get very close more quickly and isn't impacted by bed twist or wear is to take a facing cut on a large diameter (like a face plate). A lathe with the headstock misaligned will cut concave or convex on a facing cut in addition to the taper in the turning cut. By taking a facing cut and running an indicator along the back side of the cut you can find whether you are cutting concave or convex (running an indicator on the front side should read zero as it follows the tool path). Then you can adjust the headstock so that the error is split across the front and back. This will get you very close with one test cut. You can chase it from there as precise as you want.

Fixed headstock lathes HS/bed to cross slide perpendicularity is typically specified to well under 0.001" in the swing on a facing cut and only on the concave side. This is closer to zero than most of us can hope to achieve and on these imports with "adjustable" headstocks getting as close as possible as you can/desire to this is the first step in my mind. Once this is done, the lathe can be "leveled" and finally adjusted to cut without taper using RDM or two collar method and fine adjusting the twist.
 

Richard King 2

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#18
Bob,
If you need some help I can call you in the morning and tell you what to do. When you moved it down to the basement the head wasn't put back on right or got bumped. Private message me your phone number and I can give you a call. Rich
 
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