PM 1236 Headstock alignment

Bob S

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