Anyone here with a PM1236

[verbotenwhisky]

There have been previous posts on the subject, it just takes a bit of time to dial it in and very small movement on the adjustment screws as is outlined in the manual. I do not fully loosen the headstock bolts, keep some tension on them so the head stays taught. Make sure the bed is level first with a high precision level. I prefer using "Rollie's Dad's Method" for aligning the headstock or a precision MT test bar, then tightening the headstock bolts, rechecking and doing a 2 ring test.

PM 1236 Headstock alignment

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...

www.hobby-machinist.com

Looking at that thread now, greatly appreciated, this is exactly what I was looking for. Thanks.

 

[tailstock4]

I’ll start off by saying I don’t own this particular lathe although I did once own a Taiwanese 14x40 bench lathe. It had the problem I’m going to describe.

I’m not particularly a fan of mounting headstocks on ways with bolts or set screws for alignment. I prefer them to be scraped to the v-ways for many reasons that I won’t go into here. It’s not that this first method can’t be a good way. If done well, it can work reasonably well especially on lighter duty machines. The problem is that this method of headstock mounting can allow for the possibility of laziness on the part of the manufacturer.

What I mean is the surfaces between the top of the bed and the bottom of the headstock are precision surfaces that are ideally scraped or at least ground for flatness and good contact. I have seen machines where these surfaces are merely machined and not particularly carefully. This produces a less than flat surface and introduces the possibility of twisting the headstock which means that the headstock bolt torque has now become part of the alignment equation.

So it is possible to align a headstock with this condition and still not have good contact between these surfaces. This can introduce problems of rigidity and a spongy headstock but also if bad enough it can introduce spindle bearing twisting issues and out of roundness.

To check for the condition of twisting of the headstock and poor contact, I would first make sure that I have a level bed with no twist. Then I would mount a half-thousand or tenth test indicator to the bed ways and indicate off the top and the side of the spindle. Leave the headstock alignment bolts alone. Loosen the mounting bolts and tighten them just beyond finger tight. Zero your indicators and tighten each corner to full torque, record any movement, then release. Repeat at all four corners. There should be no movement. Any movement and it will introduce torquing to the headstock – something of which can be magnified on headstocks with thin castings like on these small lathes.

It is possible to shim for this error, but this is not ideal as any compression of the shims will again introduce twist. To correct the condition, it would ideally require these surfaces to be scraped flat or at the very least ground.

I may be off in the weeds a little here, but it doesn’t take much of this twist and/or poor contact condition to cause issues with accuracy and performance. I’m by no means an expert. Just someone who enjoys working on and rebuilding machines who once encountered this condition.

 

[verbotenwhisky]

I have a MT Test Bar coming, this will help.

 

[Rufustoad]

I am getting ready to pull the trigger on a PM-1440E-LB 14″x40″ Precision Lathe. Anyone suggest not to or problems other than this post I would want to know about?

 

[mksj]

Overall Precision Mathews/Quality Machine Tools offers what I would consider better overall quality lathes and better warranty compared to other vendors with similar type/priced lathes. There are fit an finish issues with the Chinese mainland machines in this price range, but function wise most people are quite satisfied, and the PM-1440E-LB design is common base style shared by other manufactures lathes. I would also look at the PM-1440-2SM-V which has been updated and has some nice features. This is now available in a VFD model which is worth considering in this price range. I like the design and features a bit over the PM-1440E-LB, and it is closely priced. If you are looking at a better fit/finish lathe than I would recommend the 1340GT, go with a 3 phase motor and add a VFD, there is some information posed in this forum for the basic 1340GT VFD install. Three phase motors will give a better turning finish, are more durable and less issues frequent start/stops. In addition for the 1340GT it provides electronic braking.

PM-1440-2SM 14″x40″ Gunsmith Lathe – Precision Matthews Machinery Co.

www.precisionmatthews.com

 

[Rufustoad]

Thanks mksj that is great info. Do you by chance know what the difference is between the "precision" and "ultra precision" models?

 

[xr650rRider]

Taiwan (ultra precision) vs China (precision)

 

[Rufustoad]

Glad I asked. I thought all PM were Taiwanese
I have been apprehensive about the VFD and trying to figure out thread turning but might be best options although I am really wanting that 2” bore

 

[Harry Knutz]

I am looking for those on the forum who have a PM1236 (the chinese machine) and have had to tram the head stock, I am going to need to do this and I am looking for those that could provide a bit of information about the procedure.

Hello,

I have the same lathe pretty much, Although much older and with a different badge on it. Your manual shows you how to do it. This way I did it is not shown in the manual. I will show you some pics of the tool I bought to do it. There are some jack screws on the back of the headstock, They are kind of hard to get to with the motor and electrical box on there. Very, Very small turns on them will move the head a lot so go slow and easy, It takes a long time to get it right. How do you know the head is out of alignment? You can take a 3 or 4 inch diameter short piece of stock and make a facing cut, Then put a high quality straight edge across the cut with a flashlight underneath it and if it's not perfectly flat (As in concave etc) Then it's out out of alignment.

I bought a #5 Morse taper test bar, It's very large, Tap it into the headstock with a good sized rubber mallet, Then put a good test indicator on it and move it back and forth checking the up and down and the side to side alignment, I was able to get mine very straight, It's a slow tedious process that can get frustrating but stick with it and you will get it done. If the up and down is off it will require shimming, Fortunately mine was within 2 tenths over the length of the bar and I was happy with that. Side to side I was able to get it within 1 tenth, So I was very happy with that.

 

[mksj]

Even when using a MT test bar, I recommend rotating the spindle and looking at the indicator to be sure that the +/- swing remains the same in either direction as you move down bar. The MT taper could be slightly off and or its seating. The headstock jacking screws only effect the horizontal movement of the headstock, scraping/shimming would be needed for the vertical, and only would be recommended if there was a significant height variance. You need a dial indicator that can measure 0.0001" increments similar to dial indicator below. Even if the test bar alignment is spot on, there can be some deflection when cutting as you get further away from the headstock, as well as the skew from the chuck.

Glad I asked. I thought all PM were Taiwanese
I have been apprehensive about the VFD and trying to figure out thread turning but might be best options although I am really wanting that 2” bore

A VFD has no effect on threading, the gears are driven from the headstock, thus the movement of the carriage is linked to the spindle speed. All the PM 1440 lathes have a 2" or greater spindle diameter. You might start a separate thread with your questions as they do not pertain to this lathe model/discussion on headstock alignment.