Thread: Alignment issue AL 330

Okay I think I'm with you now. So what you're saying is that if the bed is level then the headstock must be out?

So I mucked around a bit more and ran a few more test cuts on some thicker bar, 36mm round hollow bar, medium carbon steel, and got some funny results. I had it protruding 9" from the 3 jaw, and took some very light cuts with very sharp HSS, and got a taper of .0005" per inch for the section 4"-9" away from the chuck, and no taper for the section 1"-4" away from the chuck.
So it isn't as bad as I thought, but that seems a bit odd doesn't it?
Anyway I'll play with it some more before moving anything. Hopefully it's just me somehow.

That is correct.... The idea is not to twist the bed... From what I understand the two collars/rollies dad test is for when you have no level and have a small lathe like a Hercus..

As the headstock sits on V ways it should* be parallel to the ways as good as when it was new... it is not adjustable by any easy method..

So when doing the parallel turning test if there is any deviation you can assume it is caused by a twisted bed, so you adjust the bed bolts to untwist it and get it turning parallel.....

From what I understand most US designed lathes the headstock sits on the tailstock V ways...

In lathes designed in the UK and elsewhere like China, the headstock sits on flat ways (cheaper to manufacture) and are adjustable... I have had to adjust the headstock on an old geared head Nuttall, an AL1000C and a medium sized Purcell.... All had the headstock sitting on flat pads...

Hi tbonesmith,
Still big at the chuck end?
Stuart

Still bigger at the chuck end.

I could almost live with it. But as usual, I'll be better off getting to the bottom of it now, rather than having an issue on a job down the track.

Originally Posted by .RC.

I am not sure what he means by taking the average at each end...

Richard, you compare the average reading at the headstock end (which can be made to be zero with a 4 jaw) to the average reading at the other end. It doesn't matter that the bar isn't parallel to the spindle axis. Imagine the bar in crazy bad jaws that are 10 degrees off axis, but an otherwise perfect lathe. At the headstock end the indicator would be zero, rotate the chuck 180 degrees and measure again it would still be zero. Now go to the other end of the bar and rotate the bar so it reads the minimum, call it -10 units, rotate the chuck to find the maximum and it should both be +10 units and at 180 degrees; the average is still 0.

Now assume either the lathe bed is twisted (most likely) or headstock alignment is out (less likely), the readings at the headstock end will still be zero/zero, but at the other end they may be +12/-8. The maximum to minimum readings are averaged and then that average is compared to the average at the headstock end. I think this is quite different to what you're suggesting.

Pete

Edit: I should add that I don't for a moment advocate this approach, simply that's how it works.

Edit #2: Incidentally, before moving the headstock have you checked to see if the lathe faces accurately?

Hello tbonesmith,
My understanding is that you need to first remove any twist from the bed. Then you need to get the spindle axis parallel to the ways ("Rolle's Dad's Method" will do this), when viewed from the side (standing at the controls). This adjustment can be achieved by raising or lowering the tailstock end of the lathe or shimming under the headstock bolts. The aim is to keep both the lathe bed and spindle axis horizontal according to your spirit level if possible.
Next you need to get the spindle axis in alignment with the ways when viewed from above (looking down from the ceiling). Rolle's Dad's Method will show this as will the Two Collar method. If any taper shows up it can be removed by imparting a twist to the bed or adjusting the Headstock (preferred) by loosening the four bolts (I think your lathe has 2 bolts and 2 capscrews) and adjusting the four capscrews at the back of the head,above the motor.
Regards,
Russell

Me again,
I made a test bar by turning up two 60mm dia. aluminiun rings from 10mm plate and locktiting them onto a piece of 25mm dia.solid steel spaced about 200mm apart with the first ring 50mm from one end to hold in the chuck. I have a centre in both ends of the bar so that I can also check the tailstock alignment.
Russell

When you set your test piece up were you using the 3 jaw chuck?

Originally Posted by pipeclay

When you set your test piece up were you using the 3 jaw chuck?

Yes.

If possable do another test cut with the material set up in a 4 jaw.
Is the 3 jaw chuck your using a Set True chuck?
The amount of taper that you mention after turning could possably be caused by the 3 jaw.
The 3 jaw is not the most ridgid (firm holding) chuck to use for your testing.

Why should it be a set-tru chuck, once cuts are made it's completely immaterial how the work is held. The only time this is a factor is if the work is re-chucked, not at all relevant in this case.

Originally Posted by Pete F

Richard, you compare the average reading at the headstock end (which can be made to be zero with a 4 jaw) to the average reading at the other end. It doesn't matter that the bar isn't parallel to the spindle axis. Imagine the bar in crazy bad jaws that are 10 degrees off axis, but an otherwise perfect lathe. At the headstock end the indicator would be zero, rotate the chuck 180 degrees and measure again it would still be zero. Now go to the other end of the bar and rotate the bar so it reads the minimum, call it -10 units, rotate the chuck to find the maximum and it should both be +10 units and at 180 degrees; the average is still 0.

Now assume either the lathe bed is twisted (most likely) or headstock alignment is out (less likely), the readings at the headstock end will still be zero/zero, but at the other end they may be +12/-8. The maximum to minimum readings are averaged and then that average is compared to the average at the headstock end. I think this is quite different to what you're suggesting.

Pete

Edit: I should add that I don't for a moment advocate this approach, simply that's how it works.

Edit #2: Incidentally, before moving the headstock have you checked to see if the lathe faces accurately?

The bit I do not get is the average.... An average is readings divided by number of readings.. TIR is just a single figure..

I just did a test on my lathe where I know the headstock is pretty damn good... I found using the precision bar in the four jaw chuck, zero it at the headstock end... And rotate the spindle until you get halfway between the high and low TIR points on the free end you can get it close, but it was simply way too easy to put an error in there and get the wrong figure... Also you get the small error of the indicator point not being in the same horizontal position at either end, as the free is pointing either up or down..