Thread: my new AL960 cutting a taper

Hi Eskimo,

That figure I quoted was with a 50mm solid bar held in the 3 jaw with no support.

Only reason why I know this figure is from when I decided to make a cylindrical square and I wanted as parallel as possible. This was the best I could get and figured I was happy with the result given the lathe and my skills.

Last year I completely stripped the headstock and removed it for cleaning, when I put it back I took great care to align the headstock to the best of my ability (using RDM). My aim was to have it better than when I bought it, which I think it is going by the test results it came with.

Also if I wanted to get better accuracy then it would have been difficult for me as my most accurate mic is a 0.0001. I don't have a 0.001mm mic so I would have had to make the bar protrude longer. Also once you get to the pointy end of accuracy, those adjustment bolts get very touchy, even tightening the headstock bolts once you are happy with the alignment is a delicate process.

Anyway, not sure what the standard is but 2.5 microns over 150mm is good enough for me!

Cheers,

Simon

Originally Posted by eskimo

yeah..but the method of measurement still works doesnt it?

Hi eskimo,
Sure the method of measuring two points still works but I doubt Rollies dad can take credit for that.

Its the distance between your measuring points you want to increase, not the distance out from the chuck. (if you feel you arent close enough already).
Do you have a 0.0001" DTI?
Which end is big now?

Then the real problem.... how close is close enough....

Stuart

I'm not worried about the bed twist; its only about half a bubble on my level which measures to 0.02 mm per metre.

As for how good is good enough, attached is the accuracy standard for a British Colchester lathe of about 30 or 40 yeas ago. These were highly regarded then. Also, I expect the limits set were in accordance with some accuracy standard of the time. Please ignore the scribbles.

Graham

Originally Posted by GDD

got me thinking and mucking about with my AL960. I have got it cutting parrallel but the bed is slightly twisted to achieve this.

Originally Posted by GDD

I'm not worried about the bed twist; its only about half a bubble on my level which measures to 0.02 mm per metre.

How much taper was it cutting that moving it half a bubble fixed it?

Those specs call for +0.0012" max a foot(sort of, not exactly the same thing) . Eskimo has his set up to something around half that(maybe, depending on which end is big.)

Stuart

Eskimo,
I had a look in my test report that came with my lathe and it states that in 300mm from the chuck 0.02mm is the maximum tolerance allowable.

When I made my cylinder squares I could not detect any difference on my 0.001mm mic"s over there length (180mm I think they where) both by measurement or comparing each end by feel with the mic.

How good you get it is up to you, but as you know the closer to zero the better.

I thought of something that may help you guys with fine adjustment.
Get 3 grub screws to replace your original alignment bolts, you will probably have to anneal them depending on how hard they are.
Drill down the centre along their length and tap for metric 3-4mm and put some metric 3-4mm bolts in them that are a bit longer.

This will allow you to screw the grub screws in the original holes, but be able to use the finer M3-4mm thread for adjustment. Once it's adjusted and the headstock is tightened down you can take the metric 3-4mm screws out and firmly tighten the grub screws in the original threads.

Dave

The 3/4 mm set screw done the centre of the grub may be a big ask for most blokes on here to tap without breaking a tap let alone the amount of load that may need to be applied to the headstock to get it to move.
Generally you would only crack the headstock hold downs and apply a reasonable amount of torque to the setting screws.
It may work if the hold downs were loose but I think a lot hard if just cracked if possable at all.

Hi Dave,
There maybe one other problem. With an M8's root dia of 6.466mm an even an M3 doesn't leave a lot of meat in the bolt(found that out the hard way myself . But then I'm the heavy handed git that didn't see it coming). Of course you could swap back to solid bolts once you've finished(assuming you don't move something).

I wonder if leaving the center bolts loose so the headstock isn't seesawing on it would make the screw half an sensitive?

Stuart

You both are probably right, it was just a thought off the top of my head so I thought I would throw it out there.
With the tapping you could clearance drill most of the way and just tap the end 4-5mm, but like Pipeclay said, you would want a bit of torque on the headstock bolts so the M3-4 probably wouldn't move it.

Stuart, I think that would be plenty of meat for the M3, and if they where changed over at the end it should be OK. The M8 would only be there to hold the M3 while adjusting it, it would be like a helicoil.

The factory should have tapped them at least M8 fine for the adjustment.

Dave

Originally Posted by Stustoys

How much taper was it cutting that moving it half a bubble fixed it?

Stuart

It didn't unfold like that. I realigned it with my "two collar tool" then checked the bed twist.

Graham

Originally Posted by GDD

It didn't unfold like that. I realigned it with my "two collar tool" then checked the bed twist.

Graham

Hi Graham,
Seems like you headstock must be pretty close then. The problem I have with RDM is that is assumes either 1. everything else is set up correctly so any error is twist in the bed or 2. there is nothing you can do about the problems that are making the lathe cut with a taper other than twist the bed.

Stuart

If it's only a small amount of twist it shouldn't matter to much, and if it's doing the job accurately and you don't want to play with the headstock alignment I would just leave it.

Dave

Originally Posted by GDD

I'm not worried about the bed twist; its only about half a bubble on my level which measures to 0.02 mm per metre.

As for how good is good enough, attached is the accuracy standard for a British Colchester lathe of about 30 or 40 yeas ago. These were highly regarded then. Also, I expect the limits set were in accordance with some accuracy standard of the time. Please ignore the scribbles.

Graham

Hi Graham,

Those accuracy tests are an eye opener! I dare not post mine up here from my 12x36. how embarrising!.......... Except my headstock alignment thats exceptional!

Simon

Originally Posted by Dave J

Eskimo,
I had a look in my test report that came with my lathe and it states that in 300mm from the chuck 0.02mm is the maximum tolerance allowable.

Thats what it says for the AL960

The near end (chuck end) had the larger dia over the two inches