Thread: my new AL960 cutting a taper

Originally Posted by GDD

That's a pity. My AL960B cut a worse taper than yours and 100% of the problem was bed twist. Using a variation of "Rollie's dad's method", I got the twist out of the bed and the lathe cut parrallel. I think the problem now will be getting the headstock back to where it was after precision alignment at the factory. I'm sure there is a way to do this but I don't know what it is.

Graham

I agree with Graham .
Sounds to me like your problem is bed twist .
Rollies Dads method is a good procedure.
I wouldn't gin about with head stock alignment until it's the last resort.
I would accept .001" over 8"-10", not over the distance you turned the bar

Kev.

Hi eskimo,
I think I've asked you this before but I've forgotten.
What sort of level do you have?
Just be sure you have any twist out of the bed before you start resetting the headstock.

Stuart

How is the finish on the piece that you turned? Is it good quality? Have you tested to see how much the spindle or chuck will move when you apply upward or downward force?

Perhaps the preload on the spindle bearings were not set properly from factory?

Simon

Originally Posted by .RC.

could be deflection of the workpiece making the taper.

Wouldn't deflection make the tailstock end bigger? Because it would push away from the tool and reduce DOC?

Originally Posted by eskimo

It cuts a 0.001" taper from the tailstock (smallest dia) to headstock (largest dia) over 2 inches.

I am pretty sure he has 2 or 3 high precision levels, so he is on the level as far as that goes,

Dave

Originally Posted by Stustoys

Hi eskimo,
I think I've asked you this before but I've forgotten.
What sort of level do you have?
Just be sure you have any twist out of the bed before you start resetting the headstock.

Stuart

Originally Posted by pipeclay

It would appear if the lathe had been precision aligned that they must of forgot to precision tighten the screws.

These screws dont have to be tight. They don't hold anything. Also I would be surprised if they are used in the alignment process at the factory (for reasons below).

Its not a big drama setting the head it just takes a little time,.001" taper is not much over that short distance to chase.

I can't say as I haven't done it, but the maths suggest to me that it might not be easy. I just checked my lathe and the three adjustment screws are about 90 mm apart. ie 180 mm between front and back with the middle one in the middle. Let's assume the headstock will pivot on the middle screw. Its about 300 mm from the centre screw to the front of the 4 jaw, so any movement of the front adjustment screw will give about three times that movement at the front of the chuck. If the taper is .02 mm, (about a thou) adjustment required is half that or .01mm. This is at the job, so movement at the front adjusting screw will be one third that or .003 mm. Those screws look to me to be M8 which means pitch of 1.25 mm, so the turn on the front adjustment screw required to get the adjustment needed is 1.25 divided by .003 which is 1 over 416 of a turn or 0.8 of a degree.

It might be easy for you, but I don't think I'll try it.

Graham

Hi Graham ,
I think you forgot that both ends of the job will move. You need to move the far end .01mm further than the near end. So if my math is correct and the job is 50 long if the far end moves 0.01mm the near end will move 0.01/7*6=0.0086mm. So you'll need to move the far end 0.071mm........

Who wants to check my math?

Stuart

Originally Posted by Stustoys

Hi Graham ,

Who wants to check my math?

Stuart

Mmmmm.... too hard for me. I realise my "analysis" is grossly simplified but I just wanted to make the point that we are talking about very fine adjustments and a very coarse adjustment mechanism.

If there is a photo attached, it is my bed alignment tooling.

Graham

One of the reason why you would use the longest piece of material you can to get the greatest taper you can for ease of checking.
Not sure of any calcs involved,just using an indicator and time.

Originally Posted by Bryan

Wouldn't deflection make the tailstock end bigger? Because it would push away from the tool and reduce DOC?

That would be true in the northern hemisphere not the southern hemisphere

Originally Posted by Dave J

I am pretty sure he has 2 or 3 high precision levels, so he is on the level as far as that goes,

Dave

I've only got TWO Dave!...the cdco and CTC ones

and I used the same one for both ends....

is it just me or is this WWF server experiencing some problems just of late..yesterday and now?

Originally Posted by .RC.

That would be true in the northern hemisphere not the southern hemisphere

Of course. Silly me.

now I know why I won it in a raffle...its a dud

Originally Posted by simonl

How is the finish on the piece that you turned? Is it good quality? Have you tested to see how much the spindle or chuck will move when you apply upward or downward force?

Perhaps the preload on the spindle bearings were not set properly from factory?

Simon

Oops. If the diameter of the taper is larger at the headstock end then I guess it can't be bearings or preload huh?

Simon