Thread: Cylindrical Square

That's fair enough. He did mention the need to do very light cuts and make sure the diameter of the work was large enough so as to reduce deflection and to limit the length out of the chuck.

OK so now I have to re-adjust to my way of thinking since most of my theory has come from books like his?

Simon

Hi RC,
I was plainning on getting the tailstock alignment closer, not further away. But its going to have to wait until I get the chance to make up a toolholder try out an idea I have.




I'm not a big fan of twisting the bed for alignment, you have to assume to many things(of course thats not the same as saying I wouldnt do it ).

I'd also thought climate controlled clean rooms werent needed either unless you wanted to make absolute measurements. I've since changed my mind because of something I call "thermal lag"(which maybe a real term I dont really know). Your cylinder square is going to move with temp much faster than your granite plate.(of course how much difference that will ever make to me I'll likely never find out)

Off to make a new toolholder.

Stuart

It is interesting reading my old lathe book again here.... The first job ticket in the book is grinding the centre and making sure if it is removed to have it marked so it goes back int he same spot...

Then the second job is aligning the tailstock and it says...

Work which is carried between centres and which must be straight , requires the headstock centre and tailstock centres be exactly in line...

We now know that this is not true and only the tailstock needs to be aligned to the spindle axis..

But anyway moving along..... Adjusting the tailstock to get that perfect cylinder made (which is something unattainable anyway, the perfect cylinder that is) means tweaking the tailstock...

Not sure how other people do it, but I take the cut, then put an indicator on the work, and move the tailstock over an amount... You can get it pretty close using this method but it can be fraught with pitfalls...

Firstly, my second lathe I ever owned an AL1000C, the tailstock would shift alignment between clamped and unclamped as it was not manufactured properly.. I always unclamp before adjusting the tailstock over, then reclamp it... Just something to be aware of is your tailstock does not move between clamped and unclamped...

The other thing is when measuring the workpiece to work out the taper, put the indicator on the same spot where you measured it.. And even then you probably will not get it right, unless you hold your mouth right... Microns seem to be rather small things...

Originally Posted by .RC.

It is interesting reading my old lathe book again here.... The first job ticket in the book is grinding the centre and making sure if it is removed to have it marked so it goes back int he same spot...

Then the second job is aligning the tailstock and it says...

Work which is carried between centres and which must be straight , requires the headstock centre and tailstock centres be exactly in line...

We now know that this is not true and only the tailstock needs to be aligned to the spindle axis..

Hi Richard
If a centre is ground in the headstock spindle it will be true to the spindle axis. Then you only need to align the tailstock centre to the headstock centre or is my head sitting somewhere near planet idiot

Phil

Yes, that is true, but the statement in the book is wrong in that it automatically assumes the headstock centre is ground in place..

I have learnt not to assume anything and measure first...

Originally Posted by .RC.

Not sure how other people do it, but I take the cut, then put an indicator on the work, and move the tailstock over an amount

I've only tried to get the tail stock on my lathe dead on twice(or as near to it as makes no difference, which is a number that changes all the time). I used the indicator on the side of the tail stock indicating on the base. It didn't seem to go to well so I'll try it your way this time.

Originally Posted by Steamwhisperer

If a centre is ground in the headstock spindle it will be true to the spindle axis. Then you only need to align the tailstock centre to the headstock centre or is my head sitting somewhere near planet idiot

Only if the center is returned in the same angular position it was ground in as the spindle bore wont be perfect.(assuming you want to be able to replace the workpiece between centers at a future date.)
If we want to get picky about wording you might say you aren't aligning the head and tail stock spindle centers. Assuming the spec sheet on my lathe is correct(a fairly large assumption) and that the tailstock spindle is 0.06mm high, on 40mm bar the tailstock spindle would need to be forward by 0.0000899997975mm to turn parallel. Although, I'd think I'd be tempted to call that aligned anyway.

Stuart

I would call that aligned as well Stuart as that figure is equal to about 1/3 of what we now call 'The Marco finger dip' method of measurement. lol

Phil

Oh yes and I just remembered you have to adjust the tailstock over half the taper error...

Richard I think the book is correct in what it's saying, as from what you've written it says to first grind the centre. The centre is now the spindle axis. Then it says to align the centres, that's in effect saying align the tailstock to the spindle axis.

There are other ways to approximately align a tailstock if it's been offset, but popping in centres and aligning them is certainly one way that works and is quite quick.

Pete

Hi All,

Here's a basic question about using DTI's

Most of the DTI's I have are spherical tips, I've only got one that has a flat tip. I understand that for gaging round objects you should use a flat tip, and for flat objects use a spherical tip..

Here's my question, do you change to a flat tip when using a DTI on the lathe?

Regards
Ray

PS... it was Bryan's patent pending device that made me think of it...

Hi Ray,
Short answer "No"(though I do have a cheap set off extra points in the "one day they will come in handy" draw)

I recommend people stop reading now and move on the the next post lol

Long answer.
DTI's? or dial gauges? I know you can get longer tips(?) for DTI's, I don't recall seeing a flat one. Is it truely flat? I'm pretty sure the ones in my kit have a large radius on them.
Assuming we are talking about what I call dial gauges and that we aren't talking about very small dia work, if you fitted a flat tip to measure a round face that might be moving in more than one plane, wouldn't you have to be very careful to make sure the tip was square in two planes and to the DTI's spindle? I haven't done the math on that but I think I can see how you could get a reverse reading.(but I think there would be a lot of 0's involved)

Using what I was talking about in my last post and Bryans tailstock as an example. If you are measuring the quill of your tail stock and you start dead on center height, then moved the DTI along the ways 100mm and the quill is perfectly parallel to the ways front to back but 0.06mm down vertically over 100mm. My math says the movement of your DTI will be 0.0000899997975mm. That's assuming the DTI is a perfect point, I have a suspicion but cant prove that having a ball on the end would lessen that error.(but how many 0's do we want?)

I'm not 100% sold on "Bryan's patent pending device" unless truely flat and kept square to the DTI spindle it might make things worse(again no math just some drawings. errors WBFDT* unless the angle was way out)

Stuart

*well below finger dip threshold