Thread: Tailstock Alignment Using Test Bar- A Youtube Clip

Hi BT,
Looks pretty good. I think the only thing I would do differently is not have such a long turned length, so you know you are indicating on the same diameter.

I've done the same sort of thing with a 3 jaw. Face, turn and turn a center on a bar close to the chuck then slide the bar out to the center. You only get one shot at it though.

Not sure why he is worried about not being low with the tailstock?

Stuart

Stu, I'll have a crack at this over the weekend. Probably result in something I don't want to know.

Originally Posted by Anorak Bob

Stu, I'll have a crack at this over the weekend. Probably result in something I don't want to know.

Yes, sometimes ignorance is BLISS! It certainly is with Chinese stuff!
Besides, it's only bad if you find something you can't fix which is unlikely with you!

Simon

Good video for tailstock alignment, but he is only measuring at one point.

I would like to see him wind the carriage the full length of a uniform test bar (which is why they cost a lot more) and check the reading to see how much variation/wear is in the bed.

Good video though.

Rob

Hi

I watched that at the Library.

Would his method still be valid if the bed was worn e.g., the ways not 100% as new .

I was thinking if the bed ways are worn at the headstock end, that would give you false readings of the DTI

Mike

Originally Posted by morrisman

Hi

I was thinking if the bed ways are worn at the headstock end, that would give you false readings of the DTI

Mike

Exactly my point.

That's not to say it isn't a good method, it's just that if the bed is worn you should take several readings along it and average them out.

If the tailstock was worn by 5 thou, and that doesn't move any where near as much as the carriage, how much is the bed worn ?

I just turn up bit of round stock and use a test indicator to check it full length on both planes.

Works OK.

Rob

Originally Posted by nearnexus

I just turn up bit of round stock and use a test indicator to check it full length on both planes.

If you can turn a bit of round stock parrallel..... its unlikely you have a problem.

If you have a test bar, sure use it
The thing with this idea is that its a quick check that can be used at what ever length you like. How many test bars do you have?
Don't stress to much about vertical.

Stuart

Originally Posted by Stustoys

If you can turn a bit of round stock parrallel..... its unlikely you have a problem.

Don't stress to much about vertical.

Stuart

Vertical can be just as bad as horizontal.

As you rise or fall from centre point of the curvature of the work piece , so the cutter depth varies (ie. effectively the cutting depth becomes less).

Vertical is an issue.

Rob

Originally Posted by nearnexus

Vertical can be just as bad as horizontal.

As you rise or fall from centre point of the curvature of the work piece , so the cutter depth varies (ie. effectively the cutting depth becomes less).

Vertical is an issue.

Rob

Hi Rob,
I'm not sure it would be just as bad. The amount of movement in the vertical relative to the tool would be nothing like the movement in the horizontal relative to the tool.
Of course I could be wrong...again.

Phil

I agree.

I never said it would be as bad, given it's probably a non linear effect from the curvature of the job - ie gets worse as you move away from centre.

But you can't write it off as a non issue.

It would be enough to make you pull your hair out trying to get rid of taper in your job if it was present.

Rob

Originally Posted by nearnexus

Vertical can be just as bad as horizontal.

As you rise or fall from centre point of the curvature of the work piece , so the cutter depth varies (ie. effectively the cutting depth becomes less).

Vertical is an issue.

Rob

A vertical error is nothing like a horizontal error.

While a horizontal error of 0.1mm* gives you an error of 0.2mm on Dia, even on a diameter as small as 2mm a vertical error of 0.1mm gives you an error of 0.01mm on Dia.

On 10mm dia its 0.2mm v 0.002mm
on 50mm dia its 0.2mm v 0.0004mm

*which is pretty huge, If you halve the error to 0.05mm the numbers on 10mm Dia come out at 0.1mm v .0005mm.

Stuart

I'll agree with you there Phil, I worked it out whilst contemplating the LeBlonds worn ways.
By my math if you are turning a 1" bar and you have a .010" dip in the ways your bar will be 1.0002" at the dip. And the bigger you go the less the effect is. at 1/2" its about .4 thou, at 4" it more like .05 thou.

I have not watched all the vid yet but will when i get a spare 20 min....

Originally Posted by Stustoys

A vertical error is nothing like a horizontal error.

While a horizontal error of 0.1mm* gives you an error of 0.2mm on Dia, even on a diameter as small as 2mm a vertical error of 0.1mm gives you an error of 0.01mm on Dia.

On 10mm dia its 0.2mm v 0.002mm
on 50mm dia its 0.2mm v 0.0004mm

*which is pretty huge, If you halve the error to 0.05mm the numbers on 10mm Dia come out at 0.1mm v .0005mm.

Stuart

Agreed

Rob

Originally Posted by nearnexus

It would be enough to make you pull your hair out trying to get rid of taper in your job if it was present.

You just tweak the tailstock a micron or so and you're sorted.....

I'm not 100% sure about this.. I think there maybe a curve involved somewhere but I'd say its down in the area that only Ray has the gear to measure.

Beings up something else I want to test one day. How much the vertical height of the tailstock changes(if at all) with different clamping forces. I've seen lathes with provision to use a torque wrench for tightening. If it does in fact make much difference, being that my lathe has a flat and a vee way, one would assume one would move more than the other which would give you a horizontal error not just a vertical one............... although its possible I'm thinking a little to much about things that are likely down in the area of Ray.

Stuart