Possible problem.

[Swarf_Newbie]

Is this a problem? or is it just me?

This is 10mm ground silver steel. Chuck end.


[attachment=16437] then turn chuck 180 deg....
[attachment=16438]

Now move to other end......

[attachment=16439] then turn chuck 180 deg...
[attachment=16440]

So approx .3mm runout, this is pretty much the same with ALL stock used, so it can't be a bent bit of steel, or am I missing summat?
If I zero at tailstock end, I get approx. .3mm run out at chuck?????  

Thanks in advance folks.

Roy.

[unioncreek]

If you get the same results with other stock in the chuck,  I would suspect that maybe the chuck jaws are out of whack.  Thats just a thought hopefully someone else will come along shortly and be able to give you a definite answer.

Bob

[TomG]

If you rotate the chuck with the indicator in the right hand position, what is the total indicator runout?

Tom

[Highpower]

(12-20-2019, 08:28 PM)Swarf_Newbie Wrote: So approx .3mm runout, this is pretty much the same with ALL stock used, so it can't be a bent bit of steel, or am I missing summat?
If I zero at tailstock end, I get approx. .3mm run out at chuck?????  

Thanks in advance folks.

Roy.

Roy, I'm not sure I am understanding your method of checking the run out of your stock. Are you measuring two random points 180° apart? Please clarify. Also you've said you have .3mm run out at the tail stock end. What are you doing with the stock exactly in order to then "zero" it at the tail stock end?

[Vinny]

Have you tried stock with a larger diameter? Could it be flexing?

[Dr Stan]

Just because a piece of material is round does not mean it's straight (cylindrical).  These are two different measurements and have absolutely no relationship to each other.

Put the material on a granite or other flat surface and check to see if you can get your thinnest feeler gage under either the ends or the middle of the stock.  You could also set up a surface gage with a test indicator  to check for cylindricity. https://www.gdandtbasics.com/cylindricity

One can also simply roll the material on the surface plate to see if you can feel it "flopping".

[Swarf_Newbie]

(12-20-2019, 09:30 PM)TomG Wrote: If you rotate the chuck with the indicator in the right hand position, what is the total indicator runout?

Tom

Approx .3mm TomG.

Roy.

[Swarf_Newbie]

(12-20-2019, 10:07 PM)Highpower Wrote:

(12-20-2019, 08:28 PM)Swarf_Newbie Wrote: So approx .3mm runout, this is pretty much the same with ALL stock used, so it can't be a bent bit of steel, or am I missing summat?
If I zero at tailstock end, I get approx. .3mm run out at chuck?????  

Thanks in advance folks.

Roy.

Roy, I'm not sure I am understanding your method of checking the run out of your stock. Are you measuring two random points 180° apart? Please clarify. Also you've said you have .3mm run out at the tail stock end. What are you doing with the stock exactly in order to then "zero" it at the tail stock end?  

Zero stock in chuck, rotate 360 deg, still zero yes! (I thought it was easier to just show two points 180 deg apart)

Move carriage to end of stock, zero should(technically be zero yes?) rotate through 360 deg, I now have .3mm runout.
(I have problems explaining exactly what I mean, cos I'm still a newbie!! sorry  )

If I then adjust  zero at end of stock, I then have .3mm of runout at chuck.
Does that make more sense?
 Now I would not think that 10mm silver steel 300mm long would flex that much under the pressure of a dti? but I could be wrong!   
Go easy on me guys............learning way to much to keep in my old brain at the same time!   

Oh, and a Merry Xmas and a Happy New Year to all on here!

Cheers.

Roy.

[Dr Stan]

(12-21-2019, 07:18 PM)Swarf_Newbie Wrote:  Now I would not think that 10mm silver steel 300mm long would flex that much under the pressure of a dti? but I could be wrong!   

Go back & read my previous post.

[Highpower]

(12-21-2019, 07:18 PM)Swarf_Newbie Wrote:  Now I would not think that 10mm silver steel 300mm long would flex that much under the pressure of a dti? but I could be wrong!   

Cheers.

Roy.

Actually a small diameter bar of that length will flex quite a bit under it's own weight when held at one end. What I was trying to ask is how are you adjusting the far end to have zero run out? Are you smacking the tail end of the bar to move it, or are you moving the chuck jaws to do it?

Stan suggested checking your stock for straightness which is a good place to start. Just because a piece of stock is ground at a factory doesn't necessarily mean it will still be perfectly round and perfectly straight by the time it gets to your door.

You might try drilling a 60° center into one end of your stock (up close to the chuck jaws). Then put the stock back in the lathe the way you have it now, but support the far end with a center in your tail stock. Zero the run out at the chuck end, and then check the run out at several places along the bar and see what you get.