How accurate does it need to be

[Stuart]

Quick question for you all

I have a job to do that will be turned between centres

I have been checking the TS alinement using the cut a test bar method  ( mount the bar take a fine cut along its length test with mic. adjust TS and go back to start ad infinitum )


I have it down to 3 tenths (inches) in a foot , but now the TS adjustment is getting very touchy e.g. just barely move the screws and as we all know nothing in this world is stable leave it a hour and the reading will change by 1 tenth  .

The question is do I spend another day at this or am I near enough ?

note the bed was levelled with a bar in the chuck ( no TS support ) and the bed adjusted to turn parallel ( same method as above cut and test ) I have this down to 1 tenth in 6 inches before I commenced the TS set up


Stuart

[steamer]

Hey Stuart,

Leave it be.   The thermal errors are playing into the machine now....and your near enough in my book.....if it was a precision grinder...I'd say work on it some more....but it's a lathe and that's VERY good for a lathe.

Dave

[b.lindsey]

Stuart, I would call it a day and move on. Not sure what kind of lathe you have but unless it is very rigid and in a temp./humidity controlled environment, .0003"/ft isn't bad and  probably better than most of us work with. 

Bill

[tel]

It's more than good enough for anything I, and a lot of us, would be doing. Leave it be.

[Stuart]

Thanks Lads

I thought I had got to the point of chasing my tail


for info  its a Myford ML7 connoisseur made about a year before they sold up ( the factory was only five miles from here so pretty local

 its a reasonable lathe for its size but its not a very stiff lathe by Monarchs standard  , but it does what I ask of it


Stuart

[Arbalest]

Sounds like you're good to go Stuart but this may be worth adding to your arsenal for future reference:

http://www.neme-s.org/Rollie's_Dad's_Method.pdf

[Stuart]

thanks for the tip it would save a lot of machining steel down the those springy things .

I have tried that method in the past but it does not seem to suit my mind set , may be I am a stick in the mud but I have used the method that suits me for about 40 years with various lathes.


the reason for the question is that I need to turn some bits for a grinder  spindle to the best that I can do so as John ( Bogs ) always says clean down lubricate and adjust your mill Lathe before you start some important work

Not my luck day just had a delivery of the small angular bearing I ordered 3 as they were not expensive ( one for test fitting ) guess what look at the first package ( still heat sealed in its pouch ) , that bearing looks funny , there is a ball missing from one race , they are replacing it no problems at all

just need to order up lots of steel EN1a and EN8 and get making chips , the loco is on hold as I need to make up some special cutter hence the grinder project


Stuart

thanks again for the info

[Tin Falcon]

usually there is no need to chase tenths in the home shop. I worked in a precision grinding shop . slight temerture changes woulld throw things off.  it only takes .00005 inches of movement to affect diameter one ten thousandth.
Precision is expensive it takes a lot of time and care. and it is not always a good value for time and money spent.
Tin