Thread: runout test

forgot the pics

Hi Mike,
We where only just talking about this the other day, I think it is in Bryan's lathe thread.

Dave

Not sure was the dial touching.
Put a centre in the headstock and tailstock,bring then together with a thin piece of metal between the points,check if the material is visually vertical,then place material in the horizontal and visually check,dont apply too much pressure to the material,a nice 6" rule would be a good choice of material to start with,around .030".

Yes the dial is touching .... I will try a steel rule with pipeclays suggestion , see if it wobbles out of alignment in either plane . I've also read somewhere ,you can use a razorblade for the same purpose .Mike

Use anything which is thin but will not bend under its own weight.
If its to thick it wont give you a true indication.

Hi Mike,

Not entirely convinced your test is valid.

You will always get zero run out with a 4 jaw... (provided you adjusted it for zero run-out of course)

Then if you bring that up to the tailstock, you will always get zero runout close to the tailstock. Provided that the tailstock is somewhere near coaxial with the spindle center, and the material can flex (even slightly)

Try pipeclay's test with a thin sheet of metal to see how close your centers are to being aligned.

Check if the bar is flexing by measuring run out somewhere in the middle, measure sideways horizontal, rather than vertical, as it will probably be flexing down under it's own weight a little... A bigger diameter test bar would be nice..

Regards
Ray

MM as I see that test doesn't show alignment of either spindle. If you moved the tail stock over 1/8" it would just bend the bar and would still indicate running true.
If you had the indictor on the carriage, and moved the carriage from one and to the other, that would tell you something.

Stuart

Hi Stuart,

That's a record, crossposted twice in two days, saying the same thing again, we must be in sync or something, your not psychic are you?

Regards
Ray

Stop that Ray! lol

Originally Posted by RayG

your not psychic are you?

Well I must be. You can't be or you would know if I was or not

Originally Posted by Stustoys

MM as I see that test doesn't show alignment of either spindle. If you moved the tail stock over 1/8" it would just bend the bar and would still indicate running true.
If you had the indictor on the carriage, and moved the carriage from one and to the other, that would tell you something.

Stuart

Ok I will try that

Right, just did Stuarts test ..yep there was a definate deflection as I ran the carriage up the test bar ..getting worse towards the tailstock... 7 thou going on to 10 as it neared the end . Thankfully the tailstock has a adjustment there to compensate . I moved it over and its much better now ..about .001 . The tailstock quill is worn and it wobbles about 4 thou side to side ..so I'm guessing to some degree . Also the bar is thin but its the best Ive got right now .thanks

Originally Posted by Stustoys

Stop that Ray! lol

Well I must be. You can't be or you would know if I was or not

Some people think I'm psycho... but, both times I've beat you by a few seconds, so that means you must be the one with the psychic abilities, either that or I type faster...

Sorry Mike for the slight off-topic diversion, the short version is that Stuart and I are both sceptical of the metrological basis for the method you are using..

Regards
Ray

Originally Posted by RayG

Sorry Mike for the slight off-topic diversion, the short version is that Stuart and I are both sceptical of the metrological basis for the method you are using..

Regards
Ray

No problem ..... it's actually amazing that this old machine is still as accurate as it is . It must have been through years of ham fisted abuse by children. There are still kids names scratched into the paintwork ... 10 out of 10 to the Sheraton company .

Mike, one problem with traversing the indicator along the bar as you have is that if there is any height error in the tailstock (likely) it will throw your reading out. The skinnier your bar, the more error you'll get.

Mike have you checked to see how it cuts.
Normally after leveling the base,i machine a piece of 1", to 1 1/4" bar around 6" long set in 4 jaw,check size.
I then centre drill the same piece,set in 3 jaw,machine and check size.
I then try a smilar cut on a the length between centres check sizes.
Then I concern my self with adjustments.