Mini lathe test bar question

[R.burgy]

Hello folks
I wanted to check my lathe setup. So i made a test bar. Faced and center drilled a 5/8 steel bar. Set it up between centers. Turned on with a dial indicator and i had 10 thousandths deflection. I have a short video coming. My question is... I need a test bar to check to see if my tail stock is centered. How can I accurately center drill my test bar if my tail stock is off? When i set bar up in 4 jaw, i had a little deflection. Under 1 thou.
So my problem has to be with tail stock right? How can i center it without bar?
Thank youhttps://youtu.be/pg8lwKtegjM

[Richard P Wilson]

OK, so you set it up in the 4 jaw to just under 1 thou, and centre drilled it. Even if your tailstock is a little off, the centre drilling will be concentric within 1 thou. Check this with the clock at the extreme ends, and do your clock a big favour, just pull the machine round by hand, don't do it under power. Assuming both ends run true, what you need to check is along the front face of the bar, does the clock read the same at the headstock end as the tailstock end. All you are interested in is the extreme ends, don't worry about the middle. If you just used stock bar, chances are its bent, which is why its showing runout in the middle.

The old way of checking tailstock alignment without a bar was to fit a centre into the headstock, and another in the tailstock. Run them up until nearly touching, then slip a piece of shim stock, or an old fashioned razor blade between the 2, and tighten up. If the shim twists, then things are not lined up. Adjust until they are.

[boslab]

Stick a bar between centres, turn a short diameter at the chuck end, zero your dial, move to the tailstock end, turn it down to the zero on your dial, measure the two diameters, should be the same, if they aren't the tailstock needs a nudge, bout half the difference in diameters should do, rough and ready but effective.
Mark

[Ed ke6bnl]

I read of a guy that took a solid rod maybe 1.5in and center drilled the end and then parted it off he brings the two pieces together and can feel if they are off with his finger tip to cent the two pieces.

[R.burgy]

Thank you guys. Anytime things dont go right i assume it is something i did.
I didn't even think of the bar being bent. I am going to do one or both of these
Suggestions and get back.
Much appreciation

[RWO]

To make a center hole on dead center, bore it. Drill a pilot hole in your centered bar with the tail stock chuck about 1/2" deep and about 1/4" dia. It's not critical. Make up a small boring bar and bore the center hole at a 60 deg included angle using the compound. Make the bored land about 1/8 " wide. It will be on center if the bar is centered in the chuck.

RWO

[philbur]

Hello folks
I wanted to check my lathe setup. So i made a test bar. Faced and center drilled a 5/8 steel bar. Set it up between centers. Turned on with a dial indicator and i had 10 thousandths deflection. I have a short video coming. My question is... I need a test bar to check to see if my tail stock is centered. How can I accurately center drill my test bar if my tail stock is off? When i set bar up in 4 jaw, i had a little deflection. Under 1 thou.
So my problem has to be with tail stock right? How can i center it without bar?
Thank youhttps://youtu.be/pg8lwKtegjM

How did you ensure/check that the test bar was straight and not bent.

A center drill cuts on the side as well as the tip, like an end-mill, so it will cut a hole that is concentric with the lathe spindle axis even if the tailstock axis is not (providing the TS is concentric within a few thou.). Use a big one to take advantage of it's rigidity.

Best way to check is turn a diameter at each end with the same cross slide setting and measure/compare the diameters using a micrometer. This will tell you if the tailstock is off, but not why it is off.

Phil

[RichR]

I read of a guy that took a solid rod maybe 1.5in and center drilled the end and then parted it off he brings the two pieces together and can feel if they are off with his finger tip to cent the two pieces.

Don't you also need to take a skim cut to make sure it runs concentric with the chuck prior to parting it off?