How to test TIR when you don't have a gauge pin?

[koenbro]

I wanted to test my lathe's TIR but don't have a precision ground rod or test pin. I guess can use a broken .25" endmill but the ones I have don't seem long enough. Is it legitimate to turn a regular piece of steel then measure the runout?

Here is a 20-second video of what I tried today but don't know if its methodology is acceptable.

 

[mmcmdl]

Dowel pin will work .

You can throw your chuck off 1/4" and cut a bar . The cut will always run true . That method tells you nothing .

 

[RJSakowski]

Wrist pins from a small engine make a good test pin. I collect them from old engines and have pins from 7/16" to 1.25" diameter.

Turning a pin could work providing you cut off the section that was in the chuck and remount the pin in the chuck. You should check for variations in diameter with a micrometer, You would also want a smooth finish to prevent the test indicator from jumping.

 

[koenbro]

So I need to remove the piece and re-chuck it? Will try that tomorrow. I felt smth is fishy with my "method" as the result was too good to be true.

 

[mmcmdl]

Put a dowel or something round in the collet holder and put your indicator on it . No need to turn something .

 

[koenbro]

Is there a place I can buy a reference pin or dowel? I looked at McMaster and wonder if this 1/2" in dia dowel pin would be good?

 

[mmcmdl]

You could use a drill , broken end mill , anything round . Indicate close to the collet . Any error will be multiplied the farther away from the spindle you move .

 

[durableoreo]

Dowel pins are not always round, especially when tenths are concerned. I recommend a gage pin instead 23055A99. It's 2x the price but probably the same shipping.

 

[koenbro]

I found an old, broken (crashed) Tormach threadmill with a 0.5" shaft, so I repeated the experiment, and it is, sadly, more believable. Interestingly the runout is lower on the thinner neck even though it's farther from the chuck.

 

[mmcmdl]

I found an old, broken (crashed) Tormach threadmill with a 0.5" shaft, so I repeated the experiment, and it is, sadly, more believable. Interestingly the runout is lower on the thinner neck even though it's farther from the chuck.

Move your indicator towards the collet and take a reading .

Interestingly the runout is lower on the thinner neck even though it's farther from the chuck.

How do you know this diameter is concentric with the shank ?