Quick ? about 5c collet on lathe

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Is a collet 'true'?
What I mean is if i put a bar in my 3 jaw and turn it to say .750", and then remove it. If I were to remove the 3 jaw and in it's place install the 5c collet and holder, If if put the turned part of the bar in the collet and turn the extension to the same .750", Is the bar true on both ends?

What about using the collet to hold a bar and drilling with the tailstock. Can I do a deep drill on center and expect it to be true to the outer edge?
 
It should be close but maybe not perfect . If you leave the part a couple thou oversize , just turn it between centers afterwards . Drilling may start true but may wonder off depending on the depth . Once again , drill it thru and turn between centers .
 
My Take:

The answer to your first question depends more on your 3-jaw chuck and collet chuck/collet quality/centering than anything else.

The first circular feature that you cut will be true to its own axis, but is not guaranteed to be true to the rest of the bar.
If the chuck holds the bar offset from centre by 50 thou. then your newly turned feature would be off from the rest of the bar by the same amount.

Then when you move that to a hopefully more concentric collet and turn the other end you should end up with something very close to true.

However if your chuck adds a little angular offset things get even more complex..... that section that is turned first could have an axis that is at an angle to the axis of the bar.

I guess as long as you start with a big enough diameter bar that you can take off any offset or angular skew induced by the chuck it should work.

Of course the collet chuck and collet will have their own run-out, hopefully in the tenths of thou. but it is not zero.

You could check with a precision ground bar or even the shank of an end mill.
Hold it in a collect and measure the TIR on the shank with an indicator. Mark the alignment of chuck, collet and shank.
Release the shank and rotate one of the elements and then measure again.
It is likely that the TIR and location of the high/low spots move as the system has changed.

As for the second part; drilling is never a precise operation. Drill bits wander due to uneven grinds, material soft/hard spots, etc.
Precision requires boring.

Brian
 
brino said:
The answer to your first question depends more on your 3-jaw chuck and collet chuck/collet quality/centering than anything else.

The first circular feature that you cut will be true to its own axis, but is not guaranteed to be true to the rest of the bar.
If the chuck holds the bar offset from centre by 50 thou. then your newly turned feature would be off from the rest of the bar by the same amount.

Then when you move that to a hopefully more concentric collet and turn the other end you should end up with something very close to true.

However if your chuck adds a little angular offset things get even more complex..... that section that is turned first could have an axis that is at an angle to the axis of the bar.

I guess as long as you start with a big enough diameter bar that you can take off any offset or angular skew induced by the chuck it should work.

Of course the collet chuck and collet will have their own run-out, hopefully in the tenths of thou. but it is not zero.

You could check with a precision ground bar or even the shank of an end mill.
Hold it in a collect and measure the TIR on the shank with an indicator. Mark the alignment of chuck, collet and shank.
Release the shank and rotate one of the elements and then measure again.
It is likely that the TIR and location of the high/low spots move as the system has changed.

As for the second part; drilling is never a precise operation. Drill bits wander due to uneven grinds, material soft/hard spots, etc.
Precision requires boring.
Click to expand...
He said " Quick " ! :grin: But a great explanation Brian . :encourage:
 
Everything has tolerances (some of us less than others). Put a .0001" DTI on your set-up and answer your own question.

Regarding "deep drill" (no mention of material, diameter or depth dimensions?), it depends much more on the cutting tool(s) and operator technique than the lathe.

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If you can fit a boring bar into the hole then drill with a smaller drill and single point the hole...
 
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