re-threading

[seawolf217]

so we were working on some parts with an internal thread that had to be .900 deep. We made five parts before we realized that the thread was only .75 deep. Is there a way we can put this back on the machine or is it going to mess up the thread that is already there. The ID is 4.5" so we're using a threading tool. Do they make taps that large? Any suggestions would be greatly appreciated. Thanks.

[Tim Simmermon]

I wouldn't try it on a CNC, it won't pick it up. We chase the threads in a manual lathe if we ever need to do something like that.

[seawolf217]

alright, that's what i figured. Any advice or tips on chasing the thread on a manual machine?

[FP1]

I have successfully picked up an OD thread on a cnc lathe after re-chucking a few times. It was tedious and time consuming. Basically I would mash some modeling clay into the threads, set the RPM to very slow, set the angle of infeed to 0 degrees, offset the tool up higher than the thread depth per side, and then single block thru a few passes. Then stop the machine to see if the new thread was in the middle of the clay. If it wasn't centered I would offset the Z-axis and try again. As it got closer to center I would then set the X offset to go a little deeper. Just keep tweaking the Z and X offsets a little at a time.

[TK-32™]

quote:

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We chase the threads in a manual lathe if we ever need to do something like that.

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X2

[gcode]

quote:

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Any adice or tips on chasing the thread on a manual machine?

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Set the compound parrallel to the Z axis.

Set the gears for the correct TPI

Start a threading pass with the tool clear of the work, stop the machine with the threading gear engaged.

Use the compound dial and X dial to adjust the cutting tool into the existing thread and zero out the X dial.

Now the X and Z axis are aligned with the existing thread and you can finish the thread using regular single point threading techniques.