Shaft bending while threading

M

Maplehead

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I am making small and unique brass screws from 1/4" rod. I am lathing down to .112" for a 4-40 thread at one end. Threading a length of 1". I start the process with my die held in place by the tail stock. As I turn the die I turn the tail stock to keep it against the die. After the die is good and started I release the tailstock and freehand turn the rest. The end result is a nice thread but the shaft is slightly bent.
Could this be caused by the angle of attack from the die threads?
 
Hi Maplehead.
I do this quite frequently making stuff to repair old clocks. I find it much easier all around if I go to the minimum diameter around 0.106". Unless you really need full contact threads I find this much easier cutting the threads and provides adequate strength for what I am doing.

Like you I hold the die in a die stock and with a stump in the tailstock to keep the die aligned with the work piece. I also start with minimal material sticking out from the chuck, taking more material out as the threading progresses.

David
 
Hi David

Thanks for the reply.
Have you had end results of bent shafts?
If so, what do you figure is causing it?
 
Yes I have, and or the shaft slipping in the chuck since I felt that Ø0.112" was just too large for the 4-40 die that I had. It was taking what I felt was excessive torque. I actually sheared the shaft off on one attempt. So now I go to the minimum diameter for 4-40 and everything is much easier.

David
 
I have no problems cutting the threads with the rod at .112" in diameter. The die cuts what looks like to be really clean and even threads. My problem now is that more times than not the threaded portion of the rod is curved or bent after the threading. Before threading it was straight.
 
I agree with David. In small diameter stock the most common reason for bend in a threaded rod is excessive torque due to too large a stock diameter. It doesn't take much to twist a rod less than 1/8" OD.
 
I guess I misunderstood the smaller diameter explanation yesterday.
Tonight I will try turning down smaller than .112" before applying the 4-40 die.
 
Are you using a split die? Open the die up with the jacking screw and thread it. Then close the die down to finish the thread.

Cheers Phil
 
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