1940ís 9A Threading Stop Hole Depth
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  1. #1
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    Default 1940ís 9A Threading Stop Hole Depth

    Iíve been restoring a 9A for the past couple of months. Everything has been going pretty well so far, but Iíve had to deal with an issue of removing a broken tap from the blind hole in the cross slide used to attach the threading stop. It came that way when I bought it, and a previous owner had even drilled and tapped another hole next to it (which I will fill in before painting).

    To remove the tap, I started with a carbide burr in a die grinder. That got a little hard to control though, so I moved to my radial arm drill press and used an angle plate to position the cross slide under the chuck. I then pecked away at the tap with much better success. I believe I removed all of the tap, but I would like to confirm the depth of the hole. As it is right now, the hole is ~7/8Ē deep. Does anyone out there know if this is how deep they came from the factory?

    I would also like to confirm that the thread should be 5/16-18. Most of the threads were removed during the grinding, so I plan to install a helicoil this week once I know the correct thread type.

    Thanks, I appreciate the help!
    -Keith




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  2. #2
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    I have a 10K that uses a similar cross slide stop. The hole for the threading stop is 1/4-20 and probably not more than 5/8' deep. If you really need an accurate depth, I can measure mine.

  3. #3
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    Quote Originally Posted by Illinoyance View Post
    The hole for the threading stop is 1/4-20 and probably not more than 5/8' deep.
    Thanks! Iím 99% sure that the tap I just ground out was a 5/16-18, so the previous owner must have been trying to change the thread size from what was original. Since the threads are supposed to be 1/4-20, I think I may fill the current hole with JB Weld and then either drill and tap directly into that, or install a thin-walled insert. The threads wouldnít see much force if using a threading stop correctly, so I wouldnít think the JB weld would be an issue. Iím open to any and all opinions though.

    Thanks again!
    -Keith



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  4. #4
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    Quote Originally Posted by USNmechanic View Post
    Since the threads are supposed to be 1/4-20, I think I may fill the current hole with JB Weld and then either drill and tap directly into that, or install a thin-walled insert.
    The holeís been filled and Iíve got the 1/4-20 insert. I plan on installing this tonight so I can get to painting.

    Would anyone be able to verify the center height of the hole from the bottom of the cross slide? Thanks! -Keith


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  5. #5
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    I ended up just assuming the previous owner had kept centered with the original hole, and did my best to match it. I scribed as close to center height as I could tell, and then scribed a line the same distance from each side of the cross slide to find the horizontal center. I punched and then center drilled, followed by a 21/64 drill. I went up 1/64 from the usual 5/16 for a 3/8-16 thread, but Iíve found that the keyserts sometimes have a hard time threading in. I only had one keysert and the working load on this hole should be pretty light if it ever gets used, so I donít think it will be an issue. Everything turned out great, and it will be ready to paint this week! Only a couple more weeks and I should be done painting, then on to the bench.



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