Baby's first taper

Shotgun

Shotgun

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I bought a boring head without an MT3 adapter to use on the lathe or mill. So, I made one last night. After turning the 7/8-20 threads to a tight fit on the boring head, I mounted it between centers. First though, I mounted an MT3 taper reamer between the centers, and used the tailstock lateral adjustment to remove the longitudinal run-out on one face of the reamer. This was the first time I'd ever cut a taper. Colored the shank with a sharpie and tested the fit on the lathe by pushing it in. After using the dead blow hammer to get it out, the tells on the sharpie mark showed it was a perfect fit all the way down.
 

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Good job! One thing to store away in your memory bank for future jobs is that it would typically be best to finish both ends between centers rather than only the taper end. Finishing both ends (all finished surfaces) between centers is the best way to make everything concentric. If threading, make sure to mark where your lathe dog goes so you can be sure to get it back in the same place so you don't end up cross threading it! I also put aluminum strips/piece between my lathe dog and all contact points so things don't get marred up.

Nice work on the taper!
Ted
 
I hear what your saying, but I don't see how it can be done.

I turned down the thread end and put the threads on. Then I center drilled a dimple on that end. Turned it around, faced it off, and put a dimple in that end. I know the thread are concentric with the first dimple, 'cause they were both made without removing the part. The shoulder area is center-"ish", but that doesn't register anything, so it doesn't matter all that much. The taper then is centered between the two dimples, after the tailstock has been moved over.

How could I cut the threads, then put a dimple in both ends with the part always between centers?

BTW, I cheated. I don't have a lathe dog. I use a C-clamp meant for holding a GPS on an airplane yoke. It has a bolt coming out one side that caught on the chuck jaw. I could only take 15thou cuts at the most. But, it worked. :)
 
Shotgun said:
I hear what your saying, but I don't see how it can be done.

I turned down the thread end and put the threads on. Then I center drilled a dimple on that end. Turned it around, faced it off, and put a dimple in that end. I know the thread are concentric with the first dimple, 'cause they were both made without removing the part. The shoulder area is center-"ish", but that doesn't register anything, so it doesn't matter all that much. The taper then is centered between the two dimples, after the tailstock has been moved over.

How could I cut the threads, then put a dimple in both ends with the part always between centers?

BTW, I cheated. I don't have a lathe dog. I use a C-clamp meant for holding a GPS on an airplane yoke. It has a bolt coming out one side that caught on the chuck jaw. I could only take 15thou cuts at the most. But, it worked. :)
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Center drill each end, then turn between centers.
 
Rough the piece out and center drill both ends as Jim said above. Then, put it between centers to finish both ends.

Finishing one end in a chuck first does NOT guarantee that it will be perfectly on center after center drill the other end and putting between centers. When you finish that first end in the chuck, the opposite end that is inside the chuck will most likely be running out, wobbling around. It might not be running out by much, but it will most likely will not be running perfectly true. So, when you turn it around to center drill the other end and indicate it in, the center you are putting in will be off center with the first end, because you would have to make it "wobble" exactly the same as it did in the chuck to make that center drill hole on center.

Trust me, the best practice in a lathe to make a workpiece as close to perfectly concentric as possible is to finish the whole piece between centers.

I doubt I am explaining this very well and maybe others can chime in and help.

Ted
 
Fortunately concentricity for a boring head shank is unimportant. By definition it operates by being eccentric.

Nice work on the taper. It frequently takes several passes and small readjustments to get it right.
 
So how would you cut the internal thread at the end while between centers??
 
Cadillac said:
So how would you cut the internal thread at the end while between centers??
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That certainly is tougher. Here's one way from South Bend's book "How to Run a Lathe".

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I would most likely put the head stock end in a four jaw chuck and use narrow shim pieces between the jaws and the work piece (for minimal contact) to allow the work piece to more freely move/pivot so not to introduce stresses and torques to it. The steady rest will keep the tail stock end concentric with the OD of the work piece where it contacts the work piece.

I agree with Mr. Whoopee that is makes no difference in the case of a boring head. I was merely offering a newer machinist a bit of advice that he may be able to put to use down the road when it does matter.

Along the same lines, anytime you forcefully capture and constrain the end of a work piece in a chuck and use a center in the other end you are introducing stresses and torques to the piece as you rotate it to machine it. Turning between centers, when possible and practical, removes most of these forces/stresses and is the best practice when you want/need things to be as true as possible.

Ted
 
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