how to make a cylinder wall 'square' with a hole in the center

[dansawyer]

The project is to make an adapter for a South Bend 9a to replace the compound feed with a milling attachment. The adapter is a cylinder about 1.4 inches in diameter and .8 inches long. There is a threaded hole in the center.
I started with a cylinder about .15 inches in diameter and 6 inches long. The cylinder was placed in a chuck and the end was centered with a dial indicator. A centering drill was used to make a alignment centering hole. From there a hss bit was used to turn the cylinder down from 1.5 to 1.4 inches. Then a hole was drilled in the center and then tapped.
A rod was placed in the center and centered in the chuck. The lathe was then turned on for observation. The part had a small wobble. I believe the cause was the drill hole was off center.
I believe the order above was wrong. The hole should be drilled first and then used for alignment. The sides should then be turned parallel to the hole.
Can anyone offer any advice on better way to create a hole parallel to the cylinder walls?
Thanks Dan

 

[mikey]

Dan, your stated dimensions are confusing. You say: "The adapter is a cylinder about 1.4 inches in diameter and .8 inches long." Then you say: "I started with a cylinder about .15 inches in diameter and 6 inches long." Can you clarify what you mean?

Assuming you started with a piece 1.5" OD X 6" long, it appears you used a 4 jaw chuck and indicated in the diameter close to the chuck. Did you then use a steady rest on the other end to support the work piece before center drilling the end? If so, did you indicate that end in before drilling? If a steady was not used on such a long work piece then your hole will not be on center unless you get really lucky.

You then drilled a center hole and tapped it. Again, how long is the work piece? How big is the thread? The most accurate way to get a threaded hole on center in a hobby shop, assuming the assembly must run as concentric as possible, is to bore the hole and then either tap it with a close tolerance tap or screw cut it. Doing this on a 6" long work piece will be nearly impossible so, again, you need to clarify your dimensions for us.

 

[Tozguy]

The hole should be drilled first and then used for alignment. The sides should then be turned parallel to the hole.

Can anyone offer any advice on better way to create a hole parallel to the cylinder walls?

You are right. Drilling and tapping with precision is difficult. I would drill and tap the hole required first then mount the work on an arbor threaded for a close fit. Do not remove the arbor from the 4 jaw after its threaded. Mount the work piece on the arbor and turn the outside diameter to spec. It is much more manageable to turn the outside dimensions with precision.

 

[dansawyer]

You are correct, there was a typo. The original piece was 1.5 inches in diameter and about 6 inches long. It was placed in the chuck and centered based on measurements from a dial indicator. From that a centering hole was drilled. The work was down with the piece held by the chuck and a live center.
The adapter dimensions were machined, then cut off. The center hole was drilled after machining and being cut off. Tapping was done in the lathe by centering the tap in the live center and manually turning the tap. The tail stock was fed the keep the tap centered.

 

[RJSakowski]

Threads are not a good choice for precision concentric alignment. By nature there will be some clearance for the thread to function. A better choice would be a drilled or reamed hole. Depending on your requirements, a shoulder bolt could be used for better alignment.

You are correct that it would have been better to drill the center hole first then turn the OD. I would have drilled for a center on each end and turned between centers. If the through bore in the spindle is large enough, insert the workpiece in the four jaw so that there is just enough of the piece to dial in the jaws with an indicator. Otherwise, you can use a steady rest to true the far end and drill the hole. A third alternative is to manually indicate the center point and punch it to provide a starting point. The South Bend "How to Run a Lathe" book has an illustration of this method.

 

[Tozguy]

Dan, Please explain how you used a rod to check for wobble.