Inside Or Outside First?

[gheumann]

Hypothetical question. Say I just need to turn a bushing that ultimately is just a length of very thin wall tube. Is there a good reason to remove material from the inside first, then outside, or vice versa?

No tail stock center here - this piece is only about 1/4" long and 1/4" in diameter with wall thickness of about .015"

 

[JimDawson]

I don't think there is any advantage one way or the other.

 

[cvairwerks]

Bore it first then mount on an arbor. Clamping a tube with .015" wall is a real trick to do and not deform or crush it. A better way would be bore out a solid piece of stock well past the 1/4" depth and then turn the od to the correct diameter. Part off what you need after that.

 

[RJSakowski]

In terms of checking your work, I thunk it would be better to bore your inside wall first. You can check the diameter with less chance of distorting the wall. Your could put a temporary plug in the bore to keep the wall from distorting while you turn the od and measure it.

You didn't say what the material is but I had problems in the past making thin walled parts in Delrin when I turned the od first. One part was a cap with an id of .125; an od of .170; a bore depth of .100; and a .020 hole. My machining technique was to drill the .020" hole and bore the pocket to .125. I then parted the piece and mounted it on a custom mandrel Friction fit was sufficient to hold the part while I turned the od and faced the part.

 

[mikey]

With a wall thickness of only 0.015" I should think you would have issues with maintaining consistent ID due to cutting forces, whether you do it from the inside or the outside. Could you turn it to the required OD, rough out the bore, press it into place and final bore it on the mill?

 

[Bill C.]

That is pretty thin wall. If you are using a three jaw chuck pull the material out about half inch. I would face it, center drill the center. Turn the OD then drill and ream to size. Using a parting tool cut to length. Depending on the material. Be sure to reface the end after you pull more material out. Three jaws are great chucks for turning ID and OD in one setting. The problem is when you try to pick up a old center from the previous part. I used to do this when using a collect chuck on a turret lathe.

I also understand the abor or mandrel usage. If you were making several sleeves, drill and ream to finish then cut to length. That is a small part, the mandrel would keep it from collapsing but the part must be tight so not to slip while turning.

Good luck with your project

 

[mcostello]

My experience in steel and other haed materials has been that the thin wall heats up quickly. Finishing the outside then doing the inside gives less material for a heat sink. You can only go so small with drilling due to needing the length of hole. Outside turning can go as slow and light as necessary. Unless You have every drill in the book in suitable lengths.

 

[Micke S]

I think it is possible since it is so short. The hole must be drilled first. I made a brass bushing with 0,04 wall thicknes w/o tailstock support. It was not fully parted int lathe, the finishing
through-cut was made with a hand saw.

 

[Grumpy Gator]

My turn,
I would start with a solid piece of stock larger and longer than the job required.
First face it and center drill it.
Then if press fit turn OD down to a few thou over sized .
Then step drill the ID a few thou under size.
File and sand the OD to correct size.
Cut off and freeze in fridge over night.
Then press fit to location and finish with reamer.
******************Just Saying**************************************G***************************

 

[planeflyer21]

Bore it first then mount on an arbor. Clamping a tube with .015" wall is a real trick to do and not deform or crush it. A better way would be bore out a solid piece of stock well past the 1/4" depth and then turn the od to the correct diameter. Part off what you need after that.

Agreed.

We had some small bushings that needed to be faced for a final operation. Guy finishing them couldn't figure out why they were all out of tolerance. Eventually, with half the shop standing around his lathe trying to figure it out, we realized he was crushing the tiny bushings by having the collets WAY too tight.

He wasn't there the next morning.