Turning rings from a pipe

I was trying to make two rings from copper pipes, 1.625" OD (wall thickness 0.061") and 2.125" OD (wall thickness 0.035") respectively.
The length of the ring was to be 0.75".
I cut the pipe oversize on my bandsaw. As expected the cut was not exactly square. I clamped the first ring initially on the inside in my 3-jaw chuck trying to make sure that the sides of the piece were at right angles to the body of the chuck as determined by a square.
I faced off the first side and deburred it. I reversed the ring and clamped it the same way with the faced-off part flat against the jaws base. I faced off the other end to the required dimension. Everything looked good.
However, when I checked the final product with a square it was obvious that neither plane of the ring was square to the sides. I did an additional check with a height gauge with the ring on a flat (well, as flat as I could get) surface. There was a difference of 0.017" in height of the ring around the circumference.
I tried a second ring of the same diameter, this time clamping on the outside. I checked the position with the square in three different spots. The interesting part was that the fit was square in two of them but not in the third.
Anyway, the result was almost identical and I got the same result with the larger ring.
Although the result is adequate for my purposes I would like to know why I was unable to make the rings properly. Was I not following the correct procedure? Where in the procedure could the error have occurred? I have never before had a problem with facing-off being out of square with the sides.
Thanks.
Michael Koblic, Campbell River, BC
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 8/5/2013 9:02 PM, snipped-for-privacy@gmail.com wrote:

Copper as you know, is very soft. You can't clamp it very hard before it distorts & also it will move in the chuck unless you take very light cuts. You did not say but I assume you deburred it before chucking in the lathe?
Maybe check it with the square after you faced one end but before you unclamp it to see if it had moved in the chuck during facing?
You would probably need to put it on a mandrel for perfect accuracy.
MikeB
--
Email is valid

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Yup , mandrel . Bolt in the end with a rubber washer under a regular steel washer <I'd machine the steel with the mandrel , trim the rubber with a knife/sandpaper> . Tighten the bolt , rubber expands and grips the sleeve . Take light cuts ...
--
Snag



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 6/08/2013 10:09 AM, Terry Coombs wrote:

I tried a similar thing but to make the mandrel I used a bar just under the ID of the tube I wanted to machine. I then put pieces of thin wall tube over the mandrel with O rings spaced along in between. When it was tightened down the O rings expanded outward holding the tube in place.
===============TUBING TO BE MACHINED=================|<tube> O <tube> O <tube> O <tube> O <tube> O <tube> O| ======================================================| mandrel < BOLT< ======================================================| |<tube> O <tube> O <tube> O <tube> O <tube> O <tube> O| ===============TUBING TO BE MACHINED=================
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

How much runout did you get ? Were the pieces of thinwall between the o-rings a tight slip fit ?
--
Snag



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 6/08/2013 11:38 AM, Terry Coombs wrote:

I was actually using the setup to cleanup the outer surface of some plastic pipe - more aesthetics than anything else, so I don't have any measurements.
The thin-wall tube was just a neat sliding fit on the mandrel part (again, no measurements - I just used what I had on hand & could make work).
This was for 16mm ID PVC tube.
I got the idea from seeing those well-nut fasteners & some expanding pipe bungs at the local truck parts store.
<http://www.google.com/search?q=pipe+bungs+expanding&source=lnms&tbm=isch&sa=X&ei=HKwAUt6rN8qskgX2nIC4Dg&ved AkQ_AUoAQ&biw47&bihV4>
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Well stated!! Bravo!!
Copper moves like a freaking snake in a 3 jaw chuck. Its not easy to work with in a proper collet with a bottom in it either.
--
""Almost all liberal behavioral tropes track the impotent rage of small
children. Thus, for example, there is also the popular tactic of
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I can't make good rings that way either. I'd turn a wooden mandrel and slide the pipe onto it, then part off the rings.
You can turn a shallow parting groove and use it to guide the bandsaw blade. Saw a shallow cut, then rotate the work a little in the blade travel direction so the flexible incoming blade rubs on and is guided by the wall of the turned groove. Saw in a little and advance again. Unless the blade is new and sharp it won't dig into the wall of the groove much. Once the saw cut extends all around the blade should cut the piece off squarely, or if not you can see it deflect.
The same trick can cut under the hard shell of a scrap hydraulic cylinder rod with a tool you can easily sharpen rather than the expensive sawblade. jsw
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 5 Aug 2013 21:49:12 -0400, "Jim Wilkins"

After reading all this I am surprised the rings turned out as good as they did :-)
I will remember the mandrel trick for next time it matters.
Thanks to all,
Michael Koblic, Campbell River, BC
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com fired this volley in

If one has a slitting saw and some time, you can make an "Expandrel" that will fit tight in any size pipe you want to name, and can be CUT INTO in order to part rings or to o.d.-surface thinwall tubing. I've seen versions that will clamp to the outside of a tube to allow i.d. finishing... but those are a bit of work to make (clinching rings, and all that).
It depends on the value of the job. An hour or two making a disposable fixture might be worth the time.
Lloyd
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It is hard to chuck something accurately that is wider than it is long. You could chuck a long length of the pipe and leave more than 0.75 sticking out. Clean up the first end, then, with out unchucking, part off the 0.75" length and deburr by hand.
You could also part off a length that is a little longer, then turn it around and chuck it using the inside jaws with the flat end resting against the step in the jaws.
Other folks mentioned making a mandrel, and maybe that is the right way to do it, but it seems like too much work.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The mandrel can be an easy fit except for an inch or two beneath the rings at the tailstock end. The chuck will squeeze the tube against it to drive it. A short plug mandrel at each end might work.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Are you familiar with soft jaws? They are the answer to your problem.
Harold
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.