Indicating independednt 4-jaw chuck

While fiddling with my RedNeck lathe I came across an interesting problem:
I am trying to clean up the outside of a steel ring: 5.5" OD, 3.25" ID,
0.25" thick.
I clamp it in the 4-jaw chuck (inside the hole) and am trying to center it
using an indicator. However, the outside edge of the ring is so pitted and
irregular that the indicator jumps about to the point where the readings are
hard to interpret let alone use to center the work-piece.
Now I do not need great accuracy: The inner hole and the outer edge should
be concentric as far as possible but I am not quibbling of a 0.001" or two.
Yet this way it is hard to get it confidently within 0.010"!
Clearly the obvious answer to this is "Get a 3-jaw chuck" and I have one
already, 4" with two sets of jaws, the only problem is getting the adapter
to 1"-8 spindle and turning it down to size. But this may have to happen (in
fact if this thing merits further expense it will happen).
However, given what I got now, I wonder how others would approach this
problem.
Reply to
Michael Koblic
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Turn a mandrel to a snug fit on the ID, drill and tap it on the end in a couple or three places, cut a circle of thickish sheet bigger than the ID and smaller than the OD, and drill clearance holes in the same places as the ones in the mandrel.
Chuck the mandrel with a hair less than the thickness of the ring proud of the jaws, indicate the mandrel, slide the ring on, hold the ring with the sheet bolted to the mandrel.
Reply to
_
Indicate the inner bore. Or indicate the chuck jaws. Ignore the outer if the outer is crap - you'll turn the outer clean, no? Just need to get the inner lined up - therefore, indicate what you want to line up...
Reply to
Ecnerwal
Hold a feeler gauge, say .005" thick or so, between the indicator tip and the work piece.
Wolfgang
Reply to
wfhabicher
Checking the jaws for and adjusting for very close to concentric would be a good check. With the center hole centered, trimming the circumference will get you an equal width for 360 degrees.
Making a convex shoe for indicator stems has seemed like a very good idea, numerous times when indicating something with a rough surface, but I haven't done it yet. It wouldn't be a difficult piece to make, though. The only critical aspect would be that the shoe doesn't rotate around the indicator stem's axis.. otherwise, it would be an accurate indication of the OD. The larger contact area would indicate the high spots, without popping into every low spot/pit/valley.
Reply to
Wild_Bill
Uhmmm, convex should've been concave
Reply to
Wild_Bill
Flat works.
Reply to
Don Foreman
Indicate on the jaws. Turn the OD. Reset; indicate on the OD, and clean up the ID. JR Dweller in the cellar
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Reply to
JR North
Thanks everyone for so many suggestions how to skin this particular cat. Unfortunately the way the ring is clamped there is no way to get at the jaws but the feeler gauge method worked just fine.
Reply to
Michael Koblic
You can indicate on any part of the jaws, not just where they grab the work.
jsw
Reply to
Jim Wilkins
I understand that, but they were kind of buried in the hole - no way to get the indicator on them.
Reply to
Michael Koblic
Once upon a time they made a pivoted lever attachment that clamped to a dial indicator and reached into a small hole to indicate the ID. The turned ones are better than the stamped ones but I wouldn't pass up either type.
jsw
Reply to
Jim Wilkins

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