Positioning and repositioning

Following on from the mounting vice thread.
Assume two objects with flat surfaces which need to be positioned against each other in both xy directions, to a high degree of accuracy,
say a couple microns, a tenth of a thou, or so.
In order to improve positioning you have to know how close they are to the desired alignment, and some method like clocking a vice on a mill table can be used for that.
It would be convenient to be able to reposition the vice without reclocking and readjusting - David mentioned a key made as a close fit to your table slots, though I don't know whether that would be accurate enough?
Would the use of pins be any good?
Which is better, hardened, or spring? Why?
I expect people know this, but I don't ...
OK, now I have a bearing holder for the main bearing for a lathe which is supposed to be fairly/very accurate. It is mounted on a flat surface at right angles to the axis of rotation, the front face of the lathe if you like.
I need to align it to within a micron or less. I may need to move it 3 microns down and 2 microns left. It then gets bolted down. The first problem is, how to move it than little, under control?
Second problem, when bolting down it moves.
Help?
-- Peter Fairbrother
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I have an old Mitutoyo micrometer head that reads to microns. The knob is 55mm in diameter, advances 0.5mm per turn, and is easy to move by 1 micron.
jsw
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On 02/10/12 22:30, Jim Wilkins wrote:

Eh, a micron is a tenth of a hundredth - 0.001mm - the dial division on the dials of old metric and most modern Chinee machines.
1/25 th of an imperial thou, or thereby.
I don't know why to say it, but I have some of those micrometer heads too. Also by Mitumyoyo. Never used them for owt, so far ...
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I wasn't suggesting misusing a precision micrometer head as a heavy-duty positioner, only that micron resolution isn't difficult with that thread pitch and knob size. Optical bench lens holders use micrometer heads for positioners, but they have low-friction kinematic ways and pivots, and the micrometer thread pushes against a light return spring. You could use opposing pairs of replaceable commercial hardened bolts since you don't need precise pitch accuracy.
The standard thread on micromanipulators for probing integrated circuits was 50 TPI, about 0.5mm. http://www.micromanipulator.com/products/index.php?cat 4
At Unitrode we sometimes ordered a custom version with 100 TPI threads but the standard ones were good enough most of the time.
jsw
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Peter
I think the most common dial increment is 0.01mm rather than the 0.001mm you attributed to Chinese and modern machines. In fact the vast majority of measuring devices like digital calipers and dial gauges are also in 0.01 resolution. Digital micrometers though are normally to 1 micron resolution.
Ian


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On Tuesday, October 2, 2012 8:22:12 PM UTC+1, Peter Fairbrother wrote:

it and drop a lever over the pivot then have a bracket at the opposite end of the lever, put your micrometer head on the bracket and tension the lever against the mike anvil with a simple spring, you have a second lever at 90 degrees. Now drop the component into the inside if the angle between the two levers and tension that also with a spring. You can move the component minute meas ured amounts by turning the mikes and calculating the mechanical advantage/ velocity ratio.

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