Precision Measuring Equipment

Took some time off from working on my 10EE lathe rebuild to work on a few needed fixtures......... (for working on my 10EE lathe!)



There are a couple of home build 10sec (approx) levels. I will be building carbon fibre heatshields for the levels. I would also comment that if you are going to build something similar at this precision level, the thread pitch for the mount studs should be at least 40tpi and higher if you have it. I went with 10-32, and its very hard to move the adjust knob in a small enough increment to zero the levels. I have a .275-40 tap so will be fabbing a new set of studs, and will increase the diameter of the adjust knobs. The fixtures in the 3rd and 4th pictures will carry precision mirrors and are for use with a comparison autocollimator. The autocollimator compares the relative tilt angle between the two mirrors and is much easier to use than a standard collimator since any slight movement of the autocollimator telescope itself will not affect the readings. In use I will set the fixtures as shown in the 3rd images and one mirror will be moved along the way in fixed length increments, the tilt reading (sloping rise or drop) at each step will be converted to a height change and I can then pliot the profile of the way. The last picture is a Pratt and Whitey 15" master precision level (double master precision actually).
The 15" level base has been scraped in, I still have some work to do on the bases of the 10sec levels and the way measurement fixtures.

the thread pitch for the mount studs should be at least 40tpi and higher if you have it.

Click to expand...

Differential screws come to the rescue!

Nick

Good idea.

Here's the .1sec precision autocollimator. In practice most people call it accurate to about .25sec. That gives me the capability to measure a height difference of about 2.5 millionths of an inch using the 2" lenght test fixtures.

great technique for my interest -
years building parts for Brunson Instrument theodolites & their older autocollimators . . . . .
but never, ever got the chance to take one of their technical classes featuring optical measurement techniques/practices.
those seats went only to high profile customers.
if you don't mind the extra effort to elucidate your optical measurement practice -- i would be a very grateful audience member . . .

Well here is my plan. The Davidson Autocollimator I have is differential, that is it measures a difference in tilt between two mirrors, one stationary as a reference and the other varying in tilt angle. My plan is to incrementally (every 2") move the measurement mirror down the length of the way taking angular change measurements at each position. These can then be converted to a distance change of the leading edge of the fixture block and plotted as an overall profile of the way. One of the problems I will probably run into is that the total measurement range of the autocollimator is only two minutes (2'= 2/60 of a degree) And over the approximate 40" length of the longest and most worn way that only allows a measurement range of 40*tan(2 minutes) = .023" total. Assuming the wear of the ways is greater than that amount my plan is to re zero the measurement mirror to the stationary one at the point along the way where I have run out of measurement range then continue on. The mirrors are mounted on adjustable mounts.