Forrest, I found it. Wire sag table.

Was looking through an old book on air compressors. In the section on installation and alignment, low and behold there was a sag table for piano wire.

I'll try to get it formatted to an extent it is comprehensible and post it in the near future.

I'd do it now but I better go get some sleep, gotta go somewhere this evening and then work tonight.

Did Bill Gates write the book? Looking in a book about air compressors for info on piano wire sag is almost as bad as having "start" as the first step in shutdown.

How are the two subjects related?

Roger

[This message has been edited by winchman (edited 12-02-2003).]

Winchman: There was a time when large machines were set and aligned using wire as a straight edge. The millwright had to compensate for the droop of the wire. Steam engines, steam Locomotives large compressors ect. were lined with the center of the cylinder. A baar was placed across the end of the cylinder and the piano wire was fixed to the mid point of the bar. The bar was so made to allow it to be moved so that using inside calipers the piano wire could be centered in the bore. The wire was extended through the bore and out far enough so that the wire passed the other parts of the engine that needed to be aligned such as the crank main bearing block, ect. The long end of the piano wire was fixed to another mount on the foundation of the machine. By moving the far end of the wire it could be centered in the end of the cylinder away from the holding bar. What you got then is a taught line running through the center of the main cylinder and out to the rest of tahe machine. This line could be used as a datum for checking and aligning the components of the machine. I worked on a large locomotive wheel lathe once that had 2 headstocks, both had luggs cast into their side and finished machined in 2 planes. The luggs were for using a taught line to align the headstocks when the foundation of the machine was leveled.
Cheers Ross

Thanks for the explanation. I can see how there was a time when piano wire was one of the few things available in the length, strength, and consistency to be used for doing something like that.

Roger

Cool, Halfnut. I love it. Old lore.

When I was a pup we still used piano wire for machinery alignment. You can't believe the language when you take a shortcut through the engine room where the HP and LP turbine cases are open and their centerlines are extended with piano wire throguh the pinion bores of the main reduction gear.

It's like you're trapped in a giant spider web while bellowing monsters try to break your bones getting you untangled from the wire.

Question? Would a newer material, such as kevlar, subsituted for the steel wire,due to higher strength to weight, and be able to be stretched tighter, have less sag?

you dont have to go to far back in time,fellas. we used to use piano wire to align the turbine generators in the local power plants around phila. maybe 15 years ago. the steel wire is preferred because we used an electrical box hooked up to the wire and turbine. Wire was insulated from ground and an inside mic. would make connection at lightest touch and it would shock youre nuts off, only kidding, it actually just made a noise. we did have to calculate the amount of wieght hung on the end of the wire. thats all I remember.
thanks
Johnny O

Even as recently as a couple of years ago, piano wire, a microscope and a water level were used to rough in the bearing shims on this milling machine.

mcostello --

There are two questions that need to be answered before reliable alignment can be done using taut-line methods: 1. How straight is the taut-line? 2. How reliably can the operator sense the position of the taut-line?

A high-tech polymer line with a higher strength:weight ratio than music wire will sag less than music wire, but the ability to sense or detect the position of the line may well decrease.

Wire sensing was originally done by sight, but in later years contact with the conductive wire was often sensed electrically because electrical sensing is more repeatable than visual sensing.

Using a non-conductive line will prohibit the use of electrical line-position sensing, which would probably result in a decrease in overall accuracy . . . especially since the net effect of line sag can be reduced very nearly to zero by simple arithmetic compensation.

In theory we can easily calculate the gravity sag in any line if we know the conditions under which the line is suspended . . . horizontal separation of support points, line material, line diameter, tension in the line, and gravitational acceleration being the critical items to know. But the "old way" was to determine the sage for a given size and tension wire and put the answers into a manual look-up table such as the one halfnut found.

On the other hand, if you can sense the line position very well in some way that doesn't rely on the line to carry an electrical current that is shorted to ground through the measuring instrument to detect line contact, you're going to be very happy with non-metallic lines. Research physicists today are using carbon-fiber lines with capacitance sensors to measure micron-level displacements over kilometer-to-mile lengths. The line does need to be very well anchored, in a geologically stable environment, and in a vacuum . . . but it IS being done.

John

Motion G

Where did you find that pic????? Got a link?

Paul G

======================================
Where did you find that pic????? Got a link?
=======================================

Right click on the image, click on Properties. Select and copy http://www.janicki.com/envelope.jpg

Backspace the envelope.jpg off the end will give you http://www.janicki.com/ Follow the breadcrumbs to, http://www.janicki.com/envelope.html

Here ends the lesson Grasshopper.


[This message has been edited by Mech (edited 12-03-2003).]

Here we go.

.016 dia piano wire with 30lb weight

lenth of wire, sag and distance from end

4ft .001 at 2'

8ft .001 at 2',.002 at 4'

12ft .002 at 2',.004 at 4',.005 at 6'

16ft .003 at 2',.006 at 4',.007 at 6',.008 at 8'

20ft .004 at 2',.008 at 4',.011 at 6',.012 at 8',.013 at 10'

24ft .006 at 2',.010 at 4',.014 at 6',.017 at 8ft,.019 at 10ft,.020 at 12'

28ft .007 at 2',.013 at 4',.017 at 6ft,.022 at 8ft,.024 at 10ft,.025 at 12ft,.026 at 14'

32ft .008 at 2',.015 at 4',.021 at 6',.026 at 8',.030 at 10',.033 at 12',.034 at 14',.035 at 16'

36ft .009 at 2',.017 at 4',.024 at 6',.030 at 8',.035 at 10',.039 at 12',.042 at 14',.043 at 16',.044 at 18'

40ft .010 at 2',.020 at 4',.028 at 6',.035 at 8',.040 at 10',.046 at 12',.050 at 14',.052 at 16',.053 at 18',.054 at 20'

I hope this looks like something when I post it. Here goes.

In a training film Brunson has for optical alignment equipment they give a little history of alignment techniques using strings and wires. The practice probably goes back to ancient times. They show a line of WWII aircraft with all the noses of the airplanes looking in different directions to illustrate just how inaccurate the taut wire technique is. Production demands and quality demands of WWII were the big push to get optical alignment techniques developed for use both in aircraft and in liberty ships and other naval applications where you need a long centerline. Alignment telescopes and theodilites replaced taut wires almost everywhere. Note the picture caption said "rough alignment" read "very rough alignment". Now days lasers are replacing straight eyeball optical techniques so a lot of optical alignment equipment is being surplused. A laser theodolite is something that can be rented, easy to use and very high resolution. Wires and strings are history but brick layers get good use from string.

Cass --

Alignment "state of the art" for large structures today is taut-line-and-liquid-level territory, using electro-something sensing of line position and liquid surface. The research physicists are achieving measurement uncertainties at the micrometer-per-kilometer level using this type of equipment.

Industrial use is a different story, and here I consider the Hamar tooling laser to be the cream of the crop for "classical" alignment -- straight, perpendicular, flat, and plumb -- while coordinate measurement is the realm of the laser-radar, laser-tracker, and videogrammetric systems. All of these systems have their strong points, and they all have their weak points . . . none are fits-all solutions.

The "laser theodolite" is a contractor's tool that can replace the carpenter's or mason's chalk line or plumb line, but not often used in the machine-tool or precision mechanism worlds that I know of. Twenty-some years ago the major European theodolite makers (Kern, Wild, and both Zeiss organizations) experimented with first-or-second-order laser theodolites, but the instruments were neither technological nor sales successes.

On the flip side, there are a few large machine-tool makers and rebuilders (Ingersoll Milling Machine and Devitt Machinery come immediately to mind) that continue to use taut-wire and precision-level alignment methods because those systems still work under environmental conditions that raise havoc with "optical" methods (alignment telescopes, tooling lasers, laser trackers, interferometers, and autocollimators). As of a couple of years ago, Brown & Sharpe still produced the ex-Leitz wire-reading microscope, which is an instrument I'd love to have in my "bag of tricks".

As for roughing-in, I've used nylon monofilament fishline, a bi-filar target, and a hand-held magnifier to rough-in a 10-foot linear bearing well enough that I could not positively identify any error when I went back to fine-align it with a jig transit and parallel-plate micrometer.

So, bottom line, I argue that taut-line alignment remains a usable tool today even if it lacks the "glory" of a laser.

John

Los Alamos used theodolites and alignment telescopes to line up the optical systems for laser fusion experiments. Lawrence Livermore uses them today. The aircraft builders use them and lasers and I assume ship builders and anyone with less time than money. Hewlett Packard laser systems are much better than Hamar and there are other lasers that are also better than Hamar. You can get all the optical methods off the shelf and from service companies but the wire/string technique may be the best way considering what people are used to which is a cost consideration as much as resolution. No big deal for most readers here in either case I imagine.

I would use lasers, but the photons are too heavy and sag in the gravitational field. Even if you shoot straight up, the red shift causes error in the interference patterns and throws the whole setup off. Thats why the Egyptians used water ditches to level the pyramids. Not only is it level, its level over the horizon. Try that with your lasers and piano wire!

Cass --

A whole lot of organizations used to use alignment telescopes and/or theodolites to do a whole lot of different jobs, but the theodolite-based coordinate measuring systems are being pushed out the corporate back doors a whole lot faster than they are being brought in the front doors. A year or so ago ebay was flooded with second order electronic theodolites that had been surplused from the aircraft manufacturing plants. Reliable Tool bought one lot of 25 Wild T-2000 and T-3000 theodolites from Northrop (IIRC); Boeing and Lockheed-Martin are dumping theodolites in similar quantities.

A very few of the theodolites used in theodolite-based coordinate measuring systems were equipped with laser projectors; those that had the laser projector were used primarily to project a laser-dot "target" onto the surface of an un-targeted or un-targetable object so that the other theodolites could be pointed toward a common point on the surface of the object. One major application of this target-projection technique was to measure the surface contour of an antenna reflector too large to fit into a coordinate measuring machine.

The primary jobs that theodolite-based coordinate measuring systems were used to do in the late 1970's through mid 1990's are being done today mainly by laser tracker (sequential point measurement and evaluation, useful when building jigs and fixtures) and videogrammetric (simultaneous measurement of multiple points followed by evaluation, useful for periodic inspection of previously-built jigs and fixtures) methods.

There are probably still some theodolites at the Rad Lab, but the vast majority of the large-scale Cartesian measurement work is being done with laser trackers. I know that they are using several of both the Leica and Faro/SMX trackers.

Stanford Linear Accelerator Center is also a major user of laser trackers today, as is CERN. In both of these organizations the laser tracker has largely displaced their theodolite-based coordinate measuring systems.

Neither theodolite-based coordinate measuring systems nor laser trackers today are accurate enough for machine-tool setup and calibration. Especially with large machines, the laser-based measuring instruments are the "high tech" tools, but there's no single instrument that does everything well. The interferometers -- be they HP, Renishaw, API, Opto-Dyne or others -- are great for measuring displacement along an axis, but in my opinion they have to take a back seat to the Hamar and similar instruments when it comes to measuring significant cross-axis displacements or making deviation-from-plane measurements.

Speaking personally, my professional "instrument of first resort" is a second-order theodolite with a two-axis tilt compensator and bright-line autocollimator with an intersecting-filar filar-bifilar reticle. Of the "digital" instruments, I prefer the Kern E2EC, but can make do with a Leica/Wild T-3000A, a Leica/Wild TM-5100A, or Zeiss ETh-2. The Kern DKM-2C, DKM-2AC, and DKM-3C are the royalty of the glass-circle genre (although, in fairness, I should mention that I never used a Wild T-4), with the Wild T-3A and T-2A decent runners-up. The Zeiss Th-2 had an incredible telescope, but I never took to the circle-reading system.

Of course, there are times when a theodolite won't do the job, so I call on an SMX laser tracker or a GSI V-STARS videogrammetric system. And there are other times when I call on a "feeler" cut from a slip of paper.

John

I think we have worn this topic out and gotten far out of the interest level of others. I got a very nice theodolite from Northrop. Handy item for aligning optical systems. I have a collection of autocollimators and alignment telescopes and interferometers of various types. We use lasers on diamond turning machines. My opinion on Hamar is based on hearsay from some early users so they may have improved. I won't bore people further.

Cass --

You're probably right.

John