Wire sag table (for the retro aligners)

[Forrest Addy]

Here's the link on the mother of all wire sag tables: http://www.millwrightmasters.com/School/tight_wire-sag_1.htm

Fie on optical and electronic stuff. What was good enough for Noah and Nordberg is good enough for us.

 

[machtool]

Forrest
Those tables are as rare as rocking horse dung on the net. I’ve looked before. That would be just my luck that I don’t have any 16 thou wire here. And wire in any sort of of full length coils is hard to find down here. I have miles of 6 and 10 thou. But no 16.

It would appear to me that they have worked that out at 150,000 p.s.i tension. If memory serves you would normally be a bit higher than that? (180k)

Regards Phil.

 

[Forrest Addy]

It's the unit tension that has to be then constant. unit tension for 0.016 wire @ 30 lb is = 149,307 PSI. For a 0.010 =9.765 lb. If the wisre is that smae stuff and has the same unit tension the sag doesn't change for the same span.

The wire has to be stretched about 1% or some such figure to take the curl out of it. This reduces the section dia by an equal percentage; the total volume of metal remains constant.

When I was a first yeaar apprentice I was a beast of burden for my crew. ("Kid, grab your tool bag and come with me."). We had all sorts of fancy Pratt and Whiney wire apparatus. Neat brackes with little two asis slides, anchors with pulleys, weights, electric two axis mike sleds, electric sensing tips for ID mikes, etc.all kinds of stuff most in bulky wood boxes.

Over several trips, I delivered it on board ship across and over seeming miles of passageway and down access trunks to the engine room. The wire kings worked night shift to minimize interferance. Next morning there would be wire strung on every axis imaginable and serious dudes with the souls of CPA's would be setting bearing blocks for portable boring of the stern tubes and strut bearings. I was a dopey kid then and didn't pay enough attention but I shoulda. The next year they did the same class of work with Bruning optics and got it done in half the time. Sic transit gloria.

 

[machtool]

Forest.

1149,307 PSI

Psst. You may have typo’d in an extra 1 in the start of that number. I get just shy of 150,000 rounding up.

Regards Phil.

 

[Forrest Addy]

Yeah, well - um - we got better steel up here in the land of US..

 

[RC99]

Just curious, wouldn't wind affect the wires where they are used in the open or in areas in worshops where the wind blows through them??

While I have had nothing to do with wires used in this situation I have helped build a shed or 4 and when we stretch out the string line over a hundred feet or so even with the slightest breeze it plays merry hell with the straightness of the string...I know string is a lot more springy then wire but I assume it must effect it somehow..

 

[DaveE907]

Forrest, thanks for the memories. This makes me smile. My grandfather was a millwright, born in the late 1800s. He used the wire alignment method, used to have some of his old books. Catenary curves. My dad was born in 1905, started with wires on locomotives and progressed later to visual autocollimators aligning linear accelerators in the 50s. I was issued in Bremerton in 1945 and retired using methods they couldn't have dreamed of.

It's good to go back and touch our roots. A very great pleasure for me.

 

[machtool]

Just curious, wouldn't wind affect the wires where they are used in the open or in areas in workshops where the wind blows through them??

It certainly does. Its normally a fight to get the doors kept shut, or pick a still day. Depending on the site, you see all sorts of things on a wire. I use an alignment telescope, as opposed to the insulated micrometer that seems to be the preferred method in the States. Lowest resolution I have is 40 magnification. The wire will just turn to a blur (Vibrating) for all sorts of reasons. Wind, Gantry cranes, fork lifts, blokes touching the wire.

Phil.

 

[Forestgnome]

This all sounds intriguing, but I don't know what you're talking about. Can someone enlighten me on wire alignment and what it's used for? Thanks.

 

[DaveE907]

I'll take a simplified bite at trying to explain it.

Wire alignment refers to the practice of using a tensioned wire as a reference from which measurements are taken to establish straight line alignment of work pieces undergoing alignment. A horizontal tensioned wire in earth's gravity takes a well known shape called a cantenary curve in the vertical plane.

http://en.wikipedia.org/wiki/Catenary

By using a steel wire of known diameter and putting a tensile load on it with a known weight a calculated tensile stress is put on the wire. From that stress and the distance between the end supports we assume we know the curve of the wire so we can take measurements from the wire to our work to determine its state of (mis)alignment.

That's what the tables Forrest posted help to do. Knowing the amount of sag at any point along the wire from an ideal horizontal straight line between the end support points lets us compensate for that sag in our measurements and thus use the wire as an ideal straight line.

Direct meaurements are taken between the stretched wire and the work piece surfaces and the tables help to reference them to an ideal straight line.

In the horizontal plane the wire projects as a straight line. For fine work it's curvature in the vertical plane is accounted for by the cosine rule in taking measurements.

What's it used for? Used to be widely used for aligning things such as bearings of large turbines and as Forrest mentioned bearings of ship propeller shafts. It was also used to align the beds of large long machine tools and locomotive frames among other uses. For some of these purposes it is still used. Steam locomotive frames are still often checked with wires. It hasn't disappeared entirely as this currrent tool offering demonstrates.

http://www.powerhousetool.com/turbinealignment.htm

If the wire is oriented vertically it is assumed to be an ideal straight line and measurements don't have to account for sag. Sag for any wire angle between horizontal and vertical can be calculated but true horizontal wires are most often employed to simplify the method.

 

[Mark Rand]

One feature that is not realised by many is that turbine rotor lines are actually aligned into a catenery rather than straight. Since the individual turbine rotors and the generator rotor all sag between their bearings, aligning them with the bearings in the same plane would cause unwanted stress on the couplings and rotors as they tried to straighten the shaft. So the rotor line is laid out as a catenery (with the slope calculated based on rotor stiffness) so that the couplings end up parallel.

More engineering trivia...

 

[J Henricksen]

At Ingersoll,we used .011 wire with a 28 pound brass weight on the end. Set a column lean for a big mill there was a certain belief that the magnetism in the columns or steel weights would cause an error. Weights were always kept in old paint buckets of heavy oil for dampening. We had a few guys who used fishing line but it didnt show up as good in the Leitz wire gage, and an electric mike just didnt work. Wire snapped? whoever was setting it got an oil bath. There were some Hamar lasers around but more of us knew how to set up the wires.

 

[Forestgnome]

I get it, early laser! It would seem to have a slight advantage over laser in that you can take very precise measurement of distance to the wire anywhere over it's length. Are there any advantages to using wire or is it obsolete now? How does it compare to this: "The L-705 Bore Alignment Laser has a range of 50 feet (15 M), and under good environmental conditions, is accurate to less than .001" (.025 mm) over the whole range (although it is capable of measuring down to .0001" (.0025 mm) in 10 feet). The L-706 Bore Alignment Laser is used for longer distance alignments from 50 to 110 feet (15 M to 33.5 M). It is accurate to +/-.001" (.025 mm) in 110 feet (33.5 M) and has finer angular adjustments than the L-705. Both lasers are concentric to their OD's to within .0005" (.013 mm)."?

 

[J Henricksen]

I've used stretched wires over 80 feet long to set up runways for big gantry mills. The big bridge mills sometimes had 120 feet of ways.Sag in the wire made reading the center of this length a bit questionable. A laser may work betteron the longer bedsbut we just didnt always have one available.breezes and vibrations caused reading lasers and wires a challenge sometimes. Fighting to keep the doors closed on a hot summer day ahh the good old days. A wire hanging vertical in front of the column ways is the only thing I can think of for setting the lean opf the columns. For travelling, carrying a coil of piano wire and a wire mike was easier than getting a laser along with us.

 

[Peter S]

Forestgnome,

Here is a thread from a few years back which tries to explain one mans experience of piano wire and alignment at sea.

http://www.practicalmachinist.com/vb/showthread.php?t=80817

 

[rimcanyon]

a coil of piano wire and a wire mike

J Henrickson, interesting post. What is a wire mike?

 

[John Garner]

rimcanyon --

A "wire mike" is a micrometer equipped to electrically sense contact with a conductive wire. They are often homemade, but Ingersoll Milling Machine offers theirs as a commercial product.

A picture and general description of the Ingersoll 1) wire mike and 2) adjustable wire supports can be found in Ingersoll's "Engineered Setup Equipment" catalog, which can be downloaded as a PDF file from the Ingersoll website. (My computer doesn't want to Copy / Paste right now, so I'm not posting a link . . . but a Google search for "engineered setup equipment" finds the appropriate section of Ingersoll's website handily.)

As you'll see, the Ingersoll wire mike is based on an outside micrometer, and is especially well-suited for setting up large machine tools. Other wire mikes are based on inside micrometers, making them well-suited for measuring the location of a wire relative to large bores. In either case, though, the wire mike is almost always used to make relative measurements of wire-to-object separation rather than absolute measurements.

A commercial source for the inside-mike variant would be Powerhouse Tools at http://www.powerhousetool.com/images/VibL.jpg (son of a gun, that Copy / Paste worked fine but it still doesn't want to copy from the Ingersoll website).

John

 

[J Henricksen]

Ingersoll made a dedicated mag base with a micrometer drum mounted to an electically isolated box with a meter and LED in it. The a battery inside the box connected one leg to the mike drum and the other to the mag base. When the mike anvil touched the wire, the led and meter would let you know. A cup with a sharp edge was fastened to the mike so just a fine edge would contact the wire. .0005 was a fair accuracy to expect out of one.
Ingersoll farms out all the parts to one of my other customers now.

 

[lalatheman]

I tried the link for sag tables, in Forest's first post that started this thread,
twice yesterday and again today , i get #404 error seems to indicate the site doesn't exist .

Few hours of searching using google and searching on Google Books through old machinist books hasn't turned up anything
yet.

Anyone have any leads to sag tables ?

Dave

 

[dsergison]

with excell or any spreadsheet, I wonder why finding an old sag table is very important?