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darryl
05-19-2012, 10:02 PM
I haven't had time to play with this yet, but I now have the wire that I'm going to use for my straightedge project. Because it is music wire, it's high in tensile strength and springy. It's also got some curl to it from being packaged. I could have got it in the straightened condition, but then it's much more costly to ship, etc.

At any rate, I have a plan to straighten it myself. The plan is to string it up, with a method of tensioning it, then apply current to it. I'll force it to red heat very quickly, then remove the current. During the short time that it's red hot, it will expand and the tensioner will take that up and keep lots of tension on it. Upon cooling, the curl in it should be gone and it will be as straight as it will ever get. I will consider the bending that will occur as it goes around the pulleys on the backbone of the straightedge, and will compensate for that.

I'm wondering now what effect the rapid heating and cooling will have on the properties of the steel. Some reduction of the tensile strength will be ok, but if I'm merely going to turn it into soft wire, then I'd rather skip this step. Any ideas?

sasquatch
05-19-2012, 10:05 PM
Not an expert, but i'd say this isn't going to work.

Just going to end up with a piece of wire.

Mcgyver
05-19-2012, 10:15 PM
agreed, spring steel is heat treated...you will mess that up getting it red hot

randyjaco
05-19-2012, 10:22 PM
It you want annealed wire, it will work fine ;-)

Randy

jep24601
05-19-2012, 10:24 PM
Wouldn't fine nylon fishing line work best?

oldtiffie
05-19-2012, 10:28 PM
If I recall correctly, this is to do with using a wire under tension as a straight edge.

Irrespective of whether it is vertical or horizontal or anywhere in between it will be a catenary (curve).

Other than when it is vertical, a catenary is not and cannot be straight.

You would need the properties of the wire, its length and the load applied to calculate the off-sets at any points on the catenary if you want to use it as a reference to check something else for straightness as well as a distance measuring tool to measure the gap between the catenary and the item to be tested at the off-set points.

http://www.google.com.au/#hl=en&rlz=1W1IRFC_enAU360&q=catenary+wire+calculation&revid=198395127&sa=X&ei=dEa4T5GGE4SaiAe1qM3vCA&ved=0CCEQ1QIoBw&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=696f04903ec9d5bc&biw=1280&bih=549

Clevelander
05-19-2012, 10:29 PM
That if you simply tension the wire toward the top end of it's elastic limit you should find that the wire will be straight after you release the tension.

That said, not being an expert try googling an answer..I suspect it will be out there. Another place you might look is in the Machineries hand book.

I too am with the "not to heat it camp". It will for sure be worthless.

SilveradoHauler
05-19-2012, 10:37 PM
The above posters are correct, music wire is fine steel that has been hardened and drawn. Just like a knife blade! Heat it up past the drawing temperature and you will have soft wire.

Back in my industrial machinist days, we aligned very large Paper Machine assemblies, long steam turbine/generator sets, and other big stuff with music wire stretched extremely tight. We had small pulleys and other alignment gear that allowed us to string a long horizontal length of music wire, then turn a 90 degree so we could hang heavy weights on the wire. This gets the sag out of the wire so we could measure from the wire to the surface to be aligned. Could pluck some interesting tunes also on 100 feet of stretched music wire!

So you gotta stretch music wire very tight to use it for alignment or checking surfaces. And when you used a inside micrometer, scraping the wire to "feel" when the measurement was accurate, you could make some nasty tones.

A tight stretch gets the curl out.

Do some google work, you may find something like "Using Music Wire For Turbine Alignment" or "Using Music Wire for Paper Machine Alignment".

Do you have another post on your music wire straightedge? If not, describe your method.

If you do not stretch the music wire very tight, you will be able to easily deflect the wire, making it useless for a straight edge. If you still have curl after stretching, you are not stretching the wire enough.

Bob Fisher
05-19-2012, 10:48 PM
I believe you have to stretch it to exceed it's tensile strength, until you get it into a plastic zone it will return to at least some curl. Don't know what dia or length you need, but this could take considerable force. Difficult to do over a long length. I guess you could stretch it to the breaking point, the remnants should be straight and possibly even harder.Bob.PS, Hauler beat me to it!

darryl
05-19-2012, 11:06 PM
Oldtiffe, I'm aware of the catenary curve problem since you pointed it out earlier. I did plan on having the wire vertical for the heating and subsequent mounting to the backbone, with all the other steps done vertically as well.

Seems most of you think I will ruin the tensile strength of the wire by flash heating it like I've suggested. I will go with that idea for now. I can always orient the wire so the curl is at 90 degrees to the eventual 'test edge', which should mostly eliminate the effect it might have on the straightness of the tensioned wire.

This is music wire- by mis-communication or mistake I also got a roll of soft stainless wire with this. I expect it would be easier to straighten by tensioning than music wire, but I have thought the music wire to be more uniform in diameter along it's length. Don't know if this holds true- it would be good to know how accurately wires of this type are made. The music wire is .040 and the stainless is .051. I would tend to think that either would be about as uniform as the other, simply because of the way wire is made.

My traditional method of straightening wire may not be appropriate in this case. Tie one end to a non-movable object and the other to the bumper- give a little clutch and bump while trying not to whip it- cut sections out with vise grips. In this case I think I'll make a one-string guitar from a pair of steel beams and just rig up a threaded rod as a tensioning device. I can try to relate the force I apply to the nut to the degree of stretch and curl removal I get, just to maybe garner some info about the process.

darryl
05-19-2012, 11:27 PM
I do have a post back several days about my proposed method of constructing this, but basically my plan is to have a rectangular tube as a backbone, mount a pulley at each end, then string the wire around it and tension it from what will become the back side. I would then mark the points on the wire where it just begins to wrap around each pulley, then remove the wire and put the same radius of bend into the wire before remounting it. That should mostly eliminate the curl that would be introduced into the wire at the point where it leaves each pulley.

Beyond that, I would be carefully shimming between the wire and the backbone to keep the wire in exact position once it's under tension, then introduce a spot of epoxy at that point to fix the wire in place. Hopefully I can use shimming to prevent the surface tension of the epoxy from pulling the wire towards the backbone. I would do this at several points along it to fix the wire into place. All done vertically of course. The placement of the pulleys would be such that the wire lays very close to, but not touching the backbone. The epoxy droplets would find their own positions by capillary action.

The epoxying would not be done until the wire has been under tension for awhile, say a week or more. The tension would be raised slightly at that point, then the epoxy applied. The tension would not be altered after that time.

I have experienced stretching wire to the breaking point, but then I find that the 'remnants' are not straight. The somewhat 'explosive' de-tensioning must be an uneven process within the molecules, or at least a function of inertial bending. With soft wire it's easy to enter the plastic state without breaking the wire, but I don't know how well this will work with music wire- I'll just have to experiment. I can always add some tabs of masking tape to two points, then measure the distance between them before and after stretching.

metalmagpie
05-20-2012, 12:03 AM
Probably missing something. Guitars have lots of music wire by definition. Once tensioned, the coiling from the string packages is no longer detectable. So why is yours a problem?

Back in the day we used to stretch music wire down the length of a shaft alley in large ships, to reference setting all the bearings for the propeller shaft. Despite being strung sometimes over 100' those wires were plenty straight enough. Forrest, coming from a shipyard machinist background, would know a lot more about this than I do, coming from a shipfitter (like a carpenter, only with steel - cut out and assemble parts) background.

metalmagpie

Forrest Addy
05-20-2012, 12:06 AM
You are stabbing in the dark. Heat music wire to red heat and it's just soft wire. Music wure stretched a couple of pervent results in a straight wire and you don'tave to anneal it but you do have to handle it correctly. You will have reduced its yield strength to about 1/4 as the hard drawn stuff. When tensioned it will sag 4 x as much as the hard wire. Plus there is scaling. Scaling will reduce the wire size significantly and unpredictably.

The generations old method of ensuring a straight wire is once it's placed and mounted, it's stretched beyond yield before its finally tensioned and precisely alined with the desired axis. How much to stretch the wire beyond yield has been standardized but I don't know what it is: 1/8" in 10 ft or some such figure..

A music wire stretched to 90% yield will be dead straight in the vertical plane but it will still sag in a horizontal plane. Gravity conquers all. Further, a stretched wire has zero resistance to deflection. A gentle breeze across a stretched length will perturb the line it's intended to represent. You have to work in still air and use methods that do not move the wire - grazing electrical contact or a microscope for example.

There's a whole technology of using stretched wire for alignment. It died out in the '50's when optical tooling became available. If you are interested look in older texts and handbooks intended for the millwright. Sag tables are still obtainable but its generally simpler to solve the formula in a spreadsheet incremented over the distances you wish to reckon. To my knowledge Ingersol is the sole purveyor of music wire apparatus still serving the market and it is expeisive.

To address your problem, tight wire is not well suited for short distance straightness application. You have to acquire/build the sensing apparatus and that's the same stuff for 100 feet as it is for two.

Give up on the wire for determining the straightness of a straight edge in a small home shop. If you need to make an accurate straight edge make three and work them using the Whitworth "averaging of errors" technique.

People full of assurances of how simple a lecturer's laser pointer, a stretched wire, a pool of water, etc is to use plain don't know what they are talking about.

Be assured of this: there is no easy way to make a straight edge without machine tools or references but it can be done. When done correctly, working with the right materials, the finished product will rival those from Challenge. If making a good straight edge is important to you, dedicate yourself to the task: study the way it was done when skilled men still walked the earth and ignore ignorant advice.

Paul Alciatore
05-20-2012, 05:17 AM
I can see many problems with the heating idea. For one if it is softened, it will start to stretch at the weakest point first and you can not control where that point is. So, it will become thinner there. There may even be two or more such points. It is almost dead certain that it will not stretch equally along it's length.

I am not sure about any standard figure for applying tension to it beyond the yield point, but if you go beyond the yield point, it will yield. That means it will stretch and again, it will yield or stretch at the weakest point first. So you will have the same situation as above with one or more areas where it will have a reduced diameter.

I believe music wire is straightened by drawing is past opposing rollers that bend it first one way and then the other. Again, I have no direct experience, but I would start with a pair that bend it by a fairly large amount and then another pair that bend it less. Then a third pair for less yet and perhaps a fourth pair that bend it just a bit. Use two sets of such rollers, one that bends it horizontally and the second vertically. Do NOT tension it beyond the yield point if you want the diameter to remain the same.

Actually, it will be far easier and probably cheaper to just buy a real straight edge.

beanbag
05-20-2012, 07:03 AM
Does anybody know at what temperature music wire can be heated before it loses its springiness? I once saw a table for the temperature ranges of spring steel, and it was all over the place - I guess depending on the alloy. If you just buy normal "music wire" from the hardware or hobby store, what alloy is it?

J Tiers
05-20-2012, 11:58 AM
If you just buy normal "music wire" from the hardware or hobby store, what alloy is it?

Dunno the alloy, probably anything above 1045 or so, but "very hard" it is NOT, and CAN NOT BE.

"Music" wire is wrapped around a peg, and tightened, in "musical" use..... it HAS to be annealed back to a low temper, somewhere in the blue range, or it would BREAK.

it still is substantially harder than dead soft wire, but....

Jpfalt
05-20-2012, 11:16 PM
I have used stretched music wire for several years. At one time Machineries Handbook included instructions for the setup and measurements an I used them for aligning sawmill carriage rails. The basic setup was a pair of pulleys, one at each end of the wire. Weights were applied at both ends until the wire starts to yield. At that point, the wire is as straight as it's going to get and the only correction is for the sag due to the effects of gravity.

When released, the wire turned into a rats nest due to the yielding. At that point, it is easiest to just throw the wire out. We bought it in spools of several hundred feet.

An alternate way we used was to set up blocks at the ends with cross drilled studs. The wire was put through the stud and locked with a tapered pin. The wire was then pulled to snug with the studs and then pulled an additional 3% of the wire length to get beyond 2% offset yield. This would be an easier approach for a shorter straight edge.

The downside of a stretched wire straightedge is that any contact with the wire generates a deflection. We used an electronic contact sensor that allowed vertical adjustment to .00005 and took the reading at the point that the sensor lost contact.

On a short length, I would suggest the possibility of stretching the wire and then filling under it with epoxy to support the wire. In the end, I think you will do better to purchase or scrape a rigid straight edge.