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Undercarriage Wire

Old 08-22-2013, 06:54 AM
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davidhand
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Default Undercarriage Wire

I have a plane with 5/32 piano wire undercarriage that is obviously not strong enough. I intend to go to 3/16 and tried to buy a wire bender for this size, I was told they didn't exist and to heat it and bend it in a vice. I have tried heating piano wire before and it has destroyed its tempering qualities. Anyone know correct procedure for re-tempering the wire, would quenching in oil rather than oil help make it less brittle? if so what oil, would old engine oil be OK.
Old 08-22-2013, 08:18 AM
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flyalot
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Tower Hobbies has a K&S mighty wire bender in thier catalog
item K+SR5326 under $30.00. Will handle up to 1/4 music wire.
Joe
Old 08-22-2013, 09:11 AM
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jester_s1
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Music wire is usually 1095 carbon steel, which is a water hardening steel in most applications. Really thin sections like knife blades need to be oil quenched to prevent cracking, but that's a special case. The problem with re heat treating the music wire is that you are always going to have a section that got heated hot enough to draw the hardness out but not hard enough to reach critical temperature so that it can reharden. So unless you have a furnace where you can put the whole thing in and start from scratch, you're going to have soft spots.
It shouldn't be necessary to buy a wire bender though. If you have a piece of 1/4 inch or thereabouts rebar or steel rod you can bend the wire around that. The only real worry is putting too tight a radius on the bend which stretches the outside too much.
Old 08-22-2013, 10:56 AM
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RBACONS
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I haven't tried it but here's a link to an article by Roy Vaillancourt. I assume he knows what he's doing. http://www.nwrcc.com/articles/HeatTreatingMusicWire.pdf
Old 08-22-2013, 02:10 PM
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Gray Beard
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Heating it to bend is a bad idea. I have seen others state they can do it and get the temper back but it is an art beyond me. The bender Fly mentioned is a good one but if you have a vise big enough to hold it then instead of the bender just file in a couple of grooves into the top of the vise jaws and cold bend it. That is something I have been able to master. Up to 3/16 wire it isn't hard to do at all. When you get past the 3/16 wire it's another story, the wire gets pretty tough to bend. the grooves are just to keep you from over bending and making a weak spot in the wire or over bending.
Old 08-22-2013, 02:16 PM
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jester_s1
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I have nothing but respect for Vaillancourt, but I'll disagree with him on this point. Granted, his method might make a good enough landing gear that works just fine, but the metallurgy is going to be off. Here's a crash course: There are two kinds of steel crystals that we are concerned about- cementite and martensite. There are others, but these are the major two. Cementite is fairly smooth and contains no carbon in the crystal, while martensite is rough and does contain carbon. Martensite is the "hard" steel in that it resists deformation and wear and is extra stiff. It has those properties because the crystals resist rubbing against each other. Again, it's more complicated than that but that's enough information for the purposes of making landing gears. What determines which crystalline structure is in the steel is the speed of cooling from critical temperature. Critical temperature for 1095 is around 1475. That's when the steel actually becomes liquid and the carbon goes into solution. If it cools slowly the carbon will come out of solution and you'll get cementite, while a fast cooling doesn't give the carbon time to do that so it gets locked into the crystal, forming martensite. The actual speeds of "slow" and "fast" are different for every steel recipe. There is a third issue at stake though, and that is drawing. Martensite fresh from the quench is around 61-63 rockwell hardness, which makes it glassy brittle. A second lower heating called a draw or a temper will lower the hardness and add a springy quality to the steel. The hotter you go, the less hard the steel becomes and the less stiff but more flexible it becomes. It also becomes more prone to plastic deformation, which means it doesn't go back to its original shape. The right drawing temp to make a spring with 1095 is between 600-750 degrees, and the effect is instant as soon as the steel cools back to room temperature. That's how the music wire has been treated coming from the factory, which is why it is so good for landing gears. But if you do a fresh heat treat on just one spot, you're going to have a section on either side of your bend that got heated right up to 1300-1400 degrees but not to critical temp. Therefore, you are going to have a spot that is really flexible and hardly springy at all. The only way to avoid that is to heat treat the entire piece, which is beyond the ability of most modelers.
Old 08-22-2013, 09:12 PM
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JohnBuckner
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I would also question what the airplane is? For example there are some airplanes coming out of China with wire gear that is not piano wire and dead soft, totally not up to the job. For example the later container loads of the Super Senior from Nitro Planes the wire gear if you sat any of the airplanes on the gear it would look just like a slow motion retract gear. The wire was dead soft and never hardened.

During the time before the Sig Senor Kadet became avalible agine many of our students got the one from Nitro Planes so we always bent up new gear for the fellows with K&S wire which was totally up to the job without increasing the diameter. I use a simple pin bender in a heavy vise but in the case of the nosewheels I always leave out the coil as I feel they are uneeded .

John
Old 08-23-2013, 06:33 AM
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Villa
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Hi davishand
I have been in R/C planes since 1972 and have made many of my landing gear. I purchase 5/32 " dia. or 3/16" dia. music wire from my local hobby store and bend it cold using my work bench vice. But here is the secret: bending the wire over the vice jaws, which have a right angle, will overstress the metal and sometimes it even breaks. I always use heavy leather gloves to protect my hand in case it breaks. The secret is to grind a radius in the sharp corner of the vice and bend the wire over this radius. The radius should be about the same as the wire diameter. I hope you or others will comment on this. I NEVER heat the wire. There is no need to do that.
Old 08-23-2013, 06:40 AM
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LesUyeda
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What Jester says is valid, BUT. The stuff we get these days called "piano wire" is anything but the stuff we used to get. Now, the stuff doesn't handle anything like it "should". Out of China, who knows what it is. As far as annealing and retempering the currrent stuff; forget it. Cold work it and hope.

L:es
Old 08-23-2013, 07:39 AM
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Bax
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Usually, when you bend wire, you are actually drawing around a radius. Clamping in into a vise and then bending it will not allow it the draw, but will create a large stress riser at the bend. Wire benders allow the wire to move into the bend as you pull it around the bending post. Thicker wires need to have thicker bending posts to prevent stress cracks. One thing you never do is clamp the wire in a vise and then use a hammer to "help" the wire bend. That work-hardens the wire and makes it very brittle.

5/32" wire is about as thick as can be easily done by hand, unless you make a good bender with a long handle to give you the leverage you need.
Old 08-23-2013, 10:37 AM
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JohnBuckner
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I,ve never had or seen anyone have much luck trying to temper piano wire but have no problem bending my own cold with this tool:

http://www3.towerhobbies.com/cgi-bin...&I=LXL787&P=ML

Yes the method mentioned by both Grey Beard as well as Villa will work just as good I just prefer to not spend a lot of time grinding off a suitable radius in the jaw plates or doing that to my expensive vise even though the teeth are replaceable. T his tool has some advantage with the hex base that allows one to position the wire many different ways as you make the various bends to a comfortable position.

One hint for someone first doing there own cold bending One very handy hint is to always try to start with a full length piece 36 inch or more and plan your bend from one end as you go and do not cut off until completely done and in this way you will have all avalible length for leverage as you go. Don,t try to cut you full length stick for instance in two for making two main gear. Do one at a time as you go.

John

P.S. I suspect K&S may have pin benders for heavier gauge stuff. But not likely at your LHS.
Old 08-23-2013, 12:03 PM
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jester_s1
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You can get the radius by clamping a piece of wood in your vice to bend against. It will have enough give to let the inside of the corner have a radius without having to grind your vice jaws.
Old 08-23-2013, 09:48 PM
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davidhand
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Thank you gentlemen for the very informative replies. I think I'll get a K&S Mighty wire bender from Tower. My interest in tempering goes back to another lifetime when I worked for the city where I lived and found myself working in the blacksmith's shop. As a teenager I didn't get to do any clever stuff but I did get to put new points on the cities pick axes. As best I can remember the procedure went like this. Heat the tip to a good red heat and hammer it out to a sharpish point, quench about an inch of the tip until the red was gone, Then watch the colors as the heat was conducted back to the tip from father up the the tool. When the appropriate color appeared (probably blue) quench the entire tool in water. When watching for the colors it was necessary to rub the tip vigorously with a piece of pumice like stone to clear away any slag that was forming. Seemed to work OK never got any complaints.
Old 08-24-2013, 06:41 AM
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LesUyeda
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"Seemed to work OK never got any complaints."

Certainly valid: IF the carbon content of the "steel" is correct for tempering.

Les
Old 08-24-2013, 06:52 AM
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Gray Beard
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Right out of high school I became a welder, during high school in welding class we learned tempering, used a gas oven and had a color chart right in front of them to compare when it was time to quench the tools we were making. It worked. I have just never been able to get the temper back on piano wire. My first bipe I bent all the struts and LG wire using heat. The finished work looked great. I did have a bit of trouble when the axels I bent broke off on landing and the top wing cabanes broke but the bends were perfect. Then I was told about cold bending in a vise and I have never had the problem again. I have used a couple of different bending tools and they are pretty good. When I became a dental lab tech I learned wire bending and there isn't a lot of difference in bending wire for retainers or modeling except the size of the wire. A vise is all that is needed but it has to be mounted firmly on the bench. After you bend a gear or two it becomes really easy.

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