I remember people on Usenet saying the same thing about the Web. (I agreed with them.)
Myspace has a zillion users and scads of (dubious) information, mostly targetted at the interests of young hip people. Sooooooo, young hip people find it useful.
Dodo birds, certainly. But there were a *lot* of passenger pigeons. Estimates range as high as a trillion. If people at large were as motivated to wipe out frogs as they were to kill passenger pigeons, they'd make a big difference (which is why I think robots might do a good job: they have no problem with motivation.) The major difference being that when you can't see any more pigeons, they're all gone, but some frogs can go into weird desiccated hybernation states underground, in semi-dried mud, and come back ten years later when it gets wet again, so I don't think anything motivated purely by hopes for a quick fix -- the sorts of things that the military is good at -- is going to be successful long-term.
Good for the crows. That's really cool to hear. They're clever animals.
Seriously. That has the potential to solve these sorts of problems: an autonomous frog-eating robot, solar-powered, that just cruises around and chews them up. If you're worried about false negatives, have it capture them, take a picture, and wi-fi it to a bunch of minimum-wage outsourcing victims who mod 'bufo' or 'not bufo' and base their wage increases on a metamoderation system. Make sure the toadba units can float. Every couple of months hire someone to go collect all the ones that haven't moved in a month.
To a first approximation, that's exactly what airplane engines are. You assume that an airplane engine produces half its volume in horsepower: an O-360 makes 180 horsepower. That's coz it's running without gearing and your prop's only able to spin at about maybe 2500 rpm max before the tips go supersonic (and you make hellacious noise and chew up the prop and put all your power into fighting transonic drag.) Since power rises linearly with the RPM (until just after the torque peak of the engine) running an engine slowly means lower power. Auto conversion engines usually run at higher RPM with a gearing setup, like a car's transmission, to get high power out of a small engine, and pay the cost of reliability. There are gains that can be made: liquid-cooled engines weigh more but their mechanical clearances are better since they operate at near-constant-temperature rather than having the 300 degree engine temp fluctuations of aircraft air-cooled engines, and you can increase the cooling capacity of the system to allow the auto conversion to run at very high power settings for long periods of time. But then you run into strength and resonance issues: auto engines were not designed to run for any length of time at a single RPM, and when you do that you find resonance issues that fatigue parts and lead to premature breakage, and increasing the cooling capacity of the engine vastly increases drag (since for many airplanes over a quarter of the aircraft's drag is the cooling system for the engine unless you're going really fast and benefitting from the Meredith Effect, but that's only been used on a small handful of airplanes and doesn't apply to this situation.) If you look at the anecdotal evidence on places like rec.aviation.homebuilt, a large percentage of the people flying behind auto conversion engines (particularly homebuilt conversions rather than stuff like the professionals at Eggenfelter and the like) you see a lot of engine-stoppage-resulting-in-emergency-landing situations. You *very* rarely see this with aviation engines, tho' you see it a lot more in the homebuilts than in the commercially built aircraft. The NTSB indicates that commercially built aircraft tend to crash because they run out of gas or get flown into bad weather -- pilot error, in other words -- and homebuilts tend to crash because their engines fail -- builder error -- or they're flown too aggressively and stall/spin or break apart -- pilot error. Choose your poison.
Probably someone else has already mentioned this but if you can keep the flyer's weight under 254 pounds and its speed under 65 miles an hour, it's an ultralight and the FAA doesn't get to say much about it other than that you can't fly it in controlled airspace. And if you can land off-airport and don't have big registration numbers (which ultralights aren't required to have) it's not like anyone can catch you, in any case.
HP built many, many liquid-cooled processors, with tubing leading to remote heat exchangers. They were doing them as early as the late '80's, and quite possibly earlier.The problem is: in the end you're still dumping heat into air, on the end of the heat exchanger. I know there are systems that actually have full-loss water running through them and out into the sewer but that doesn't seem to be very popular, doubtless because there are environmental and ongoing-cost concerns.
This is going to be mostly for show, so I'll probably just forge it out of a truck leaf spring and through-temper it so it doesn't bend: I won't even worry about hardening since it won't have a real edge on it.
That toilet bowl cleaner can be nasty stuff. I was thinking "gee, if they sell it for fifty cents at Big Lots! it must be pretty lame stuff" so I bought a couple quarts and dropped a piece of galvy steel tubing in and a tiny droplet blipped up and landed on my hand and I knew in about a quarter second that it was really concentrated stuff. I haven't titrated it but I'm betting it's in the 60% pure range: nasty, nasty stuff. Be careful if you use it: keep a box of baking soda handy.
What sort of swords are you making? Have you done any work with titanium? I know someone who did a bunch of ti forging for an art project -- 4'x8' 22 ga sheets -- and it seemed to work really well for her tho' she said she only got about three anneal/forge/work-harden cycles, after which it just stayed hard, pretty much.
otherwise known as a steinmetz solid, which is often used as a demonstration for engineering drawing or architecture classes to show that a 3-d drawing of an object is not sufficient to determine its actual shape. A mouhefanggai in 3-D drawings looks like a sphere, but is actually a ridged object with a surface consisting entirely of flat-wrapped curves, rather than compound curves.
I was using uncoated mild steel wire. I also found (one of my other projects is making crazy bike frames) that toilet bowl cleaner -- hydrochloric acid -- does a fantastic job of quickly and accurately removing zinc from galvanized metals prior to welding. Put it in, and wait until the foaming subsides and the metal's just bubbling gently, remove, and scrub well with a brillo/scotchbrite pad, dry, and it's fresh, raw steel. (mind the 'foaming subsides' part because that's hydrogen-and-acid bubbles, both flammable and really nasty, especially should it foam over the container.)
For butted mail, I prefer the look of cut links, because I can butt them closed to the point where you can't see, at first glance, the joint. They look seamless until you turn them. I've never had clippers that gave me that good an edge. For the welded stuff, yeah, I'm clipping it. I need about 1/8" overlap for lapwelding, although a crazy new zealand guy (google welded chainmail hamish edgar) has a setup for buttwelding them, that I'll have to mod the spotwelder to try.
The sawing is definitely slower than the clipping, but finally I ended up making a tablesaw for metal: metal slotting saw on an arbor shaft, and I'd just run springs through it. It was *fast*. The intent is to build a semi-automated setup, where the springs come off a winder in 4' lengths, I put them in the slotter and get rings, then a (at this point very prototype, made of LEGO's) robotic arm grabs the individual rings, puts them in a compressor to smoosh them to overlap, then rotates them so the overlap is in a known position (fiddly optic stuff) and runs them through the spotwelder, so I have half the rings pre-welded closed. No telling when it's actually going to start working, because, yeah, job stuff intervening. And now my girlfriend's starting sword training in aikido and she wants me to fire up the forge and make her a sword. No rest for the weary...
I've always made my rings by rolling then cutting with a hacksaw and/or slotting saw. A while back I built a spotwelder out of a broken arc welder and now I find myself in need of thousands of overlapping rings -- a pain in the neck to make. (try to cut overlapped? ugly. Cut normally, then press through a funnel-shape to constrict? time-consuming. Pleh.) Stainless welds so beautifully, compared to mild steel, that I'm going with that for all my new construction... but I like the look and feel of mild. And yeah, stainless wears better against the skin. I'm wearing a bracelet that's been on my wrist for 15 years nonstop. It's mild. The rings are worn to eccentric, curvaceous shapes. My then-gf is still wearing the one I made for her of stainless at the same time and it still looks pretty new.
Spring steel is *expensive* and a bear to cut unless it's annealed, which cancels a lot of the advantage. It also breaks a lot more often during linking because it's already pretty hard and the work-hardening of a couple back-and-forths puts it into failure.
To bring this back to the original: titanium wire's great stuff, tho' a bit slow to cut. But it makes pretty mail. So far I'm completely unable to make decent spotwelds with it, but I'm still trying.
I thought I'd let you know that I've been using one of your mp3 players for, what, six years now? and it's been working beautifully? and only one of my friends has managed to buy an mp3 player with more capacity than what I've had for six years, so I swapped out drives in, oh, the time it takes to copy 70 gigs and plug in an IDE cable, just to trump him? That player rocks. The interface: a little primitive. (didn't spring for the LCD.) But it's perfect for a shuffle player in the car and in rental airplanes.
We're talking about a country in which schoolchildren are forced to make fireworks during school hours. I think it's unclear that the adults coming out of this sort of system are acting as rational agents any more than people who grew up in Jonestown were acting as rational agents. You're making some very Western assumptions about choice and free will.
Steels for machining are generally designed for interrupted cutting: serious impact. They spend a lot of time working on rupture strength to keep the material together.
I make chainmail, lots and lots of it. I've found, through testing, that stainless doesn't work as well as mild steel because mild has better impact/rupture characteristics. Not that I will ever use mail to that level, but it's interesting to know.
First off, these are field effect transistors, which they don't specifically mention (although they do use the correct terminology for FET's.)
Secondly, it's not really that they have three gates. It's that they have a block of silicon that can conduct from source to drain, and a gate in the middle of it that can deplete/enrich the adjacent silicon to change its conductivity. Where most FETs have the gate on one surface, or 1/4 of the conduction channel's surface area, this one has a gate that stretches around 3/4 of the channel's surface area. Instead of gating like stepping on a hose, this gates like clamping the hose with pliers (for analogy = depletion-mode). Pretty cool, but that should come with a 3x increase in the gate's capacitance, shouldn't it? and fighting capacitance is one of the major struggles of increased speed, right? People doing very low-power stuff should love this. People doing high-speed design, maybe not so much.
I hadn't thought about that, and you might be right. I'll have to go back and read some of my ME texts. I think I remember that machinists worry about both the shear modulus and the tensile strength when they're dealing with near-single-point contact during machining, which they seem to model as a tearing action, but I'm not sure that machining, at high feeds, works quite the same as sawing. I know the metal is disrupted to a quite significant depth beneath the cutting surface in heavy machining, which wouldn't seem to be the case in hand-sawing. (Especially not with the ring cutters I've used, which are basically slotting saws turned by hand.)
Rockwell numbers are kind of arbitrary. What the hell does 57 on Rockwell C mean in real-world terms? Think about what Rockwell and the like test: you apply a known force to a ball or diamond of a known cross-section and measure the resultant deformation. Force per unit area... is PSI. Or KPa. Those are non-arbitrary terms, or at least they're one level less arbitrary than Vickers or Rockwell numbers. "The yield strength in tension is about 1/3 of the hardness" and yield strengths are measured in KPa (if you're in a civilized country) or PSI (otherwise).
You can look at hardness as being a combination of deformability -- which is precisely elastic modulus -- and resistance to abrasion, which is a really complicated thing to measure. Wikipedia defines:"hardness is the characteristic of a solid material expressing its resistance to permanent deformation" which is also the definition of the yield strength: the point at which a material does not return to its original form when applied stress is removed. For metals, an approximation is that "The yield strength in tension is about 1/3 of the hardness". Stiffness is distinct from hardness: elastic modulus is largely independent of alloying, depending almost entirely on the base metal, but actual stiffness is determined mostly by the shape, thickness, cross-sectional area of the beam.
Actually, most gold worn by people in the US, at least, is 14kt or 18kt, which is about 60% or 75% pure, the remainder being taken up by hardening alloys. Silver, however, is almost always 92.5% pure. Some 18kt gold is pretty hard stuff, and platinum is QUITE hard. Nothing like hardened steel, but it sure takes a while to saw through thick platinum ringstock, when you're used to silver.
Yeah, the alloy and heat treatment make an enormous difference. I think there are aluminum alloy/treatment combinations that increase the material's yield strength by well over 10:1 compared to the base metal, and I think I remember reading about a weird Aermet steel that was similarly nearly 10x low-carbon steel.
Bauxite's what they use to get aluminum, isn't it? Is titanium a contaminant/major trace mineral in bauxite? I thought generally people mined rutile for titanium ore.
In any case, that's a classic colonial tactic: extract raw material from colony, bring to mother country, invest the intellectual and manufacturing capital, and then sell it right back to the place it came from. England did it with the US (cotton -> cloth; iron ore -> finished castings.)
First I had a Gios, with 531 tubing. It already had 60,000 miles on it when I got it and I put on another 40,000 -- and the frame still felt wonderful. Then I put it through the windshield of a Ford. Sigh. So after that I had a Cannondale. It cracked. I got another. It cracked. I got a Kestrel carbon fiber. It cracked. (all those in the space of 5 years.) So I got another steel Gios and six years and about 50,000 miles later: it's still going. All of those got some racing time in. The Gios is a lousy bike for serious touring given its angles, but I think I'll be riding steel until someone comes to take me away.
You make your own steel frames? That rocks. I'm just starting down that path. Any hints, books, websites that have come in particularly useful, would be very welcome.
Steel *can* be harder, but it isn't necessarily. Pure ti ranges from 35,000 PSI to 100,000PSI yield strength, depending on the route of manufacture. Some ti alloys go as high as 250,000PSI. (Converted from the article's 1725 MPa datapoint.) I've found references to steel having a yield strength in excess of 2000 MPa, but Wikipedia claims that titanium alloys are harder.
With all that said, I cut ti with a hacksaw, and snips for sheet, on a regular basis. It's no problem. It's *much* harder to cut than gold or silver, and somewhat more than platinum, so *standard* ring-cutting tools might not, well, cut it, but any jeweler can get a sawblade through the inside of a ti ring and cut it in under half a minute.
You're right those Teledyne forks were flexy. I've seen one of those collapse entirely under heavy braking on a downhill. Those things were dangerous: good thing you got rid of it, in my opinion.
If you decide against the Serotta -- which I wouldn't: Ben builds *great* frames -- check out Moots or Dean, both of which are truly great-feeling ti frames. I don't personally like ti frames, but the Moots nearly makes me change my mind.
Titanium doesn't rust at *all*. But neither does stainless, and it's really pleasant to work with, and you can spotweld your rings together really quickly. I've been making a bunch of mail this way lately and it's amazingly lightweight. I'm using stainless steel safety wire for airplanes, 18 gauge, on a 1/4" mandrel, welded, and it's unfreakingbelievably strong. A ring will support my weight. So, imagine a 12-pound hauberk that can stop an arrow from my compound bow. (hunting tip: I think a field point would go through.)
Spotwelding titanium, however, is not pleasant. So far I've yet to get good, consistent results where the weld is as strong as the surrounding wire. Oftentimes, in fact, the titanium splits and peels because of the thermal expansion.
Well... Titanium has a lower Young's Modulus than steel. Aluminum is lower yet. But if you calculate the specific modulus of elasticity, they're all pretty amazingly close to one another. Sheldon Brown talks about this a bit. If you need rigidity, you increase the cross-section, since stiffness is a function of a high power of cross-section times modulus of elasticity. A very modest increase in diameter, with corresponding decrease in section thickness, gives you a ti structure with the same weight and stiffness as a steel one. The interesting thing about ti is that it has about the same yield strength as steel, despite being only half as dense, so there are some advantages to using it.
Slashdot Mirror
I remember people on Usenet saying the same thing about the Web. (I agreed with them.)
Myspace has a zillion users and scads of (dubious) information, mostly targetted at the interests of young hip people. Sooooooo, young hip people find it useful.
Dodo birds, certainly. But there were a *lot* of passenger pigeons. Estimates range as high as a trillion. If people at large were as motivated to wipe out frogs as they were to kill passenger pigeons, they'd make a big difference (which is why I think robots might do a good job: they have no problem with motivation.) The major difference being that when you can't see any more pigeons, they're all gone, but some frogs can go into weird desiccated hybernation states underground, in semi-dried mud, and come back ten years later when it gets wet again, so I don't think anything motivated purely by hopes for a quick fix -- the sorts of things that the military is good at -- is going to be successful long-term.
Good for the crows. That's really cool to hear. They're clever animals.
Seriously. That has the potential to solve these sorts of problems: an autonomous frog-eating robot, solar-powered, that just cruises around and chews them up. If you're worried about false negatives, have it capture them, take a picture, and wi-fi it to a bunch of minimum-wage outsourcing victims who mod 'bufo' or 'not bufo' and base their wage increases on a metamoderation system. Make sure the toadba units can float. Every couple of months hire someone to go collect all the ones that haven't moved in a month.
To a first approximation, that's exactly what airplane engines are. You assume that an airplane engine produces half its volume in horsepower: an O-360 makes 180 horsepower. That's coz it's running without gearing and your prop's only able to spin at about maybe 2500 rpm max before the tips go supersonic (and you make hellacious noise and chew up the prop and put all your power into fighting transonic drag.) Since power rises linearly with the RPM (until just after the torque peak of the engine) running an engine slowly means lower power. Auto conversion engines usually run at higher RPM with a gearing setup, like a car's transmission, to get high power out of a small engine, and pay the cost of reliability.
There are gains that can be made: liquid-cooled engines weigh more but their mechanical clearances are better since they operate at near-constant-temperature rather than having the 300 degree engine temp fluctuations of aircraft air-cooled engines, and you can increase the cooling capacity of the system to allow the auto conversion to run at very high power settings for long periods of time. But then you run into strength and resonance issues: auto engines were not designed to run for any length of time at a single RPM, and when you do that you find resonance issues that fatigue parts and lead to premature breakage, and increasing the cooling capacity of the engine vastly increases drag (since for many airplanes over a quarter of the aircraft's drag is the cooling system for the engine unless you're going really fast and benefitting from the Meredith Effect, but that's only been used on a small handful of airplanes and doesn't apply to this situation.)
If you look at the anecdotal evidence on places like rec.aviation.homebuilt, a large percentage of the people flying behind auto conversion engines (particularly homebuilt conversions rather than stuff like the professionals at Eggenfelter and the like) you see a lot of engine-stoppage-resulting-in-emergency-landing situations. You *very* rarely see this with aviation engines, tho' you see it a lot more in the homebuilts than in the commercially built aircraft. The NTSB indicates that commercially built aircraft tend to crash because they run out of gas or get flown into bad weather -- pilot error, in other words -- and homebuilts tend to crash because their engines fail -- builder error -- or they're flown too aggressively and stall/spin or break apart -- pilot error. Choose your poison.
Probably someone else has already mentioned this but if you can keep the flyer's weight under 254 pounds and its speed under 65 miles an hour, it's an ultralight and the FAA doesn't get to say much about it other than that you can't fly it in controlled airspace. And if you can land off-airport and don't have big registration numbers (which ultralights aren't required to have) it's not like anyone can catch you, in any case.
HP built many, many liquid-cooled processors, with tubing leading to remote heat exchangers. They were doing them as early as the late '80's, and quite possibly earlier.The problem is: in the end you're still dumping heat into air, on the end of the heat exchanger. I know there are systems that actually have full-loss water running through them and out into the sewer but that doesn't seem to be very popular, doubtless because there are environmental and ongoing-cost concerns.
This is going to be mostly for show, so I'll probably just forge it out of a truck leaf spring and through-temper it so it doesn't bend: I won't even worry about hardening since it won't have a real edge on it.
That toilet bowl cleaner can be nasty stuff. I was thinking "gee, if they sell it for fifty cents at Big Lots! it must be pretty lame stuff" so I bought a couple quarts and dropped a piece of galvy steel tubing in and a tiny droplet blipped up and landed on my hand and I knew in about a quarter second that it was really concentrated stuff. I haven't titrated it but I'm betting it's in the 60% pure range: nasty, nasty stuff. Be careful if you use it: keep a box of baking soda handy.
What sort of swords are you making? Have you done any work with titanium? I know someone who did a bunch of ti forging for an art project -- 4'x8' 22 ga sheets -- and it seemed to work really well for her tho' she said she only got about three anneal/forge/work-harden cycles, after which it just stayed hard, pretty much.
otherwise known as a steinmetz solid, which is often used as a demonstration for engineering drawing or architecture classes to show that a 3-d drawing of an object is not sufficient to determine its actual shape. A mouhefanggai in 3-D drawings looks like a sphere, but is actually a ridged object with a surface consisting entirely of flat-wrapped curves, rather than compound curves.
I was using uncoated mild steel wire. I also found (one of my other projects is making crazy bike frames) that toilet bowl cleaner -- hydrochloric acid -- does a fantastic job of quickly and accurately removing zinc from galvanized metals prior to welding. Put it in, and wait until the foaming subsides and the metal's just bubbling gently, remove, and scrub well with a brillo/scotchbrite pad, dry, and it's fresh, raw steel. (mind the 'foaming subsides' part because that's hydrogen-and-acid bubbles, both flammable and really nasty, especially should it foam over the container.)
For butted mail, I prefer the look of cut links, because I can butt them closed to the point where you can't see, at first glance, the joint. They look seamless until you turn them. I've never had clippers that gave me that good an edge. For the welded stuff, yeah, I'm clipping it. I need about 1/8" overlap for lapwelding, although a crazy new zealand guy (google welded chainmail hamish edgar) has a setup for buttwelding them, that I'll have to mod the spotwelder to try.
The sawing is definitely slower than the clipping, but finally I ended up making a tablesaw for metal: metal slotting saw on an arbor shaft, and I'd just run springs through it. It was *fast*. The intent is to build a semi-automated setup, where the springs come off a winder in 4' lengths, I put them in the slotter and get rings, then a (at this point very prototype, made of LEGO's) robotic arm grabs the individual rings, puts them in a compressor to smoosh them to overlap, then rotates them so the overlap is in a known position (fiddly optic stuff) and runs them through the spotwelder, so I have half the rings pre-welded closed. No telling when it's actually going to start working, because, yeah, job stuff intervening. And now my girlfriend's starting sword training in aikido and she wants me to fire up the forge and make her a sword. No rest for the weary...
>Of course, mounting your kill is perfectly acceptable.
Necrophilia is so passe.
I've always made my rings by rolling then cutting with a hacksaw and/or slotting saw. A while back I built a spotwelder out of a broken arc welder and now I find myself in need of thousands of overlapping rings -- a pain in the neck to make. (try to cut overlapped? ugly. Cut normally, then press through a funnel-shape to constrict? time-consuming. Pleh.) Stainless welds so beautifully, compared to mild steel, that I'm going with that for all my new construction... but I like the look and feel of mild. And yeah, stainless wears better against the skin. I'm wearing a bracelet that's been on my wrist for 15 years nonstop. It's mild. The rings are worn to eccentric, curvaceous shapes. My then-gf is still wearing the one I made for her of stainless at the same time and it still looks pretty new.
Spring steel is *expensive* and a bear to cut unless it's annealed, which cancels a lot of the advantage. It also breaks a lot more often during linking because it's already pretty hard and the work-hardening of a couple back-and-forths puts it into failure.
To bring this back to the original: titanium wire's great stuff, tho' a bit slow to cut. But it makes pretty mail. So far I'm completely unable to make decent spotwelds with it, but I'm still trying.
I thought I'd let you know that I've been using one of your mp3 players for, what, six years now? and it's been working beautifully? and only one of my friends has managed to buy an mp3 player with more capacity than what I've had for six years, so I swapped out drives in, oh, the time it takes to copy 70 gigs and plug in an IDE cable, just to trump him? That player rocks. The interface: a little primitive. (didn't spring for the LCD.) But it's perfect for a shuffle player in the car and in rental airplanes.
We're talking about a country in which schoolchildren are forced to make fireworks during school hours. I think it's unclear that the adults coming out of this sort of system are acting as rational agents any more than people who grew up in Jonestown were acting as rational agents. You're making some very Western assumptions about choice and free will.
Steels for machining are generally designed for interrupted cutting: serious impact. They spend a lot of time working on rupture strength to keep the material together.
I make chainmail, lots and lots of it. I've found, through testing, that stainless doesn't work as well as mild steel because mild has better impact/rupture characteristics. Not that I will ever use mail to that level, but it's interesting to know.
That's why I'm in apps, rather than being a designer. Thanks: I didn't know these things.
First off, these are field effect transistors, which they don't specifically mention (although they do use the correct terminology for FET's.)
Secondly, it's not really that they have three gates. It's that they have a block of silicon that can conduct from source to drain, and a gate in the middle of it that can deplete/enrich the adjacent silicon to change its conductivity. Where most FETs have the gate on one surface, or 1/4 of the conduction channel's surface area, this one has a gate that stretches around 3/4 of the channel's surface area. Instead of gating like stepping on a hose, this gates like clamping the hose with pliers (for analogy = depletion-mode). Pretty cool, but that should come with a 3x increase in the gate's capacitance, shouldn't it? and fighting capacitance is one of the major struggles of increased speed, right? People doing very low-power stuff should love this. People doing high-speed design, maybe not so much.
I hadn't thought about that, and you might be right. I'll have to go back and read some of my ME texts. I think I remember that machinists worry about both the shear modulus and the tensile strength when they're dealing with near-single-point contact during machining, which they seem to model as a tearing action, but I'm not sure that machining, at high feeds, works quite the same as sawing. I know the metal is disrupted to a quite significant depth beneath the cutting surface in heavy machining, which wouldn't seem to be the case in hand-sawing. (Especially not with the ring cutters I've used, which are basically slotting saws turned by hand.)
Rockwell numbers are kind of arbitrary. What the hell does 57 on Rockwell C mean in real-world terms? Think about what Rockwell and the like test: you apply a known force to a ball or diamond of a known cross-section and measure the resultant deformation. Force per unit area... is PSI. Or KPa. Those are non-arbitrary terms, or at least they're one level less arbitrary than Vickers or Rockwell numbers. "The yield strength in tension is about 1/3 of the hardness" and yield strengths are measured in KPa (if you're in a civilized country) or PSI (otherwise).
You can look at hardness as being a combination of deformability -- which is precisely elastic modulus -- and resistance to abrasion, which is a really complicated thing to measure. Wikipedia defines:"hardness is the characteristic of a solid material expressing its resistance to permanent deformation" which is also the definition of the yield strength: the point at which a material does not return to its original form when applied stress is removed.
For metals, an approximation is that "The yield strength in tension is about 1/3 of the hardness".
Stiffness is distinct from hardness: elastic modulus is largely independent of alloying, depending almost entirely on the base metal, but actual stiffness is determined mostly by the shape, thickness, cross-sectional area of the beam.
Actually, most gold worn by people in the US, at least, is 14kt or 18kt, which is about 60% or 75% pure, the remainder being taken up by hardening alloys. Silver, however, is almost always 92.5% pure. Some 18kt gold is pretty hard stuff, and platinum is QUITE hard. Nothing like hardened steel, but it sure takes a while to saw through thick platinum ringstock, when you're used to silver.
Yeah, the alloy and heat treatment make an enormous difference. I think there are aluminum alloy/treatment combinations that increase the material's yield strength by well over 10:1 compared to the base metal, and I think I remember reading about a weird Aermet steel that was similarly nearly 10x low-carbon steel.
Bauxite's what they use to get aluminum, isn't it? Is titanium a contaminant/major trace mineral in bauxite? I thought generally people mined rutile for titanium ore.
In any case, that's a classic colonial tactic: extract raw material from colony, bring to mother country, invest the intellectual and manufacturing capital, and then sell it right back to the place it came from. England did it with the US (cotton -> cloth; iron ore -> finished castings.)
First I had a Gios, with 531 tubing. It already had 60,000 miles on it when I got it and I put on another 40,000 -- and the frame still felt wonderful. Then I put it through the windshield of a Ford. Sigh. So after that I had a Cannondale. It cracked. I got another. It cracked. I got a Kestrel carbon fiber. It cracked. (all those in the space of 5 years.) So I got another steel Gios and six years and about 50,000 miles later: it's still going. All of those got some racing time in. The Gios is a lousy bike for serious touring given its angles, but I think I'll be riding steel until someone comes to take me away.
You make your own steel frames? That rocks. I'm just starting down that path. Any hints, books, websites that have come in particularly useful, would be very welcome.
Steel *can* be harder, but it isn't necessarily.
Pure ti ranges from 35,000 PSI to 100,000PSI yield strength, depending on the route of manufacture. Some ti alloys go as high as 250,000PSI. (Converted from the article's 1725 MPa datapoint.)
I've found references to steel having a yield strength in excess of 2000 MPa, but Wikipedia claims that titanium alloys are harder.
With all that said, I cut ti with a hacksaw, and snips for sheet, on a regular basis. It's no problem. It's *much* harder to cut than gold or silver, and somewhat more than platinum, so *standard* ring-cutting tools might not, well, cut it, but any jeweler can get a sawblade through the inside of a ti ring and cut it in under half a minute.
You're right those Teledyne forks were flexy. I've seen one of those collapse entirely under heavy braking on a downhill. Those things were dangerous: good thing you got rid of it, in my opinion.
If you decide against the Serotta -- which I wouldn't: Ben builds *great* frames -- check out Moots or Dean, both of which are truly great-feeling ti frames. I don't personally like ti frames, but the Moots nearly makes me change my mind.
Titanium doesn't rust at *all*. But neither does stainless, and it's really pleasant to work with, and you can spotweld your rings together really quickly. I've been making a bunch of mail this way lately and it's amazingly lightweight. I'm using stainless steel safety wire for airplanes, 18 gauge, on a 1/4" mandrel, welded, and it's unfreakingbelievably strong. A ring will support my weight. So, imagine a 12-pound hauberk that can stop an arrow from my compound bow. (hunting tip: I think a field point would go through.)
Spotwelding titanium, however, is not pleasant. So far I've yet to get good, consistent results where the weld is as strong as the surrounding wire. Oftentimes, in fact, the titanium splits and peels because of the thermal expansion.
Well...
Titanium has a lower Young's Modulus than steel. Aluminum is lower yet. But if you calculate the specific modulus of elasticity, they're all pretty amazingly close to one another.
Sheldon Brown talks about this a bit.
If you need rigidity, you increase the cross-section, since stiffness is a function of a high power of cross-section times modulus of elasticity. A very modest increase in diameter, with corresponding decrease in section thickness, gives you a ti structure with the same weight and stiffness as a steel one. The interesting thing about ti is that it has about the same yield strength as steel, despite being only half as dense, so there are some advantages to using it.