Mod-out

Make it better or design it better? It all depends on the tools available to you. The design is so basic there isn't much to improve without making it more complicated. I would make all the inside radii be the same dimension, that way you can use the same endmill for the entire inside cutout. Your drawing is complete, which is good. You haven't called out any tolerances anywhere on the drawing, however. Then again, when I made the unicycle frame pictured, I didn't make any drawings at all, let alone picking tolerances. If you have a waterjet or laser rig available, then blank it out with that, and just deburr. If you're using a manual milling machine (such as a bridgeport), there are a host of things you could do differently. Instead of doing a million punch marks (note, you only need two punch marks to define and scribe a line. The fewer the punch marks, the better), scribing, and complicated layout, just figure out the size of the rectangle you would need to make the part out of. Mill a chunk of aluminum to that shape. Then calculate the location of the center of each inside radius relative to two perpendicular edges of the rectangle. Drill a hole of twice the radius at each of these locations. Then use an endmill to mill between these points to remove the rest of the material. Do all of those operations in the same setup, without removing the part from the vise. For the outside radii, use a belt sander and a radius gauge, or a file. It's a decent first machining project, but if you are careful you can do a much, much better job. Once you do so, mill out the middle of the part to thin the web (making a sort of I-beam section). This will do very little to reduce the strength, but will do plenty to improve the looks and reduce the weight.

Really nicely done. I like how simple you kept the design and fabrication. Glad to hear it works well, too. For the next frame, I agree with rainsco, really focus on the geometry, and worry about weight and strength (and appearance) later. Just make the frame quick and junky to test the geometry. Then do another to tune it again. Don't make either of those to last (consider them prototypes). Once you think you have the geometry really nailed, go buy a titanium or steel tube set, get the miters done right, and do a good job. Then you'll have a kickass bike, tailored to you. And the fabrication quality will be good, because you will have had practice on 2-4 frames before it to really hone your skills. It appears you are bronze brazing the joints. If that's the case, no titanium tube sets for you. You gotta TIG titanium. As for droupouts, headsets, and bottom brackets, anyone who tells you they're hard to make (even out of titanium) is full of shit. Dropouts are a reasonably simple job on a manual mill, and headtubes and bottom brackets are cake on any quality screwcutting lathe. Hell, you could do 2D CAD drawings of the dropouts you want, get them cut at a laser, plasma, flame, or waterjet shop (i'd go with waterjet, as no slag or heat affected zone), and then just grind the parts that fit the tubes to fo

Sketchup is the best free software, I'd say. That said, it seems much more aimed at architectural work than machine design (which is what things like bashguards fall under). If I were you I'd find a copy of Solidworks 2009. It's very functional, and also includes good rendering and FEA programs for checking out a part. Solidworks is a direct competitior with Pro/E (here in the states Pro/E is popular at bigger companies, but Solidworks is what you will find being used at most machine shops, etc). Solidworks is very easy to learn if you follow their tutorials. It also interfaces with MasterCAM very, very well, which means it's easy to transfer your files into a program for machining them. CAD programs don't have much of a spectrum on price. They are either free, or insanely expensive (thousands of dollars here in the states). Student versions are usually a bargain at a couple hundred dollars, but they If you want to kill an ant with a nuclear weapon, try Catia V5.0. I believe a seat of it is $15,000+. It's the program used to design things ranging from cruise ships to submarines to the Mirage jet fighter.

Oh please, listening to all these poor folk talk about their wussy titanium-this, aluminum that. Don't you know the real pros ride beryllium frames? They're just careful not to scratch them, and ride in well-ventilated areas. When I don't feel like pulling out my beryllium comp bike, I practice on my junky old maraging steel frame with Aermet axles and bottom bracket. The point is, there are materials out there that make titanium look like junk you'd find on a Target bike. But I don't understand why people argue about these things. Don't worry about material choice until you are designing your own bike. Until then, just look at which frames last the longest and weigh the least. Those are the frames you want. Because a broken frame is a broken frame, whether it be aluminum, aermet, 6al-4v titanium, lead, 4340 steel, or play-doh... And the same thing goes for a light frame. http://en.wikipedia.org/wiki/Maraging_steel http://en.wikipedia.org/wiki/Aermet http://en.wikipedia.org/wiki/Beryllium

I got into bike trials through uni riding. Rode uni trials "seriously" from about 14 until 17. At my best I was riding some handrails, 36-38" sidehops, 5-6' gaps. I stopped when I left for college, as there aren't any good trials lines on campus. I still ride downhill on a unicycle. It's more similar to trials biking than downhill. The emphasis is on steep and technical, not fast. I decided to start bike trials because it's much more elegant and the moves are smoother. Unicycle trials is basically riding a pogo stick, especially since almost nobody does uni trials on 26" wheels; everyone rides mod, which seems like a joke. I ride the same 24x3" with an HS-33 for downhill, XC and trials these days. More fun that way. Uni trials is easier in some ways, and harder in others. Big moves are harder to develop on a unicycle, but precise moves are easier. There are also much fewer basic skills for trials (rolling hop, basic hop, seat in front hop, rolling seat in front hop, still stand, and pedalgrab). Still stands (the unicycle equivalent to track stands) are much, much harder, but skinnies (especially curved ones) are dramatically easier on a unicycle than on a bike (no rear wheel to worry about). Last I checked, the record sidehop to rubber on a unicycle is ~133cm (52"). To pedal, add ~6-8".

Come to California! It's 11º C (52ºF) and sunny, and been like that for the past 2 weeks. Perfect riding weather...

It depends, are you trying to protect from dents, or scratches? If just scratches, the coke can advice sounds great. If dents, maybe you could try putting an old punctured innertube under the coke cans, making a dual-layer armor of sorts.

I'm not sure if it's necessary to practice just actuating your brake without the pedal kick. In the process of learning to hop on the back wheel, it's common to release the rear brake for a moment in order to "re-level" the pedals after they ratchet vertical. During this process, you get a bit of a feel for brake control as you hop. At least that's how I did. Then again I'm still not very good on the back wheel, and often feel as if I have to pedalkick to keep from dropping the front wheel. It has helped a lot to focus on leaning extra far back when landing from a pedalkick. Once you do get used to basic pedalkicks, mix things up. It can get very boring (and tiring), just stringing pedalkicks together in a row (As soon as I could, I practiced by starting on one side of a tennis court, and pedal kicking across to the other side the short way, not in one kick, of course. Then repeat). Lately it's helped to mix up practice by starting about 4' from a curb or drop, pedalkicking to the edge, then going either up or down (depending on the obstacle, of course), trying to not drop the front wheel after the obstacle, and being sure to pause and hop a couple of times between pedalkicks. It's more satisfying than just practicing on flat, and the crashes keep things exciting... I hope things work out. As long as you can keep practicing, you'll get there. If you get frustrated, stop. Either take a break and come back, or come back the next day. Balance skills often improve just by sleeping on them.

If it means anything, I'm 21 and started practicing trials a full nine days ago. Maybe it's worth asking yourself why you want to get into the sport. If you're in it to be the world's best, yeah, it wouldn't have hurt to start earlier. However, if it's just to have fun and enjoy the journey, then so long as your body can handle the moves, it's never too late to start. And even if you want to compete at the top level, you still aren't too old. At 17, you haven't even finished growing!

I'm just curious as to any techniques for rear-wheel pivots on a long bike. I ride a 2004 Zoo! Pitbull (1090mm wheelbase), and am 5'8". I have read the trashzen tutorials, but it's just such a struggle to lift the front wheel, let alone pivot once lifted (read, i can't pivot at all). Is there any trick to pedal-assisted pivots, or are they just not useful? I can front-wheel pivot OK, but I find that I can never go more than 90º (it's been that way for maybe 2 years). I assume the trick here is going to be working up the will to lift the rear wheel higher... To give an idea of my "level", I can trackstand (brakes on) in any position, backhop, do about 10-20 back wheel hops, and 10-20 consecutive pedalkicks consistently. Background: I got into bike trials through trials unicycling *dives for cover*. I've ridden offroad and unicycle trials for 8 years, and bike commuted for 5 (rode a 2004 Fuji Panic). That's how I learned flat bunnyhops (whoops), trackstands, and basic pivots. I switched because unicycle trials got boring (there's much more emphasis on urban moves in unicycle trials than bike trials).