"Bicycle" frame

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My younger son is nuts. Today he's on Mount Washington, known for the worst weather in the world. Today NH is covered by heavy rain. I assume Mount Washington is experiencing heavy snow. Wearing specialized ski boots made for climbing, he will climb over 6000 feet of elevation, something like seven miles, then ski down Tuckerman's ravine.  His idea of fun in summer is launching himself down a mountain on a "downhill" Bike. These things are custom built to tailor the frame to the rider's size. They are pieced together from component parts. A plan is available, those I've seen are coped and TIGged aluminum tubing. Everything seems manageable, but there are a few questions I have. Is it some exotic alloy or 6061? Welding aluminum will leave the heat affected Zone Annealed, as each member of a frame is strongest in the middle where it needs to be is this acceptable? Do builders have ovens sized to heat treat the welded frame, or is this unnecessary?Does anyone have any experience with this?
Reply:I don't know too much about this but i do know a lot of road bikers around here use steel framed bikes due to the terrible roads. The aluminum frames have been known to crack with the continuous vibrations. I can only imagine that the off road bikes would go through much worse abuse, albeit the frames are much beefier. My coworker used to do this downhill biking. I would highly consider steel instead of aluminum. The last thing you want is for the bike to fail while going 40+mph or off a jump. I really don't know that much about bikes though. Hopefully an expert will respond to your post.2 invision 456 mp, 456 pheonix, 3 hypertherm 1250, Hypertherm 45,Dynasty 200dx, Millermatic 210 w/ spoolgun, Bobcat 250, 12vs extreme, slugger dry cut saw, slugger mag drill, O/A rig, Piles of tools
Reply:I don't have an answer to your questions, but have a question for you on it. Are you getting into assisted suicide by helping him build the bike? I've seen some videos of those guy plummeting downhill like that on bikes. Tell him if he wants a REAL challenge, to go the other way on the mountain at similar speeds, UPHILL.
Reply:Zank on this board is the resident professional frame builder. But from what I know, yes 6061 is the most common frame material built domestically, and it is post weld heat treated back to t-6. But there is 7005 also which the Asian builders use that can be welded and not require an aging if the welding is done quickly enough not to let the base metal go into solution. 7000 series alum takes a LOONNG time to go into solution compared to 6000 series alum which goes right into solution. Typically 7000 alum can get it's stress relief from the powder coater so that is why you will find the Asian built frames painted instead of anodized. Good reading here too.http://www.eastoncycling.com/bike/wp...-7005_6061.pdfWeld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:OK, it sounds like it is probably beyond my skill and equipment level. The welding I could handle, The heat treating, I have neither the knowledge, or equipment to do. I guess you've got a point, contributing to this activity in any way is assisted suicide. Of course he's gonna do it anyway. In my misspent youth I never participated in sports where gravity provided the energy for thrill, but still managed to get injured a number of times. This kid has WAY too much energy!I'm not sure why these bikes are aluminum. Maybe because before you crash down a mountain, you must carry the bike up the mountain.
Reply:Originally Posted by Willie B. I guess you've got a point, contributing to this activity in any way is assisted suicide. Of course he's gonna do it anyway.
Reply:Willie B,Just a couple of days a go while channel surfing I came across part of a Modern Marvels episode that dealt with this exact thing.  Parts of this were filmed in the shops of two high end downhill bike building businesses.  One of the places was welding up the frames from formed sheet metal pieces.   I distinctly remember the guy from one business saying how that after all the welding was done the assembly was sent out for heat treatment.   Wish I could remember the name of the episode because I think it would really help you out to watch it.   There was some really interesting stuff in it.  These guys were building downhill bikes that sold for around $6000.   This whole heat treating of a welded aluminum bike frame to bring it back to a T6 temper may not be as complicated or undoable as you might think.   The procedure that details the time and temperature profile you need to follow can probably be found on line with a little research.   I've got access to an electric heat treat oven that goes to 1350 F.   It's computer controlled and is pretty accurate at holding specific temperatures for specific lengths of times.   The down side is that it's pretty good sized and wouldn't be very economical to run for just one bike frame.   The oven is of a size that 50 frames at a time would probably be possible.You know another possibility for doing this might be to use a commercial gas fired pizza oven.   Wouldn't that be a neat solution to the problem if it were possible?
Reply:Willie,Just did a quick search for "T6 temper procedure" and got this right at the top of the list.http://www.thefabricator.com/article...ation-for-6061Very informative one, short page read.  Looks to me like it's pretty much what you need to know.   Next thing you need to know is how hot your local pizza place's oven will go.   You could also check with your local powder coating business to see what their oven is capable of.   Then all you'll need to have is a timer you can set and a thermocouple probe run off a Fluke meter to help you keep track of the time and temperature profile.
Reply:Hi Willie,There's a lot to this (more than can be laid out in forum post), but here are a few points as food for thought. As Terry mentioned, a builder can choose between 6061 and 7005. The advantages of 6061 are that it is readily available, outside contractors are accustomed to working with it, and the quality of the material itself can be excellent if purchased from a reputable source. The main disadvantage is that it must be solution heat treated and aged after welding. Bringing a bicycle frame up to 1000F and then quickly dropping it in water does quite a number to the frame. You have about thirty minutes to then straighten and beat the frame back into a shape that resembles a bike frame. I'm not exaggerating here. It can get pretty ugly. Then the frame must be force aged at around 350F for a number of hours. 7005 only requires a forced aging at 250F - 300F for 10-12 hours. Frames can be aligned after aging. The main issue with 7005 is that it is more difficult to source, there aren't as many shapes and tubes available, and the material itself varies in quality. Most of what is readily available is geared towards road and cross country mountain bikes. Fixturing is something to consider. If it's a one-off project, you can get creative and make it work with materials you already have. It will take more time compared to using a frame jig, but it saves you the expense. The welding is usually what gives the most heartburn. A lot of guys get nervous about welding thin wall tubing. But you have this part covered. Aluminum is often the choice for a downhill bike and other suspension bikes because the tubing can be quite large in diameter and heavier in wall thickness without being exceedingly heavy compared to steel for example. The stiff frame allows the suspension to function more efficiently. Hope this helps. Let me know if I can help any further.
Reply:I used to ride quite a lot (road cycling and XC) and I fail to see the need for a custom DH frame.Surely there are those who feel that none of the currently available frames will serve them but honestly unless a rider has really weird body proportions he can find a frame that fits properly.Unlike a road bike you have lots of other stuff than affect handling, eg suspension design, which honestly I doubt you can improve on the currently available especially without any previous bike design and building experience.I will not go into the difficulties in frame building as others and especially zank who is a great frame builder covered it.Bottom line: Have your son find a DH that ticks all the boxes and bring out the check book.
Reply:The first downhill bikes were Schwinn beach cruisers.  The hot set-up was clamp on brakes for the front fork.  Many early MTB frame builders, some that are still around today, started their careers riding up fire roads in the back of a pick-up and then down on an old Schwinn scrounged together from parts found in the county dump.All downhill bikes are luxury items and as such, they are subject to conspicuous consumption.  Like everything else available, down to face cream, people feel the more they spend the more they get.  I have no doubts that 4130 and OAW would do just fine and possibly last longer but it just won't sound as cool as a 7xxx alloy heat treated and welding with TIG.
Reply:Thanks guys, I'm spent tonight, I'm going to bed. I'll read up on it tomorrow. Bistineau, It's not that I don't approve, but I do worry about his belief that he is invincible. I'd prefer he choose safer pursuits like B.A.S.E. jumping, or even car surfing. Just kidding! I believe the reason colleges are able to exist is that parents are willing to pay more than they can afford to have trained professionals warehouse their narcissistic children until they mature to a point where they can go forth and seek their fortune. As his mother says: "you'd have to experience this kid to understand." Oh, you were a lot sexier in your old avatar!
Reply:Originally Posted by BistineauI don't have an answer to your questions, but have a question for you on it. Are you getting into assisted suicide by helping him build the bike? I've seen some videos of those guy plummeting downhill like that on bikes. Tell him if he wants a REAL challenge, to go the other way on the mountain at similar speeds, UPHILL.
Reply:I weld aluminum everyday and there is no way i would even think about building a frame. If you were wanting to start a frame building business then go for it (very competitive niche). I dont see it as something you just decide to build one or two of. Here is a cool video showing a true master of frame building. It should give you a good idea of what it takes to build a frame the right way.www.performancealuminumfabrication.com
Reply:Originally Posted by Willie BHe has ridden up countless mountains, including Mount Washington. He's constantly beating his own record for getting to the top in record time. Lazy, he is not!
Reply:All of the frames I buy are heat treated and we have tried to weld cracks on bike frames before and they would end up cracking again with out heat treating.  These were hardtail and FS XC bikes so abuse wasn't as bad as a DH bike.  Well I had a friend who was a professional welder do it (not me but on my bikes) and were non-critical parts so when they cracked again it wasn't going to kill me (seat tube, seat stay, chain stay).  He warned me about the heat treating and he didn't have the means to do it.
Reply:I ride DH on a regular basis.  Some say nuts (mainly my wife), but no different than moto, skiing or anything else.  Zank covered the basics, but most frames are made from 6061 and heat treated.  I believe most builders sent out their frames for the treating.  There have been plenty of steel downhill bikes built, but the most prevalent is aluminum.  FWIW, they are made out of the same materials that motocross bike are, where guys consistently send 50+ foot gaps.  Like most other things, they wear out after a certain amount of time and need to be replaced.  I typically get a new frame every 3-4 years.This is me in Bootleg Canyon, NV.Shot of my current bike...although I just recently installed new forks.Last edited by kazlx; 04-28-2014 at 07:01 PM.
Reply:Build your own BBQ Pit.Build your own trailer.But don't build your own downhill bike.I know master bike builders who have said in retrospect, they wouldn't ride any of their first 20 bikes.
Reply:If everyone took that route, nothing would ever get built....
Reply:Originally Posted by kazlxIf everyone took that route, nothing would ever get built....
Reply:Originally Posted by BistineauBut is he doing it(going uphill) at the speeds he is planning on hitting going down hill?
Reply:Originally Posted by zankHi Willie,There's a lot to this (more than can be laid out in forum post), but here are a few points as food for thought. As Terry mentioned, a builder can choose between 6061 and 7005. The advantages of 6061 are that it is readily available, outside contractors are accustomed to working with it, and the quality of the material itself can be excellent if purchased from a reputable source. The main disadvantage is that it must be solution heat treated and aged after welding. Bringing a bicycle frame up to 1000F and then quickly dropping it in water does quite a number to the frame. You have about thirty minutes to then straighten and beat the frame back into a shape that resembles a bike frame. I'm not exaggerating here. It can get pretty ugly. Then the frame must be force aged at around 350F for a number of hours. 7005 only requires a forced aging at 250F - 300F for 10-12 hours. Frames can be aligned after aging. The main issue with 7005 is that it is more difficult to source, there aren't as many shapes and tubes available, and the material itself varies in quality. Most of what is readily available is geared towards road and cross country mountain bikes. Fixturing is something to consider. If it's a one-off project, you can get creative and make it work with materials you already have. It will take more time compared to using a frame jig, but it saves you the expense. The welding is usually what gives the most heartburn. A lot of guys get nervous about welding thin wall tubing. But you have this part covered. Aluminum is often the choice for a downhill bike and other suspension bikes because the tubing can be quite large in diameter and heavier in wall thickness without being exceedingly heavy compared to steel for example. The stiff frame allows the suspension to function more efficiently. Hope this helps. Let me know if I can help any further.
Reply:Thats a picture of the bike he has, and this is the site where he found the bike he wants to build. http://www.pinkbike.com/news/first-r...omad-2014.html
Reply:Note: The guy who doesn't have sufficient computer skills to post pictures still doesn't.
Reply:@Willie B Wow! Your son and I have a ton in common. I used to race downhill at Killington. And I've climbed mount Washington during the winter on a mountaineering trip. Was a great time.Why would he want a better bike then that? That's one of the best bikes you can buy for downhill racing. Heck he could sell those demax rims and fork and get enough to get a different frame but I wouldn't bother. I woulda killed to race on that Specialized bike. For perspective I raced on a Norco six (6 inches of rear travel) that had 150mm of front travel. Paid $500 for it and beat several guys who had $7500 bikes. Its not the bike, it's the rider.Craftsman 90 amp Arc welderI wasn't sure what you were talking about at first, WillieB. Snow and downhill "biking" as you put it made me first think of a ski bob, basically a bike frame on wheels. It triggered my memories of the time I was on the Canadian ski-bob team, with a pair of short skis on your feet and 2 skis inline mounted on the frame made for an incredible ride. Plenty of speed and plenty of control, going through fresh deep powder through the trees remains as one of the best experiences of my life. We raced Slalom and Giant Slalom, tons of speed, we were pretty good over jumps, too, just squeeze the seat with your knees to keep it from falling out under you. The ski bob is fairly popular in Europe, but ski hills on this side of the planet are reluctant to let them onto the chair lift.I agree that I think downhill biking is nuts, probably because I haven't done it yet, but at my age I don't really want a stainless steel hip. I cycle regularly and love the exercise, your son is setting himself up for a life of good health (if he can avoid the trees), so hats off to him! Once he gets over downhill biking, you could turn him on to cross country Unicycle which is equally nuts...Kids these days!!My Alu mountain bike broke on the downtube right behind the headset/forks, aparently this is quite a common problem for aging Alu frames. Attached ImagesLast edited by bearston; 10-15-2014 at 09:01 PM.When a welder tells you to "stick it", what do they really mean?"In a time of universal deceit, telling the truth is a revolutionary act." - George Orwell
Reply:@Bearston ski Bob's are sweet. Lots of fun.Craftsman 90 amp Arc welder
Reply:Unless you're someone like Zank, you don't build your own frame for some hardcore use just to get a custom size frame... you order a custom fame bike...Welding/Fab Pics: www.UtahWeld.com