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Thread: 1st Frame

  1. #1
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    1st Frame

    I've been reading this forum for the better part of a year now, and as a senior in high school, I'm building a rigid 29er for my CADD project. I'm basing my jig off of an extrusion I-beam design. I've haven't had access to my drawing at school, so I've attached a scan of a previous printout. I know the 2nd top tube doesn't do anything, but from what I read as long as the down-tube is ample it won't hurt. For the miters I was planning on using a hole-saw to get close, and then hand filing. I'll be riding it for cross-country trails here at Bootleg Canyon and in the Golden/Denver area when I go up to school. I'm about 6'5" and 240lbs.(without gear).
    I rode various 29ers at Interbike, so I based the geometry somewhat off of what I liked about those and with what I have and like, a demo 7 and a 24" bmx bike(that'd I've been using for the cross country trails). It will mostly be used for cross country but also messing around(doing wheelies around campus and what not). So what I came up with:
    Head tube:130mm(68/69 angle)
    Effective Top Tube: 635mm
    Seattube:500mm(74 angle)
    Chainstay length: 450mm
    Bottom bracket drop:66mm
    Wheelbase: 1160mm
    I plan on using a 470mm atc fork with 38mm rake
    The thing I might want to change is the chainstay length. I think it would probably be better for me shorter, but I'd like to use straight gauge 7/8" with a single bend, so I'm not sure how short I can get them like that to still have clearance for a larger tire. I plan on running a 1x9 gear setup. It will most likely be TIG welded by a professional that has been welding for a long time and has done a few bike frames in the past(the founder of Redline actually worked for him for a while) so I'm not worried about heat control but I'm not sure about tube thicknesses and changes to geometry I may want to make.
    Thanks,
    Aaron
    Attached Thumbnails Attached Thumbnails 1st Frame-frame-jig-4.jpg  

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    You should go with shorter chainstays if you plan to do wheelies or even lift the front wheel at all. Its going to be very hard to lift the front on a bike with 450mm stays. I'm at 425mm on my 650B and I wish I had gone about 10mm shorter. You can offset your seat tube forward on the bottom bracket to get a little more tire clearance. I'm sure your professional welder can give you some advice if he has done bikes before.

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    440mm stays are just fine. Going shorter will be hard to manage in terms of tire clearance. If you like wheelies a 29er might not be your cup of tea. People get way hung up on short chainstays but 430mm to 445mm will ride just fine.

    Wheelies are silly but it's not just about chainstay length...
    Chad Cottom's Mundo Wheelie - YouTube

    You don't need the small brace on the chainstays especially with TIG welded 7/8" stays. The little bridge does not add much strength or stiffness and is a pain to TIG. The extra top tube is also sort of silly because it makes the bike heavier and gets in the way of water bottles so I am not sure what the point is.

    Good luck and have fun with the build!

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    Well he's a welder, not a bike frame builder so I'm not sure if he'll have much advice in that area. I'm not sure if I'm just taking your comment the wrong way Dsaul or if my statement of "professional welder" rubbed you the wrong way, but I wasn't saying that I'm getting my frame welded better than anybody else, I just meant I know the person is a proficient welder and its not a friend of a friend of a friend who may or may not be able to do this.
    To febikes, should I remove only the chainstay bridge or the seatstay bridge also? I'm considering removing the 2nd top tube, but I do really like how the bike looks with in(sorta like some of Coconino cycles) and I figure if I'm making my own frame might as well make it different.
    I hope your car has a big trunk because I am going to put my bike in it.

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    Quote Originally Posted by mtnbikinggolfer View Post
    To febikes, should I remove only the chainstay bridge or the seatstay bridge also? I'm considering removing the 2nd top tube, but I do really like how the bike looks with in(sorta like some of Coconino cycles) and I figure if I'm making my own frame might as well make it different.
    Loose the chainstay bridge but keep the seat stay bridge.

    Also, use 5/8" round for seat stays or 16mm tapered. Use 7/8", 3/4", or bicycle specfic oval tubes for the chain stays.

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    Move the chainstay brace to the area between the rear brake boss and the chainstay.

  7. #7
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    Aaron;

    - I think you are reading DSaul wrong. He just thought your guy might have some ability to help you with the mods he suggested re; offset ST/BB, and other things to make the build easier and more successful.

    - The 2nd TT is redundant, but of course you know that. Adding a pure style piece is just fine as long as you can rationalize the extra weight. You might get a piece of .028 straight gauge to pare the weight down a touch, or even thinner if you can find it.

    - 17.5-ish CS is just fine. You can go shorter of course, but at the possible expense of some ultimate climbing traction. A 74* ST would shift your weight forward more, and that with the "longish" stays might make it harder to loft the front. However, I am the same size as you. I've got a 20mm longer TT, 454mm CS, and a 40mm longer WB, and I can still loft the front pretty much at will. I'll give you a traction for-instance; even riding my Kroozer in 6-8" of snow, I can climb a pretty steep grade, feel the front wheel floating off the ground a bit, and not lose traction at the back. Impressive.

    - I think .875 is overkill for the CS. I use .750 and it seems to work just fine. You can probably also use .625 for the SS without trouble, and save a bit more weight to offset your 2nd TT. Smaller tubes will also free up some tire space for you!

    - I wish that I had ditched the CS bridge on my Kroozer. It really catches a lot of muck. While it did add a noticeable amount of stiffening, that is when bending stays together with no wheel attached, and I'm not sure that is a valid test for any realistic action. My next frame will not have one.

    This from a two-frame-wonder with about 25% of a clue on any of this, so...
    Last edited by TrailMaker; 04-16-2013 at 10:58 AM. Reason: Spellung. ;)
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    TM is correct. I was just thinking your guy might have some experience that could help you figure out whether you should make changes to your design. With regard to chainstay length, I'm just sharing my experience. My frame also has a slack 69 degree head tube angle that lengthens the front center and puts the weight of the front wheel further forward. I ride fairly aggressively and like to lean back and loft my front wheel over obstacles while descending. I found that very difficult with the sliding dropouts at 435 and considerably easier at 425. I think it would be perfect for me at about 420.

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    Dude, he's 6'5"! I think he can probably lift the front wheel.

    Sheesh.

    -Walt
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  10. #10
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    Why the 74 seat angle?

  11. #11
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    The second TT will be welded into a thinner section of the down tube. No biggie, just harder to tig thin stuff but do it for the look if you'd like.
    cheers
    andy walker

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    tubing

    I'm dropping the chainstay bridge, and I didn't realize this printout didn't include the disc brake bridge. The second top tube will go for now, and if its all done and I decide I still want it, it can be added on without much trouble. I don't think I'll need to offset the bottom bracket for this one. The things I was unsure about were the effects of the seat tube angle and the fork trail.
    As far as tubing goes, I think it'll be;
    Head Tube:
    1.625" x .156" 4130 tube (Aircraft spruce), turned down to 1.6-1.7mm wall
    Top Tube
    31.8 x .7 / .6 OX Plat (BikeLugs)
    28.6 - 8/5/8 Ox Plat (Bike Lugs)
    31.8 x .9 Stress Relieved(VERHT1?)(Bike Lugs)
    Downtube
    34.9 x 1.2 / .8 x Stress Relieved 4130(Bike Lugs)
    Seattube:
    28.6 1.2/0.6/0.9 4130(NovaCyclesSupply)
    Bottom Bracket:
    1.5" x 73.5mm 4130(Paragon)
    Chainstays:
    3/4" x .035" 4130 tube(Aircraft spruce)
    Dropouts:
    Boomerang plate dropouts HD(Naked Bicycles)
    Seatstays:
    5/8" x .035" 4130(Aircraft spruce)

    Thanks for the tips and help everyone,
    Aaron
    I hope your car has a big trunk because I am going to put my bike in it.

  13. #13
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    Why a disc bridge with the Boomerang dropouts?

    Why not buy a head tube?

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    Didn't come across the Boomerang dropouts until just now, so I didn't realize I wouldn't need the bridge(correct?). As for buying a head tube, I don't want the 44mm Paragon one and I don't mind making one.
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  15. #15
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    No way would I use a .7mm toptube if I weighed two-fiddy. Supertherm the toptube. Supertherm the downtube and go 38mm - 35 is way too wimpy. Use whatever the thinnest thing you can find is for the kicker tube (or whatever you call it).

    Otherwise I'd say you're good.

    -Walt
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    Where should I look for supertherm tubing?
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  17. #17
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    Henry James has it.

    -Walt
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  18. #18
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    I find it interesting that big Riders keep shelling for smaller Dia downtubes. If you are spidery like me, I can get away with it, but boy!! 250 pounders....38mm min, if you like to play, 42mm. The strength increase of a couple of mm is huge for little weight gain when, now that the redundant tube is out of the picture, won't add diddly squat to the big picture weight wise. The riding quality reward for the bigger tube is just too much to compromise on. Top tube = 31.8mm with a .9mm butt. No problem with turning a head tube, its not mythical, Paragons are turned. 74* ST = about 10mm at the seat for a longer leg over 73*. Its tuneable for seat adjustment, but if a more aggressive ride position is adopted, it uses the riders leg power better, though compromises the ability to wheelie. Also, that 635mm TT will keep the wheelie balance firmly planted at the front end. Big bikes will always be a challenge to get all the ticks of the boxes. Looks good otherwise.

    Eric
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    So would a 38.1mm 1/.7/1 ST downtube and 34.9mm 1/.7/1 ST top tube work? And would it be worth getting a .9/.6/1.22 S3 seattube too than? Or is it not worth the extra trouble for reaming it?
    Thanks for helping me
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  20. #20
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    74 seat angle is a little odd for a guy your height - is there a reason you picked that?

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    Thought I addressed it, must've forgot. No reason really, just sort of based it off what I had ridden since I don't really know anything else. I'll be more than happy to hear if you have any advice about that.
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    I wasn't aiming for smaller tubes, I just forgot about Henry James. Would a 44.5mm 1/.7/1 ST be better for the downtube then, or is that pushing it too large? I'm not too concerned about weight. As far as seat tube angle, that was more so an arbitrary number and I welcome suggestions. I may considering shortening the front end too.
    Thanks,
    Aaron
    I hope your car has a big trunk because I am going to put my bike in it.

  23. #23
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    SuperTherm, where's Walt, this is his area.
    If I don't make an attempt, how will I know if it will work?

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    He gave me suggestions for the Supertherm, and said 38 for the downtube. I didn't notice there was a 44 Supertherm downtube. I don't really care about the extra weight, but was unsure if there would be a reason not to use that.
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  25. #25
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    Since crank arms don't scale proportionately to the range of frame sizes, you often see bigger guys on slacker seat angles to account for it. But without knowing your proportions and seeing what you ride now we can't say whether it will or won't work for you. You won't run into any mechanical problems with it, like you would if you were trying to do a really slack seat angle with really short stays.

    Same goes for the front end - hard to say without more information. It's long, but you're tall, and the long back end would probably balance it out.

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    Alright thanks. Do you think a 72 degree angle would be better to try?
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  27. #27
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    OK.

    I think maybe a halt might be wise here. The reason is that there is a need to digest the info a bit, but also suggest more info might be needed to not confuse the original request. Progress has been made, but a proper fitting with an experienced builder might be a good direction to go, then, a purpose built frame can be successful. The right elements exist here, but a personal fit would really be needed to go forward on.

    Eric
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  28. #28
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    Hey;

    I am exactly your size, although you being so young, I imagine we have it distributed a bit differently! My inseam is 36, with a 37" sleeve, so I am quite evenly proportioned frame-wise. When I built my first fatbike frame, I used an amalgam of bikes I knew fit me (my Niner RIP9), and the Salsa Mukluk fatbike. Those bikes are surprisingly similar, believe it or not. I used the basic Salsa geo. I made the front center longer by 30mm or so, but otherwise copied what the pros had done. I am generally happy with the results. The base numbers are 70* HT, 73* ST, 744mm Front Center, 450mm CS, 484mm ST, 330mm BB height.

    I developed a friendship with a fellow that has worked in the bike industry for many years as a fabricator/welder/machinist, and also builds bikes "on the side." He suggested tubing sizes for me based on my size, his experience, and my desire to keep things a bit simple to start. I used all straight gauge .035 CroMo. 1.375 TT, 1.5 DT, 1.25 ST, .75 stays. The results have been quite good, if I do say. I am interested in building one with shorter stays, and I might like to try shortening the FC back to where you are speaking of, but other than that I am happy with what I have, for my style of riding, which is techy, rocky, rooty, creek beds, and tight tree filled classic Northeast trails. Oh... and as little climbing as possible. I'm better pointed DOWN hill!
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
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    Quote Originally Posted by Eric Malcolm View Post
    OK.

    I think maybe a halt might be wise here. The reason is that there is a need to digest the info a bit, but also suggest more info might be needed to not confuse the original request. Progress has been made, but a proper fitting with an experienced builder might be a good direction to go, then, a purpose built frame can be successful. The right elements exist here, but a personal fit would really be needed to go forward on.

    Eric
    +1 on this. If you're considering a 2 degree slackening of the STA and asking if that would be better, then you need to understand more about your particular fit before you start making a frame to fit it.

  30. #30
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    Don't sweat the seat tube angle. Make sure your front center is where you want it. Then even if you miss the target by a few degrees on STA, you can just move your saddle around and/or get a setback post to get you where you need to be.

    People obsess over STA for no good reason. It's 15mm per degree if you're tall, folks. Less if you're short. You can move a couple degrees in either direction just by moving your saddle and/or swapping posts.

    -Walt
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    15mm per degree, and he's talking about 2 degrees already. How many 30mm set-back seatposts are on the market? I think Velo Orange's 32mm is about the only one (and it's a roadie, so would likely be short). I submit it's pretty important, if this frame is meant to be a keeper. If it's just a throw-away educational experience, by all means go for it.

  32. #32
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    Did you miss the part about moving the saddle on the rails?

    Most have ~40mm of total adjustment (so plus/minus 20mm) or more. You can make up most of the difference between 74 and 72 degrees without even swapping posts. Once you throw even a 15mm setback post into the equation it's pretty much academic.
    From the center of the rails, assuming a 74 STA, you can go forward about 1.5 degrees and back about 2.5 degrees using commonly available stuff.

    Is it a good idea to know what your saddle setback needs to be and design for it? Of course! Is it the end of the world if you miss by a degree or two? No.

    -Walt
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  33. #33
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    I would just buy the 1.6mm wall headtube stock from either HJ or Nova.

    Also, keep in mind that 42 and 44mm downtubes mean that you have to do a little bit of ovalization at the HT and BB to get them to fit up right, as they have a larger diameter than the HT and BB shell. It's not hard to do (just carefully squish it in a vise). The hardest part is making sure you have the orientation correct.

  34. #34
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    Quote Originally Posted by Walt View Post

    Is it a good idea to know what your saddle setback needs to be and design for it? Of course! Is it the end of the world if you miss by a degree or two? No.
    Sure, but if you don't know what you want, why not at least put it somewhere in the middle to give you the most range in both directions to experiment with? If most of his range is going to come from shoving things backwards, at his weight (and with a 27.2 seatpost) that's not where you'd really want to end up. There's certainly nothing gained by the steeper seat tube unless he has odd proportions.

  35. #35
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    Hey;

    I think there is merit in ALL the ST talk here. From my less than experienced perspective, I think that while it is not critical to hit the target dead on (and I certainly have not), it is at the least an exceptionally good thing to HAVE one, and further, to have one based on some solid reasoning. I know little of fitment, but from what I can reason, it seems like to me that a steeper ST angle would benefit a shorter leg, putting the body over the BB more. Is this correct? If so, that would not seem to be indicated here, as the boy is a biggun like me. Adding to that, and from my own experience, a 20-30mm shorter FC than I have on my builds would at the least set him quite upright, and might even overly cramp the cockpit.

    As mentioned, I might like to try an FC shorter by 20mm or so. Alternately, I might simply try a shorter stem. Besides reasons of Clydesdale fitment, I don't guess I would want to decrease my ability to loft the front by setting myself farther forward with a 74* ST angle.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
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  36. #36
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    It is really all preference. You can find >80 STA on some TT and tri bikes, especially from back in the days before the UCI killed the funnybikes (smaller front wheel than rear) but obviously those don't need to get wheels off the ground (or worry about going over a drop). Recumbents run less than zero effective STA, and there are head-first 'bents that are something like 180! So you can ride a bike with almost anything, but as I think everyone agrees, it's good to have a target for some kind of reason.

    I guess my point was that there are a lot of things that I'd obsess about before STA: trail, FC, BB height, CS length being the big ones. I'm not arguing that it's entirely pointless. But 95% of production bikes have a 72-73 STA for a reason - it works for almost everyone for most riding. Unless you have unusual tastes or physical attributes it's pretty safe to be anywhere near that range.

    I think it's also worth remembering that most of places where how the bike handles/weight is distributed matters are also places where you aren't actually sitting on the saddle.

    -Walt
    Waltworks Custom Bicycles
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  37. #37
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    Well...

    Nice of you to get to your point, Walt!

    No, seriously... I'm about the least technically knowledgeable "builder" you'll ever meet, and so I find when there is a discussion like this - like a funnel where wide ranging ideas merge at the center before hitting the container - I get a fuller, rounder understanding of the variables at play. It's all good!
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
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