3rd Frame - Wanted to Share - Also have a few questions- Mtbr.com
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  1. #1
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    3rd Frame - Wanted to Share - Also have a few questions

    So I built a 3rd frame for my wife - it's the first time I've built a a frame for anybody except myself which left me understanding how little I know about geometry... I ended up basing a decent amount around PVD's Glamorous Glennis - with a few exceptions as my wife is only 5' tall.

    Main frame geo:


    I tried something new for me this time, where I machined a 2 piece yoke and bullet-type ends for the CS, adapting to 3/4"x0.035" straight gauge tubing. I learned quite a bit making these parts at home and would like to eventually take this a step further whenever I finally decide to attempt a full suspension frame.



    I also welded this frame differently than I have in the past... previously I have welded frames with the pulser set ~40Hz, 35% on time, 35% background current with 0.045" filler rod... however this time I welded with the pulser set to ~1.5Hz-ish, 25% on time, 25% background current and 0.035" filler rod. It took me a little bit to get used to this, but the end result I feel was much better - this frame definitely had much less distortion and twist than my previous frames. I really only gut-check alignment on my home-made jig, but this is the closest end result that I have had:



    The final bike turned out pretty good I think... my 2 yr old son picked out the paint and so far my wife enjoys the ride, particularly the low stand-over and dropper post that actually fits her.



    Feel free to criticize if you have comments - maybe I can learn something new.
    Attached Thumbnails Attached Thumbnails 3rd Frame - Wanted to Share - Also have a few questions-akp-frame-geo.jpg  

    3rd Frame - Wanted to Share - Also have a few questions-yoke.jpg  

    3rd Frame - Wanted to Share - Also have a few questions-yoke-bullets.jpg  

    3rd Frame - Wanted to Share - Also have a few questions-ht-twist-akp.jpg  

    3rd Frame - Wanted to Share - Also have a few questions-seat-tube-twist-akp.jpg  

    3rd Frame - Wanted to Share - Also have a few questions-akp-frame-finished.jpg  

    3rd Frame - Wanted to Share - Also have a few questions-img_20200414_200645660.jpg  


  2. #2
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    Questions

    While everything is relatively locked down with COVID19 and I've got more time at home, I figured I would build another HT for myself... Mostly just small updates to my last frame... I also figured I'd ponder the prospect of one day building a full-suspension frame... but I have a few basic questions:

    Weld leg width - typically what is a safe weld-leg width? what do you guys usually aim for? I feel like it was mentioned to me when I was building my first frame to aim for a width of 5mm, however I have a difficult time getting it much wider than 4mm...

    3rd Frame - Wanted to Share - Also have a few questions-img_20200414_200645660.jpg

    Whenever I try and increase the weld width, I feel like things get too hot - the puddle gets squirly and/or I end up with holes... if I just need more practice please let me know, but I want to know if 5mm is the right goal. My weld settings are mentioned in the above post, and I typically set the machine to 115-120A, occasionally using the full pedal but not typically.

    Final question - I found this informative post about building an FS bike that I like, seems there are a lot of good suggestions around tube choice and keeping things simple which fit my MO: https://forums.mtbr.com/frame-buildi...r-1076824.html . Are there others like this that I have yet to find you guys are aware of?

    Thanks again.

  3. #3
    pvd
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    1. The handlebars look very high. Had you modeled them into your print? Saddle and bar position are more important than most numbers. Bars, stems, and spacers | Peter Verdone Designs

    2. Did you attempt to use the PVD-RAD calculations? I'm soooo RAD! | Peter Verdone Designs

    It looks pretty good otherwise. You learn the most designing for very small and very tall riders. You are forced to figure out what really matters.

  4. #4
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    PVD, you bring up good points and thanks for the links... and to answer your questions - no I did not have the bars/saddle modeled in nor did I attempt to use the RAD calculations. When I started this (frame building) I put most of my focus on how to actually build a bike and figured I would get to the geometry/fit/ride afterwards... I may actually be at that point now.

    I think I may also be at the point where I should spend the time needed to learn BikeCAD - it appears that as far as setting up geometry goes, it's very useful. Though I will say that the free-trial, web-based version is sooo slow it doesn't encourage me much to purchase it - I'm assuming the Pro version does not have this issue?...

    I did start taking some measurements of this bike today to figure out where the handlebars and saddle actually land. I don't have time to run through much more of it today or to measure anything with my wife, but I will get to this in the next little while and if/when I learn anything I will get back to you. I did notice however that the center of the grips are ~110mm higher than the saddle which seems to coincide with your first comment.

    While I've got your attention - do you have any links, forum posts, or thoughts on my question about weld leg width?

  5. #5
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    I have also wondered about weld width, i see some conflicting information around. I have settled on a width similar to yours between 4mm and 5.5mm. I find i can maintain a small HAZ comfortably and still buid a puddle quickly and all that.

    Im sure there's some engineering that could be done to determine the minimum width that is safe, however i have heard 3-4* the smallest wall thickness as a safe bet. Most of the frames i build are 0.65mm or 0.7mm tubing (road frames/light riders) so i guess you could get away with just under 3mm if you wanted to? However i dont really see any reason to push it. Your welding looks very tidy as is.

    Anecdotally there is a few builders near me (south east uk), whose work i have seen, they are (IMO) pushing what i would say is sensible (re weld width), for the sake of small HAZ i think. AFAIK neither have had any failiures so who knows.

    Im sure someone like PVD or others could produce a more informed answer, just my 2p

  6. #6
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    Regarding bikecad, its really good, worth the money. You could do it all in solidworks or other para cad, but its time consuming (for me atleast). Bike cad is an excellent program, runs great on my machine and is constantly updated with new stuff

    worth the investment for sure.

  7. #7
    pvd
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    Quote Originally Posted by a_j_p View Post
    While I've got your attention - do you have any links, forum posts, or thoughts on my question about weld leg width?
    Welding is one of the least important factors of a bicycle. Your work there is fine. The big problem here is that you didn't really sort out a design prior to building. Basics matter.

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    First off, your welding looks fine to me. If that was my work, I would t be worrying at all.

    Quote Originally Posted by pvd View Post
    Welding is one of the least important factors of a bicycle.
    Ha ha, more PVD comedy gold. I bloody love it!!!

  9. #9
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    Thanks for the feedback - I'm gonna dive into PVD's website and wherever else I can find and see what I can learn about geometry. I'll take some measurements and whenever I feel like I've actually started to learn something or have more questions I will get back. With any luck I can start scratching the surface and get another frame for myself built to learn more from before I have to go back to work...

  10. #10
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    Quote Originally Posted by Cord View Post
    Ha ha, more PVD comedy gold. I bloody love it!!!
    He's not wrong. As long as the welds hold together it's fine. Same goes for endlessly chasing your tail to get the frame perfectly straight, useless on the trail.

    Geo and fit are at the top of the pyramid.

    All to often we see threads from beginners that are worried about construction and jig/fixture then they decide to copy the numbers off a bike they know or think they will like. While it's not "wrong" (nobody's path is truly wrong) it's just not focusing on what's really going to make a difference on the trail.

  11. #11
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    A bike with chainstays that are 15mm too long or a 2į too steep seat angle or a head tube 20mm too long etc.... will all still get you along the trail just fine. A bike with an incorrectly welded headtube is a timebomb. Anyone thatís ridden a bike and had a catastrophic front end failure will know EXACTLY how important structural integrity is. Anyone that considers welding to be ďthe least important factor of bicycle designĒ is someone whoís advice should be taken with a pinch of salt.

  12. #12
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    Should I re-quote myself where I point out about the bike holding together?

    It's really really easy to braze a joint that will be strong enough to hold a bike together.

  13. #13
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    Quote Originally Posted by shirk View Post
    Should I re-quote myself where I point out about the bike holding together?

    It's really really easy to braze a joint that will be strong enough to hold a bike together.
    Eh? It was PVD that said welds werenít important not you?? And when did brazing come into it? Sorry, have i missed a post somewhere?? Iím confused!!!

    But I do disagree saying itís really easy to make a joint thatís strong enough to hold a bike together. Itís only easy if you can already do it, and if you canít do it, itís easy for it to end in tears. Where as getting geometry or fit wrong wonít end with you on the floor with a bike in 2 halves. Youíll just end up with a bike that either doesnít fit, or just rides a bit crap. For me, structural integrity is 100% the most important. If you canít make strong joints, it doesnít matter a damn if youíve just created the first ever perfect geometryíd bike.

    Anyway, the OPís welds look fine so I think Iím dragging this off topic. Sorry.

  14. #14
    pvd
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    Quote Originally Posted by Cord View Post
    A bike with an incorrectly welded headtube is a timebomb. Anyone thatís ridden a bike and had a catastrophic front end failure will know EXACTLY how important structural integrity is. Anyone that considers welding to be ďthe least important factor of bicycle designĒ is someone whoís advice should be taken with a pinch of salt.
    Welding is a very simple task. It can be done well enough and be fine and never cause any problem. Someone producing dangerous welds are far outside those that I'm talking to. You practice until you make a usable weld, then you can move on to things that really matter in a custom cycle.

    Welds that fail, failed at the welding bench or before that. Any knowledgeable metal worker will know how to handle a dangerous weld before it moves too far from the table.

    I'm speaking from approximately 30 years of experience in and around bicycle, motorcycle, and auto racing. I'm personally a terrible welder. I've seen failures and I've seen things work. I've tested almost all of my work personally and near the design limit.

    I can say, most people that talk about welding are either students or make terrible bikes. Their not terrible because of their welds. Their terrible because their maker put more priority on welds than what was important.

    Again, just 30 years of very specific experience talking.

  15. #15
    pvd
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    I was phoning in a bike build and in a rush one time. It wasn't important to me and I was in a bad place. Forgot to weld about 20mm of joint between the seat tube and bb. Didn't see it until it got back from paint. I went for it. Nobody has ever noticed it. Nothing bad has happened. Everything is fine. I'm not suggesting doing this. I'm just saying, running around like chicken little doesn't make one's advice valuable. Knowing what's important does.

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