Making a wood and Aluminum XC MB- Mtbr.com
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  1. #1
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    Making a wood and Aluminum XC MB

    Hi all,

    I've been talking with Peter Charnaud about his mountain bike and have decided to build a similar XC bike. I'm borrowing from Orange 5's single pivot design. It will be made from plywood with internal and external aluminum reinforcements. I do design and have a small cnc shop. I've made several machines using plywood and aluminum so I feel right at home with this build. Below are some early concept sketches. I'm getting close to finalizing things. I hope to start actually cutting out parts within the next week or 2.

    My head tube angle is 67.3 degrees. Which from my research goes with the type of riding I like to do. Nothing too aggressive just a little fun here and there. Mostly light duty trails. I'd be surprised if I'm ever 10 inches off the ground.

    My biggest question right now is reach and wheel base. No idea what my ideal reach would be. I'm 5'9"

    The wheel base is currently 45" or 1143mm. Researching wheel bases that's on the small side of things. I come up about 30-50mm short. I'm guessing that's not going to make much of a difference. But I dunno.

    On wheel size I'm thinking 27.5. Was planning to go 26 but I think I would feel more comfortable going 27.5 with a little extra front flip over protection.

    I'm sure I'll have more questions down the roads, just wanted to say high and get this thread started.

    My best,
    Chris

    Making a wood and Aluminum XC MB-side.jpg

    Making a wood and Aluminum XC MB-top.jpg

  2. #2
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    I'm attaching some more pictures of how I plan to do the BB and the pivot. For the BB I'm going to braze a support to it that will be sandwiched and epoxied between the wood. For the pivot I'll just make some bearing blocks.Making a wood and Aluminum XC MB-crank.jpgMaking a wood and Aluminum XC MB-pivot-point.jpg

  3. #3
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    I don't have much to contribute, I just want to see how this thread goes :0)

    Plywood as been around for a long time. My bet is that bikes are not made out of it for good reason.

  4. #4
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    @ Mr. Pig

    I think it comes down to mass production and quality control. Plenty of wood and plywood bikes have been made. Renovo's business is just wooden bikes. https://www.youtube.com/watch?v=EkmbCGdTZ98

    I think for the type riding I'll be doing it will be fine. We will see.

  5. #5
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    Seems like wood would expand/Contract too much with variations in humidity in applications where precision matters

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  6. #6
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    Interesting video, thanks for that :0)

    My concern would be that unless you'e done a whole bunch of stress analysis and testing your frame could fail. Love that you've got the skill to build such things but before I rode the bike I'd want to do more than 'think' it would be ok. It's not a patio door, bike crashes can be life changing, or worse.

  7. #7
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    Quote Originally Posted by Weaponized View Post
    Seems like wood would expand/Contract too much with variations in humidity in applications where precision matters

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    You deal with that with your finish. A great example is wooden boats. But no doubt bolts should be checked each season for swelling and shrinkage.

  8. #8
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    Quote Originally Posted by ChrisFandz View Post
    You deal with that with your finish. A great example is wooden boats. But no doubt bolts should be checked each season for swelling and shrinkage.
    Yeah I considered the use in boats but boat hulls don't have to hold bearings and pivots. I'm sure it's doable but I don't see any advantage to it other than being unique

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    I see what you are thinking but they do hold oars, motors, and rudders to name a few. Also the wood won't be holding the bearing blocks for the pivot. They will be bolted to one another and will be sandwiching the frame.

  10. #10
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    Quote Originally Posted by ChrisFandz View Post
    I see what you are thinking but they do hold oars, motors, and rudders to name a few. Also the wood won't be holding the bearing blocks for the pivot. They will be bolted to one another and will be sandwiching the frame.
    The bearing/pivot thing wasn't in the context of strength...was thinking more along the lines of the effect of expansion on the position of those items. Maybe if you could bake the wood to remove residual/natural moisture content before sealing you could avoid issues. Interesting project and good luck.

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  11. #11
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    Quote Originally Posted by Mr Pig View Post
    Interesting video, thanks for that :0)

    My concern would be that unless you'e done a whole bunch of stress analysis and testing your frame could fail. Love that you've got the skill to build such things but before I rode the bike I'd want to do more than 'think' it would be ok. It's not a patio door, bike crashes can be life changing, or worse.
    Yeah that's a tough one. I use deflection calculators and such but it's hard to stress test this sort of design with it's mixed of epoxy materials. The bottom tube/beam is my biggest concern as it gets a lot of torsion. I've thickened that area from where I started and moved the shock mount to it. The shock mount will be in the center of the frame to hopefully give it even more torsion resistance.

  12. #12
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    Quote Originally Posted by ChrisFandz View Post
    The bottom tube/beam is my biggest concern as it gets a lot of torsion.
    I would be looking at ways to prevent sudden, catastrophic failure. If the wood starts to crack or separate it's not to big a deal as long as it does it gradually and you can spot the failure before bits fall off your bicycle.

    My biggest worry would be the head-tube. Your rear pivot blocks are also cutting holes in an area that sees some of the highest loads. What about putting the bearings on some kind of strap that's banded around the seat-tube?

  13. #13
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    Quote Originally Posted by Mr Pig View Post
    I would be looking at ways to prevent sudden, catastrophic failure. If the wood starts to crack or separate it's not to big a deal as long as it does it gradually and you can spot the failure before bits fall off your bicycle.

    My biggest worry would be the head-tube. Your rear pivot blocks are also cutting holes in an area that sees some of the highest loads. What about putting the bearings on some kind of strap that's banded around the seat-tube?

    The pivot point does have a lot of reinforcement. One thing I could do instead of using though bolts to hold the bearing blocks is change to threaded rod and tap the wood and center BB support plate in one go. That way any movement would have to move everything.

    On the head tube, Peter recommends I use Fiber glass tape that goes around the head tube and back 6 inches into the frame. 7 layers of that epoxied in and it isn't going to go anywhere. I'm looking at ways to work that in now.Making a wood and Aluminum XC MB-pivot-supports.jpgMaking a wood and Aluminum XC MB-pivot-supports-top-view.jpg

  14. #14
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    What type of plywood are you using, and are you going to glass it when done for strength like a boat?

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    Keen to see how this turns out so keep us posted please?

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    Quote Originally Posted by Kolchak View Post
    What type of plywood are you using, and are you going to glass it when done for strength like a boat?
    On the plywood, I have some 3/4" Birch in my shop that I know of being relatively void free and of good quality. But it's only 7 Ply. Marine grade plywood with more layers (21? I forget) would be recommended and it has waterproof glues. I think I'm going to use the birch for the core and use 1/4 marine grade plywood for the 2 outside layers.

    I also have some Bamboo 3/4 ply. It has the strength but I don't trust the glue. I've had some scrap of it left outside and I've seen the top layer peal away after a while.

    On the finish I'm going to get with Peter and see what he recommends. But I'm pretty sure it'll be some sort of clear epoxy finish system with a UV varnish clear coat. Just not there yet.

  17. #17
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    Subscribed. Looking forward to this.
    Disclaimer: I run Regular Cycles (as of 2016). As a profiteer of the bicycle industry, I am not to be taken very seriously.

  18. #18
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    Quote Originally Posted by Drew Diller View Post
    Subscribed. Looking forward to this.
    Thanks Drew. Was talking with Peter Charnaud over the holidays and he recommended that I don't use ball bearings for the pivot as they will wear out early since they won't make full revolutions. So now I'm reworking the pivot using a steel shoulder bolt and a brass bushing. I should have some updates soon.

  19. #19
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    I grew up as a cabinet maker, under my father and uncle. I left that trade for something new, and became a machinist. I moved from there to being a foundry patternmaker; today we do almost all of our work via CNC, but my woodworking skills are still intact.

    I would NOT reccommend using commercially available plywood with alternating grain directions.

    I would reccommend looking at vacuum bag gluing and making your own "plywood". The actual frame itself can be then CNC milled if you have access to a machine with enough X/Y capacity.

    Perhaps "laminating" would be a more accurate term: many items are made with alternating species of wood for a pleasing visual look and strength/stiffness can be modified as a function of wood species, grain direction and kinds of glue. Epoxy, Urethane, Aldehyde, Ester and Cyanoacrylate adhesives come to mind, but there might be others.

    Not to be the wet blanket, but the frame you build will probably be heavier than most butted steel frames and certainly heavier than aluminum or carbon. If you wish to have a lively, "resonant/forgiving" ride choose springy, lightweight woods like spruce or laminates containing hickory or pecan.

    If your bike is to be more of a work of art, choose something like purpleheart and lacewood...it will be stiff and 'dead', but look killer.

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