How hard is it to make a kids' bike?

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  • How hard is it to make a kids' bike?
  • Premier Icon stevied
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    I made a balance bike a while ago, for my daughter, which she has now outgrown and we are looking at getting a bigger (16″ wheel) bike for her.
    The wife asked last night “why can’t you just make one like you did with the balance bike?”
    So, do you lot think it would be doable?
    I suppose the best place to start would be with a decent geometry chart?

    bencooper
    Member

    Like making an adult bike, only smaller – probably actually trickier than an adult one too.

    But your balance bike was stunning (it was the CNC’d one, wasn’t it?) – if you can make that then it shouldn’t be hard.

    thepodge
    Member

    Shouldn’t be too hard based on your skills. Depends what you want out of it.

    Premier Icon stevied
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    Yeah, that was mine BC :-). Thanks podge

    I guess one of the tricky bits would be sourcing decent 16″ wheels (probably with SS hub and, maybe disc on the rear), short crank etc. Can do a normal BB shell, head-tube for headset etc so that shouldn’t be too hard πŸ˜•

    bencooper
    Member

    I can get some reasonable 32h 16″ black rims, can do short spokes om my machine too if you get stuck.

    For cranks, it’s not too hard to shorten them as long as they’re not hollow.

    Premier Icon stevied
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    Ah, cool, thanks Ben.

    My mind is going off in all sorts of places now…thinking carbon tubing bonded to CNC’d lugs πŸ’‘

    Premier Icon midlifecrashes
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    Edinburgh bike coop do a kid’s size crank for cheapness.

    https://www.edinburghbicycle.com/budget-r-junior-chainset.html

    thepodge
    Member

    I guess it depends on what you mean by bike.

    Do you just mean a frame and bolt off the shelf bits to it or do you want to make as much as possible from scratch?

    If its just the frame then you could just buy an Isla / Frog / Hoy and transfer all the bits, probably little to no value in selling a frame so you’d just reassemble it and sell when they move to the net size.

    If you want to do the whole lot / as much as possible then why not start thinking like Hope and designing one around what is best, not whats available.

    This is what the Swarf guy did

    tpbiker
    Member

    .thinking carbon tubing bonded to CNC’d lugs

    i dread to think how long a carbon tube would have lasted on the bike i had when i was 8…

    thepodge
    Member

    oh and this is clearly a benchmark for you.

    Premier Icon mick_r
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    Will this be a Christmas deadline or slightly more relaxed? πŸ™‚

    Deadlines make it much more fun…..

    I’m just making a copy of my lad’s 26″ wheel mtb frame (originally built 3 years ago) for a friend’s daughter. At the moment it is a finished front triangle and he is filing the joints. I’m currently killing time waiting for dropouts to arrive from the nice guy at the laser cutter. Latest day for the powder coat is 16th December so we should make it in time……

    Can’t wait to see what you’ll come up with this time.

    Premier Icon stevied
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    Sounds like a good project Mick, be good to see what you’ve come up with. I presume it’s steel if you’re having laser cut dropouts?
    Only deadline for this is probably just her birthday in April so no rush which isn’t a bad thing as we’re really busy at work

    Premier Icon dirkpitt74
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    Wish I had the skill set to do this.
    Best I can do is bolt stuff to an existing frame.

    Geometry wise I don’t think you’d go far wrong looking at Frog/Isla frame geo.

    Good luck with this it sounds brilliant.

    km79
    Member

    How about one of those bamboo kits as a starter?

    Premier Icon mick_r
    Subscriber

    I don’t think stevie needs a kit… πŸ™‚

    Mine is steel, trying to shave weight wherever possible. Just done the bends in the skinny 12.7mm seatstays. Quite nice leaving someone else to do the drudge filing and polishing whilst I chip away at one little job each night.

    No online photos at the moment after Google archiving all Picasa stuff.

    April gives you time to do something really special. Sounds like your wife has given full permission!

    Premier Icon stevied
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    Nice to have a minion helping out Mick πŸ™‚

    Idea so far:
    16″ wheels, geometry based on an Early Rider, carbon tubes bonded into CNC’d aluminium lugs with the rear stays bolted on to the front triangle as I think it would make it much easier to assemble. Disc rear brake, single speed with short (or shortened cranks).

    If I go carbon which tube should I go for?

    Premier Icon mick_r
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    That all sounds a bit mundane. How about single sided enclosed drivetrain in a structural chaincase? I notice all Isla singlespeeds now have Hebie chaingliders to keep fingers out of cogs.

    Use a reversed 6 bolt front hub with both disc and sprocket mounted on the rhs. Then a freewheel on the cranks (like some trials bikes).

    thepodge
    Member

    I don’t like the classic carbon weave so I’d say use the bottom one but isn’t bonding alu to carbon a proper ball ache? something to do with alu oxidisation or something?

    However Mick’s ideas are way cooler.

    irelanst
    Member

    isn’t bonding alu to carbon a proper ball ache? something to do with alu oxidisation or something?

    Yes, you need to electrically isolate the carbon from the lug, a layer of glass cloth will work. Or use titanium lugs instead of ali, I mean do you really love your child or not?

    Premier Icon stevied
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    Would having the lugs anodised help?

    Premier Icon Rusty Mac
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    @stevied

    Bastion cycles do something similar to what you are describing however they make the lugs from titanium.

    You may get some ideas from their web site

    Process

    thepodge
    Member

    That’s what Robot do too isn’t it? carbon in Ti lugs.

    I’ve read people use fibreglass but never fully taken notice.

    How much would CNCing carbon mess up a machine? maybe do it all out of tubes & cnc carbon lugs / joints.

    Premier Icon stevied
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    maybe do it all out of tubes & cnc carbon lugs / joints.

    That’s the plan πŸ˜‰

    irelanst
    Member

    Would having the lugs anodised help?

    Yes, as long as the oxide layer (anodising) is intact and isn’t scratched during assembly.

    Premier Icon stevied
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    Mick, nice idea but I wouldn’t know where to start…A basic frame shape I can do.
    Had a little doodle this morning. The front triangle should be easy enough to do, will get a bit more complex on the rear end which gave me the idea of bolting the back on, gives me a bit of freedom to make sure I get it right.

    Dilwyn
    Member

    There are no issues bonding Ali to Carbon. Just make sure you use the correct primer (or seal in an airtight container until bonding) after you’ve prepared the surface of the Ali.

    Burchy1
    Member

    Just keeping an eye on this… let me know when you want me to cue the A-team music πŸ˜€

    Came across this a few days ago which might be of interest?
    Hope made a kids bike

    qwerty
    Member

    Bastion cycles do something similar to what you are describing however they make the lugs from titanium.

    3D printed IIRC.

    Premier Icon mick_r
    Subscriber

    Those cnc lugs are crying out to make a bolt on single sided rear end πŸ™‚

    I’ll just leave this here….
    http://julieracingdesig.canalblog.com/albums/_1_2_jrd____l_unijambiste/index.html

    Velosolo do disc mount 6 bolt fixed sprockets.
    http://www.velosolo.co.uk/shopdisc.html

    And a little more inspiration
    https://neilkoster.wordpress.com/tag/system-integrated-chain-case-technology/

    See also Mike Burrows 2D

    Premier Icon stevied
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    I was thinking of going single sided (with a Lefty hub?) but would then have issues with brake disc & sprocket on same side?
    Would still need to do some sort of freewheel, if the cog was bolted to the disc mount..

    Premier Icon mick_r
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    A lefty hub would allow a nice big stub axle. Easy option is brake disc and velo solo fixed sprocket mounted using 6 bolts and spacers between the two. Then freewheel at the crank end (see TartyBikes for examples of trials freewheel cranks). This would however be a finger remover if no chaincase fitted…..

    Could you make a freewheel carrier that attaches using the disc bolts? Disc bolt PCD is 44mm, freewheel thread is 35mm O/D I think, and M6 cap heads are around 9.5mm head diameter – so with a little head skimming it could just about fit.

    Premier Icon stevied
    Subscriber

    Could you make a freewheel carrier that attaches using the disc bolts? Disc bolt PCD is 44mm, freewheel thread is 35mm O/D I think, and M6 cap heads are around 9.5mm head diameter – so with a little head skimming it could just about fit.

    That’s a great idea πŸ™‚

    Premier Icon stevied
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    Starting to make a bit of design progress πŸ™‚

    After receiving a couple of carbon tube samples I’ll be going with a 35mm weave finish as it just looks way better.

    Bit more design work done on the rear swingarm/hub and I think I should be OK with a nice 20mm bolt through hub with disc and freewheel on the same side allowing me to do a single sided swingarm.

    CAD done for the front triangle lugs, geometry sorted….just need to get some time on a machine to make a start πŸ˜€

    Premier Icon mick_r
    Subscriber

    Fabulous!

    I was thinking about it the other day. Freewheel needs a shoulder on the carrier to screw up against. That will be bigger than 35mm diameter so needs 6 cutouts to allow fitting the bolts.

    My minion brings the finished front triangle back tomorrow. No dropouts until Thursday then final push to finish and paint before Christmas….

    thepodge
    Member

    How about using a centre lock hub and modifying a 6 bolt adapter to run the freewheel?

    Premier Icon stevied
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    Cheeky 1/2 hour on the machine today. Got the headtube/downtube/crossbar lug roughed out πŸ™‚

    Premier Icon stevied
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    It’s always good to get into work early πŸ˜‰

    Premier Icon mick_r
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    Cool. Rear end cad over Christmas?

    Lots of late evenings this week finishing Alice’s bike. Just got to face bb and ht then off to powder Monday. Hopefully deadline hit…..

    Premier Icon stevied
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    Ooh, cutting it fine Mick. Don’t forget to pop some pics up when it’s finished πŸ™‚

    Premier Icon mick_r
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    Alice’s dad somehow got permission to soak the flux off the frame in their bath! It then made it to powder this morning. Not done a full dummy build so fingers crossed – offering it up against my lad’s bike it didn’t look like I’d screwed up the angles…..

    Stickers are cut and ready, and we’ve got a pile of parts (just released Sram NX 32t cranks in 155mm are very cute – just for info when you make the 26er version in about 5 years). Not sure what day we get it back.

    Need to sort somewhere to host photos.

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