# 60% scale model Mixte build



## JackOfDiamonds (Apr 17, 2020)

One of my other hobbies used to be scale modeling airplanes. At a flea market I saw a little bicycle decoration made out of wire, that was just a decoration, but it was built to scale, and looked like a little city bike, and I thought it was cute, so the evil thought occurred to me, what about building a scale model that actually works, whether or not anyone could ride it.

I've built a bunch of bikes (8 total) for my kids, and scaled them down as much as possible. So for functional reasons I'm already doing the scale-down thing when it comes to handlebars (1/2 and 5/8 tubing), hubs (45mm OLN - 110OLN), cranks (40mm wide BB's), and sometimes custom pedals, but otherwise I never tried to make them LOOK to scale, and I used standard parts wherever humanly possible (1" headsets, off-the-shelf brakes, etc.) so they can look a bit whacky, but who cares about looks? But I just kept thinking about it....

A 60% scale model would be a 16er, that means either 305 or 349. I was able to find rims and tires on eBay for both sizes and decided to go with the 305. Unfortunately the rims are red, and the 32m tires are much fatter than I wanted, but if anyone else can find 25-305 tires anywhere in the world, I would be really happy to hear about it. There's nothing I can do about the fat tires so it's going to look a bit balloon-tired...

Next problem: figure out how to make scaled-down headset, cranks, chain? and brakes...


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## JackOfDiamonds (Apr 17, 2020)

Hubs....

For the front hub I found a 65mm wide folding-bike hub on eBay. It's not as narrow as I would like, but it's super light and should be OK with the fat tires.

For the rear hub I made one on a standard pattern I had from other bikes...75mm wide with track threads. In theory, I planned these so they can be run either fixed or with a 16t freewheel. But so far, I've never switched one to freewheel because the kids like their fixed bikes better. It can either take a QR skewer or 6mm bolts. The bolts weigh exactly the same as the skewer, and I kind of like the bolts.

I'm pretty happy that my red anodizing dye is a somewhat decent match for the rims.


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## pvd (Jan 4, 2006)

I don't understand why your showing parts being weighed on the scale. That tells me nothing. It would seem that there are about 1000 things more important than showing that.


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## JackOfDiamonds (Apr 17, 2020)

That's the pictures that I happen to have. But if it makes you feel better, you can just pretend the scale isn't there.


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## JackOfDiamonds (Apr 17, 2020)

3D printer is a good way to visualize parts. I took some regular pedals, modeled in FreeCAD to life size, then scaled to match the wheel size. I have made aluminum pedals before, but 3D printed ones might be good enough for a model.


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## JackOfDiamonds (Apr 17, 2020)

According to my reckoning I need a 5/8 steer tube to look about right. For the headset, I was all ready to make a threaded steer tube, and bearing races and everything, I even bought a bar of O-1 steel for the races. But then I found out that you can get angular contact ball bearings in 15mm, which is pretty close to 5/8. It's even a fairly common bike bearing, apparently for suspension. 71802AC. They are a little bigger OD than I wanted, but this is a prototype anyway. So I'll make a threadless headset which will be a lot easier. I still think a tiny quill stem would be next-level adorable, so I want to make a threadful headset for a future bike. This is just a prototype.

It turns out typical mixte top tubes are 9/16. When scaled down it means 3/8 is too big and 1/4 is too small. So I had to order some 5/16 x 0.035 chromo for the top tubes. Which is thicker than I wanted, but it's more important for it to look right. It's a prototype anyway.

In the meantime I bent some bars. I slacked by doing an integrated stem... but it's a prototype anyway. I still don't know if this will be anything ridable. I'm just kinda in build-first-dont-even-ask-questions-later mode.


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## cmg (Mar 13, 2012)

subbed, interesting idea


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## JackOfDiamonds (Apr 17, 2020)

Minus the drop bars, this is one of the bikes I'm using as inspiration. A random mixte I saw at the zoo and suspiciously took a hundred pictures of. Although it's looking like I need to shoot for a small/xs size frame actually, based on the wheel and tubing sizes I can get.










While waiting for tubing and laser cut parts to come, I've been 3D printing other bits. I don't normally start with the seat but the seat is actually going to be a problem. I wanted to make a cool leather seat but can you tell how I'm getting lazy? It might have to just stay 3D printed for this one.


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## JackOfDiamonds (Apr 17, 2020)

I was able to come up with a head tube and steer tube. The bearing cups are too big, because of using cartridge bearings, but like I said I'll make a proper loose-ball headset next time.

Technically it could have a slop problem because I don't have a wedge cone thing. However I honed the top bearing seat to a very close fit. If you warm up the steer tube with your hand the bearing won't slide on, if you warm up the bearing in your hand it slides right on. That means it's within a fraction of a thousanth. With a coat of grease on the steer tube I don't think there will be any perceptible play.


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## JackOfDiamonds (Apr 17, 2020)

I found a Primo Comet 305-32 tire on the internet. It's a little bit smaller than my other Kenda tires, but it's quite a bit heavier, and I already designed the frame to fit the Kendas, so I think I will stick with the fatter ones.










I also got a batch of laser-cut parts. Dropouts, fork crowns, and sprockets.

I have two ideas for the sprocket...either a 58mm spider and 22t-24t chainring, or a single 22t steel sprocket. Since a single sprocket will take up less space, it will probably be the single sprocket.

I could easily do a unicrown fork, but some sort of crown would be more aesthetically correct for this type of bike, so I went for a plate crown. Of course I couldn't do tapered fork legs...I checked some tapered stays that I have, but they were still too big, so I just had to use straight tubing.

I edited out the pictures of scales, so as not to trigger the sensitive.










I'm tentatively happy with the fork so far. Of course I included rack tabs...I think I could use model airplane pushrod hardware to make a tiny rack in the future.


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## JackOfDiamonds (Apr 17, 2020)

I normally do kid cranks with 15mm spindles with pinch bolts, but a proper vintage city bike should really have cottered cranks, so I had to design a cottered crank/bb. Normal cottered cranks use about a 17mm spindle. That scales nicely to 10mm. Seems small, but everything about this project seems small. 10mm spindle allows a sealed bearing bottom bracket exactly matching a standard 68mm BB. I tried two different bearings for giggles.










Of course there's no way normal 7 or 8mm cotters will work, but it looks it will be easy enough to file 6mm cotters.










It's really no wonder old bikes used cottered cranks. To make the crankarm you literally just need to drill 2 holes in about the right spots. No other precision machining, threads, splines, or anything. And the spindle can just be a round rod with some flats on it. Very stone-age technology, in a good, like why-isnt-everything-still-this-simple way.


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## wschruba (Apr 13, 2012)

Very cool work. I'll admit that I was a bit 'eh' on it when I saw the wheels, but there is some nice work going on here.

You've already cut the sprockets, but for future reference, chain drives are available in a ton of different pitches.



JackOfDiamonds said:


> It's really no wonder old bikes used cottered cranks. To make the crankarm you literally just need to drill 2 holes in about the right spots. No other precision machining, threads, splines, or anything. And the spindle can just be a round rod with some flats on it. Very stone-age technology, in a good, like why-isnt-everything-still-this-simple way.


Cotters are great right up until they're not. Under conditions expected on a working bicycle (that is, a vehicle, not sporting equipment), they work fine. The worst to contend with there is someone not installing them correctly. On sport bikes--especially under powerful riders--the cotters would deform and be quite difficult to remove. Also, having worked on bikes that are 60 years old with cotters to match...screw cotters.


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## JackOfDiamonds (Apr 17, 2020)

I bought a few lengths of smaller-pitch chain to test. I could have cut a front sprocket for it, or even made a rear cog, but that would rule out ever using a freewheel. Plus, what sealed it for me was the smaller-pitch chain was actually wider and heavier per length. I still think it would look better. I even thought about using 3D printer belts and making a belt drive. But I had extra 11spd chain from my cargo bike and that sealed the deal.


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## JackOfDiamonds (Apr 17, 2020)

A chainstay


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## JackOfDiamonds (Apr 17, 2020)

3/4 seat tube, 1/4 seatstay and M5 binder


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## Sparticus (Dec 28, 1999)

Is that a dropper post? 
=sParty


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## Cord (Dec 10, 2006)

Didn't think i'd care about this, but have been completely drawn in. Keep up the good work. 

p.s. I miss the scales. :-(


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## JackOfDiamonds (Apr 17, 2020)

Well, after doing some pre-assembly, I realized the braking problem.

I have a lever design for 1/2" handlebars already, where I make a custom perch but use an off the shelf cyclocross lever. I think that will work OK here.










Calipers though, regular road calipers fit the 30mm tires, but look dumb, just way wrong. And there's no hope of fitting a caliper on the rear either. It doesn't help I chose a frame design that has challenging rear brake placement anyway. I knew this, but yeah no denying it now.










Scale modeling is weird because one item that looks out of scale will destroy the visual effectiveness of the model, literally one conspicuous bolt that is way out of scale can just ruin the effect. Another weird thing is that building exactly to scale doesn't always work either. Almost all scale airplane models have cockpit bubbles or wing chords that are significantly bigger than scale, in order to "look right". If you really built it to scale, it would paradoxically "look wrong". So it's just about what looks right. The full size brakes are wrong enough that it just ruin the whole thing. So it looks like I'm making custom brakes. Which is a bigger project in itself than making the whole rest of the bike, but luckily it's autumn and I'm booking this time as hobby time and not working time. Plus, I have other bikes with brake clearance issues, and there's a sliver of a chance that the R&D might actually pay off somehow for "real" bikes.


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## JackOfDiamonds (Apr 17, 2020)

Update on the "miniature bike project" which is now a "making custom tiny bike parts like brakes project".

I decided center-pull brakes would be best; they are common on Mixte frames, and the rear cable routing is simple and clean.

Before going further with the brakes themselves I worked out the cable routing. This required finishing the top-tubes and making teeny-tiny brake bridges / cable stops.










I didn't have any 5mm barrel adjusters, so I had to stop and make some homemade barrel adjusters. With matching anodizing of course.




















After making the brake stops, I realized an off-the-shelf straddle cable looked way out of scale. It won't do to have miniature brakes and use a big ugly normal straddle cable, now will it? How to miniaturize a straddle cable? That took a day by itself.




















The brake arms themselves are fairly easy to make on my 3D printer. After a couple more iterations in plastic, I will get the outlines laser-cut and finish them with files. But it is a TIGHT squeeze in there.


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## cmg (Mar 13, 2012)

bloody good work, the lengths you're going to are amazing (to me anyway)


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## JackOfDiamonds (Apr 17, 2020)

How to make a 15t track cog that fits 11 speed chain.

Sensible way: grind down the steel one a little bit.

My way:

Scan the steel one on a flatbed scanner:











Trace it and scale it in CAD:










Test it in plastic:










Have it laser cut out of 3/8 aluminum with next batch of parts for zero marginal cost. Make a lathe fixture to bore and thread:










Test fit:









Use another fixture to finish it, file it, test it:









Anodize it:










(Not shown) make a lock ring while waiting for anno.

C'est fait. 32 grams lighter than steel and runs great.


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## Wombat (Jan 25, 2004)

Thanks for taking the time to record and post all of this. I enjoy it greatly!

Tim


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## JackOfDiamonds (Apr 17, 2020)

Brakes Mk1


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## NorCal_In_AZ (Sep 26, 2019)

Are you going to find a 60% to scale human to ride this piece of art when it’s done?


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## JackOfDiamonds (Apr 17, 2020)

I'm not really sure if it will be rideable for any human or not. I have plenty of kids who could give it a go, but kids aren't really 60% humans. I'll have to see how flexy it is once it's built. At this point it's just a "concept car".


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## Shark (Feb 4, 2006)

Interesting, nice work

Sent from my SM-G991U using Tapatalk


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## compositepro (Jun 21, 2007)

JackOfDiamonds said:


> That's the pictures that I happen to have. But if it makes you feel better, you can just pretend the scale isn't there.


Maybe its just easier to pretend he isnt here


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## compositepro (Jun 21, 2007)

Cord said:


> Didn't think i'd care about this, but have been completely drawn in. Keep up the good work.
> 
> p.s. I miss the scales. :-(


Me too its way more fascinating than people are giving the guy credit for


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## Darth Lefty (Sep 29, 2014)

JackOfDiamonds said:


> I'm not really sure if it will be rideable for any human or not. I have plenty of kids who could give it a go, but kids aren't really 60% humans. I'll have to see how flexy it is once it's built. At this point it's just a "concept car".


Yeah, little kid bikes fit weird. Kids have shorter legs. Their weights are all over the place. And they want, maybe need to flat-foot. It looks weirder yet because of your higher perspective.


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## JackOfDiamonds (Apr 17, 2020)

Totally, if I were really making a kid bike I wouldn't have done a Mixte frame, or at least I would have left the seatstays off so the saddle could be slammed. Also I would have raised the BB a little bit and given more toe clearance and a slacker HT. I might build one like that someday, but honestly a small 20-incher is good basically as soon as they get off a balance bike, so I don't see myself building many 16ers. I have extra 349 rims now... maybe I will use them on a recumbent or cargo bike or something.


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## JackOfDiamonds (Apr 17, 2020)

I have a BMX-type drive bolt for the cranks, but with only 40mm wide BB, there's not a lot of space for the bolt head. Instead of countersinking it, I just brazed the sprocket onto the spindle, since the spindle is steel. What if I want to change the sprocket? I'll just make a new spindle out of a piece of 10mm rod. I painted the sprocket with some "shiny aluminum" professional spraypaint. It looks pretty good and I might try to paint the bars with it.










I got the frame together and the headset bearings look like they are going to work out pretty well. 

For the "star nut", I brazed in a water bottle boss on a washer.


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## shwinn8 (Feb 25, 2006)

Ullr Fest!!!


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## JackOfDiamonds (Apr 17, 2020)

In accordance with the prophecy, the tiny brakes have been a total pain. I'd really like to have a word with whatever idiot designed these things. Talk about fiddly. I think they are going to work out though.

After trying dozens of springs, extension springs, elastics (I even bought some music wire to make custom springs), braze-on spring mounts, 3D-printed spring mounts...I ended up with two little stubs of welding rod holding a somewhat re-bent off-the-shelf torsion spring, with a little plastic core/washer inside.



















Glad to be done with that. In the meantime I dropped the frame off to be blasted and re-worked the lever perches


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## Sparticus (Dec 28, 1999)

Well done. I can hardly wait to see this thing in it's finished state. By all means please carry on.
=sParty


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## JackOfDiamonds (Apr 17, 2020)

Took forever to get the frame back... going to take me a week or two to get it painted since work is busy again.










I was a little disappointed in the weight of 545g, since my small 20" frames come in at about 690g. I guess those 5/16 top tubes really bumped up the weight, plus this one has the integrated headset and brake posts.


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## stuartm2 (Mar 5, 2020)

This is a fascinating project. Subscribing!


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## D.F.L. (Jan 3, 2004)

For future reference, smaller-pitch chain and sprockets are available if you want them. Fun project, and nice work!


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## JackOfDiamonds (Apr 17, 2020)

"A couple weeks" turned into "about nine months" because work got crazy and then it was ski season. It just got warm enough to spraypaint around here. White Rust-Oleum professional it is. It really deserves a better paint job. One day maybe I'll get an airbrush or something.


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## JackOfDiamonds (Apr 17, 2020)

It always amazes me it takes just as long to paint a frame as to build it, or more. Time to start assembly.


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## Sparticus (Dec 28, 1999)

Still following. Eager to see the end result. 
=sParty


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## cmg (Mar 13, 2012)

it all looks smooth, great work


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## JackOfDiamonds (Apr 17, 2020)

I just realized I didn't make a kickstand plate. Oh well.


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## plummet (Jul 8, 2005)

I'm loving the engineering. I'll be honest, I'm not a fan of the actual bike looks. But the process to make the parts is awesome.


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## JackOfDiamonds (Apr 17, 2020)

I tentatively finished it. It turned out ok. I'm a little disappointed it still weighs 6lb12oz. Basically not any lighter than one of my 20-inch roadies. Oh well at least I can get started on my gravel frame.


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## wschruba (Apr 13, 2012)

Somewhere, there is a model builder that is looking at this thinking, "why didn't I ever try something like that?"

Bravissimo.


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## cmg (Mar 13, 2012)

well done, 
l think l said it earlier in this thread that l dont understand but if youre having fun all good. The engineering and workmanship is cool.

Will the Gravel Frame be full size?


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## JackOfDiamonds (Apr 17, 2020)

Yeah it's just a regular normal bike for biking


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## plummet (Jul 8, 2005)

Can you ride it?


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## JackOfDiamonds (Apr 17, 2020)

I think it would surely break if any adult tried to ride it. I might put a kid on it later, it should hold up to some cruising at least.


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