# Full suspension kids 20" wheeled Nukeproof MiniMega



## Cord (Dec 10, 2006)

This build probably asks more questions than gives answers, and some geo/fitment purists will shake their heads in disgust at my choices, but feel free to ask me why. Like all engineering projects, its all about pro's and cons. i'll give a run down on what i did.

I started with a medium 2012 Nukeproof mega, my aim was a full suspension bikewith 20" wheels for a friends son. I wanted Nukeproof as he runs that brand's race team, and he didn't really want him on another brand, also we couldn't find another full suss that ticked enough boxes to be worth buying.

I'd have loved to change somethings, but that was just un-achievable from the outset. A lower Q-factor, and weight. This was the original geometry, but things shifted a little on the way.


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## Cord (Dec 10, 2006)

This was the frame i started from. I installed it into my jig to help me check that it was what the geometry said it should be, check how flat/square it was and to generally give me a good starting point. Note rocker link and shock position, that was destined to never work with the stand-over we needed.


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## Cord (Dec 10, 2006)

My jig has position adjustable vee blocks that the main tubes sit in, tapered cones to hold head tube, tapered cones to hold BB and a threaded rod to hold rear axle. As the jig is seen in the first picture with it laid on its back, they are all "height" adjustable, so i can set the centreline of the frame true and parallel to my jig. Several parts are removable, but then can be re-inserted to the exact same location and or height. This is so i can gain more access to work on certain areas, but then clamp it back to same position with minimum fuss. 

As far as i can tell my fixture is fairly unique (maybe other people have tried something like this and realised its failings, hence nobody does it like this?) I've another thread on here showing the fixture in more detail. I'd love some comments on it, i've so little experience, and there are some clever types on here who's brains i'd love to pick. Walt? PVD? anyone??? 

And if there are any super-pedants out there, this is a jig, not fixture as i have actually used it to guide cutting of tube ends.


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## pvd (Jan 4, 2006)

1. Why FS? Most kids would do well on a 20" rear 24+" front rigid. FS is a really poor choice.
2. Print needs a lot of work.
3. What is the question?


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## Cord (Dec 10, 2006)

1.- Full suss, because not everything is about the perfect bike for the job, but just being the perfect bike, you'll have to bear with me on this, i'll explain best i can. Dad, and all dad's mates are on full suss, one of the goals was to get the little man out riding more, once he was out on his little hardtail he loved actual riding, but getting him out there and started on a cold wet morning was the hard bit. So, it had to be the raddest bike he'd ever seen, if he had the coolest bike in the history of the known universe, the ipad/xbox whatever,,, would take the back seat. So a full suss maybe too heavy, maybe to wide, maybe to slow handling etc,, but from the little man's point of view. It's beyond perfect, Dad and all dad's mates, and team riders are on Nukeproof full suss bikes. Now he's on one too. it worked more than can be imagined, now he LOVES riding and can't get enough, so thats what i meant. It IS the perfect bike at the moment.
2.- Print? Sorry no ida what you mean?
3.- No question at all just someone asked what i'd made so I thought i'd share how i did it. I'm not new to engineering, but new to bike building, i just wondered what other peoples opinion on what i'd done was good/bad. I love to learn, and i figure any input is better than none!


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## Cord (Dec 10, 2006)

As i said standover was never going to work as is, soooo. Without having to go to the hassle of machining a new rocker link i figure the existing one would work well upside down. I could position the pivot location so the link still provided me with a leverage curve very close to ideal. And it would be possible (with a new shorter shock that would take travel down from 160 to 100mm) to have shock mounted on the down tube.








Looks like we are getting somewhere :thumbsup:


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## Cord (Dec 10, 2006)

I can't remember exact dimension, but i needed to lose something like 100mm out of the front centre. Cutting at headtube was doable, i could lose about 80mm and still leave the top/down tube intact, an then just weld in a new headtube. so this was originally my option 1. However, it still left standover/ set tube ridiculously to big.

option 2, Leave the headtube alone, and cut at bottom of down tube and top tube, this made lots more sense. I gained a shorter seatube (due to the fact i'm making a triangle smaller) but i also gained standover due to the shape of the top tube, where it normally upswept is near as damn it exactly where i needed to cut. Bonus! Also the big machined bottom bracket assembly left me lots of room to land my new downtube, and it even did it maintaining the angles i want. DOUBLE BONUS.

Black lines are my approx new tube ends, time to get brave and get cutting. 







I wasn't brave enough to fully trust my new tube end lines, so i had a test cut about 20mm to long.







i should have just committed!! it worked fine.


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## Cord (Dec 10, 2006)

ratchet strap and some masking tape, looks like a front triangle to me :thumbsup:


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## Erichimedes (Jul 30, 2010)

Interesting project! I'm surprised everything is fitting in there. But it seems to be, so that's great.

I don't know what those Nukeproof frames are made of, but there's a good chance they're made of 6061. If that's the case, know that 6061 anneals at welding temperatures, and will not be as strong as it is in it's heat treated state. Most 6061 frames are heat treated post welding.

I'll let you determine if this is applicable to your project.


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## shirk (Mar 24, 2004)

Awesome thanks for sharing. It took a bit but I remembered now seeing the finished bike in some Fort Bill coverage. When you need to keep up to Sam Hill you need a custom 20" full suspension bike


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## Cord (Dec 10, 2006)

Erichimedes said:


> Interesting project! I'm surprised everything is fitting in there. But it seems to be, so that's great.
> If that's the case, know that 6061 anneals at welding temperatures, and will not be as strong as it is in it's heat treated state. Most 6061 frames are heat treated post welding.


It is indeed made from 6061T6, i figure the HAZ will lose approx 30% of its original strength. Seeing as the frame was built originally for big mountain riding, with adults on board, I'm not at all worried about strength for a little kid. It was something i considered at the start of the project tho.


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## Cord (Dec 10, 2006)

shirk said:


> Awesome thanks for sharing. It took a bit but I remembered now seeing the finished bike in some Fort Bill coverage. When you need to keep up to Sam Hill you need a custom 20" full suspension bike


There' a vid or 2 knocking around on youtube somewhere, I'll find them and post up when i get to the end of this build thread. Don't want to spoil the surprise too soon!!!!


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## rockcrusher (Aug 28, 2003)

I just came in here to say this is awesome! Thank you.


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## Cord (Dec 10, 2006)

rockcrusher said:


> I just came in here to say this is awesome! Thank you.


Cheers, I'll post up some more tomorrow.


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## pvd (Jan 4, 2006)

Cord said:


> 1...
> 2...
> 3...


We're on totally different pages in all regards so it's not really worth debating.

Regardless of anything else, that's a 6061 frame. You're going to have to re-heat treat it after you're done to make it safe to use. Have you sorted that out? I'm sure you don't want to permanently cripple a little kid...


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## VegasSingleSpeed (May 5, 2005)

Cord said:


> There' a vid or 2 knocking around on youtube somewhere, I'll find them and post up when i get to the end of this build thread. Don't want to spoil the surprise too soon!!!!


I saw the bike check vid on YouTube. Killer work, Cord!


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## dr.welby (Jan 6, 2004)

Cord said:


> As far as i can tell my fixture is fairly unique (maybe other people have tried something like this and realised its failings, hence nobody does it like this?) I've another thread on here showing the fixture in more detail.


The geometry reminds me a lot of the Doug Fattic waterjet cut jig, but made with t-slots instead of flat sheets.

If it works for you, then it works, right?


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## Cord (Dec 10, 2006)

dr.welby said:


> The geometry reminds me a lot of the Doug Fattic waterjet cut jig, but made with t-slots instead of flat sheets.
> 
> If it works for you, then it works, right?


Never seen that before, yes very similar principle indeed. He has a more robust way of locating the BB, I've pondered ways of altering mine, but never come up with a plan i'd like. Ideally all my Vee blocks would stand taller from the main jig, in order to let me have better access with the torch. However with them currently just on M8 stud they wouldn't be rigid enough. Maybe 1 day i will machine up some form of spacer.

Yes, it does work tho! Cheers.


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## Cord (Dec 10, 2006)

pvd said:


> We're on totally different pages in all regards so it's not really worth debating.
> 
> Regardless of anything else, that's a 6061 frame. You're going to have to re-heat treat it after you're done to make it safe to use. Have you sorted that out? I'm sure you don't want to permanently cripple a little kid...


Err, Ok i suppose, thanks for debate in the non-debate. Genuinely hope i haven't taken up too much of your time.


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## Cord (Dec 10, 2006)

Shock mount as it stood was no use, so off it came.


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## Cord (Dec 10, 2006)

Front triangle now welded together. A plan is already hatched within my head for the rocker linkage pivot, but its'e easier to deal with the front triangle as 1 piece, this way i can mount it in my jig nice and square.









The eagle eyed will spot i have no room for a seatpost binder, this was on purpose as i wanted every possible bit of space for lowest possible saddle height. We'll get back to this later when i find the pictures.


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## Cord (Dec 10, 2006)

Swing arm time, The whole thing needed shortening by 102mm, i worked to 100 just to make my life a touch easier!

One side of the swing arm is a straight line from pivot to axle, this is the side i worked from, and would weld first. It made it "simply" a case of removing 100mm of tube. The other side has an angle in it, so more work/maths would be involved.

First off, chop it up, nice and easy! On the side with an angle at the yoke interface i just chopped through the weld, all i needed here was to maintain the original flat angle portion. On the other side i chopped maybe 20mm back from the weld, i wanted to ensure i didn't scarifice the spigot portion of the yoke that would help align my tube when it came time to weld.

































After chopping i jumped on the milling machine and cut away the remaining 20mm of tube/weld to leave myself with a nice square spigot. I then cut my tube to the correct length (ie removing a further 80mm) this again i did on the miller to keep it square. Square tube + square spigot = less alignment issues!


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## Cord (Dec 10, 2006)

First side of the swingarm was easy, and made the other side relativley easy as well.







So non-drive side just needed 100mm removing, that was plain sailing as it was a straight line from pivot to axle, and also there was a nice parallel section long enough to remove my 100mm. I made sure everything was square as i could by eye, tacked it, then set the hole thing back up on my jig.















Non-drive drop out was in almost perfect alignment, i had a spacer the correct size so i could clamp it square to the Jig. Drop outs handily had 2 12mm holes in them (axle and pivot) i turned up 2 spacers so that i could then mount both drop outs in their correct place. Once i'de checked all this was square and central, i just chopped the other side to fit.


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## Cord (Dec 10, 2006)

In the jig all set up square, some joints tacked, some clamped.







My mate Ben doing some welding, it was a bit of a 3 handed job to get to bottom of 1 joint and maintain tubes in position. Plus he's an amazing welder, i need looooooooots and lots of practice.







Starting to look like a small bike now. :thumbsup:


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## .WestCoastHucker. (Jan 14, 2004)

moar pics please..


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## Cord (Dec 10, 2006)

.WestCoastHucker. said:


> moar pics please..


 :thumbsup:


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## Tim-ti (Jul 27, 2005)

Find the shortest old school road bike derailleur you can. Ground clearance gets tight with 20" wheels.


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## Cord (Dec 10, 2006)

When the bike will first get used, standover and mainly saddle height will be a massive issue. It won't take long for him to grow, but i still need it to work when he first gets it.

I chopped seatube as short as possible, and top tube is welded very close to the top. I did think of putting some kind of split wedge assembly in a tube welded into were the tubes intersect, it would have indeed been a bit fancy, but i realised i was getting carried away with what was meant to be a quick project.

So, just a normal aluminium seatcollar.













Lots of filling, actually this was easier said than done, it was awkward to hold, i have a piece of scrap tube inside it to stop vice deforming it. but then it also need a big chamfer on inside edges to clear the existing weld.













And then weld it on top and bottom.













I forgot to take picture of a small hole being drilled, and then a split in the back of the tube. Super happy with how it came out. It takes up very little height, approx 1.5mm.


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## Cord (Dec 10, 2006)

Lots of thinking on this next phase, and very few pictures. What i had so far was back in the jig so i could do lots of measuring, and head scratching. I knew my shock and linkage had to fit in here.








Courtesy of a VERY nice man on the Rockshox race van i had the smallest stroke shock, with the best tune he could do. I'd given him a few numbers and we'd arrived at something we thought would work. Very hard work for him, as my pivot locations weren't yet nailed down, and the rider was a growing! Lots of best guesses!

I spent a huge chunk of time getting the bottom pivot location of the swinglink in the correct place so that it 1. Fitted 2. Had the correct leverage ratio. My upper shock location was vaguely defined in that it had to attach to the down tube, my seatstay length wasn't set yet, but i only had a small window where it wouldn't foul the downtube. And the bottom pivot had a relatively big space to aim for.

Anyway i got there after lots of mock up's with allen keys as pivots and various clamps. Best thing was, the original front shock mount could be used, and with plenty of cutting, i was going to re-use the upper pivot mounts well.

These pics are slightly out of sequence, because i actually ended up cutting seatstays before tacking in place, but at least you can see what i mean.


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## xy9ine (Feb 2, 2005)

super cool project! love the crafty ingenuity employed re-configuring the various bits. can't wait to see the finished product.


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## Cord (Dec 10, 2006)

xy9ine said:


> super cool project! love the crafty ingenuity employed re-configuring the various bits. can't wait to see the finished product.


Cheers, it was an enjoyable little build. I'll keep posting updates.


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## armyofevilrobots (Oct 4, 2013)

Norco just released a similarly sized (but with an inverted rocker relative to yours) kids FS bike.
https://www.pinkbike.com/news/norco-bicycles-introduces-progressive-new-youth-mtb-platforms.html

Kudos on putting this together. Looks awesome. Feeling oddly jealous of this lucky little grom!


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## Cord (Dec 10, 2006)

Seat stay time, these needed shortening, and the bridge replacing. 
Chop the ends off, and cut out the bridge.







Back in the jig and work out where about's my new joints would be, and some length measurements







Cleaned up the outside and old weld in the milling machine, also and more importantly i machined an angle on the end of them, so i can then use square ends on my tubes, and hopefully less distortion when welding. Again, tight cut lines and minimal gap makes everything easier with regards to pulling when welding.













Tacked up in the jig













Finish welded.

I needed a bridge, the one i'd cut out wasn't worth re-using Luckily had this offcut of oval tubing from some Ducati WSB subframes i'd been helping to make, seemed the right profile to match the build. It couldn't be to wide or it would reduce tyre clearance, or hit seat tube on bottom out.


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## Cord (Dec 10, 2006)

Shock mounts finish welded. I think thats it for the frame.


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## Cord (Dec 10, 2006)

Also made some short cranks, nothing ground breaking, filled the hollow in the back with a touch of weld to add some meat. Drilled, spotfaced, tapped and then cut down to size and shaped a little. I was going to spray them satin or matt black to try and match the original finish. The way the anodise faded was to cool an effect to paint over tho. :thumbsup:


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## rockcrusher (Aug 28, 2003)

thanks for the updates! Look forward to getting the notifications in my emails for this thread.


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## scatterbrained (Mar 11, 2008)

Looking forward to seeing this thing finished.


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## Cord (Dec 10, 2006)

Frame all finished, even managed to keep enough cable guides to make it nice and neat.

Build wise we went with Avid code's as the adjusters can be modified a tiny bit to make the levers come nice and close to the bar for small hands, Some super trick little flat pedals from DMR, Halo rims on some older Nukeproof hubs. Nukeproof bar/stem/seatpost. 10speed DH rear mech as it was shortest we could find. SR suntour forks, that work really well. And rear shock that works brilliant with our really low pressures. To give you an idea of how light we had to have the forks/shock, we ended up with just 6 psi in the tyres, any more and they weren't deforming enough to give any kind of grip.


























The finished article, minus some cool graphics that mimic the then current CRC/Nukeproof race bikes.








Don't seem to have a picture of it finished? These were grabbed on Nige's instagram














And a little vid from Fort Bill world cup, Nige reckoned this thing got more attention than Sam Hill's race bike :thumbsup:





Am sure that a designer of kids bikes could tell me lots of things I've done wrong, i know some, but would love to know more. Am quite definitely not a bike designer. Which is going to be a pain, because am sure a 24" version is on the cards :madman: Good job i like a challenge.


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## mickuk (Jul 6, 2007)

Thanks Cord - really enjoyed this write up.

You've nailed THE ONE important thing with kids bikes - get the damn thing made fast before they grow! I've made a few kids hardtails and you're always trying to aim ahead of a constantly moving target - it would be lovely to spend months finessing a CAD model but that is zero use if they are too big to ride it when you finally finish.

I think we're pretty local to each other. There is also a guy in Chorley that makes some nice road frames, but as he was internet flamed by *** for daring to use a paper drawing we'd better not discuss him here 

If you make the 24" and want to do heat treatment then I'm pretty sure the Empire cast frames were heat treated somewhere in the NW (I'll see Craig at Ride On this week so will ask where they used).


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## Cord (Dec 10, 2006)

mickuk said:


> Thanks Cord - really enjoyed this write up.
> 
> You've nailed THE ONE important thing with kids bikes - get the damn thing made fast before they grow! I've made a few kids hardtails and you're always trying to aim ahead of a constantly moving target - it would be lovely to spend months finessing a CAD model but that is zero use if they are too big to ride it when you finally finish.
> 
> ...


Paper!!!!! How dare he!  Who's that then, didn't know a frame builder in Chorley? I only live maybe 7 miles away.
Got any pics of your hardtails? Always interested in anything thats been handbuilt.
You are right on the speed front, when i first made this, even with the seat as low as it would possibly go, H barely fitted on it. Now only 18 months later, you can see the seat height in the last picture, which is very recent. Not really any chance to make it "rider specific".

I think the 24" will be another chop up job, making full suss from scratch is way too labour intensive. If thats the case, then i will think I'll have to heat treat. The way kids are sending bikes these days it's going to need to be strong. I'll have to look into whats involved in re-treating an already heat treated frame. If Craig know somebody, then please ask, he knows Both Nige and i quite well, I haven't seen him in a good while tho. Say hello!


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## mickuk (Jul 6, 2007)

I'm also about 7 miles away from Chorley so our proximity probably depends which direction  (will send you a message sometime)

Chorley guy Stephen posts some of his stuff on this link (mainly lugged road bikes) Links | Novice Framebuilder

I'd suppose you anneal everything before welding and then heat treat at the end - so lots of scope for everything to distort..... I'm sure some of the local aerospace places will be able to do it. Will let you know what Craig says.

I should really post some current frames as the forum has been pretty quiet recently - will start another thread for them sometime soon. The ones below were my son's (outgrown years ago) and a tweaked copy for a friend's daughter - also already outgrown and transferred to her younger sister.


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## xy9ine (Feb 2, 2005)

nigel page's kids bike! so cool. such a rad project, thanks for sharing.


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## Cord (Dec 10, 2006)

The little bike is getting a bit more use than it was designed for. Still going strong after nearly a year tho (with no post weld heat treatment)

@ 7:30


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## stuartm2 (Mar 5, 2020)

I'm so glad you posted an update on this thread and got it onto my daily digest email. What an awesome bike, and such a lucky young lad!


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## compositepro (Jun 21, 2007)

I thoroughly enjoyed that


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## Cord (Dec 10, 2006)

Yep, the bike gets a sh1t ton of use. (By a child not Elliott!) He loves it, and it works a charm. Another year or 2 before he’s on 24” wheels.


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