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Middleburn Bashring Project


Alex Dark
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Right,..... basically I've turned into a bit of a weight fag now and have really started to try and ditch some pudge off the Coust ( 10.3 ). The obvious place to start was the crankset... a tanky set of Echo CNC's, Surly steel cog and Echo old bashring. After having a lil nose around I decided on either some Burns or Try-alls....as a mate had some burns on an old frame I want down that route.

After a few hours and copious amounts of sweat and tears I finally managed to get them off, only to discover just how silly heavy those Pro trials bashes really are ( 180g ). So... either buy a TNN bash, or Heatsink. Trouble is neither fitted the bill.... the cloud 9 was a full ring , and the TNN were all steel and non-replaceable cog. So why not make my own? Decided to recycle the old bash as I couldn't find an easy way of making the spline without CAM routering it ( which is cheating :P ). Lots of milling, some careful drilling ( cog and bash ) and i should have a damned light, strong crankset if I don't balls it totally.

Soo..... 5 bolt M6 design, 18t bolt on cog and a half bash....Below are all the models I made for it , and all the revisions that got it to the final stage. I realise that the bolts are the wrong size, as I later changed them, and the spline is wrong in the centre....but these were just reference models to see what It'd look like.

I'll post up pics as I go through it, and some weights when I can be bothered :)

180g starting weight.

post-11254-127230288689_thumb.jpg Just the standard Pro trial bashring

post-11254-127230292798_thumb.jpg Same as above, just with the 5 holes drilled for the new, smaller 18t cog.

post-11254-127230304515_thumb.jpg Just after milling the excess to give a half ring kind of shape.

post-11254-127230309232_thumb.jpg Shows the rear with the original 5-arm mounting milled off.

post-11254-127230313333_thumb.jpg This is the final one, shows the bash has been fly-cut right down from 14mm profile to a lightweight 6mm.

post-11254-1272305481_thumb.jpg Final version, but assembled with cog and bolts.

So far.... I've drilled the 5 mounting holes, but should get on the main milling job in the next couple of days. :) Any comments welcome, especially to make it look naice.

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I reckon you could take more off, you could take a load off around the centre and make it a halfring, and thin out the rest to a similar thickness to a regular old bashguard

HOWEVER!

I'm a sucker for all them lines and curves and it looks damn sexy right now. weight vs looks I guess

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And the final mass should be...? Looks good, nice to see the little details like clearance for the crank arm itself modelled as well rather than being lazy and ignoring it!

From 180g ( Solidworks says 226g ) to a predicted mass of 76g ( bash only )

Looks really interesting Alex, be interested in milling down one of the ones i have at home if it works, either that or modding my Cloud9 bash.

Thanks man, well I'll keep you posted... the only hard thing is lining up the drilling of the bash and cog to be honest....modding a cloud nine is very easy by comparison :)

If you were to do that, I'd say fly cut the circles off...half ring it then drill straight through. Also, weight to be saved on the back too.

I reckon you could take more off, you could take a load off around the centre and make it a halfring, and thin out the rest to a similar thickness to a regular old bashguard

HOWEVER!

I'm a sucker for all them lines and curves and it looks damn sexy right now. weight vs looks I guess

Yup, I'm thinking about milling a channel round the front edge, kind of a scoop...and drilling in between the bolt holes. I'll model something up now to show you what I'm banging on about :).

what are you doing about chainring?

You mention an 18t, but the PCD of a 5 bolt compact drive will be too large to run an 18t ring surely.

18T cassette chainring, drilled out to fit five 10.9 Hi-ten bolts. And yup, smallest size for 5-arm is 20t :)

It's splined.

Yup...

Who says you have to use a regular chainring, could just use a a cog like the Heatsink C9 bash.

Bingo, but I reckon the cloud9 is wayyy too much overkill :) Hence stronger bolts, but less of them.

Think disc rotor...6 m5 bolts with a 23cm lever acting on it...compared to 5 high tensile bolts with a 17cm lever. I know which I'd trust more :)

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Have you taken account for the clearance required for the lockring which holds the crank onto the bash? Also clearance for the chain once the ring's bolted up- looks like you'll need to run some kind of spacer in there. Finally are you going to helicoil the M6 threads into it? The bolts will obviously be really short not to pass through the bash and foul the crank arms and that doesn't leave much meat for the threads if you just tap the ally.

Anyway, looking really good and look forward to seeing 'in progress' pics and the final item (Y).

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Fancy doin a few protos? I'd love to try and break one, i'm trying to get a cloud9 off heatsink but he's out of stock of sprockets.

It's a definite possibility, I do have access to a CNC router that I could use :)

Have you taken account for the clearance required for the lockring which holds the crank onto the bash? Also clearance for the chain once the ring's bolted up- looks like you'll need to run some kind of spacer in there. Finally are you going to helicoil the M6 threads into it? The bolts will obviously be really short not to pass through the bash and foul the crank arms and that doesn't leave much meat for the threads if you just tap the ally.

Anyway, looking really good and look forward to seeing 'in progress' pics and the final item (Y).

The lockring fits fine actually, as the sprocket is spaced away from the cog. I'll show you a picture of the original actually drilled in real life :) Nope, tap straight into, but because of the scoop into the crank arm all the bolts can pass straight through. If this turns into an issue I may just have bolts going from the front side and neat little allen nuts on the t'other / normal chainring bolt style :)

If it all works, do you want to make me one.... But for left foot forawrd not right.? I think It looks really good.

Sure If i can actually use the CNC router...which hopefully I wills :) and yep, that's no problem at all, I may change the design so it suits both anyway. Cheers man, appreciate the feedback from you all :)

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The lockring fits fine actually, as the sprocket is spaced away from the cog. I'll show you a picture of the original actually drilled in real life :) Nope, tap straight into, but because of the scoop into the crank arm all the bolts can pass straight through. If this turns into an issue I may just have bolts going from the front side and neat little allen nuts on the t'other / normal chainring bolt style :)

I'd use chainring bolts right away rather than screwing into the aluminium. There's a reason why chainring bolts have such a small tpi. If you are to screw straight into the bash, I wouldn't have thought there would be enough material to safely secure the chainring. If you use chainring bolts you can clamp from both sides, making it impossible to rip out. It'd also look better than seeing bolts sticking out the front of the bash.

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Alex, if you were to build one, i've got a spare bash you can mill down for me when you've perfected your design, i just might prefer a less holey design, have you used any computer modelled stress testing software to see what it can take?

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I'd use chainring bolts right away rather than screwing into the aluminium. There's a reason why chainring bolts have such a small tpi. If you are to screw straight into the bash, I wouldn't have thought there would be enough material to safely secure the chainring. If you use chainring bolts you can clamp from both sides, making it impossible to rip out. It'd also look better than seeing bolts sticking out the front of the bash.

Hmm I suppose, although he bolts will be machined down so they aren't sticking out.

The heatsink cloud9 uses the same m6 standard pitch bolts...and that never seems to be an issue? I appreciate they have more of them though :)

I have a couple of other ideas, but I Guess the only way to find out is to test them really.

I still have space to tap and thread 5 longer than usual chainring bolts through, so that's still an option.

Any other comments please keep them coming :)

Alex, if you were to build one, i've got a spare bash you can mill down for me when you've perfected your design, i just might prefer a less holey design, have you used any computer modelled stress testing software to see what it can take?

I can model one in a mo...and yup less holey is no problem at all :)

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Hmm I suppose, although he bolts will be machined down so they aren't sticking out.

The heatsink cloud9 uses the same m6 standard pitch bolts...and that never seems to be an issue? I appreciate they have more of them though :)

I have a couple of other ideas, but I Guess the only way to find out is to test them really.

I still have space to tap and thread 5 longer than usual chainring bolts through, so that's still an option.

Any other comments please keep them coming :)

I can model one in a mo...and yup less holey is no problem at all :)

Sweet, i'll take one :lol:

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Fail....I can't stress test an assembly at home, but I can assure you nearly all the force is acting through the splines... Erm, I have this...but I don;t think it really shows anything as the crank isn't mounted, and the force is only perpendicular, not a cyclical torsional force.

post-11254-127236456702_thumb.jpg

Got a picture below of the latest revision, but without the drilled holes, only the large scoop :)

post-11254-127236459518_thumb.jpg

Cheers

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Fail....I can't stress test an assembly at home, but I can assure you nearly all the force is acting through the splines... Erm, I have this...but I don;t think it really shows anything as the crank isn't mounted, and the force is only perpendicular, not a cyclical torsional force.

post-11254-127236456702_thumb.jpg

Cheers

RE: The stress test picture;

There's a reason that Cloud 9's have 9 bolts and as much as Steve might market it as "more bolts = better attachment" that's more a side effect. 18t cog + 9 holes = as much material between holes and teeth as possible to keep it as strong as it can be. You may be absolutely fine running 5 bolts, but you will have a weak point there on both the sprocket and the bash. Whether it's a weak enough point to cause failure will have to be modelled very well or tested.

Good luck with it though, would love to have access to all the kit again for stuff like this! :P

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That looks fantastic, have you got a sprocket in mind for it?

I'm just being cheap and drilling a standard 18t singlespeed cassette sprocket....but I'm sure I could find out where Steve gets his from...or London Fixie has some that were designed to take the IS disc mounting.

RE: The stress test picture;

There's a reason that Cloud 9's have 9 bolts and as much as Steve might market it as "more bolts = better attachment" that's more a side effect. 18t cog + 9 holes = as much material between holes and teeth as possible to keep it as strong as it can be. You may be absolutely fine running 5 bolts, but you will have a weak point there on both the sprocket and the bash. Whether it's a weak enough point to cause failure will have to be modelled very well or tested.

Good luck with it though, would love to have access to all the kit again for stuff like this! :P

That is very true Luke, like I said this is just a... 5 holes may as well put another 5 there as they fit nicely in between the spider :P If i ever made them I'd run 6 10.9 bolts probably. I'm not worried about the sproket giving out at all...after all disc rotors have massively more leverage, smaller bolts and shit loads of material removed from in between the holes E.g rock_rotor.jpg

I'm definitely going to properly model this with a chain and sprockets as soon as I'm back at college if I've got enough time between doing end of year coursework :)

Best case scenario is I'll have the first one finished and on the bike for a ride in Plymouth on Sunday where you can have a look if you wish :)

Haha yeh it is pretty cool, love playing with the Mill and lathes to make this interesting shizzle :) Just aiming to make as much as possible for my project bike really, or at least modify it so I've put my own twist on it.

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