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you are a better brother than i am

that is awesome! not my size though : (

LDC do some really nice and relatively cheap childrens BMX cranks that go down to 110:

good price, if it was a large or XL i would be all over it :(

Hi all,

I was planning on building a mad FGCX build with these but never got around to it. so i have for sale:

1) a rear archetype black rim laced to a chub hub with some scratchs on the hub (i cleaned it with a slightly too abbrasive squigy on one side) hence the lower price. comes with Ti bolts as standard. the wheel is hard as nails as shown in the pictures below.

2) a front chub hub which takes disc, its been laced but i dont htink its been ridden, no marks at all. its in prestene condition. it is suppliued with cups for a 20mm through axle (but others are availabel online)

will accept 120 for both. this is excluding postage and im based in bristol

heres a few pics of the hard ware

and here is a pic proving the rear hub is bomb proof. i did this riding up a hill, no collision

aaaayyy an ESB, love mine. weirdly though mine doesnt have the gussets around the head tube :/

is the rear hub actually branded prototype? because he also made a few custom hubs for them, mine has them and they appear unbranded. i only found out when i sent him photos of it trying to get some more details on the frame

my girlfriend is 160cm and rides a 48cm TT bish bash bosh for reference. really nice frameset, specially this time of yuear because it can take some chunky tyres. OP" is saying 42c max but i think it can go much higher than that.

thats a sick bike. wish i had a spare grand

beautiful, but i just got a pair of macks :(

pm incoming

would you consider disc brakes? then having the rear caliper inbetween the seat and chain stays? I think that would look sick. although when you lose the brakes for the track set up, the brackets will always stand out quite alot.

Good work! you will have issue milling it though because the disc brake mount might obscure some one the flange cut outs. you would have to laser sinter this (not a problem, just google a company in the UK and get a quote).

I cut the carbon tubes today for the axle/hub body. cutting carbon is a pain because it can produce nasty particles, as a result im using a large slow spinning liquid cooled cutting disc:

with a target length of 67mm, i was pretty happy with the result:

Ive been having issues getting my shady printing done, but hopefully i can take a different route to get it all sorted though :)

So, i wanted to know what affect the mesh has on the simulation, so i just amped the mesh resolution up (5.5 million nodes). we get a much nicer picture of whats going on, problem is, the file size of the output data base is 30Gb, so i wont be doing this often.

Heres a few pics of the simulation results:

We can see the areas that need more material added, and the areas which can have some cut away, but as a whole, i think its approaching its final geometry. so its time to buy some carbon fiber :)

small update, i was wondering through the office and actually found a piece of carbon fiber tubing that was the exact correct diameter for the axle. happy days.

Interesting - why does this happen? And is it possible to make a printer that overcomes this? Or are there post-printing techniques that can be used?

SLS printers work by melting a powder. unfortunately theres always gaps between the powder particles (like balls in a ball pit). some of the gaps disappear (surface tension of the liquid steel pulls it in to the gaps i think?).

considering this, and the surface finish that Screwball brought up, check out the manufacturers example finish, no gaps, pretty darn smooth:

Personally, ive never achieved something like this, so i guess they are heat treating the parts afterwards. when ever i print something it looks like like very fine sandpaper. heat treating isnt off the cards, but i dont actually know anyone at work who does it.

How solid (in terms of the percentage) are the parts that your DMLS machine produces?

Its probably in excess of 98% solid. In order to avoid any issue with this, im not making any load baring part too thin. Also, im applying a factor of safety of 2.

I remember being taught that sintered materials (was titanium we discussed) can have a higher strength than machined materials. That is all I remember mind.

So, alot of people are asking about the material properties so I decided to actually look it up! Elastic modulus - 200GPa, Yield stress - 470MPa, Tensile strength - 570MPa. If we compare that to stainless 316, Elastic modulus 193GPa, Yield stress - 205MPa, Tensile strength - 515MPa.

The Elastic modulus is roughly on point, but the tensile strength is increased if printed, and the yield strength is HUGE if its 3D printed. Unfortunately, this isnt the whole story. 3D printed parts are not isotropic (if you take a single point in a part, the material properties are dependent on the direction to which the point is stressed). Im guessing they are cherry picking the best material properties and going with it. This is the exact same story for carbon fiber. Carbon fiber is incredibly strong in the direction of the fibers, but in any other direction, its shite. To get around this you have to make a carbon fiber weave or wrap a ribbon in multi directions, but then all of a sudden your strength/weight ratio has dropped significantly (carbon fiber rant over, steel is real).

Now what do these anisotropic material properties mean for a hub? the material properties are best in the plane the printer prints in. If the hub is sat on its end, then the flange will be in this plane. Since the front hub predominantly has to deal with radial stress, im laughing :)

Finally, when i looked up the spec of the printer, the layer thickness is 20microns, and that laser moves at 7m/s, and the machine weighs in excess of 3000kg!

Theres all kinds of reasons it would want to jump about. Residual stress is a big one, if you had a ring and started sintering along it, so the laser takes a circular path, the residual stress is huge. By breaking it up into sections it can reduce the residual stress.

If you had two parts really close together (I print parts with a 0.3mm gap), you need leaked thermal energy to dissipate between printing each side, otherwise material can bridge the gap.

The laser direction also alters the material properties, its strongest in the direction of the laser sweeping (i think), this generic pattern is an attempt to make it uniform (but you can do very clever stuff to make it strongest in the direction you want).

right off the bat, these posts are getting long. im trying to answer everyones questions, but its pretty tough. if i havent answered a question, please PM me and ill be happy to clear anything up.

Have you seen how Gokiso hubs work? cyclingtips.com/2014/02/gokiso-cl­imber-hubs-review/

That seems like a lot of effort to reduce bearing wear, which isnt really an issue. plus the "suspension" theyve added is surely nulled by the tyre? Not the first hub with suspension like that Ive seen though, and really, a 3D printer would be great at making it, but to make it effective is really hard.

Anyway, im sending a few jobs through the printer. If you want to see what it looks like, check out a video here:

https://www.youtube.com/watch?v=p7WFVw6JOKg&feature=youtu.be

You can see a chris cross pattern on one of the rings in the top right. This is because the direction the laser is sweeping across the material changes, which in turn gives it a different reflective surface. Sorry about the shoddy video quality though, my phone was struggling to focus on it through the glass.

You should really do a convergence plot of multiple tests to make sure the model is working and tending to an ultimate stress value

I am doing convergence analysis, but not in the area you expect, instead im looking at impact. If a shed load of weight is applied to the hub over 0.01 seconds, as opposed to 0.1 seconds, how do we think it will react? well we can find out:

0.01 second loading:

0.1 second loading:

We can see the high loading rate slightly increases the stress in the heavily loaded spoke. But this is pretty meaningless because i have got no idea what the loading rate is when you go over a bump. The tyre will absorb alot of it. How much? no idea.

This is so cool. I played around with FEA tools with fusion 360, as it not only shows the stress areas but the plastic deflections on the item. Might be worth a look.

Im using Abaqus CAE for this analysis. It can essentially show me anything I want it to. And if it cant, I can always use a script to plot the analysis elsewhere. Heres the plastic strain for the model around a spoke hole. as you can see were talking about small values, which are most likely associated with the course mesh and loading conditions, so are greater than what abaqus actually thinks.

Im going to update the geometry based on these results and resubmit it.

Ideally, everything should be red. That way we will know that optimum weight has been achieved, however, im going to leave quite alot of weight on around the spoke holes, just to be sure (although, the chances are this hub will still explode :P).

Ive also shaved alot of weight off the hub. Heres the latest iteration, we can see weight savings going on in the cups

The other side of the cups is the interseting part though, these shapes ive cut out of it can be CNCd, but i really wouldnt want to try it, and it would be expensive. For the printer however, this is easy stuff.

The hub flange has also has a treatment:

That's gonna snag shorts.

im gunna prototype, then if this is a problem ill alter the design. although im not that acrobatic on my bike.

How about exploiting the gap so the bottle approaches from the side of the bike? Fewer tyre clearance issues (or toptube issues for this with the bolt at the front)

theres actually a company that tried to kickstart this design:

http://www.swarmeffect.com/designs/seatclamp

It was actually successful, but they arent producing them anymore :(.

its actually quite a hard design challenge because a bottle opener is quite large relative to a seat post clamp. the bottle cant be sideways either. plus, both CNC and SLS must be capable of manufacturing the thing. my mark 2 design cant actually be CNC'd. Which is a massive fail on my behalf because it easily could have been, and missing this also makes it much more likely to fail.

Stupid question, but will you be able to do up the bolts still?

thats actually a pretty good question. its something we should be able to do in theory,but no one at our work has actually done it....

strictly speaking, theres no reason why we couldnt use the printer itself to cut the thread. i thought that was a bit ambitious though, so im going to try tapping it by hand instead.

Also - could you have "LFGSS" cut out/ embossed on the front of it?

yes we can. the printer can probably achieve a minimum line width of 0.1-0.15mm, whch would allow for very intricate lettering. the model i sent to the print centre actually says "Refuel" on it.

Iteration 2 of the bottle opener. better opener positioning, it means you can functionally use both at the same time. plus this will fit all frames, not just my one :)

that is genius. I think that could make you a few quid

this might go on kickstarter. how much do you think people would pay for it?

Oh no. It would only work if mounted sideways as there's not enough space to move a bottle between clamp an rear tyre.

with this design, the bottle is horizontal, then you pull it downwards towards the tyre. for me thats no issue because my frames weird. if i took it to production i would probably make a few tweaks to make sure it universally works :)

edit: when its made ill get a video :)

seat post clamp with double bottle opener on the back! this is a game changer.

OK, so stress analysis is done. time to see what we have.

Firstly, with the visualisation, i have set the maximum visualised load to 200MPa, anything above that will appear as grey. The yield strength of this steel is likely to be in the 600MPa region, by aiming at 200MPa, we have effectively set a factor of safety of 2. That is, I have to be wrong by a factor of 3 for it to fail (easily done when youre guessing quite a lot of stuff :P).

Heres a flange with a radial spoke pattern, loaded purely by a spoke tension of 150kg:

What we are looking is the von Mises stress (MPa) applied to the hub, red is bad, blue/green is good (or is it? well come to this later).

this is all fine, no high stress except around the spoke holes. The spoke hole stress is probably an analytical error assocaited with the manner to which im applying the load.

Now, lets imagine im on the bike. I weigh 70 kg, but in the near future i may put a load of weight on, so im assuming i weigh 100kg. the worst loading manner possible, is 100kg applied through a two spokes, one on each flange (this is not realistic, its a massive load in comparison to what you would typically expect, but over estimating is completely fine, its just under estimating).

With this loading, the hub now looks like this:

No prizes for guessing which spoke is loaded! the spoke width appears to be about spot on (complete fluke there...). We can also see an additional stress concentration on the outter most edge of the hub next to the loaded spoke.

Now, heres the fun part. lets look at what isnt under much load, and cut the material away. Looking at it, not much is going on around the body of the hub, or the material that connects adjacent spokes on the outer most edge. So i removed material from these two areas, and i will resubmit the geometry. The updated geometry is right here:

Just so we are all on the same page, this hub is still predominantly made of steel. its going to be heavy. i would be pretty happy if it ended up sub 200g :)

i know. problem is, its a top cap. theres not much you can do with it. the hub project is working that way though, im bleeding weight out which involves some unusual surfaces.