How are the Director dropouts held together

I did a post a few days ago listing the Director patent. It was chalk full of interesting stuff. But the question quickly came up: How is the dropout insert held in place. The drawings show a seam weld, but those don't appear on production models. Eggit helped clear it up with some rawing and bluing of his:

Dropout insert from patent


Eggit's photos show spot welds holding it together


Edit: Comment from G

No spot welds.

Read the patent, look at fig 5 and item 67 in particular...

G.

Director Patent and Construction

I was pleasantly surprised to find this in my Google Reader list this morning. If you don't know about Reader, it is a web based application for aggregating RSS feeds, updated search results, and other periodicals. The recommendation and searching functions are pretty good, but some of the BMX RSS feeds are surrounded by noise (i.e. one good feed with a bunch of dead ones).


Director Forks have interested me since they were first unveiled. Integrating the dropouts with the fork legs is a logical step that was taken by road and some mountain quite a while ago. Eliminating the weld at the dropout avoids cracks there as well. And using a simple insert gives good compression support, while maintaining a hollow dropout for weight. Overall a nice design. Unfortunately, since this is included in the patent, any other company who wishes to go the integrated dropout route will have to find a manufacturing method that does not violate George's patent.

The crown junction is another unique feature of the directors (unless you look at sunday's chainstay wishbone that G had a hand in as well). The claim is that it reduces localized stress and extra material found in conventional open ended steerers.

I'll dig into this deeper after some discussion, but I really have to head off to class, so this simple post is all that is going up for now :)



Some random feeds I subscribe to (post yours up!):

- Bicycle Design is not updated all that often, but can be interesting.

- Sweeter Skins for those of you with Android phones, this is really the future in UI.

- Roues Artisanales mostly posts in French about the road bike weight weenie scene.

- Cool Tools updates often with some neat little productivity tools.

- Scheier on Security is one of my favorite blogs. Written by a security expert who is often contacted to comment on security issues by media, government, and private agencies. He takes a very logical approach to dissecting issues. His post "Fear and Over-reaction" really struck a chord in me.

- Google Patent "Bicycle" Search feed updates every so often with new results (usually patent applications or updates). You can use Google patents to get customized results.

- Endless Innovation has some good posts, but can be a bit repetitive at times.

- Physics World has some neat, informative updates about research findings in classical, relativistic, and quantum physics.

- The Big Picture has great photography, and is updated very regularly. Each post contains a link to 40 high-def photos about a certain topic.

- F-Secure has regular, detailed computer security reports.

- Cycling Tech hasn't been updated in 2 months, but it has some cool stuff when they do.

- Industrial Design has a lot of design *cough* Crap *cough*, but you can find some real gems in there. Be weary of hub-less bicycles, there is a reason they haven't gone to production.

- Ted Talks are a great way to look at a situation from a particular (speaker's) perspective. They are all free videos on a very wide range of topics.

Investment Casting

I was catching up with the 2009 Interbike coverage, when I came across We The People and Fly Bikes. They were using a process I had not heard about: Investment Casting. After a quick Wiki, I thought it would be easier to find a video. This one appeals to my background in titanium.

So in real world terms, what does this mean for BMX?

• Smoother transitions than weld joints help to reduce stress risers.
• Material can be better placed to reduce unnecissary weight.
• Sexier components. For some reason, I have this feeling that the sexier a component looks the better it will perform. We'll have to see how that one pans out...

However, there are a couple of issues to address. The one that really jumps to mind is metal grain orientation. This is an interesting comparison between casting and forging in industrial steel manufacturing.

As previously stated the forging process produces a part that is anisotropic. This means that the mechanical properties of a forging are better in the longitudinal direction (parallel to lines of flow) direction versus the transverse direction (perpendicular to lies of flow). Conversely a casting is homogeneous this means that the mechanical properties of a casting are the same, regardless of the orientation of test bar material.

In essence, what we want is for the material's grains to be alligned with the long direction running along the length of the tubes and dropouts. This orientation is analogous to fiber orientation in a composite. Below is a rough comparison of grain orientation is a few different methods:

Casting: Grain orientation is not easily controlled. However, more complex shapes can be produced with lower capital investment.

Forging: Grains are aligned perpendicular to th movement of the forging hammer. However, the grains are aligned in the 2-dimensional plane, not along a single line.

Extrusion: As the extrusion is made, the grains are aligned parallel to the pulling direction

Welding: Reliant on the quality of the substrate material. Any metal that is melted and resolidified (which will be the immediate weld zone) will have non-directional grain formation. However, the material of the tube (block, whatever) that is not melted, like the Heat AffectedZone, will retain its orientation.

There is another issue that we ought to address is welding. Even though investment casting can get rid of the 90* weld at the dropout-tube interface, we still need to join the dropout to the frame/fork (see WTP Scorpio forks above).

Fly aslo does this, but in a bit cleaner way (think Klein aluminum frames).

This joint requires high quality welding to be done right. Although BMX has evolved to the point where this is not a leap, I lean more to avoiding joints wherever possible.

Which leads right into the Conclusion: I am very excited to see this process being used in BMX. Fly and Eclat appear to do it a bit cleaner than the standard WTP stuff, but it is good none the less. As noted above, there are still a couple limitations to using this method. As far as forks go, I think the issue has been solved by the Odyssey Director forks. Hopefully they will become more polished as time goes on, and maybe we will one day see one-piece forks *fingers crossed*. The next step is how to do this on the frame (one proposal is to use the seatstays as the top of the dropout, and the chainstays as the bottom, then just weld the middle-front of the dropout).

About-me-tidbit: I worked with a company doing titanium metal deposition using a plasma welding method. One of the major issues we ran into was the uncontrollable grain orientation in the work piece. In some situations this was not an issue, others a blessing, and others still, a real issue. It shows how we ought to design components with specific manufacturing methods in mind.