One Problem With Welding (HAZ)

What changed when Odyssey introduced 41 Thermal? Aside from finally focusing on the quality of their components, and backing them up with easy customer service, they started to heat treat their welded components after welding.

The issue with welding

Although there is extra material when you weld two components together, the biggest detriment is the Heat Affected Zone (HAZ). The area immediately around the weld becomes stiffer and less ductile. These properties lead to more propensity to crack. Take a look at cracks, and you'll find many of them occur around welds (cracks in welds are always a manufacturing defect, usually arising from voids in the weld).

Gussets

This is a problem that has plagued bicycles since we switched from lugged and brazed frames to welded. Gussets are one attempt at fixing it. The idea is that welding a plate effectively moves the HAZ farther down the tube, reducing the likely hood to crack. However, this adds a thick plate, and welds to the structure, leaving us with a heavier component. And let's face it, gussets are just not an elegant solution (take a look at the cool design/gusset below. Reminds me of lugged steel road frames).

Internal Gussets

Internal gussets are NOT gussets. They are a type of offset butting. Although a good idea (because it places material where it can most effectively support the loads encountered), these do not move the HAZ. You may be able to argue the added thickness slightly shrinks the HAZ, it does not significantly affect it.

Heat Treated Tubing

Tube manufacturers, like True Temper, Sanko, etc, will heat treat their tubesets after extrusion to optimize their mechanical properties. However, this heat treating is altered in the HAZ. Farther down the tube, where the material is no heated significantly, the mechanical properties introduced by heat treating still stands. Does using heat treated tubes reduce cracking? Hesitently, yes, heat treated tubes MAY help to reduce cracking, but cannot make significant changes to the HAZ.

So what do we do?

Post Weld Heat Treating works to relieve the HAZ. The irregular shape of the weld remains, but the brittleness of the surrounding tubes can be significantly reduced. This simple step is often overlooked because it usually requires shipping the component off, or adding machines to the shop. But it is worth it. Take a look at Odyssey's post weld heat treating and how it has brought that company (along with a better business model) to great status in BMX.

So the next time you see a company bragging about 4Q Baked, 420 Baked, or these other marketing ploys (including 41 thermal, but they actually did it right), see if there is an alternative from a company telling you something meaningful: post weld heat treatment. Luckily, more an more frames are going this direction. We can only hope to see the same from Bars, cranks, forks, etc...

Shadow Torrid V2 Cranks

Flipping through Dan's I saw the shadow Torrid cranks. Now I realize these are not new, but they are interesting. If you take a look at the patent for it, they originally designed the crank to use a chromoly spine (4140 not specified), with an aluminum shell. I'm not sure if they ever made this in a production run, but there are a few reasons why this is not necessarily a good idea:

• Different materials have different properties. Specifically, they have different elasticity, and different rates of thermal expansion.
• Joining (welding) dissimilar materials is difficult. Although there are filler materials available for joining Aluminum and Steel, but they make structural sacrafices in order to get proper fusion of both materials.
• There is no purpose in using two materials. Profile and the new Torrids show how steel is enough on its own.

Now the current version of the Torrid cranks use a 4140 spine and a 4130 shell... Again, I am not so sure this is really necessary, or even advantageous. We can't really know what their goal in using different materials is. However, we can speculate they wanted the stiffness of 4140. I assume they weld the shell to the spine along the ridge, which would stiffen the whole structure by making virtually the whole crank a heat affected zone. Well they could post weld heat treat (anneal), as all welded components should be, but I would assume they would market that as well.

After running a few circles, where are we? Boasting that it is patented, the use of two parts, and two materials, all makes me weary this is mostly just marketing. Does that mean they are crap and will break? No, not at all. But if we are to aim for the highest strength to weight ratio, this design is probably not the way to go.

BMX Wiki!

It's been a while since I posted, I have been working on getting a bmx wiki up. Thanks to a few cats over at http://www.bikeguide.org/forums it is getting filled up. Take a look, and please contribute what you can. Even the smallest stuff helps. http://www.bmx-u.com

Flash Welded Rims

I was browsing through Eclat's site when I saw their rims were Flash welded

It'd be interesting to see how other rims are welded. Perhaps there are many other rims that use this technology. Especially since bicycle rims are noted in the TWI article.

They do also say the Bondi Rim "... features a unique wide design which spreads the impact load of harsh landings more thoroughly" I don't know about that. They're also lower profile, which would reduce stiffness radially. I would expect this rim can take a hit axially (i.e. Whips, spins, etc)

Note: TWI is a very reputable resource for info on welding. We used them for some research on titanium welding.

Freecoaster Clutch Styles

Essentially, there are two styles of clutches: Axial Clutches and Radial Clutches. The differing characteristic being The direction the clutch moves, along the axle, or radially out.

Axial (KHE Geisha):

Radial (KHE Rollex):

Axial Clutches

The majority of clutches are axial because of the system offers. For the purposes of this analysis, axial clutches can further be broken down into sub catagories:

• Push type clutches push the clutch from driver to hubshell (only stock ones I know of are the Sym Hub and the Stolen/Chosen.

• Pull type clutches pull the clutch toward the hubshell and driver (Geisha, reloader, etc)

An inherent characteristic of the axial mechanism is side load on the bearings. Push systems side load both the driver bearing(s) and one of the hubshell bearings. Which bearing is loaded is dependent on whether the push mechanism is located between the hubshell bearings, or outside the bearings.

Axial-outside-push system (sym-hub)

Welding two clutches together work to convert to a LHD-axial-inside-push system (modified taska)

In Contrast, pull type systems only load the drive-side-hubshell bearing. In all unsealed and some sealed hubs (such as the KHE Reverse ACB), the balls contact the races at an angle, which supports side loads much better.

Axial-inside-pull system (KHE Geisha)

In hubs where the drive-side-hubshell bearing rests on the driver, not the axel, the driver bearings must withstand sideloads from axial wheel loads (i.e. when whipping and the wheel lands at a funny angle). Repeated impacts can cause damage to the drive bearings. Interestingly, unsealed hubs are much less likely to have damage to the bearings. This is due to the angular contact that the cup and cone system provides.

Radial Clutches

Radial clutches are much less comon. The only two I can think of are the KHE Rollex, and the yet to be produced, G-sport Coaster*. The former uses roller bearings and ramps, while the G-coaster uses a cam mechanism and, what can be compared to brake shoes.

The major advantage of radial clutches are they do not interfere with the hubsell bearings, and no sideload is on the driver bearing (unless you are pedaling really hard while landing a tailwhip at a funny angle). These systems avoid the major durrability issues that are all too common in coasters.

We must, of course, note a potential issue of radial clutches: contamination of the freecoaster mechanism. Any hubs that come out with a radial system will have to make sure a good sealing system is in place.

KHE Rollex Explosion

* George from G-sport confirmed that he is still working on the coaster. Seeing how the rollex never quite succeeded, it's probably a good thing he is taking his time.

Plastics IN Pedals

After my first post on the prevalance of plastic pedals, I recieved and broke my Odyssey glow-in-the-dark pedals... In one day! I was immediately surprised, as I had used some black Odyssey plastics for a long time without an issue. After some thinking and research, I came up with why there was such a dramaic difference between the two: the black pedals were nylon, while the glow pedals were polycarbonate. This post will focus on a few different materials used in plastic pedals.

Nylon's major advantage is directional nature, and toughness. It was originally designed for use in tooth brushes, and has since been adapted for seat belts, safety vests, and ballistic cloth. What this shows us is the direction in which nylon has developed: to be tough and reliable. The fiber/directional nature of nylon lends to its higher shear modulous.

Polycarbonates, although exhibiting excellent impact resistance, lacks in shear strength. This is where my pedal failed. The right hit, at the right angle cracked the pedal. There must be advantages in polycarbonates for BMX, right? Well, yes, they have a lot of pretty colors, including UV activated and glowing, and are increasingly used in other industries (reducing prices).

So where does that leave us? Well for me, the colors are not worth the annoyance of changing pedals often... even at such a low price. That leaves me leaning toward nylon. In thinking about it, though, I wondered if there were pedals out there using fiber reinforcement (i.e. composites). Quickly, I came across Eclat, a brand I am becoming more fond of. They are using fiberglass reinforced nylon in their Surge PC pedals. Although I would prefer carbon fiber, it is a definite improvement. The weight is virtually the same, and the price is still low (that's where the fiberglass has the advantage). Now the real question is which semi-transparent color...

EDIT: I just saw that Fly is also coming out with nylon-fiberglass ruben pedals. Woohoo! But I need pedals now, not December, so Eclat here I come.

EDIT 2: As Martin pointed out in the comments, Eastern is using carbon fiber re-enforcement in their pedals. Though, they do not list what type of plastic is used. We'll have to see which pedals survive in the market, but CF is not a bad idea.

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.

Plastic Pedals

In the past few years, plastic pedals have become much more prolific in BMX. My first experiences started by just grabbing some Welgos from the shop to try saving a bit of weight. I never had much trouble with the grip of even those! And the weight savings was substantial. Since then, Odyssey, Animal, and virtually every company with a pedal has a plastic version available too. Why am I so excited about this?

1. They're cheap, and lets face it, BMX is full of cats who want good components, for as little money as possible.
2. They're light, light, light. At around 13 oz per pair, who can complain?
3. The colors man, the colors! Odyssey has really shown the potential with using polymers in pedals (and seats, but that is another discussion). A wide range of colors are available from most manufacturers. Odyssey even offers Glow-in-the-dark, and Chameleon (UV activated, color changing) . Lets face it, aesthetics do play a role in our component choices. And rightfully so, if you like the way your bike looks, you're more likely to get motivated to hop on it.
4. Grinding/sliding, whatever you want to call it, is more Kosher with plastics. If you ever get bother for hopping on a ledge, just point at you pedals and say plastic. Certainly, there are some thick-headed people out there who will still give you trouble (because their "girlfirend" left them, no body calls to see if their ok, and they generally have personal issues they feel you are responsible for).
5. You can finally stop feeling bad for riding a bike... wait a minute... Haro Recycled plastic pedals

One thing I will try to do throughout this blog is to show both sides of the story. Plastic pedals are not for everyone. There are definite trade-offs with plastics.

1. Grip. Some people complain that the little "pins" in plastic pedals either do not give enough grip, or wear down too quickly, so there is no grip. This is a fair concern, as some people prefer more grip than others. I would say it comes down to riding style. I thought I had seen something like the Hoffman Solemate pedals, where a nut and bolt are used as pins, avoiding the whole "what?!? Stripped? I didn't even tighten it! ARRRGGGG!!!" problem. Edit: The new JC pedals from Odyssey will have an interesting new pedal design:
2. Weaker spindles. When these pedals first started coming out, people pointed out that the spindles were just run-of-the-mill, cheap steel spindles. This is a big concern to pedal destroyers. However, since competition in plastic pedals has increased, companies are putting in the same grade spindles as their aluminum-bodied counterparts. I still think pedal spindles are designed backward, but that is for a future post (after some CAD work).
3. Having such cheap pedals may lead some people to the idea that it is ok to just toss them out every month or so. Which is fine, as long as you find a new home for the old ones. Donate them to some new rider, or use them in a side project. We should avoid the idea of disposable products.
4. No Anodizing. And lets face it, ano is sexy.

Conclusion: Plastic pedals are great for BMX. Their low cost and low weight fit right in. However, we will likely never see them owning the market, as some people will want the look, grip, or feel of aluminum-bodied pedals.

What's the point?

This blog was started after seeing how many cloned parts there are flooding the market. Granted, this isn't anything new. However, after a little break from BMX, I find that there are quite a few good designs out there. So we will be exploring technologies, new and old, in the hopes to garner a better understanding of the mechanical principals that make up a high quality BMX bike.