Cold Forging at Shimano

Primo Powerbites, and now Hollowbites are advertised as being manufactured using cold forging technology. Effectively, they are smashing a blank piece of metal into the shape they want. Cold forging offers the advantage of precise control over dimensions, no need for heat treating, and aligns the grains along the surface of the part, perpendicular for forging direction. Hot forging, on the other hand, works better at aligning all of the grains of the part (up to a certain thickness, based on material characteristics), but cannot control dimensions as well.

Here is an article on Cozy Beehive about the cold forging at shimano. You'll notice the following graph, which may explain why some of the newer forged sprockets (such as Eastern's Medusa Lite, and Stolen's Mood Ring) are forged from 6061. Kudos to Primo for using a stronger, albeit tougher material to work with:

An Issue (and Solution) with Investment Casting

I was flipping through the Industrial Design Guide that I posted up a few weeks ago, and came to the page about investment casting. When I read some issues with the casting process. Typically, when the metal is poured into the mold, there are some unindented inclusions like Oxygen, metals, or other containments. Also, the act of pouring the metal creates turbulence and may allow pores to form, leading to compromised product integrity.

A solution to this is the Hitchner Counter Pressure Process. Basically it is filling a mold from the bottom up: You use vacuum pressure to pull the molten metal into the mold at a controlled rate. By doing so, the metal flows freely, with significantly reduced turbulence, and a better finished product. Certainly, there is an initial investment cost for moving to this method. But as with all manufacturing, diligence in pursuing cost-effective advancements will lead to better competitiveness.

Swaging

I've noticed a lot of forks and frames using "swagged" and tapered tubes. But what exactly is swagging? Usually it is a colt working or forging operation to reshape a tube. Here is the Wikipedia link. And some videos: 1, 2, 3

Although the three videos here show increasing the tube size, it is used in BMX to reduce or reshape the tube.

An open attempt to improve axial free coasters

A few members on BikeGuide have started discussing how to improve axial coasters. The idea is to come up with a design that can be easily made and will at least improve the issues faced with axial freecoasters. Here are some requirements (see the thread for more details):

• Low cost (i.e. using as many existing components as possible)
• Low(er) weight; sub 20 oz
• Suitable for peg use, not necessarily abuse.
• Better bearing system, especially in the driver
• Easy, and safe maintenance (i.e. no little pieces to damage)

If you have suggestions, or would just like to participate in the process, please post your comments in the BG thread, or here and I will forward to the thread. Once we come up with something suitable, I will post the dimensions, CAD files, and any other info on BMX-U.

Rim Materials

Just a reference of Rim Materials:

6061-T6

Density: 2.70 g/cc

Brinell Hardness: 95

Yield Tensile Strength: 276 MPa

6066-T6

Density: 2.72 g/cc

Brinell Hardness: 120

Yield Tensile Strength: 359MPa

7005-T6

Density: 2.78 g/cc

Brinell Hardness: 94

Yield Tensile Strength: 290 MPa

7075-T6

Density: 2.81 g/cc

Brinell Hardness: 150

Yield Tensile Strength: 503 MPa

Interesting results. I don't think 7075 is really used in extrusions, but I thought it was an interesting comparison. I first heard of 6066 when I looked at the Eclat Rims.

Handlebar-stems: An analysis

Ever since I saw the Cinelli Ram handle-stem, I have been fascinated with why we haven't moved to integrating in BMX. In this posting, I aim to to address the issues that come up in the upper steering system.

Note: a discussion on BikeGuide has pointed out two things: 1) I jump to the conclusion that forward/backward loads will not bend your bars without evidence; 2) The major challenge with 1-piece systems are their lack of adjustability both in reach (stem length) and bar angle (if, for some reason you don't want it in line...)

Vertical loads defined by loading both ends of the bar equally. In this case, the bends are stressed, and once the load exceeds the yield strength of the material, it will deform plastically (i.e. bend). During vertical loads, the stem is stressed vertically. Although longer stems will act as longer levers, when was the last time you bent a stem down?

Torsional Loads are typically qualified by loading of one side of the handlebar. These loads exhibit the traditional stress to the bends, but create a torsional load on the stem. A quick side note: torsional stiffness is proportional to stem body diameter, material choice, and thickness

Forward Loads are those times when you land a bit flat-bottom and find yourself shoving the handlebars forward. These loads are not characterized by large forces, but often end in the bars slipping in the stem. Promptly followed by a trip to the tool bag. Now some people claim that it is better the bar slips in this situation (or the opposite load where the front of the bars are loaded backward). The probability that either of these situations would end in plastic deformation is very small. Seeing as forward/backward loads are the only loads that can make the stem slip, and there is little chance of damaging the bars, I see little reason to not fix the bars to the stem.

So what do I propose? I would like to see more integrated bar-stems in the BMX market. As we get more market saturation, integrated bar-stems will be available in all the different geometries stems and handlebars come in. And let's face it, there are so few innovations in handlebars, the sector could use a bit more spice. We'll have to change our perspective on how these are clamped on the steerer tube, but that will spur innovation, and reduce overall weight.

Some examples...

The 2-Hip splined bar/stem

http://www.nordischer-rahmenbau.de/

KHE Anchor Bar

Carbon Fiber Suspensions

There have been a few mountain and road bikes that use the inherently high fatigue strength of carbon fiber to design dampening systems into the frame. Looking through some of these designs, I found an interest in carbon fiber composites as suspension (or spring) systems.

Here is a patent about carbon fiber coil springs.

Clip in pedals with carbon fiber retaining springs:

Many super-lite road brakes have been using composite springs for a while now. This is where I see some potential for BMX. We may be able to design a U-brake with a linear spring that will allow more design freedom.

It would be interesting to read an analysis of the Histeresis involved in composite springs...

EDIT: Our rep left a Keo Blade pedal with the carbon spring, in the shop. It is very nice, and actually a cool manufacturing desing (i.e. those flat carbon springs must be significantly cheaper to produce than Ti coil springs)

Pedal Sustainability

A recent discussion on BikeGuide spurred my interest in the sustainability of component manufacture. At the center of the debate were plastic pedals (1, 2), and their disposable nature. Most people, as soon as the pins have worn off of the pedal body, will simply toss the pair of pedals and buy some new ones. Even if you were to recycle those pedal bodies, spindles, and bearings, we still have to use extra energy to recycle those components, as well as manufacture new spindles, bodies, and bearings. On top of that, many thermoformed plastics are much more difficult to recycle. Note: This last comment about thermoformed plastics is not necessarily true. If you have a link to help, please post it :) -Peter 1/19

So where does this leave us? Can we use plastics in pedals? Yes. Odyssey's JCPC pedals have a good solution by using steel pins to hold the pedal together, allowing the pins to be replaced. Odyssey also provides replacement pedal bodies and spindles. By doing so, we can now replace only the part that fails, reducing waste. Reports are that the nylon used in the pedal bodies are recyclable, which is another plus. Now, in fairness, I should say that these are some of the ugliest pedals I have seen on a bike. 0 sex appeal. And they use a bushing setup, which can develop a bit of lateral play. Some people (such as myself) are bothered by this, but there is little reason it shouldn't work well.

And then we arrive back at the Aluminum pedal. For a long time, these have had replaceable pins, and (on high end pedals) spindles. Although there is a lot less probability of damaging the pedal body, I do not know of any BMX manufacturer that provides replacement pedal bodies. Aluminum pedals, due to their higher cost, and resiliancy, are a longer term investment.

Which pedal is right for you?

The Pedal Grinder: look for replaceable pins, and a tough pedal body. The worst situation is investing in a nice pedal only to knock a chunk out of it on a grind or stall, and not be able to get a replacement. In this situation, Nylon, or a thicker aluminum body is the appropriate choice.

The Spindle Bender: Usually you will see this when someone takes an impact to the end of the pedal. Look for sealed bearings or bushings bearings. Unsealed spindles must be case hardened to slow spindle wear, whereas sealed bearings or bushings allow the spindle to be focused on strength and stiffness. Of course spindle diameter and material play a significant role in strength. Here is a a few measurements of spindles from BMX-U

The Budget Rider: This has been the great aspect of plastic pedals: inexpensive, with fair performance. However, I would argue that this rider would be better served investing in a better plastic pedal (JCPC with all it's replaceable parts is a good long-term investment), or an inexpensive aluminum pedal (Un- or sealed bearings are your choice. Though if you dislike play, go with sealed). Why avoid the myriad of cheap plastics available? The pins. As soon as those are gone, so is your grip. And lets face it, slipping a pedal, even on plastic, is annoying. As more pedals come out, we may see some resilient pins, but until then, replaceable pins are the safest choice.

The Weight Weenie: I know you are looking through catalogs searching for the lightest pedal. I did this too, and ended up with a pair weighing 9 oz! But performance sucked, and the bodies were mangled easily. Even though most plastics are lighter than aluminums, I suggest investing in some good aluminums, for a few reasons: 1) they will run longer without problems; 2) they are available with good bearing systems (i.e. sealed); 3) they come in pretty colors, and BMX is about fashion isn't it ;)

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...

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.

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.