The History of the Lathe

Here is a very in-depth look at the history of the lathe. He does a good job of explaining what advancements were made, and how those affected the materials used and the quality of finished turnings.

Gun Drills

Gun Drills are used for deep bores. And are usually equipped with channels for feeding coolant from the base to the end of the drill. Using a normal drill would not work because the flutes are not long enough to evacuate chips and flood the cutting surface with coolant. Drills are available in straight or spiral flutes (spiral drills are made by taking a two flute straight drill, heating, and twisting).

Here is a link that talks about making air gun barrels. Kind of a good description.

Book Recommendation: The Noblest Invention

The first picture made me smile :)

300+ pages, but with short naration, packed full of side stories, short biographies, and historical perspective. It is a great, easy read (i.e. to be left out for guests or customers) that explained my love affair with bicycles better than I could. In a word, my bicycle represents Freedom. There is nothing I have felt better than the silence of a bicycle focused mind, hard-worked muscles, and a smile that just wont fade. This book kept me in the right state of mind.

p.s. I got my copy at the local library.

Sprocket/Crank Interface

In recent years we have seen a shift in sprocket/crank interface paradigm... Ok, that may be a bit exaggerated... At least there has been a change in design.

Traditional, Perpendicular Bolt

My first introduction to crank torque transfer was with the integrated stud on one piece cranks. Although effective, tolorances were often poor, and low-end sprockets were usually thin steel, further compounding any issues.

As BMX progressed, we moved to a bolt to secure the sprocket to the crankset (usually 3/8" or 10mm). Today, virtually all cranks use the bolt-on design. This helped solve some of the tolerance issues and has served as the standard for bmx. From a structural perspective, this design requires either a larger spindle boss or a separate hole cut in the crank arm for a sprocket boss.

A slight hybrid of one and three piece mounting systems, that has resurfaced recently is the use of a headless bolt. Mechanik makes a bolt called the Pin Head. The purpose of this design is not to hold the sprocket to the crank, but only to transfer torque. Using this design allows small spacers to be inserted between the arm and the sprocket to dial in the chainline.

Nano-drive

As Sprockets reduced in size (with flatland at the forefront), a need for less offset in the mounting position. Enter the nano-drive. Most nano-drive bosses use smaller bolts than the standard bosses.

Spline Drive

When faced with the challenge of small sprockets, Tree Bicycle Co. decided to redesign the mounting design. What they came up with was transfering torque through the spindle, rather than the crank arm. With most cranks now using 19mm, 48 spline, Tree's spline drive has a large potential market. Recently Profile decided to release their own version of spline drive (releasing a spline drive sprocket was logical for Profile as they are known for their 48 spline cranks). Unfortunately, Profile decided it was best to use 8 large splines on the adapter, rather than the 9 available on the Tree. I don't know why this happened, but it may be just to avoid any patent issues.

There is one big problem with spline drive: it is limited to 19mm, 48 spline cranks.

Socket Drive/ Nonogram

Flatware's (Odyssey) response to shrinking sprockets was to standardize. Well, sort of. They are the only company making a crank that works with the 9-sided mating surface, but do provide the specs and drawings(PDF) on their site. If this design is adopted, adapters can be made to adapt socket drive to a 48-spline crank, in effect making it another spline drive. The big advantage to this over standard spline drive is it does not limit the spindle design.

BMX-U Sprocket Page

KHE Clone Hubs: Calculating Slack

I recently posted this on BMX-U

Ok, this should apply to all KHE Clone coasters, as well as Odyssey and other "butterfly spring" coasters (though they may have different room in the hubshell. However, if you have an externally adjustable hub, you will just have to measure by backpedalling 1 revolution to 0* (or 90, whatever works for you), then pedaling forward and guestimating. Note: You cannot get 90* slack on these hubs, even with a relatively low 2.5 gearing and min spacers!

Driver/clutch thread pitch: 15mm per rotation (23mm/1.53 total)

KHE Spacer thickness: 1mm

Tophat Spacer: 5/7.5mm depending on orientation.

X= Total spacer stack (i.e. tophat set regular 7.5mm + 1mm spacer = 8.5)

G= Gear Ratio or Chainwheel (sprocket) size / Driver size (i.e. 25/9= 2.78)

( 12.7 - X ) / 15 * 360 / G = Degrees slack at pedals*

*assuming good chain tension, etc.

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 ;)

Bearing Specifications

Another great link. This one about the different designations given to bearings. It has helped me with bearing selection in some components.

EDIT: Wow, a long time later, I finally realize that I never posted the link. Sorry about that. The info its up at BMX-U now

Interesting Chain site

It's not BMX, or even bicycle specific, but a great link I picked up:

http://chain-guide.com/toc.html