Lesson in humility: failed headset crown race press

Part of doing-it-yourself is failing to do it yourself. It's not a bad thing unless you refuse to learn from it. Up until now, I had made it a point to only post my successfuly hacks/tweaks/mods/etc to this blog. However, today's post is abouta well-planned diy tool that didn't work. Let's try to learn something from it.

While doing my annual bike tune-up, I realized that part of my headset was installed incorrectly. I designed and built this tool in an attempt to fix that.

First, a bit of terminology.

A press is simply a tool that works by pressing things together, in contrast to a jack which pushes things apart. There are lots of kinds of presses: simple ones use a screw, complicated ones use pneumatic or hydraulic pressure.

A bearing is a mechanical component that acts to reduce the friction between two parts which move relative to one another. A ball bearing is a bearing which uses balls to accomplish this (though many other types exist: the brass bushings on cantilever brakes are an example of non-ball bearings).

And now some bike terminology.

The fork is the fork-shaped piece of a bike which straddles the front wheel (n.b. the things on the back are called the stays, and are NOT a fork). The steer tube is the tube which extends up from the fork to the stem, which connects to the handlebars. The fork crown connects the steer tube to the two tines of the fork.

The headset is a pair of bearings which connect the fork to the rest of the frame, allowing you to steer without much friction. Those two bearings in the headset are cup-and-cone style bearings. These types of bearings are popular in older bikes, but are being gradually replaced with cartridge bearings. This is unfortunate, since cup-and-cone bearings can be adjusted for a prolonged life, while cartridge bearings must eventually be thrown out and replaced. Nonetheless, because the main force on headset bearings are thrust forces (parallel to the axis of rotation), and because of the size of the bearings, cup-and-cone style bearings remain the standard for headsets.

A cup-and-cone bearing consists of three pieces: two races, and a set of balls. Sometimes, those balls are held in a ring formation by an unnecessary, though helpful piece of metal or plastic called the retainer. One of the two races is concave (the cup), and the other is convex (the cone). The fork crown race is the cone which is seated on the steer tube just above the crown, on what is called the crown race seat.

The crown race is press-fit onto the crown race seat, which is to say that the crown race seat is slightly larger in diameter (1.185") than the internal diameter of the crown race (1.180"). This minor difference in diameter (only 0.005 inches) is enough to make it hard to install, though once installed, it may as well be a piece of the steer tube.

So, as I was stripping my bike down for its annual paint job, I noticed that the crown race was incorrectly seated, and I decided to remedy it. It only took a few seconds for me to decide that I wouldn't be able to press it on by hand, and so I went forth building a tool.

I tried two variations on the same design. The first attempt failed: as I tightened the drive bolt, it worked well until the steel bar bent, and then the plastic snapped, and ultem shrapnel ricocheted off of my luckily-closed eyelids. Although a failure, it worked for a while; the race was halfway pressed onto the race seat. I was encouraged to try again, using a heavier construction that hopefully wouldn't snap, crackle and pop.

I have annotated the picture on the left.




I used my lathe to turn a piece a ultem plastic (a metal replacement, similar to delrin) into a race guide. The race guide had a 1.125" hole bored through the center of it, so it could slide along the length of the steer tube, and had a larger recess bored at one end of that hole to snugly fit the crown race.




I then drilled and tapped two holes on either end of the race guide, and used bolts to fasten the race guide to a bar of steel placed between the two tines of the fork. A third bolt--the drive bolt--past through the center of that steel bar against an ultem plunger, which pressed against the other side of the fork.

Again, I have annotated the picture on the left.






I wrapped some fabric around the new paint on the fork, and began torquing the drive bolt. Just like the first time, it began working. In fact, this second attempt put the race close to the right position.

But alas, it too failed.




The failure was very similar to the first time. First, the steel bars bent. And again, since it seemed so close to being complete, I chanced tightening even further. Unlike my first attempt, however, the plastic never broke. Instead, the press tore the head off of one of the hanger bolts.

Disheartened, I decided I would need to try a different technique. But what? I couldn't easily make this design larger, since I was already working with the largest plastic stock I had available. I read and re-read Sheldon Brown's advice, until it came to me.

Duh! I have a lathe.

I chucked the crown race, and took a few (i.e. added) a few thousandths to the race's internal diameter. The race still had to be pressed onto its seat, but I could do that under hand power using the race guide I had already built.

So, as I mentioned earlier, there is a lesson hiding in here somewhere. I'll try to be thorough it down, but please let me know if I elide anything:

Lesson 1: Keep it simple, stupid (KISS). This is the prime directive of engineering. By elaborating the design, I added too many points of potential failure.

Lesson 2: Determine which problem constraints are true constraints, and which are only constraints in name / by convention. The crown race should be tight on the crown race seat so that the steer tube doesn't rattle within the bearing. But does it need to be press fit? There will be no motion between crown race and steer tube, so long as the bearings are doing their job. By increasing the internal diameter, I allowed easier installation, but without sacrificing holding power.

Lesson 3: Wear eye protection.

Single-serving tools

Every so often, you find yourself in need of a unique tool to fit the situation. Most of the time, such a tool can be bought. Though, because of their limited need, stores must sell these for a higher price to average out the lesser demand. Compounding this fact, no one wants to pay a lot for a tool they'll only use once.

I've collected a list of all the one-time, single-serving tools from recent memory. If you have similar single-serving tools, I'd like to see them.

(1) An improvised headset press.

I needed to install the bearing cups to a 1-1/8" threadless headset on the bicycle I was building. But, I was only going to do this one time, so I didn't feel like buying a tool, even if it only cost $20.

My solution was this. A 1/2" screw is used to push two soft plastic plates together. These, in turn, push the cups into the headset. The plates were made out of some plastic from an old cutting board.

For best results, stick the cups in the freezer for half an hour--they will contract slightly and fit more easily.

(2) An exceptionally long allen wrench.

Have you ever needed a really long allen wrench? Well, I did when I was constructing the drawer set for my new lathe. Local hardware stores didn't sell allen wrenches this long--at least not in metric--so I built my own.

Take a normal allen wrench and hacksaw-off the bend. It's hardened steel, so it will mess up your blade--use a worn-out blade. Take a length of 3/8 round steel, bore a 1/4" hole at one end, at least 1/2" deep. Insert the hex bit, and then weld it on to the rod.

Also, bend the far end of the rod, or weld on some sort of handle. I used my lathe to turn the rod down a bit, making it easier to bend.

Ultimately, this 5mm wrench will reach more than nine inches deep into a 1/2" hole.




(3) An easy way to measure angles.

When I moved into my apartment, I immediately devised a plan to build an long shelf above head level in the hallway. Because this apartment had been sliced off of a single family residence, it had an awkward hallway in the wrong place. The hallway space seems like a significant fraction of my apartment, and without the shelf it would all be lost.

The problem was that the walls in this hallway didn't meet at right angles. It's very ad-hoc, with three turns at angles around 13-31 degrees. I needed to measure these angles or the wood wouldn't meet right.

Sure, protractors are cheap, but one wasn't available when I had my inspiration.

I built this out of some 1" extruded aluminum angle-stock and a small machine screw, nut an washers. The trick? A hole is drilled on each bar, 3.5" from the pivot point. For any angle, the two holes and the pivot point make an isosceles triangle. Then, if I measure the distance "h" between those two holes, I can calculate the angle between those bars as 2 * sin ( h / 7 ).

The shelves, by the way, look great and line up perfectly.

So, anyone else have single-serving tools to share?

Multi-color lamp from (some) reused materials

I've seen this style of fabric-draped, muted-light lamp all over new york recently. I decided to build my own, and make it glow funny colors.

The schematic is really simple; I wanted to keep it that way. A PIC16 is used to create three PWM signals. Those three signals feed into three NPN transistors to drive a stack of colored LEDs. I proper design would use resistors both at the base and the emitter, but I was lazy last night.

Also, this thing has source code.




Tryin' to keep it simple. I put it on some perf board, and wire wrapped it. I tried to space the LEDs evenly on both sides of the board. The obverse:






And the reverse.










Then, I made a frame out of two coat hangers. I wrapped them with some packaging material from my new job's recent Ikea visit, and sewed it on.







It starts to look a little bit better as more sewing is done.









Finally, it looks like this in the dark:

HOW TO replace the chamber in an American Lock Padlock

All too often you'll find one of these heavy-duty padlocks just laying on the street. Wouldn't it be nice if you could use this abandoned lock? Here's how:

1. Drill out the old chamber. This will be much easier if you use a drill press.
   
   


2. Open the lock. Sometimes this is really easy, other times you have to whack the lock against something hard so the pins will fall out. Try using a flathead to turn the chamber.
   
   


3. Locate the screw hidden in the shackle hole.
   
   


4. Unscrew it.
   
   


5. Remove the retainer plate.
   
   


6. Make sure you have all the pieces: the retainer plate, the screw, the nut, and the old chamber. You can discard the old chamber.
   
   


7. Insert a new chamber, and reassemble. Make sure the new chamber is oriented as shown.
   
   

This is all easy, but you might ask, "Where would I find a new chamber?"

Well, it depends on your scenario. If, for example you have a key and lock, but your lock is otherwise damaged (e.g. shackle has been cut), you can transfer your chamber to another lock for which you don't have the key. Chambers can also be bought in bulk from the manufacturer.

Thanks to John at 123 Tompkins!