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.

Spring bike maintenance

Spring is finally here, even in the frigid New York City, and time has come for my annual bike tune-up. Sure, I could take it to a bike shop, but then I'd miss out on all the greasy hands, the hundreds of little cuts on my hands, the OCD adjustments that a bike offers, and the feeling of triumph of riding the optimized bike.

Now, I admit that my hand was forced into doing a tune-up. Work has kept me busy enough that I just put off the repairs, one weekend after another. It was a mechanical failure that got my focused.

Daya, Chris and I were at Ben's surprise birthday party at a brewery on the ground floor of the Empire State Building. Eventually, we got sick of paying $7 / pint, and decided to go back to Brooklyn. Our destination was a bar called "Alligator Lounge," serving $5 drafts and a free pizza with every drink (no, really). We set up a race: Daya and Chris took the subway, I rode my bike.

I took 5th Ave down to Union Square Park, and got onto Broadway. I kept flying south until I hit Grand St, realized I went too far, and backtracked to Kenmare. I took the Williamsburg Bridge, landed in ... Williamsburg, and then started looking for the bar. People on the streets tried to give helpful directions, but each pointed me in the wrong direction. Finally, when the alligator lounge was in sight, I started pedaling from a read light, and then ...

My chain fell off.

This is rare, but not unheard of. I have my bike rigged with only 1 chainring up front, and no front deraileur. Thus, as the rear deraileur shifts from side to side, there is a slight chance (say, once in 200 miles) that my chain will fall off.

But not this time.

As I started to put my chain back on, I noticed that my chainring had inexplicably bent itself beyond repair. My bike could be pushed, but not ridden, and I was still miles from home. Knowing that I had lost the race, but that I should have won, I pushed my bike the last few blocks. Daya and Chris were there, smug with their victory. This was the first time I had lost a Subway-versus-bicycle race, and I was not happy.

But I digress; this post is about my spring bike tune-up.

I replaced my broken 48T chainring with a new 53T chainring. This has upped my ratio significantly, but still in my comfort zone. I also replaced the chain, and put on a new 8-speed 11-28 cassette (same as before). I put on new brake shoes, bought new cycling shoes and installed new cleats.

But that's the less interesting part of the tune-up. I also did some work on my headset, and I repainted. Each of those is a big enough task to warrant their own posts. So, those posts come next over the next few hours. Stay tuned.

Shout-out to Dennis Ferron

Dennis recently linked to me from his blog, and I wanted to say thanks, and to point out a particularly cool post. Ferron's Guaranteed No Mess No Mixups Method for Swapping Rims without Relacing is something that I wished I had happened upon years ago.

The problem: you have a new rim, and you want to build a wheel. This task is typically a pain, though some people enjoy doing it.

The special circumstance: you already have an old wheel built.

The critical observation: in addition to re-using the spokes and hub from the old wheel, you can preserve the information stored in the old wheel's lacing.

The method: put the two wheels side by side. Transfer one spoke at a time from the old wheel to the new (in careful order), and you save your self a lot of hassel.

Well done Dennis.

One liner updates

I have accepted Princeton's offer. In September, I will be a graduate student at the Computer Science Department at Princeton University.

The weather has been beautiful recently.

Work is going well. I work at a rate of one todo list page per day. There, I have observed quite a bit about ruby on rails, and I think I'll have to post about that soon.

My mother is coming to visit soon.

Although I had a minor in math, I still think that taxes are confusing. The astute reader will note that math is not arithmetic.

I just went through a week of infirmity... Something gastrointestinal. I'm happy to report that has passed.

I've been playing with my lathe a lot. I built a crank puller, as I said I would. Now I just need to convince myself to stop making minor changes to it, and to move on to a new project.

My apartment has a mouse. I'm trying really hard to kill it, but it is apparently smart enough to take the cheese off of the traps without dying. Bastard!

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?

My minilathe, and several mods thereof

It's been a while. There are various excuses for that, but the main excuse is that I've been putting in long days at my new job.

The big news (on the diy/hacking/modding front) is the arrival of my minilathe. I had been dreaming about owning a minilathe for a long time. I had always been frustrated by the cost and accessibility of various machine parts; to me, it's torture when you have a great idea and no way to build it. I looked forward to all of the rights and responsibilities given to lathe owners.

This lathe is just one brand of a common chinese lathe, sold by Cummins, Harbor Freight, Grizzly, and others.
One benefit of this oft rebranded tool is that many online communities have sprung up about how to use or modify it, for example the right-wing 7x10 minilathe group. However, the Cummins model is in a class by itself. It is simultaneously the cheapest, and shipped with the most accessories, including a faceplate, a 3-jaw chuck with both internal and external jaws, 5 HSS tool bits, a tailstock chuck, a dead center, a set of change gears, a steady rest and a follower rest. It is a great value.

Let me first say that, despite the limitations inherent to small lathe, this lathe is quality. Every moving part has a gib or some other way to adjust it. Although each part may slowly wear out, the designers have provided the end user with a way to compensate.

Let's compare it to the famous Sherline Mini-lathes. Among hobby machinists, Sherlines have a good reputation for quality, and are comparable to my Cummins in size. However, Sherlines do not include change gears and a feed screw -- necessities for cutting internal / external threads -- nor do they include a compound slide, thus one cannot cut bevels. Oh yeah, Sherlines cost more too.

Enough about comparisons, on to the juicy stuff. I unpacked the lathe. The first thing you need to do with a machine like this is take it apart. I took it down to it's solid pieces, cleaned off the factory grease, re-greased. re-assembled and adjusted it. These preliminaries are critical, since they give you a good understanding of how the machine all works, and yield a certain confidence toward using or modifying the machine.






So, what modifications have I done? First the simple shit: I removed and recycled the two chip guards. Then, I removed the plastic do-hickey covering the emergency stop button. Perhaps I'm misunderstanding it, but it seems much safer to have a clear path between my left hand and the stop button. Additionally, I replaced the bolts that secured the hand wheels, since they tended to hit my knucles.


Next, I grabbed some strong magnets pulled from a scrap hard drive, and used them to keep track of the various chucks. I find that the use of a magnet is just slightly entertaining, perhaps only on the subconscious level, but that is enough that I never forget to replace the key. I don't imagine I'll ever accidentally leave it in the chuck.




I don't own a grinder with which I can grind my tool bits, but I can put a small arbor-mounted grinding wheel in my lathe. The beauty of this is that I can use my lathe's compound slide to get a precise angle onto the tool bits. Similarly, I realized that I can use fragments of hackway blades to shim-up the cutting tool.




My lathe came with a lot of accessories, and suddenly I had nowhere to keep them all, let alone work. So, I went to work building a drawer set. I collected a bunch of scrap wood and plastic from around the neighborhood (and trash day in Brooklyn contains enough wood to build a few houses, I'm sure). The drawer set is sturdy as hell. I added in a few solid brass drawer pulls that I found at the Park Slope Flea Market to finish the effect. So much of this sort of improvised building involves moments of inspiration. This simple allen wrench holder is one such example.

Most recently, I built a apron chip guard, inspired by the one that Varmint Al made. One failing of the minilathe design is that it leaves the gears behind the apron exposed, and poised to collect metal chips from the cutting action. As Jobst Brandt once said, "Commercial abrasive grinding paste is made of oil and silicon dioxide," and so I was concerned about these chips, even though the gears were otherwise greased. So, here is how I built it:

Cut a sheet of 1/8"-thick pastic to the rough contours of the lathe's apron. I used some plastic that used to be part of a printer's enclosure. Drill a hole large enough for the gear's shaft (I cut mine 7/8" since I had that bit available, though smaller would do). Drill and countersink five holes around the perimiter of the chip guard.




Transfer those holes from the plastic chip guard onto the back side of the apron using a center punch. Drill and tap those holes. I used a #36 drill, and a 6-32 tap, though anything of similar size will work. The apron is made of cast iron, which is a surpisingly soft metal. Nonetheless, proceed with caution so you don't break your tap, and use lot's of wd40.







This is a view of the back side of the apron after the five holes have been drilled and tapped.








Clean out all metal chips from the area, and re-install the gears.








Drench the gears in a heavy grease. I used an old hacksaw blade as a spatula to really muck it into the nooks and crannies.







Install the chip guard. It is secured down by five 6-32 machine screws. Re-install the apron onto the lathe, and rejoice in your apron's newfound ability to repel chips!

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: