Monday, January 20, 2014
Life is still busy. After this post there is at least one more to go in the series, and in the meantime I'm going to be riding my new bike to work tomorrow for the first time.
When I left on Friday of the first week, my front triangle was brazed in two locations, but still needed the rest done.
Monday morning I was back at it, finished off the brazing and grinding of the Front Triangle. What I didn't mention previously was that after each brazing step on the front triangle we check the alignment, clamping the head tube tightly into a jig on a set-up table and then checking that the seat tube is perfectly parallel to it.
When things don't align (and they don't - adding heat and metal to the frame causes everything to shift) you figure out which way to pull it, and then you apply brute force and hopefully no ignorance. The very last alignment step I had my frame securely clamped at the head tube, supported at the bottom bracket, and I had my full weight on the top of the seat post, and I was bouncing hard. Five bounces later it moved by a millimeter or so. It's scary the first time, but you quickly learn that a fillet brazed steel frame is STRONG. In the end, this is what you want to see:
After that was done, it was time to grind down the fillets, and Voila! I had a complete front triangle
The rest of the day Monday was spent installing braze-ons for cable routing, filing, and general clean-up of what I had done to that point.
I took the frame home that night to show everyone how I was doing. and even remembered to take it back the next day!
Tuesday morning is where the fun started. Remember how I'm using a Rohloff Internal Gear Hub, and how I'm using sliding dropouts for adjusting chain tension? This picture shows a lot of different styles of rear drop-outs for different bikes, and I've highlighted the ones I'm using. Seriously, the ones that I highlighted are mine - Paul took this photo for his blog while I was standing right next to him.
The sliders fit into rails machined into two inserts that are welded into the frame, and by moving the dropout back and forth in the rails I can adjust chain tension.
Rohloff provides a set of engineering drawings for people to build both the sliders and the inserts. Paul had several pairs of sliders, but has chosen to have his students that use Rohloff IGH's (I'm only the second) machine their own inserts. Here's the Rohloff drawing of the insert; you can certainly use these inserts, but they just won't be customized to your frame.
I then had to figure out how I wanted my insert to look. I decided I wanted the rails to be aligned with the chainstay, so I had to figure out where the rear axle would be relative to the chainstay and get the chainstay angle correct:
From there, I needed to work out the angle of the seatstay, and then I needed to draw out the insert with the correct dimensions:
If you look closely, you'll see I added drilled mounting points for a fender and for a rack, and also removed a circular volume for purely cosmetic reasons. What you don't see in that picture is how much planning was involved in making sure there were clearances for everything, and because the dropout (and everything attached to it) can slide that's a bit tricky!
At that point, I had the plans and everything seemed to work, so it was time to start making that happen. Starting from a 3/8" piece of cold rolled steel, I first had to mill it down to 7mm:
From there, I laid out the key reference points and drilled the ends of the sliding cutouts.
Then its time to mill out the inside of the slider rails:
And then the inside of the sliding cutouts:
Finally, I removed the remainder of the metal on the surface, leaving the rails raised 2.5mm above the rest:
Then it's over to the bandsaw to do a rough cut-out of the two inserts:
Then over to the drill press to put in the mounting points and remove the circle, then filing and sanding, and they are all done:
Sounds easy, right? The reality was that this took me until mid-day on Wednesday to complete, which put me behind, so my picture taking suffered from this point on.
The next step was to select the chainstays. We had several different bend profiles to chose from (and we could bend our own if we chose, but that would have been a lot of work), but with a 68mm bottom bracket, a 430mm chainstay, and the wide rear end I had good pedal and heel clearance with straight chainstays. After cutting them, putting them in a jig, and tacking them, everything looked good:
From there, it's brazing the chainstays to the bottom bracket, and the inserts into the chainstays:
Then came the chainstay bridge:
From there it was into the home stretch. I cut and installed the seatstays much the same way as the chainstays, followed by the seatstay bridge. The final few steps were installing the braze-ons on the left seatstay for running the disc brake and the Rohloff shifter cables, followed by seatstay braze-ons for a rack and bridge braze-ons for fenders, and everything was finished.
We all congratulated ourselves on a job well done, and the course was over.
This was the end of the course, but not the end of the project. It was a lot of fun, and I learned a lot. It was a total break from everything I do on a day-by-day basis, and a good opportunity to recharge. And at the end of it, I have a frame. MY frame, that will become MY bike. How many people can say that?
Wednesday, January 01, 2014
This one's taken a bit longer to write up; life got in the way. Lots of pictures here!
So to start, a bit about the course. Years ago Paul Brodie started a small company, Brodie Research and Development (now called Brodie Bikes) in Vancouver to build mountain bikes. He had been a machinist, and had become a bike mechanic almost by accident, then ended up thinking that building frames would be just up his alley. Over the years the company built up quite a reputation for building hard-tail mountain bikes, building custom bikes for many of of the top racers and they branched out and also built road bikes. After several years, Paul decided to sell the company (he has no involvement other than friendships with the current company) and build custom motorcycles. When he sold the company he kept hold of his original jigs. Eventually, he needed money to purchase a new Trials motorbike, and sold his jigs to one of his earliest clients. In turn he (the client) turned around and said that he would donate the jigs if Paul would teach a frame buliding course. After back-and-forth's with a couple other schools, Paul got in touch with the University of the Fraser Valley (located in Abbotsford, which is East of Vancouver), and things went from there, so now UFV has a 4130 steel frame building course.
The course is taught in a corner of an aircraft hanger at Abbotsford International Airport (UFV runs airframe maintenance courses in the rest of the hanger), and from Paul's initial cold call to UFV it took about 6 months to get things sorted out and the first course session. The course is two weeks, Monday-Friday, 8am(ish) to 4pm(ish), and according to Paul when he first started out he was thinking "What am I going to get the students to do for two weeks?" and by the end of the first week of the first session he was thinking "How am I going to get them all finished in two weeks?" They all finished. By the third session it was running pretty smoothly, and my course was session #24. There are a maximum of four students per session, but there are most often two or three, and there has been only one a couple times - it all depends upon how many people register. Everyone has managed to finish their bike frames by the end of the two weeks, and almost all of them are now being ridden.
On the first day three of us showed up not quite knowing what we were getting into. Andy traveled from Alberta, and was building a Fat Bike, and is like me - an office worker going through a bike crazy period and wanting to say that he was riding a bike he built. Todd traveled from Saskatchewan, and a commercial welder (dealing with big iron) looking to gain some skills dealing with smaller stuff - he and his wife are working to gain skills to go into business together doing custom bike, snowmobile, and ATV components. Andy was going to build a Fat Bike (the first in the course), Todd was going to build a straight-forward front suspension mountain bike, and I'm was building my mutant Rohloff CX bike. None of us have done TIG or fillet brazing before, and the last time Andy or I held an Oxy torch was in shop in High School.
The shop may just be in a corner, but is well set up, with a milling machine and a lathe, as well as several benches and jigs.
We started out, one at a time, practicing in the TIG booth, joining a few plates. Meanwhile the other two of were learning fillet brazing, first by practicing heating the work surface and rod until the rod flowed while building stacks of bronze fillets heading off to the sky:
And then by joining a steel tube to a plate using nickel silver brazing:
It was pretty clear that TIG was not for me and I would be brazing - usually the students that end up TIG welding their frame have extensive welding experience and have had months if not years of practice beforehand. Thankfully I was not alone - both Andy and Todd would be brazing too!
From there, it was time to start practicing. We would start out by building a Baby Frame:
It is essentially replicating the front triangle of a standard bike, just at a size that your cat might be able to ride (if it were a very small cat). We would be cutting and mitering all the tubes, nickel silver brazing them together, and then bronze fillet brazing over top and grinding to get them all nice and smooth. I don't have too many pictures of this, because I was quite busy, but I have to note that my very first braze, done at the end of the day Monday joining the baby frame's seat tube to the bottom bracket, was HORRIBLE. I had my torch too hot, had too much oxygen in the flame, and as a result I was burning the flux and had no strength in the weld. Tuesday morning as a test I we put the bottom bracket in the vise and slipped a helper bar over the seat tube to give more leverage, and I pulled:
It failed BADLY. Good lesson in what not to do.
Starting over, I went on to building my baby frames. Gratuitous Action Shot:
All three of us finished our Baby Frames Wednesday Morning (it doesn't always happen) and I now have a conversation piece on my shelf at work. Maybe I'll build it up for our cat one day.
From there, it's off to full-scale drawings. We all had pretty good ideas of what we wanted to do, but given a blank sheet of paper we all had an opportunity to do back-and-forth with Paul as we worked through geometry and tube placements. Andy and I had a number of challenges given that we were doing something out of the ordinary - Andy had to work through a number of extra clearance challenges posed by the Fat Bike's 100mm Bottom Bracket and 170mm rear axle, while I needed to work out the details of the sliding dropout.
Todd was able to get started on his frame construction late Wednesday afternoon, while Andy and I weren't able to start until Thursday. Part of my "fun" was the top tube; Paul had had several 4130 tubes rolled into curves, and I ended up deciding to use a curved top tube to improve the bike's stand-over while keeping the head tube size (and therefore the steering tube stack height) under control. Choosing my seat tube and down tubes from a big collection, I was ready.
The first step was to cut the seat tube and then nickel-silver braze it to the bottom bracket (this was the step I had screwed up in my Baby Frame - that was a bit nerve wracking, then it was time to cut the rest of tubes. Each tube needs to be cut and mitered to fit around the tube it's attached to. As an example, here's the sequence of operations for the top tube to seat tube connection. Starting from the full-scale drawing, I figured out the correct angle:
I cut the tube roughly to size with a powered hacksaw, then brought it to the milling machine. First I centered the tube relative to the milling head:
And then I used a circular hole cutting saw with the correct diameter and held at the correct angle to cut the tube to the correct length.
If I've done my job correctly, everything will fit nice and tight.
Eventually I had all my tubes for my front triangle:
And then it's time to put them into the jig, which holds them in place for tacking.
From there, it's time to first nickel-silver and then fillet braze the top tube to the head tube, seen here in "before-and-after" grinding form:
And then fillet braze the down tube and seat tube to the bottom bracket.
You'll notice that I didn't fillet braze around the back of the seat tube yet - that's because the chainstays will be added there after and if I had fillet brazed the back of the seat tube they wouldn't have fit. Paul says that a couple students missed his "don't do that!" statement and it's been a real mess!
With all that done, it was the end of Week 1.
My front triangle was together but not yet complete, and it was time for me to take the weekend with my family.
Sunday, November 10, 2013
So I'm building a new bike. From the ground up. Because I can.
A while back I decided (and my wife agreed - thanks Honey!) that I needed some "me time". I'm an engineer, so relaxing ("me time") for me means building something, because building things is what makes me happy. I normally build things that are measured in picoseconds, nanometers, and microwatts with long hours spent in front of a computer screen, so to disconnect I needed to do something completely different. I had heard of a local Bicycle Frame Building Course ( www.ufv.ca/bicycle-technology/bike-f
rame-building-101/ ) and had it on my bucket list, so I thought "why not?". A couple other guys from work were also thinking of taking it, but for one reason or the other couldn't make the commitment, so I was the only one.
However, before I start talking about the new bike, I need to talk a bit about my current bike. My current bike is a 56cm 2012 Brodie Once. When I was looking at bikes two years ago, I had been running through a string of bad experiences with the external derailleur setup on the bike I had at the time, and had been looking closely at Internal Gear Hubs. I knew what gear range I needed for my daily commute, and knew that the Shimano Alfine 8 (or Nexus 8) would not cut it, that I really wanted the Alfine 11 IGH.
The problem was that there were very few production bikes with the Alfine 11, and that most Alfine 11 installs involved either a fair amount of custom modifications to a production frame or a full custom bike. The Brodie Once (pronounced "on-say" which is Spanish for "11") was one of those production bikes, and on paper it looked great and was on top of my list. At the same time, in the back of my mind I was thinking "it would be even better if it had drop bars".
I went into one Local Bike Shop that I knew was a Brodie dealer, but they didn't currently have either an Once or an Ocho in stock. The Ocho is the 8-speed bike that uses the same frame, Ocho being Spanish for 8. There is also a Brodie Dos, for 2. That store, however, phoned around for me and found out which stores had the Once in stock, so I went off and ended up wandering into another LBS, Mighty Riders, and talked to Ed the owner. As luck would have it, Ed had just gotten in the Versa-11 drop bar shifters necessary to put road-style drop bars on an Alfine 11-equipped bike (the Shimano shifters are twist-style for flat bar bikes), and had just put them onto a 56cm Once as an experiment. I said I was looking for an Once, and that I wasn't sure if I needed a 53cm or a 56cm, and after a bit of experimentation on a trainer with a 53cm Ocho, it was clear the 56cm was the better choice. Then the subject of drop bars came up and I said I had been thinking of drop bars, so he pulled the experimental Once over, and put it on the trainer, and I gave it a whirl. It felt good. He then put his fit stem/handlebar on the bike, and we experimented a bit with combinations and rapidly found a great fit. I walked out, having put down my money to purchase that experimental 56cm Once with the bar combination we had worked out.
(after adding fenders, a rear rack, panniers, and a frame bag)
That bike has been my daily commuter now for almost two years, and it's been great, and I've ridden it almost exclusively on the road. It's not really set up for any off-road use, not even on well-prepared trails. When I decided to take the course, I had to decide what bike to build. I wanted an "everything" bike that was a bit more rugged than the Once, which would allow me to do a little bit of off-road trails riding if I wanted. I love the Alfine-11 IGH, but felt that if I were to take it more off-road and/or on hills that are a bit worse than I normally commute on I wanted a bit lower low gear. At the same time, I wanted a bit higher high gear - at this point on the straight and level on the road I'm limited by my bike's gearing, not by my legs.
As a result, decision #1 was that if I were to stay with an IGH, I wanted to use a Rohloff SpeedHub 500/14, and use a 46T/16T or 48T/17T single-speed drivetrain. The SpeedHub 500/14 is a bullet-proof 14-speed IGH that was originally designed as the ultimate MTB hub. They've been manufacturing the hub, almost unchanged, since 1998. Some of the oldest hubs have over 100,000km on them, and they have proven to be extremely reliable. They started out in MTB's, but they have since found a lot of use in commuters, touring, and tandem bikes, with some crazy people also using it on road or Cyclocross bikes. I also spent a lot of time thinking about how I ride on the Once, thinking about how things feel, and what I wanted to change, which wasn't much. From there, I spent a fair amount of time reading up on bike geometries and found out that I was one of the crazy people because I ended up being heavily influenced by Cyclocross bikes.
Decison #2 was the geometry: I chose a 56cm seat tube at 73 degrees, a 56.5cm top tube, a 14.5cm head tube at 72 degrees, a 43cm chainstay, a 7cm bottom bracket drop, a 102.5cm wheelbase, and a rigid fork and rear end. A modern Cyclocross bike has slightly slacker seat tube/head tube angles (road bikes are often 74 degrees, sometimes more) than a modern road bike, longer chainstays (a road bike is most often in the 40-41cm range), similar bottom bracket drops, almost flat top tubes, and rigid forks and rear ends. A modern mounain bike (including 650B's and 29er's) generally have shorter seat tubes, even slacker (71-69 degree) seat/head tubes angles, similar chainstay lengths as a CX bike, smaller bottom bracket drops (5-6cm), sloping top tubes, front suspension forks, and many have rear suspension. Touring bikes, depending upon the designer, can have almost geometry combination but almost always have slack tube angles, even longer chainstays (up to 47cm), and rigid forks and rear ends. My geometries are quite close to the Once but I've ended up with a slightly shorter (1cm) top tube and a slighly shorter (1.5cm) wheelbase. I'll use a slightly longer (1cm) stem, which will give me the same riding posture, but one that's a bit closer to the front wheel.
From there, I needed to figure out how to maintain chain tension. An IGH has a single-speed (i.e. "Track" or "Fixie") chain, without a derailleur, which means that there has to be a way of adjusting the distance from the crank spindle to the rear axle to maintain chain tension. Most Track or Fixie bikes use horizontal dropouts, allowing the rear axle to move back and forth, but IGH's use a series of planetary gears internally and require one or both sides of the rear axle to be rigidly attached to the frame, and these attachment points need to withstand immense torques, especially when climbing hills. This requirement means that horizontal dropouts are a "challenging" problem with IGH's, so many standard frames with IGH's attached require special torque arms to be added to the frame to create these rigid attachment points and then use a chain tensioner, essentially a much-simplified derailleur. Frames that are designed with IGH's in mind use different approaches.
One of the most common solutions is an Eccentric Bottom Bracket where the spindle center isn't aligned to the middle of the bottom bracket shell and the bottom bracket can itself rotate in the shell to adjust the spindle location. This is the solution used on the Once, but I've occasionally noticed the most common issue with EBB's: squeaking. The EBB needs to be secured using set screws and/or clamping mechanisms built into the shell, and if it moves at all during peddling (even a mm or fraction of a degree) it can squeak. Nonetheless, I was thinking of building an EBB frame, but after talking to the course instructor (Paul Brodie, the founder of Brodie Bikes, the manufacturer of the Once) about the additional machining steps necessary to avoid the squeaking I chose the alternative solution, a sliding rear dropout. A sliding dropout consists of two pieces, a fixed piece (known as the "insert") attached to the frame with rails that the second piece (the "dropout" that the axle is attached to) rides on.
Decision #3 was to use Rohloff's sliding dropout, which they they refer to as "Type F", which is then combined with the "OEM Plate" which then slides into the long slot on the dropout.
Here's a picture of a "Type G" dropout, which is the EBB variant, but it uses the same style slot and OEM plate to create the rigid connection to the frame.
Decision #4 was that I wanted to use disk brakes. Pretty much a no brainer - I want the braking surfaces as far from the road surface as they can be.
With all the up-front decisions out of the way, so it's time to get the components I need before I take the course - Paul strongly recommended that students have the wheels and the fork before starting the course. I talked things through with Ed; I want to do as much work on the bike as possible, but at the same time I want someone who knows what they are doing to check my work. I said I was willing to purchase components through him, but with a condition. We both knew up front that he would't be getting much (if any) mechanic time on this bike because I wanted to do much of the work myself. As a result, any money he makes for his time will come from me purchasing components, however the Internet has made things difficult for LBS's on component pricing because it's just to darned easy for customers to shop around. I don't want to screw him over by working out components with him and then going and purchasing them all online, but at the same time there are a couple components (the SpeedHub in particular) where the difference between online and his list price was just simply too big to ignore. He asked that if I ran into this situation to talk to him and he would see if there was something he could do to match the price. With that out of the way, we put together my initial shopping list.
The front hub is a 32-hole Velocity ATB Disc Lightweight Front Hub, anodized black.
The rear hub is the 32-hole Rohloff SpeedHub 500/14 CC DB, anodized black.
For the rims are Hed Belgium C2's 32-hole 23mm rims. Nice and strong and light.
The fork is a steel Salsa Vaya Road/CX fork, with a 45mm rake. It's not a light fork, but at the same time it's not the heaviest out there.
The spokes are Saphim Leader 296's.
Taken as a whole, these components together should make for strong wheels and a strong front end, able to take years of (ab)use.
Once I had it all, I built the wheels, starting by 2-cross lacing, then centering, truing, and careful tension adjustment. I borrowed a co-worker's truing stand and dishing gauge, took advantage of the large amount of info that's out there on the 'net, and took my time.
Once the wheels were built I installed Shwalbe High-Pressure Rim Tape.
I then installed my Continental Contact 2 Reflex winter tires from the Once as place-holders for the course, and I was set.
The next installment is the course itself. Plenty of pictures to come!
Tuesday, June 18, 2013
Well, I've done it. I've gone and registered for the bicycle frame building course that I mentioned a couple times last year. Think of it as my 43rd birthday present to myself, because it starts on September 9th and my birthday is on the 10th. As a result of my highly elevated work-induced stress last year I took advantage of a program at work to spend some time talking to a councilor. One of the suggestions from that was that I needed to take some more "me" time, and this course is one of those "me" times.
That high-stress period of time pretty much knocked me off SP, and I've been only sporadically here since then, but I'm still kicking around from time to time. Still cycling to & from work, still running occasionally.
Work is fun right now. I'm right in the middle of the early design stage for a product that'll come out in 2014, right in the middle of all the cool technical problems. I'm also coordinating 5 or 6 other people all working on aspects of the project, and am already working on two patent disclosures discussing some of the new inventions. Fun times. Busy, and yes there is stress, but it's the *good* stress!
Now that I've registered for the course, I really need to do some more serious planning. Sorry, Bruce, no bike porn with pretty pictures this time, but I'm sure I'll do one or two of those as things come together.
At this point, I'm planning on building a CycloCross frame, and outfitting it with a Roholoff 14-speed Internal Gear Hub and Disc brakes. Given that I've never done TIG welding, I'm probably going to be braising - old school! A lot of people have mated the Rohloff Hub with a Gates carbon belt drive system, however the belt drive system is extremely picky about the chain line and given that it'll be my first attempt at building a frame I'm going to go with a more forgiving chain. It's also in line with the old-school CroMo braising. I'm planning on vertical drop-outs, and want to use an Eccentric Bottom Bracket for chain tensioning, and I want to run the cables through the top tube and then down the seat stays, keeping them away from the ground as much as possible. The Rohloff hub uses a twist shift system with all the indexing in the hub (their initial goal was to build the most reliable MTB IGH hub they could) so the shifter is set up primarily for use on flat bars, but there are several options for using it on drop bars, and I need to do more research. One thing I'm sure of: I want to take advantage of the Rohloff's wider gear range to give myself a little bit lower gear than I have with my current bike, 21 or 22 gear inches instead of 26, while still giving myself a bit more at the high end.
I've built up a great big list of links, discussing bike design (including the older edition of the Patarek manal), frame geometries, frame construction, components, as well as a couple YouTube how-to videos on a whole bunch of topics. I'm wanting to do as much of the work as possible (including building the wheels!) but I'll be going to Mighty Riders (my LBS) to do some of the things I can't do or don't have the equipment for. I'll also get them to check over my work just to make sure I don't royally screw it up! It's a hole in the wall, but Ed (the owner) is one of the most knowledgeable bike mechanics in Vancouver, and his shop is the go-to place that both Shimano and Rohloff send people to if they need IGH servicing in British Columbia. He also does custom fitting, and I think I'll book a session this summer to work out the geometries to make the bike fit me. My goal at this point is to have the wheels built up and have my fork before the course, and have a pretty good idea of everything else. Given that, I might have a chance to have everything together and take it for a spin before Halloween!
Of course, after I have a frame and before I can attach any components I'll need to get it painted. Given that it'll be a "go out and have fun" bike, and will probably get used for a little bit of everything including commuting in the rain, I'm thinking that I should get it painted in the most garish day-glo high-viz yellow I can get. Perhaps with retroreflector glass beads in a clearcoat on top? Perhaps that might be a bit much. Oh, and I need to think of what to call my bike, and come up with a head badge design.
This will be fun!
Thursday, January 31, 2013
Way, way back in the mists of time (97 days ago according to SP) my status update (in several chunks) read:
In order to understand my job right now, imagine that you have a Lego set that can be built up as either a cargo truck or a helicopter. Now imagine that you've built the truck. Now imagine that overnight someone broke into your house and glued half the pieces together. Now imagine that you've been given the task to build a helicopter. It doesn't have to be exactly the same as the original helicopter, it just has to work like it, but you aren't allowed to use any pieces that weren't there in the original set. You don't *have* to use the pieces that were glued together, but so many of them were glued together that it would be difficult to make anything useful without using some of them, glue and all. I'm choosing to look at this as an opportunity for creativity, not as a challenge. It's the only way to keep sane.
Oh, what prophetic words!
To give some context for the what was actually going on, it helps to know what I actually do for a living. My company designs and manufactures microchips that go into networks, storage systems, and large RF systems. The chips we design aren't household names, and most of the companies we sell to aren't household names either, however there is an excellent chance that each and every byte of data that you send over the internet or store "on the cloud" will go through one our chips, most likely many of them. There are even a couple microchips we've built that might be in your home today depending upon where you live and what type of broadband connection you have.
When I say we manufacture microchips, what I really mean is that we contract with large foundries in Asia who actually do the manufacturing, then contract with other large companies (mostly in Asia) to do the assembly and packaging and testing, although we do some of our testing ourselves. We design the chips, develop the software that runs on them, create the test programs, do the debugging, and then sell them. Hopefully through all of this, we make money.
As I said, we have the chips manufactured at a foundry. The steps involved in doing this are many, and I'm not going to go through them all, but the Wikipedia page on "Microfabrication" ( en.wikipedia.org/wiki/Microfabricati
on ) has a reasonable description. The pictures down the side show a representative set of steps for a relatively simple process with a single metal (we use much more advanced process steps with many more metal layers), but show how everything is built up using layer after layer of photolithographic masks. Think of each mask as a negative for a picture, and think of a completed microchip as a stack of 20-40 layers of different materials, each patterned by a single mask. Depending upon what the mask is used for and how precise they have to be they can be either relatively cheap (less than $10,000) to quite expensive (more than $100,000) to produce, and as a result a complete "mask set" required to produce a particular type of microchip is an expensive piece of equipment. Because of this, creative people (like me) are often asked to make changes and fix errors by editing a smaller set of masks. It's quite common to talk about "all-layer" revisions and "metal-only" revisions, meaning revisions that change all mask layers compared with revisions that only change metal layers. Another class of revision, a "base-layer" revision, isn't all that common because the masks for lowest level of the microelectronic stack (steps 1-8 in the Wikipedia figure) are relatively expensive, and more often than not if you have to edit the base layers it's because the error is too massive and you may as well do an all-layer revision.
Metal-only revisions have another advantage: time. When a company like mine orders a new type of chip the first time, we often start more wafers (the big circular silicon substrates that microchips are built) than we need. After the base layers are processed, we will "hold" some of the wafers, meaning that they're taken off the production line and safely stored away at the foundry until such time as we re-start them. This is an insurance policy of a sort, ensuring that if we find errors in the first run of chips we have the opportunity to re-start the processing on the held wafers with a new set of metal masks to fix the errors. This can be very important because it often takes more than half the processing time to process the base layers, and less than half the time to do the metals. When you have customers waiting for your chips, the time that you can save by using the held wafers can be incredibly valuable!
We've had a chip back in our labs since June, and like most new devices it had what can politely be called "issues". OK, they were bugs. The most serious bugs were in a circuit that we actually sub-contracted out its development to a company in Maryland, and identifying what was wrong took a massive amount of work. We had held wafers, and we had tight customer commit dates, and given that the fixes to the sub-contracted block were metal-only, we decided we would attempt to do a metal-only revision. Of course, we had to then fix the rest of the bugs. We had a "hit list", and there were two blocks that had minor problems, but we had another block that had major problems - a key feature of this chip, one that our customers were depending on, did not work. A co-worker and I were given the task of deciding if we could indeed do a metal-only revision. After looking at it for a couple days, we decided we had a fighting chance, and given that we really didn't have time to do an all-layer revision we said we could do it.
This is when I made my update.
In this context, the Lego pieces are the individual transistors that the block was originally built from. The transistors, being on the base layers, were in fixed locations, and many of them were interconnected with diffusion and polysilicon, also base layers. That's where the "glue" comes from. We were free to re-wire the glued-together Lego (i.e. the interconnected transistors) in the bottom three layers of metal. I think Barb's the only person who really understood what I was talking about.
It was not easy, and involved a lot of cursing and late nights as we continually fought with the original design (it was done badly) and had to find ever more creative ways of using the transistors we had. Along the way we actually found several new bugs in the original design, bugs we did not know about when we started, buts that if we had known about when we started I suspect we would have said "all layers, please". Our stress levels went through the roof, and I burned out. I took a couple unplanned days off (not enough) but returned to work and we eventually succeeded, came up with robust solutions to all the bugs, and sent the revised metal masks off to the foundry. Over that period of time I made various cryptic status updates about helicopters and was probably not the nicest person to be around.
December was a quiet time and my stress levels went back down to a more typical level. The foundry was processing the new metal layers on the old base layers, and then we got the new revision back in early January.
Disaster. Not only did it not look like we had fixed the original bugs, but it looked like we had created new ones. The helicopter wasn't flying - it was crashing and creating collateral damage. For the past three weeks, we have been staring at it, trying to figure out what was up, trying all sorts of different tests and simulating all sorts of crazy scenarios. Nothing made sense. Sometimes, under some conditions, the block would work perfectly. Other times it would fail in ways that made no sense, and we were looking at the very real likelihood that we wouldn't be able to meet our customer commit dates. As you can imagine, my stress levels have been going up. I've tried to compartmentalize and keep the work stress at work, but I've not been 100% successful on that. Thankfully my Achilles injury has healed so I've been able to re-start running at lunch hour so I'm able to burn off some stress and shut off my brain for a while in the middle of the day.
Today we found the root cause of the issues we're having in the lab. In order to clean up a problem on an unrelated block, we had made a modification to the power supply for that block. In doing so, we modified the power supplies for all the blocks, including the one we fixed. As it turns out, the problem isn't with the block, it's with its power supply. Continuing the helicopter analogy, the problem wasn't with the helicopter itself, but we put sugar in the gas tank. Remove the sugar, and the helicopter flies.
There are probably a couple more days to follow up on this front, but when I look ahead in time, I see my stress level dropping rapidly. I so need this.
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