Cargo Rack, Part 2

In this series: Part 1, Part 2, Part 3, Part 4.

Yesterday I started brazing the rack, which was pretty exciting.  In this step, I just laid down a bit of bronze to hold things in place.  Later, I'll build up fillets.  A fillet is a meniscus of metal that joins pieces together.  When done properly, the metal creates a nice smooth transition between the two.  

Tabs

I cut the tabs out of some sample sheets of chromoly steel that I had lying around.  They're basically little metal guitar picks.  When the bike is done and all of the attachment points are installed, I'll drill them.  That'll let me level it out if something weird happens.  

I'm pretty sure, but not positive, that the sheets will be thick enough to resist bending when I'm carrying things.  If I was using it for loaded touring, I'd double them up.  I still may add a bit of reinforcement.  

Once the tabs were done, I slotted the vertical tubes of the rack, lined them up with the tabs on my basic sketch, and then squeezed them with a pair of pliers just enough to keep them from shifting (much).  

Brazing

I started brazing by securing the tabs.  I did each of the four connections one at a time.  The hard part was dealing with the last joint.  It kept wanting to spring free, as the rack widens slightly near the rear (for aerodynamic effect, or something).   I solved that with the sheet-metal vice grips that appear in one of the pictures below. 

Next, I attached the rails, where a bag will hang.  I clamped the first on one end, rotated it level, then tacked it on the other.  Then I was able to remove the clamp and tack the remaining end.  

The second rail was about 100 times harder, since it had to line up exactly with the first.  At one point I probably would have hurled it across the room if there weren't other folks around working.  Thankfully, after quite a bit of trial and error, it fell into place and I was able to tack it down before it slipped and hit me in the eye or something.

Here we go!  I need to finish the fillets and grind the ends a bit, but the look and geometry work.  

Next time: finishing fillets, adding tabs for the wooden deck, and making the strut to connect it to the seat cluster.

In this series: Part 1, Part 2, Part 3, Part 4.

Jigs and Rattlecad

It's Time For a Jig


I've decided to make a jig to hold the frame tubing while I tack things in place.  It's possible to do the job without a more formal jig, but I think that I'm going to be better off with fewer things to think about while I'm putting everything together.  I'll still have to get my skills pretty sharp to keep the frame straight, but at least this way I have a good solid place to start from.

I've decided to make the Jig out of 80/20 aluminum extrusions.  Basically, 80/20 is a system of interlocking parts for building frames, jigs, supports, etc.  They bill it as "the industrial erector set" and that's basically what it is.  Here's an example of one of the extrusions.

This isn't too much of a shot in the dark.  Many builders have made their own 80/20 jigs, and a few pro's have even made production ready jigs out of it.  Mine won't stack up next to an Anvil, but if I'm careful about aligning everything, it should be good enough for me.

I'm basing my design on Suzy's over at Little Fish.  She's been cool enough to put up a plan here.  I'm going to use similar extrusions, but I'm going to move the vertical braces to the front of the jig.  That will make it a bit harder to line up, but it should also allow me to work with a shorter head tube.  As it stands, it looks like you need a really long head tube in that jig to clear the central spine, and then cut it down later.  This will also mean that I'll have to remove the dog leg that centers the axle.  It won't be as precise, but I think it'll serve.

Rattlecad!

I discovered a discrepancy today in the spec's for the fork I'm going to use with my frame.  It's a Surly Pacer fork and I've found the distance between the dropouts (where it holds the wheel) and the crown (where it fits into the bearings of the headset) listed as 371 in one place and 376 in another.  Yikes!

I've mentioned before that I'm using RattleCAD to make my plans and diagrams, instead of normal CAD software or BikeCAD (which you really need to pay for to get all of the information that Rattlecad gives you).  It seems to be the best option for new builders, but it's also being constantly updated (at least 3 in the last month, maybe more).  So, while adjusting the diagram to find out what the changes would have to be if that second number was the right one, I noticed that I could no longer manually change the virtual length of the top tube.  That's the length that it would be if it didn't slant down a bit.  For non-bike people following: this is a really important number because it has a lot of impact on where your handlebars end up.

I made a post in the RattleCAD forum about it and had an answer from the person making the software in less than a day.  And it worked flawlessly.  That's service, and on free software to boot!  So yeah, if you're looking for a way to design your first bike or two, give it a try.

Full disclosure: I don't work for Rattlecad dude, nor do I sell 80/20 as a side gig... I just think they're neat.

We Need Those Stinkin' Badges, Part 2 (+ some brazing)

Bending the Badge

If you haven't read it yet, here's We Need Those Stinkin' Badges, Part 1.

I made one more badge at a slightly smaller size a few days ago.  Today I decided to get it finished and ready to attach to the bike.  I started by trimming the excess off carefully with the band saw and this giant sanding disk.  Then I lightly sanded the raised bits with a fine grit sand paper.  That really set off a nice contrast between the higher and lower sections.

The next step was to curve the metal to fit the front of the head tube.  One of the guys at Techshop was nice enough to cut a half-cylinder out of a piece of wood for me with the same radius as the tube (I haven't gotten checked out on the wood shop machines yet).  I initially tried hammering the plate directly into the wood form with a mallet... but I couldn't get the angles right with the mallet I had.  For my second attempt, I sandwiched the sheet between the form and a scrap piece of head tube and then squeezed them all in a vice.  It worked... and also cracked the form down the middle.

 

For the final piece, I held the form together from side to side with a clamp, and then used a combination of the mallet, a second clamp, and the vice to get everything straight and squished together.  I used a sheet of paper towel to help the metal slide over the wood without leaving little scrapes near the edges as it was pressed inwards.

 

When released from the form, the plate sprang back a bit, making the sides pull away from the tube.  Some work with the mallet, first squishing the whole thing a bit, then spreading it back open over the tube, solved that.  Because the mallet was plastic, and much softer than the metal, it didn't mess with the etch.

I encased the badge in a layer of rubber that someone happened to be messing with, to prevent corosion until I could clear-coat it... and then immediately found out that there was clearcoat up for grabs.  So, I cut it out and used that.

Here it is finished!

More Brazing 

I also did a test-braze today.  It turned out messy.  As usual, I had issues flowing filler over the top of the lug, but I got most of it underneath.  When I cut the joint open, it looked like it was pretty well filled with one small gap.  I think it could have been used on a frame without much danger, which is reassuring.

Seat Stays, Practice 1

Today I worked on a potential finish for my seat cluster.  The seat cluster is where the seat stays join the top tube and the seat tube.  There's more variation in how builders construct this joint than in almost anything else on the bicycle, and many builders make the seat cluster their signature.. 

Seat Stay Diagram: The Movie

While I'm not up to the challenge of doing anything truly unique yet, I decided to try something that I've seen on a few of the prettier custom bikes that have come though my work.

First I mitered the stay so that it would fit up against the side of a 31.8 mm tube.

Then I cut a piece of said tube, and brazed it onto the stay.

I treated it like a fillet, where you build a smooth transition between one tube and the other.  It was more brass than I really needed for this cap, but it was a fun experiment.  I think that I could really enjoy fillet brazing.  Something to think about when it comes to frame #2.

Here's the finished piece.  It'd be attached to the side of the seat tube with the longer side in.  I think that two of these will look pretty sweet on there.

We Need Those Stinkin' Badges, Part 1

Chemicals


I'm using ferrous chloride to etch my head tube badge out of copper or bronze.  My initial tests have been with copper.

Ferrous chloride is pretty mild, as a far as stuff that can eat metal goes, but that's still a scale you have to respect overall.  As long as you don't get it in your eyes or let it linger on your skin, it's not going to mess you up (use ventilation too).  It will eat metal, obviously, including your sink.  The copper ions it absorbs when you use it are also environmentally harmful. You have to save your waste and dispose of it properly (local hazardous waste disposal should have some idea how to handle it).

It won't eat through plastic, glass, or a few other random things.  I made sure that all of the dishes and bottles that I used were plastic.

Resist


I won't go through all of my trial and error, because there are a million sites up with different instructions for etching with ferrous chloride, for both art and making circuit boards.  The short version is: we need to get something onto the metal that the etchant won't eat (a resist) in the shape of the image.  Then we dip it, and everything else gets eaten down a few mm.  

Eventually, I ended up printing the design (reversed and inverted) onto a page out of a National Geographic using a laser printer (toner makes a great resist, inkjet ink doesn't).  Any shiny magazine paper should work as well, but National Geographic adds a bit of class.  I ironed it in place, soaked it and sprayed it with water until most of the paper flaked off, leaving just a thin layer stuck to the toner.  I found that the transfer worked best if I left the iron on the back of the plate for about five minutes to get the plate nice and toasty, then flipped it and heated the back of the image for another five.  I touched up the finished product with a few dots of Sharpie marker, which is a passable resist, and then used a vertical band saw to trim the metal around the edges.

Etch

I did a quick test piece first, which failed miserably.  I was pretty bummed until I put together that the 40 degrees out on my porch probably wasn't an optimal temperature for this reaction.  I suspended the plate upside down in a piece of Tupperware using tape, with ferrous chloride just covering it.  Leaving it upside down keeps the waste products of the etch falling off of the plate so that they don't leave uneven bits.

Next, I moved the whole deal into my apartment (inside a trash bag, to prevent leakage and contain fumes), and left it in a shallow plastic dish of hot water for an hour and a half.  

Success!

When I removed the plate, I had this:

Good so far!  To neutralize the residual etchant, I dipped it in a mixture of baking soda and water.  Then I scrubbed it with acetone and, as a quick final touch, repeated the entire process with a slightly different design.

Now I just have to hammer it until it'll curve around the head tube and then paint it.  I plan to add some black paint to the lower sections and then clear coat it.

Ignore This Boring Post About Butts

One quick bit of advice for anyone else embarking on this whole frame building thing.  Always ALWAYS measure your tubing.  Most of the tubes we use to make a custom bike are butted, meaning that they are thicker on the ends and thinner in the middle.  This lets the thicker section soak up the higher stresses near the joint, while the thinner section makes the finished bike a lot lighter.

This instructive daguerreotype, found in my great grandfather's memoirs, should help to illustrate what's going on inside the tube.  

You have to be careful though, because you can cut too much off of one of the ends and end up with some of the thinner tubing forming the joint... which may then fold like a coke can.  Even worse, tubing often comes with the butts shorter or longer than the spec sheets tell you they should be, so you really have to measure for yourself to be sure.

I held my tubes up to a bike light and stuck the depth measuring tool on a caliper into it, set for the point where the transition was SUPPOSED to start, then made sure that it lined up with the actual change in reflection indicating the start of the slope towards the thinner spot.  It can be hard to see what's going on in those things, so I had to bracket the measurement (-10mm is DEFINITELY falling short, +10mm is DEFINITELY going over that line).

I found two discrepancies: my seat tube started getting thinner about 1.5 cm lower than it should have and my chainstays (which are ovalized) are about 2.5 mm too wide and a bit too short.  The first won't be an issue provided that I leave the tube as long as possible when shaping the end to fit into the bottom bracket lug.  The chainstays will probably need to get just a kiss from the vise to be the right shape.  I'm a little nervous about that, but it shouldn't be a big deal.

Now I have everything marked, so I will know EXACTLY when I'm in trouble as I trim stuff to length and shape the ends.  Next post will likely be about some more practice welds, which will hopefully be more interesting than all of this measuring.

Blueprints

Today I put together the blueprints for the new design.  I use Rattlecad, an awesome free open source program that does a lot of the calculations for you.  You give it important information, like the slope of the seat tube and the drop of the bottom bracket, and it calculates the less exciting stuff.

I started with the geometry of a bike that I knew I liked, then lengthened the head tube about 4mm, bringing the imaginary bars up and back a little.  I entered the sloping top tube (6 degrees to match the lugs), and the offsets for where the tubes enter the lugs (how far one tube extends beyond the intersection with another).  I also tweaked the water bottle locations.

I'll print this full scale so that I can line the tubes up against it.  It'll let me quickly double check pieces and dimensions without TOO much measuring.

Center-lines

A few operations in the construction of a bicycle require you to have a clear center-line for the tubes.  The top tube, for instance, needs to be cut on both sides so that it will mate up with the head tube and down tube.  If those cuts aren't lined up with each other, you'll end up with a very twisty frame.  If you have a center-line, you just match it up to your templates (more on that when I post about mitering).  If you don't, it gets more complicated.

Before drawing on the tubes, I needed to figure out which way they bent, since it was pretty unlikely that they'd be perfectly straight. To do that I used an alignment table.  An alignment table is a big slab of stone or metal that is ground carefully until it's perfectly flat across the top.  It seems like any table would work, but it has to be pretty damned precise to make this work.  I rolled the tubes on the table, looking at the gaps underneath, until I found the flattest axis... then marked those as the "sides" of the tubes.  The center-line would be 90 degrees around the tubes from the "sides", because the tubes being slightly curved towards the front or back of the bike wouldn't make as much of a difference as having them lean slightly to the right or left.

Actually making that line is one of those things that seems easy, but ends up being really hard.  Lining up a straight edge with the tube is difficult.  Keeping it there while you mark things is pretty impossible without designing some kind of a fixture to hold everything.  I basically held two tubes together, with the point that I wanted the lines to start from deep in the "V" between them and dragged a marker down the center... again and again until the line started where I wanted it to. 

I then used the alignment table to check if they were straight with a specially made caliper.  If both ends of the line were the same distance off of the table, then I was good.  Otherwise, back to the drawingboard.  

When finished, I taped over them so that I wouldn't accidentally rub them off when working with the tubes. EDIT: NEVER DO THIS.  Taking off the tape is a full time job.  Next time I do this, I'll just get the miter templates and bottle cage mounts aligned right away.  

That's it for today, next time I'll share the diagram that I'll be working off of.