Alex Wetmore is always busy with something…

I published a blog entry a long time ago with a “simple” way of bending tubing. It is far more complex than what I actually do today. I’ve been meaning to write a followup for over a year, but always forget to take photos when I’m bending up a rack deck. I’m going to just do it in words. Hopefully I’ll update this in the future with photos, but in the meantime this drawing will have to do.

The instructions here are for making a 10″ x 14″ rack deck using roughly 4′ of 5/16″ tubing and a bender that has a 15/16″ radius. The straight sections of the rack deck will be 12″ and 8″. The 15/16″ radius for each bend makes the rack about 2″ wider and 2″ longer than the straight sections in each of those directions.

I always make my bends to the right. There is no math in this method except for basic subtraction and dividing by 2″.

Bend 1:

• 
  Mark a line 6″ from the start of the tube.
• 
  Align that mark with the 0 on your bender.
• 
  Bend to 90 degrees and mark where the 90 is on the tube.
• 
  Check with a square to make sure that it is actually 90, tweak as necessary.

Bend 2:

• 
  Mark a line 8″ from the last mark (the start of the next straight section)
• 
  Align that with the 0 on your bender
• 
  Check that the bends are in the same plane. I do this by spotting down the bender to align the tube with the bending form.
• 
  Bend to 90 degrees and mark the 90
• 
  Check the 90 with a square. Check that the bends are in the same plane using a flat surface. Tweak as necessary.
  

Bends 3 and 4:

• 
  Repeat the same technique for bend 2 with distances of 12″ and 8″.

Closing the loop:

• After bend 4 mark a line 6″ from the start of the last straight
  section. That should line up with the start of your rack deck. Cut
  off the excess tubing (a couple of inches) and splice.

If you want a different size of rack deck then just pick different numbers for the straight sections. Most of my recent racks have been 12″ x 11″ long, so I’m using 10″ and 9″ straight sections.

You can put the splice anywhere that seems good. I just tend to center it because it keeps the math simple.

Jeff Lyon brought up the idea of making these a few months back, and now I’ve gone and done it. They are “mass produced” tabs for racks where the rack attaches to the bicycle frame. Everyone makes these one at a time and it is time consuming to make ones that look good.

They started with some basic sketching in CAD software that produced this:

I sent that off to Vashon Image Works and made a few tweaks here and there and then they turned into real pieces of metal.

I had 160 made in size small (designed for M5 bolts), 64 in size large (designed for M6 bolts, but with an M5 sized hole). Many already have homes to go to, but I have extras (mostly in M5) for sale. Both are made of 4130, the M6 ones are .125″ thick, the M5 ones are .100″ thick. If you are interested send me an email. The tabs are .400 wide to work well for 3/8″ tubing, but can easily be filed down to work with 5/16″ or 1/4″ tubing.

Alistair just finished up this large porteur rack for his tandem and posted an extensive series of photos documenting the process. He also annotated many of them, giving a lot of hints along the way. It’s recommended viewing if you are interested in rack building.

Some folks have been asking me in comments about tricks for making miters that aren’t 90 degrees. Alistair covers this well starting at this photo.

Another flickr gallery that I’ve been enjoying comes from Mike Flanigan of ANT Bike. He has a lot of shots showing his homemade fixtures.I’ve been interested in making fixtures of my own and there is a lot to learn from these photos.

It’s been a long time since I’ve posted a Rack Building Basics entry, but I still have some in the queue.

Today’s photo series is about making the eyelets that connect the rack to the fork or frame. There are a couple of ways of doing this, but this series focuses on doing it with brazed in tabs made of flat stock. This is similar to how dropouts are made.

The first step is making a slot in the end of the tube for the tab. I draw the slot and then use a hacksaw and a thin file to make it:

Now we need to cut a piece of flat stock to fit. I purchased 3′ of 1″ wide 4130 which is perfect for this purpose. You only need to make a single cut. I use the tubing as a gauge to how wide it should be.

The tab is the same width as the tubing:

Brazing just the tab in is probably strong enough. Note that I filed the end of the tube to slope the tubing towards the tab:

I like to fill the whole end of the tube with a “plug” of brass. To do this you heat the whole end of the tube and draw the brass around below the tab. I’d do a few tests first and cut them apart to see how well you do at pulling the brass in. It is a bit hard to see in this photo, but the whole end of the tube has brass in it.

After removing the flux I doa little work with a round file (12″ round which is about 10mm or 3/8″ in diameter) to make a nice clean scallop. The tab has also been bent to match the angle needed for this rack:

A bolt hole is drilled and a file is used to ease off the edges:

A final photo showing where this tab is used on the rack. It connects the stays to the fork blades:

At the start of the entry I mentioned that there are other alternatives. A nice and easy one is to braze a piece of tubing perpendicular to the stay and run the bolt through it.5/16 x 0.035 tubing is a nice fit for an M5 bolt. This is an especially good idea if you need a spacer to clear part of the fork blade. In this example the tubing is extended on the inside so that the rack can clear the fork blade even if the fenders aren’t installed. This is from the first rack that I built:

Another option is to simply flatten the tubing in a vise and drill a hole through it. I think that this looks a little less refined, but it is strong. Sorry, I don’t have any photos of this approach.

Basics

Selecting tubing for a rack is an important first step in building a rack. The number of options is fairly limited based on weight and the accepted standards to work with things like pannier hooks. Selecting tubing sizes will also help you decide which bender to buy.

The three basic outside diameters to choose from are: 3/8″ (about 10mm), 5/16″ (about 8mm), and 1/4″ (about 6mm). There are two wall thicknesses that I’ve worked with: 0.028″ (about 0.7mm) and 0.035″ (about 0.9mm).

I made this spreadsheet to help figure it all out. For these three sizes of tubing and two wall thicknesses it provides the weight of a foot of tubing and the deflection when there is 10 pound load on a cantilevered beam. That second measurement isn’t specifically useful by itself, but it gives an idea of the stiffness of the tubing. I hope that I got the deflection math correct, I didn’t do a test to verify it.

There are some interesting properties to note:

• The 0.035″ wall thickness tube of one size is close to the weight of the 0.028″ wall thickness tube of the next size up.
• Outside diameter has a bigger influence on stiffness than the wall thickness, but both matter.
• 1/4″ OD tubing slips nicely into 5/16 x 0.35 tubing, and 5/16″ OD tubing slips nicely into 3/8 x 0.028 tubing. This is very handy to know when you are splicing two sections of tubing together.
• The heaviest tubing is over 4x stiffer than the lightest tubing, but less than twice as heavy.

Handlebar Bag Rack

A handlebar bag rack is designed to support the bottom of a handlebar bag. It is smaller than the bottom of the bag. The bag isn’t tightly connected to it in most cases, so the rack doesn’t need to be designed for high lateral loads. They connect to the fork blades at the mid-point or higher, so there aren’t long unsupported beams. As a result of these design parameters they can be made with fairly lightweight tubing. So 1/4″ x 0.028″ tubing everywhere is probably enough. Some of the classic French racks are made with even smaller tubing (4mm outside diameter).

A standard sized handlebar bag rack has a platform of about 4×7″ or 5×7″. There is one cross member at the middle of the platform and two stays going to the fork blades. For a 5×7″ platform with 8″ stays this gives us a total of (5*2)+(7*2)+5+(8*2)=45 linear inches of material. There will be a little more for the backstop and fork crown mount.

Using 1/4″ tubing we can build the basic rack (no backstop, no fork crown mount) in 4oz of tubing. Using 3/8 x 0.035″ tubing the rack would weigh 7.5oz, a pretty large weight gain since we don’t need the stiffness. Going with 5/16″ only adds an ounce,so that isn’t too big of a deal (especially if you don’t have 1/4″ tubing or bender).

Porteur Rack

A porteur rack is a much larger platform rack that is designed to have the load strapped directly to the rack. The rack is expected to work with loads of 50lbs or even more. The stays on the rack usually connect directly to the fork dropouts,so there is a longer unsupported span (from the fork dropout to the front of the rack).

On these racks lateral stiffness is important. We can get some lateral stiffness from smart design (good triangulation), but we also need to get some of it from the metal. The stays are over a foot long, and we wouldn’t want the rack to shift by an inch or more with a moderate side load (as you’d find when going around corners).

Porteur racks also have a lot more metal. I’ve been building them with 4′ rack circumference (this is a roughly 14″ by 10″ platform), 4 cross members (10″ each), and two staysper side (around 15″ each). That is about 148″ linear inches of metal. One made with 3/8 x 0.035″ tubing would have about 25oz (still under 2lbs) of steel.

You can optimize the weight be mixing and matching tubing. The circumference can be made with 3/8 x 0.028″ tubing and still handle most loads. 3/8″ x 0.035″ tubing makes sense on the stays to minimize side deflections. The cross members can probably be made with 5/16 x 0.028″ since they aren’t that long and each cross member doesn’t carry a lot of weight. By mixing and matching we can get the weight down to 21oz (4oz savings)without compromising the integrity of the rack.

Recommendations

• 1/4″ or 5/16″ for handlebar bag racks (5/16″ if you plan to zip tie a basket to the rack or carry heavier loads)
• 3/8″ for heavy duty porteur racks
• 5/16″ for cross members on porteur racks or lighter duty porteur racks

If I were starting out I think I’d get a 5/16″ tubing bender. 5/16″ is a good balance of being big enough to make moderate duty porteur racks and cargo racks (Bruce Gordon racks are 5/16″) and 5/16″ x 0.028″ is light enough to make a decent handlebar bag rack. The benders are cheaper too, a Ridgid 405 5/16″ bender is about $60, while the Ridgid 506 3/8″ and Swagelok 3/8″ benders are about $200ea (Ridgid also makes a cheaper 406 3/8″ bender, but I don’t know how well it performs with cromoly steel).

You can go too flexible. Rory and I built a handlebar bag rack for his bike out of 1/4 x 0.028″ tubing. The stays connect to the fork dropouts and the bag connects just to the rack. It works, but he says that it is pretty flexible with heavy loads. I think that we’d both use 5/16″ tubing if we were building it again. We’re going to build a couple of small porteur racks with 5/16″, and I’ll report back on how that works once they are done.

Tubing Sources

It’s hard to find tubing in these dimensions in the US. I know of two reliable sources, Aircraft Spruce and Dillsburg Metal. Aircraft Spruce has much easier ordering (you can order online), but Dillsburg is a bit cheaper, especially if you need high quantities.

I’m going to be away for about a week, so it’ll be a little while before the next entry. Leave comments or email me if you have any requests. I know this one didn’t have the interesting photos, next week we’ll be back to photo oriented entries.

I find the combo of vice grips (or other clamps) and spokes to be really useful for holding small brazeons in place. Today I installed mid-fork eyelets onto a fork, small guides for headlight cable routing, and a headlight mount.

Another favorite tool is the flat stainless stock that is used to secure Blackburn-style racks to bikes. This stuff is really handy for making temporary fixtures.

I used a fender stay here instead of an old spoke, but a spoke really is superior. Brass won’t stick to it and it bends more easily. These guides are cut for 1/4″ tubing, but you can also pull the rollers out of used chain.

Watch out for the vice grips, they can distort tubing pretty easily. Used with care they are very handy for temporary clamps.

Most racks have some sort of cross member, straight tubing that goes across the rack platform. They are pretty easy to build.

One of the tricks is getting the two miters to be parallel to each other. I find it simplest to put some scrap metal in the miters and then eyeball them for parallel. You want to check early and often because you do want to be parallel when you have the tube the correct length. In this case you can see that I’m a little off:

It is important to clean the inside and outside of the metal before brazing.To clean the inside of the tubing I make a simple bit for the drill. This is a piece of 1/4″(or smaller)tubing with a slot cut in it to hold a small piece of shop cloth. Scraps of shop cloth are always somewhere on the workbench.

Support the tube in a vise and put the bit inside of it. The sand paper will remove any deposits on the metal and make for better joint.

Once you have the cross members cut, mitered, and cleanedyou need to lay them out. I find that it is best to number which position each one is in and draw alignment marks on the cross members and the rack. I measure to get even spacing across the rack, but use my eye to determine when they are parallel to each other and the sides of the rack. The rack platform may not be a true rectangle and it’s more important that everything look good than that everything is perfectly measured and square.

The rack is parallel to the ground and held in the vise after the last step. With everything laid out I tack each of the joints with a small blob of brass. I don’t use any clamps or fixtures for this, the cross members stay in place on their own. This isn’t the only possible option — Alistair likes to position the rack vertically and use clamps to prevent the stays from sliding down. Once everything is tacked I rotate the rack in the vise and make sure that the valley of each miter is pointing down. This lets me use gravity to flow the brass where I want it to go and to get the best fillet.

Once you’ve brazed everything on one side you flip the rack and do the other side.

In this entry I’ll show how I build the fork crown mount for a rack. This is the part that goes from theback of the rackthrough the fork crown.

On a rack that is designed for very heavy loads I would recommend connecting the rackto the fork crown using two stays, one over each fork blade. This single stay setup is not as good at resisting high lateral loads. It does work with almost everyfork though, where thetwo stay method only works with forks that have extra eyelets on thetops of the fork blades.

I don’t have a lathe, so I use a bolt as the threaded stud that runs through the fork crown. This is a M6 bolt that I’m removing the head from:

The bolt will be held inside some larger diameter tubing. First I need to cut the tubing square. Note that to make sure that it is square I need to check the cut in two orientations 90 degrees from each other.

This is an exploded view of what is going on. I have a 6mm (close to 1/4″) threaded stud that will be inserted into some 5/16 x 0.035″ tubing. This is then inserted into some 3/8 x 0.035″ tubing. The 3/8″ tubing is bent and will be brazed into the fork crown. The 5/16″ tubing is pulled out from the 3/8″ tubing in this view, but when brazed together the 3/8″ and 5/16″ tubing will be flush. This creates a nice face to sit against the fork’s crown.

Everything is loaded up with flux and ready for brazing:

A view after the three parts are brazed together.

Here is a shot showing how I hold the piece in place while brazing it to the back of the rack. I’m using vice grips on the rack and a piece of scrap metal (PCI slot cover from a PC) to hold the piece in place. I checked with a square to make sure that the threaded stud is square with the back of the rack.

Here I am checking the angle. The bike that this is going on has a 73 degree head tube angle, so the face of the fork crown is also 73 degrees. I want it to sit flat (or close to it), so I need to angle my mount at 17 degrees (73 + 17 = 90). I’m using a simple engineers protractor to check the angle. My reference is one of the stays on the rack. I’m a little shallow here, but that is okay. It will make the front of the rack slightly higher than the rear, and that is acceptable.

The other option for doing this is to mount the fork crown mount into a fork and then use a fixture to hold the rack in place. The advantage of this method is that you can see how everything will look before it is brazed together. Alistair designed this nice little jig out of a test tube holder for holding the rack in place while brazing. I like the jig, but find that things are a little more secure using my method. Give both a try and see what works best.

The fork crown mount is half brazed onto the rack. I flipped the rack over to finish the brazing on this side.

All done

This is mitering for a basic 90 degree joint with 3/8″ tubing.

The tube directly after cutting with a hacksaw. It’s a little messy:

Make a notch in the centerline of the tubing using a file or hacksaw. This keeps the file centered in the next step:

File. A handy hint is that a 12″ Nicholson bastard file has a 3/8″ diameter, so it makes a nice miter into 3/8″ tubing. A 10″ file works for 5/16″, a 8″ for 1/4″ tubing.

Once filed you have a miter, but it’s pretty ugly:

Clean up the inside of the miter with production cloth wrapped around a piece of tubing:

Then clean up the outside with production cloth:

Check the miter. It looks pretty good to me:

This will be the first in a multipart set of blog entries with some basic information on rack building. I’m going to start by discussing tools. If you have any requested subjects please let me know in the comments and I’ll concentrate on them in future entries. The next entry will be about mitering tubing. I don’t plan on doing any entries around the use of a brazing torch, I think that you should learn that hands on from another person who is skilled in brazing.

My existing toolkit already had some of what I needed, such as a good vise and a hacksaw. However I also needed to buy a number of more specialized tools such as files, clamps, and machinists squares.

My most used tool is the vise. It supports tubing when I’m cutting it, mitering it, and brazing it. I have a pretty basic Japanese made vise that has 4″ wide jaws. I haven’t found the need for anything bigger yet when building racks, but this one is probably too small for mitering larger tubing used in frames. I often clamp rack sized tubing directly into the jaws of the vise, but it is better to make tubing blocks. You can see a homemade behind the vise. I have my vise mounted in front of the workbench so that I can access it from three sides. Framebuilders often have a vise mounted on a pedestal for 360 degree access.

My torch kit started out as a Victor Superrange II, but I quickly replaced a number of the parts. It would have been cheaper to buy a kit from scratch. I use Oxy/Propane (Oxy/Acetylene is more common). My welding shop swapped the stock acetylene regulator for a propane one. Propane doesn’t burn as hot as acetylene, but it is hot enough for brazing. It’s nice being able to use the same fuel tank as my propane BBQ. My oxygen cylinder has a 55 cubic foot capacity and that seems to last me about 6 months (maybe10 racks?).

I’ve upgraded the hoses to the Smith Kevlar hoses (around $50) and replaced the torch with a smaller and lighter Victor J-28. I primarily use a W-1J tip when making racks.

A great early project is a torch stand. This one is made from pieces of a BMX frame that I found in the trash. The stand lets me keep the torch turned on when I need to put it down for a minute and also holds short pieces of brazing rod andmy striker.

A lot of small tools are involved in making racks. I laid out some of them on my workbench. From left to right we have:

• Drill and bits
• Tubing bender
• Clamps (Kant Klamps are the specific brand)
• Pliers
• Shop cloth or production cloth. This is sandpaper on a roll and 1″ or 1.5″ wide. I buy 80 grit shop cloth and a roll seems to last a long time. Enco has it pretty cheaply.
• Sharpies are really useful for marking on steel.
• Machinists squares in a couple of sizes are useful for keeping things square. Enco has a small kit for $20 with 4 sizes.
• Vise grips are useful for clamping fixtures.
• Round files are useful for mitering. More on this in a future entry.
• A welding magnet can also be useful for clamping.
• A center punch makes drilling holes in tubing much easier. You need to drill small vent holes in most of the tubes that you braze.
• Sitting under the center punch is a deburring tool. It cleans up the inside of tubing nicely after you cut it.
• Brazing flux and a flux brush.

You need to wear some sort of eye protection when brazing. These safety glasses are special in that they have didymium lenses with a flip-up #3 brazing lens. They are large enough to fit over my regular glasses (yup, I look like a dork with three pairs of lenses on my eyes). You can get them from Sundance Art Glass. Without didymium the flame and flux produce a bright orange sodium flare that is very difficult to see through. It makes it hard to see the underlying metal,which is necessary to know when the flux is getting hot enough (it turns glassy) or the steel is getting too hot (it turns orange). Here is an example without the glasses:

Can you see anything under that huge orange flame? I can’t. This is what happens when you put the glasses on:

Whoa. That tube is too hot.

The glasses are expensive and a luxury,but they are a really useful luxury. I think that they help my brazing quite a bit.