Introduction: DIY Bike Rear Rack With a MAGNETIC U-lock Mount! (no Welding)

About: I've been making Instructables since I was 13. Now, I mostly make videos of my projects, however I'm still active here, so don't hesitate to reach out! Sick with a deadly disease called DIY-itis!

My bicycle, as you may know, is the official transportation device I use to alter the geographic location of the garbage people throw out on the curb.

A fantastic carrier of junk, to my room workshop, that is!

I also ride my bike to school every day.

This ends up being 1000-2000km (~500-1000 miles) every year, most of which I'm carrying a heavy school backpack, along with a large U-lock for lock my bike, which is no fun - my back can attest to that.

I always wanted a bike rack to assist in carrying things I find, which end up being the materials for a vast majority of my projects (including this one!), and had the idea of integrating a mount for my bike lock inside the bike rack, to reduce the unbearable amount of weight on my back, as well as ensuring that I always have my bike lock on my bike, as I always forget to take it with me!

Now in case you're wondering if a homemade bike rack can actually survive being on a bike being exposed to the elements, an endless amount of vibration, being hit quite often - due to the current coronavirus pandemic, I had to delay the creation of this Instructable several times, and I have ridden my bike ~200km (~100 miles) so far with the bike rack - and so far - so good!

In this Instructable, I will show you how to make a custom bike carrier rack with built-in magnetic storage for your U-lock - all from junk!


(Watch the Youtube build video and see it in action!)

Tired of skipping through boring DIY videos? In case you don't already know, I now make short, tightly edited Youtube videos about homemade tools, tool hacks, woodworking, electronics, metalworking projects and much more - Subscribe to so you don't miss out! :)

Step 1: What You'll Need

Want to make this project? Here's what you'll need, or at least what I used!



Hardware, Materials & Consumables:

I made it for FREE since I already had everything that was needed on hand. The links above are affiliate links, meaning that I earn a small percentage of what you paid (helping me fund bigger projects), at no extra cost to you. If you want to know more about a specific tool/part that I used, need ideas for alternatives, or don't see something you think should be here, please let me know in the comments.

Also, check out my Ultimate Bike Accessories Kit! It includes all of the additional small gadgets & accessories you may see on my bike. I'm always on the lookout for more cool biking accessories, so please let me know if you have any!

Approximate Build Time: Well, it's April as I type this. And I started it in October. Yup. I didn't work on it full time of course, and filming a step by step Instructable & video slows me down significantly, but starting a build like this with zero knowledge about what I wanted has taken so much time! I believe one could be built from scratch in 2 or 3 weekends.

Step 2: Prototype

Sketching and prototyping the bike rack took me several weeks, because every time I thought I had finished, I had a new idea for improvement. It's easy to look back at the outcome and have every part look obvious, but I had never had a bike rack before, and the idea of integrating a bike lock inside the rack, while being constrained by the geometry of my bike - was actually extremely complicated!

I could only compare it to designing a laptop, which of course is way more complicated, but every part relies on many other parts: the larger the screen, the more processing power you need, which requires a larger battery, which requires a larger laptop to enclose all of the parts, requiring a larger screen... But how do you even know how large a laptop screen should actually be? How do you even know what you would want? I suppose this is the reason for why there are so many laptop, phone, shoe, camera, car companies etc. with such a vast amount of options - oh, and bikes!

None of many of my previous projects (even SpectrumLED!) had so many parts that rely on others, making a build so complicated. With that said, I now have a lot of appreciation for people who design things!

Making several prototypes helped my come up with the final design, which includes finding many problems, which when solved, create other problems, all of which I don't believe I could have solved if I had started with the final materials right away. I would highly recommend making one only to make sure your legs don't bump into the sides of the bike rack while pedaling, getting on/off the bike, etc as this may differ significantly with different bikes.

Step 3: The Platform

I thought that it would make the most amount of sense to build the bike rack "around" the lock, since the most important part of it is that the bike lock can be slid into its holder effortlessly.

I started by cutting all of the parts so size, which were three aluminum angles, cut to the length of the aluminum plate.

The aluminum plate was a little too wide for my bike, so I cut it down, and also cut down the aluminum angles since they were too wide when side by side. I glued them in place with CA glue as shown in the pictures, but only temporarily so I could continue with the build, without having the parts fall apart as I move on.

I thought this shape, similar to a U-channel would be very rigid, yet lightweight.

After that, I glued the third aluminum angle, which acts as a shelf that holds one side of the U-lock. Note that I'm assembling it upside-down in the pictures.

On the other side, the lock slides into an aluminum tube. I didn't have any aluminum angle that had the correct dimensions, so I decided to go with two shelf brackets, which I also glued in place. I had also taken into account the thickness of the magnets that would be glued between the brackets and the pipe, but that's for a later step.

Step 4: Aluminum Adapter

I subscribe to the idea that if you can't make something perfect, make it adjustable - and I think this is especially true for parts on a moving bicycle.

The platform would be connected to the bottom of the bike with a steel angle on each side, and I didn't want to connect it directly to my bike because it would later be it harder if not impossible to adjust, and for several other reasons having to do with the specific design of my bike.

I found 2 thick scraps of aluminum which I remember scavenging from some type of desk. What matters here is that the material is strong, lightweight, and won't rust.

I CA glued them together, this allows me to work on both of them at the same time, and later break them apart due to the brittle nature of CA glue.

I drilled two holes the same distance from each other as the threaded holes on my bike (see picture 2), and a third which will later get bolted to the steel angles. The shape of the piece of the aluminum adapter doesn't really matter as long as none of the holes are too close to one of the edges. I used an ice pick to scribe lines, then went over them with a red pen. I find that this is an easy way to ensure that the lines don't get smudged accidentally. I then cut it out using a hacksaw, and filed down the rough edges.

Mounting it was easy, with four black oxide bolts whose threads matched the threads in my bike. If your bike doesn't have any threaded holes, you could use the hub/bolt, though this may make removing the wheel more difficult.

I have a hard time imagining someone stealing the bike rack, but I will be replacing the bolts shown here with all sorts of bolts with odd and rare heads, just to deter a possible crime of opportunity. Why not?

Step 5: Steel Angle Bar

To connect the platform to the aluminum adapter, I decided to go with galvanized steel angle. I had a lengthy debate with an engineer who advised me to use aluminum due to the weight savings, but I disagreed and don't regret it. These have to be stiffer than you may think, and I didn't have any thick aluminum angle anyway. In fact, I don't think I've ever seen thick aluminum angle being used anywhere! Another option would be to use the C-shaped channel from a ball-bearing drawer slide, as it's usually pretty thin and very tough.

The scrap piece of steel angle that I had was barely long enough, but I cut it in half, drilled a large hole for a large black oxide bolt, and bolted it to the aluminum adapter with a locknut. The rubber seal in the locknut will prevent water from entering the threads and rusting, as well as stop the nut from loosening from the vibrations.

The only parts of the bike rack that can rust are the edges of the steel angle since they aren't galvanized, so I'm considering painting them. If anyone has any recommendations regarding primer and/or spray paint that, your comments will be highly appreciated!

The rear side of the aluminum angle happens to be as wide as an LED strip, so you may be able to guess what I'm going to be making in my next instructable :)

Step 6: Seat Adapter

I originally planned to connect the bike rack to the seat post, but later changed my mind when I realized I could utilize both the threaded inserts in the frame, and the pipe/cam clamp that's used to tighten the seat post, to increase rigidity.

I made two identical adapters from aluminum flat bar, drilling a hole in each side, making sure I was able to bolt it to the bike. I did have to use my flex shaft rotary tool with a burr to grind down the pipe clamp, as it was too thick and I wasn't able to clamp it back, and didn't have any alternative bolts.

I bent two more short pieces of aluminum bar, by hand, and clamped them to the adapter. They turned out better than I expected, but not symmetrical unfortunately.

Step 7: Clamp!

Because of the large number of (potentially) moving parts/de facto hinges, I thought that instead of connecting everything together bolt by bolt, I should clamp all of the moving parts in the proper place, so I could verify that everything fits properly, and to stop parts from moving completely, which would mess up the alignment.

The lower the platform is, the more stable it will be, but you should leave a gap between it and the wheel in case you get a larger tire. I left a large gap because I will be utilizing the space between the U of the lock to store a homemade battery pack - for a future project!

After everything was aligned perfectly, I started drilling. The aluminum angle on the right side and the shelf that holds one side of the lock barely overlapped, but luckily I was able to drill both holes exactly in the center so the clamping pressure from the bolts would be distributed evenly. It's crucial that this is done properly.

Six holes, and six black oxide bolts later, it was finally ready to...move on to the next step.

Step 8: Excess Steel?

The way I assembled it - leaving the steel angles exposed - was done purposely to account for any possible errors because I couldn't risk making a mistake, as I didn't have any other comparable steel angle that I could use as a replacement.

I hacksawed the exposed parts off, and fixed the rough and sharp edges with a diamond wheel in my rotary tool. This methods works much better than files: a diamond wheel removes quite fast - much faster than hand-filing, which means I don't get lazy and saw very close to the line, damaging what I'm working on, and never learning my lesson, of course!

Ready to ride!

But not completely done, yet, unless if you aren't in need of any fancy magnetic lock storage!

Step 9: Repair Time!

Two weeks had passed since the previous step, as well as a fair amount of riding my bike. I kept the aluminum top clamped to the angles just in case of an impact.

As expected, the CA glue acted like CA glue, and didn't hold due to its brittle properties, along with the endless amount of vibration that occurs while biking.

I took it apart and applied a large amount of clear super 7 adhesive on both sided, and clamped it together with a lot of clamps. For two hours I kept having to tighten the clamps, and clean off the glue that kept oozing out This adhesive was recommended to me, and it breaks every law in the book.

Generally, the more unbearable the smell of an adhesive is, the better it is. But not in this case - it only has a slightly noticeable odor! They aren't paying me to say this. Just for the record - I only endorse using the remnants of the adhesive in the tube after someone else paid for it and used it. Note that I mentioned paid, as this adhesive is NOT cheap!

I assumed it would take a few days to cure - based on no information that was written, so a week later I drilled six holes, countersunk them, and bolted a matching number of stainless steel countersunk screws with their (adorable) tiny locknuts. I don't believe the bolts were actually needed since after gluing, the rigidity improved significantly, but it never hurts, I guess.

No way on earth this is coming apart!

Step 10: Don't Buy Magnets!

In case you don't know, old hard drives are a fantastic source for incredibly powerful magnets. Desktop computer HDDs like the one pictured above contain two large neodymium magnets, and HDDs from laptops contain two smaller and thinner ones.

Salvaging the magnets is as easy as removing all of the screws (there is usually a hidden one under the sticker) which may require a torx screwdriver set, and prying out both magnets. In some HDDs the actuator arm may also need to be unbolted.

I used two large magnets and one small magnet to make the magnetic holder for the U-lock, however yours may differ.

Step 11: Bike Lock!

As you may have seen earlier, I thought I could have an aluminum pipe on the bike rack which I slide the U-lock into, and magnets keep it there, even while I'm riding.

First, to strengthen the platform, I added another bolt to each side.

I glued both of the large magnets to the shelf brackets, pushed an aluminum pipe whose internal diameter was only slightly larger than the diameter of one side of my bike lock, and covered it with a lot of adhesive, connecting it to the inside of the bike rack permanently, and waterproofing the magnets - more than what is visible from the pictures.

If I ride my bike without the lock inside, it actually looks like an exhaust pipe which is pretty cool.

Step 12: The 3rd Locking Magnet

From my experiments, both of the previously added magnets added a significant amount of friction, however not enough to hold it securely in place.

I glued and bolted the third, smaller magnet, to a small piece of aluminum angle, and bolted it to the aluminum top plate of the platform where it makes contact with the lock when I push it in all the way.

The lock ended up sticking out more than I would have liked, but it doesn't get in the way as much as I expected it to, and the magnet holds onto the lock very well, snapping it in place.

The only scenario in which I could imagine the lock falling out is if I do a wheelie and jump down stairs at the same time - and I don't know how to do that.

Step 13: Last Bracket

I glued another small piece of aluminum angle to one bracket. I originally intended to do this to make sure the pipe didn't detach itself and slide to the right, because this was what I had seen when I filmed myself jumping off of things in slow motion as I show in the video. But it ended up being much stronger than I had anticipated and I see not structural need for it, other than making it look more appealing.

Step 14: Reflective Tape

I had some leftovers from a while back, when I bought a roll of reflective tape to cover my helmet and bike frame, and thought I should use it on the bike rack, since it makes me 10x more visible when riding in the dark.

It's much more reflective in real life than on camera. I've seen these tapes in many different colors.

Step 15: Sanding

Brushed finish

If you watch the video (1st picture), it looks fantastic, maybe even better than real life. But through my DSLR it looks much worse than real life (last picture).

Aluminum is very soft, and it doesn't really matter because I'm sure it'll get scratched up very fast.

I was actually quite surprised at how oxidized (white) the aluminum looked after sanding.

Step 16: ​DONE!

See it in action, on Youtube!

Some more thoughts:

  • This bike rack was a TON of work, but I've been using it for the past 2 months and love it - I couldn't recommend it more!
  • I also thought of making a folding wing/shelf, but decided not to.
  • I also thought of making a basket from steel mesh, but I didn't want to carry it everywhere, and didn't want to block the lock. I even thought of making a folding one (think of an origami paper cube), but I would only uses it very rarely and it wouldn't be worth carrying it on my bike. I found these stainless steel grilling mesh/nets that you may find useful.

I also will be giving away free Instructables premium memberships (please read before commenting) to members that make their own bike rack based on this Instructable. Will you be the first one?


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