Working it out first.

Could this work?

It’s often the case in more complex projects that the whole can be broken down into various parts. For example, if I’m asked to make a large working model of something I often find that it breaks down into a number of smaller tasks each of which has its own challenges to overcome and in a resultant way its own design brief. What does this assembly need to do, how will it function and how am I going to achieve these criteria. The same was very much the case with the build of the bike. Controls, rear section, front section, exhaust etc all had specific things about them I wanted to achieve, not just visually but also functionally. The construction of this rear fender area then, had its own set of requirements that I needed to satisfy. A little brief all of its own.

Going back to my original brief that I’d set myself, that the bike was for everyday use, I knew that durability and robustness were important things to consider. British roads can be pretty bumpy and London’s are no exception. The parking bays that we are all invariably required to use in and around town can often be a totally unsympathetic battleground, with people cramming their bikes and scooters into the smallest of spaces with scant regard for any damage caused to your adjacent bike by footrests, handlebars and anything else that protrudes. So with all this in mind I knew that whatever I built would need to be pretty sturdy and resistant to bending and scraping. This rather delicate piece of rolled aluminium fender section was going to have to be turned into something a bit more substantial.

Can you see where I'm going with this?

Another habit that I’ve got into on any job is to have a sketch book or pad handy at all times during the job. This helps me to organise workflows, keep track of component purchases and budgets and the like. But it’s also very handy for sketching out ideas and thoughts when trying to solve specific problems. Importantly it enables me to keep everything in one place, there’s nothing more frustrating than constantly having to find loose bits of paper in a pile, especially the one that often manages to fall behind or under a workbench. Similarly I also go and buy some of those plastic document envelopes from the stationers for collecting all sales receipts, brochures and technical sheets one invariably accumulates during a job.

Getting somewhere now.

These three sketches above are from my notebook and show my thinking about how I could overcome the stability and strength issues with my rear fender. The top two sketches show a rough idea of the kind of upper support I wanted, a tapering finger of material with some holes pierced in it for a kind of lightweight look. This would be coupled with a large strip of slightly heavier gauge steel than ran down the centre of the underside of the fender piece. This strap would mount at the front end via a hole to match up with that on the mounting plate and at the back end two spaced holes would line up to accept the two mounting bolts passing through the fender from the rear lighting cluster and numberplate mount. Like a kind of backbone to the whole affair. I reckoned this would contribute significantly to the rigidity of the fender piece both in a vertical plane and horizontally. There was still the issue of dealing with any twisting action though. The final sketch is me investigating how to fix the upper mount to the assembly already in place for holding the seat in place.The first thing to do then, was to translate my sketched ideas into three dimensions and see how it worked.

No batteries required, just a brain and a pen.

Before I get on to that it’s also worth mentioning that one of the best tools to have in your work space is a dry wipe board. It doesn’t matter what size it is but, my advice is get one if you can. Working in conjunction with your notebook it assists in organising what you’re doing and helps you prioritise your tasks. I find it invaluable. Its perfect for creating lists of things to be done and in what order. Time and time again you read in magazines about other peoples builds and often they mention the value of such a device and attest to the immense sense of satisfaction to be gained by erasing jobs on the list as you go and replacing them with new ones. Two other great things about it are that you can sketch on it at an enlarged size to really work things through and, if you place it sensibly and write large enough, you can see it from anywhere in your work area. I picked up this one from a discount store for a couple of pounds. Some of the wall mount parts were missing, hence the price, but worth every penny.


Cutting metal at last.

Graphic ideas appearing.

Whilst I had been deliberately distracting myself I had been fiddling around with a number of other things as well. Stripes of white electricians tape had appeared on the tank to see how it would look, various graphic devices had arrived on the side panels and I’d been playing around with ideas for a front fly screen.

So now I want to tell you how I made the rear fender. What I also want to do is try and make it a bit more interesting than just a plain old description, blow by blow as it were, of cutting bits of metal and bolting them together. It’s something that’s started to creep into my thoughts as I try and create more posts for the blog. As you well know from very early posts, or you may have read my “About” page, I spend a great deal of my professional time making models and prototypes for people. That process invariably involves employing lots of techniques and quick fixes to achieve particular results. So I’m always thinking about how I could pass on any of these things to my readers in the way of useful tips etc. The fabrication of the rear fender seems a great place to try and communicate some of these things. So here goes, though having said that I may very well get to the end of this bit and not passed on anything at all. The following piece will certainly contain some.

Plenty to play with.

As you will have gathered, my start point for this next phase of the build is a bike frame with the two rear seat support stays cut off and a moulded plastic inner fender which I’m retaining to help keep all the road crud out of the back of the bike as I’ll be using it in all weathers. I’ve also got my hands on a large rolled section of aluminium mudguard, sold by those wonderful folk at Burton Bike Bits. I’ve chosen a rounded section with a rolled edge, for neatness. It arrived as almost a full circle of material. The plan was to first figure out how to mount it securely, I didn’t want it flapping about as I bounced down London’s crappy roads, and then to decide on a length that would offer good protection and cut the piece to size with the end shaped how I wanted.

Mounting plate attached to cross member.

The first task was to secure the plastic inner guard, which only loosely clips to the frame and relies on the original mudguard for support. Conveniently nearby is a cross brace on the frame under the seat so I made a plate with a protruding finger of material out of 16 swg mild steel sheet that I could secure to the cross brace and to the plastic guard. I couldn’t weld at this time, and only now can do rudimentary stuff with a MIG welder, so I had to screw the plate in place. I always find putting threaded holes directly into thin walled tube a bit of a fudge and on this occasion used what I know as Pull-serts or Grip-n-serts. These are threaded inserts specially designed for creating blind threaded holes in sheet materials. Very handy things, available in most thread sizes and they give a great result where you don’t have enough material to provide a decent thread length in a tube wall, sheet thickness and even extrusion wall. Three of these at M5 size into the cross member worked a treat and provided a very sturdy mount for my plate. A happy coincidence was that the plate also formed a neat compartment under the seat for the electrical connections to the rear lamp cluster.

Foam block and tape doing their jobs.

So now I had the plastic guard secured and with a single central hole drilled, a place to mount the rear guard metal section enough to allow me to start to think about its length, angle and subsequent mounting points. I’d cut the big piece of rolled section down a bit to make it more manageable and found a handy lump of scrap modelling foam that I could sit on top of the tyre to support the piece while I decided on angle and length, helped, as you can see in the photo by a piece of duck tape on top.

Anyone familiar with a retracting tape measure knows that curved sections of sheet material are only rigid in one plane and waggle about like no ones business when you least want them to. The same applied to the rear fender section so the next challenge was to come up with a way of preventing that action occurring at the back of the bike. Time to get the sketch book out.

I’m not sure if Pull-serts live up to being a top tip but it’s a start.

The chain run.

Does it make sense?

I knew that having made the clock mount and its accompanying surround I should really have got on with some kind of front screen, but I didn’t. I decided to make a chain guard instead. In a funny kind of way I found myself in the situation where I’d tried to plan everything out as much as possible, in a loosely efficient project management kind of way, and then found myself deliberately jumping from one part of the plan to another rather randomly. I’d call it something like organic execution. Having planned everything out systematically, I was free to approach the list of tasks depending on how I felt on the day. That day I was much more in the mood to make a chain guard than to start to get to grips with the next big thing which was the rear mudguard or fender.

At least with this next part I followed very closely one of my guiding principles of the build which was to lose weight. The standard part, as any GN owner will tell you, is a substantial piece of kit. Whilst I understand fully the need to prevent ingress of foreign objects into the chain run, I can’t for the life of me see why said part has to be the depth of a piece of industrial guttering and sturdy enough to shake off an attack of rocket propelled grenades. Whatever, it weighs a ton and made its way swiftly into the ever growing pile of discarded ironwork growing in the corner.

A bit blurry I'm afraid

It would have been much easier I know, to have followed the weight saving creed to its maximum and not fitted anything at all but I wanted something there to stop things like loose rucksack straps getting too close and prevent the back of the bike and ultimately me, getting a good spattering of flung off chain lube.

A quick trip to the DIY store and I’d got myself a very handy length of aluminium ‘L’ section, the angle to give it some rigidity, and a length of flat bar as well for making a couple of brackets. By trimming off part of the angle, to create a flat section, it was easy enough to bend the strip around a quick wooden former to get a radius that would sit nicely above the rear sprocket. I could then trim the length of the whole thing at the end that goes over the front sprocket. Duly done it was just a question of working out how high off the upper chain run I wanted it to sit. As the chain can flap whilst your traveling, too low and each journey would be a rattling affair. To tell the truth I did get it a bit low to start with and modified it very quickly soon after the first test ride. For the rear of the guard I made the bracket at an angle to match the rake of the rear shocks, to kind of blend in, and secured it to a conveniently located hole above the chain adjuster on that side. The front bracket was a simple piece with a single 90 degree bend in it, and I cut it to a length which would allow me to raise or lower the guard at that point should I need to, which I did as you’ve already read. I attached the brackets to the guard using some ‘Pop’ rivets, another godsend to the home builder, and it was complete and ready for a coat of trusty old black paint. Job done. Now I knew I couldn’t put off the rear fender any longer.