Thursday, 12 September 2013

On Guard

As promised last time, I've spent my shedweek making the gear guard.

The original guard.

From the literature of the day, the sole purpose of this gear guard is to protect the gears from mud, stones and other debris thrown up from the unsealed roads of the day. By all accounts it was very effective. One reviewer mentioned that he threw a handful of mud at the guard just to see what would happen. It mostly got deflected and what did hit the gears apparently just got squished out. The guard is not designed to protect fingers belonging to inquisitive, small children. The Victorians were unconcerned about such things, at that time common sense was still reasonably common. You lived or died by your wits, unlike today where the government of [insert country of residence] manages your health and safety on your behalf. But I digress.

I did consider making a one off rolling machine to make this guard and also the rear mudguard. I decided against it at present although I may review this later.
So a quick scratch of the head and then get cracking. I approached Autobend again (they did a sterling job bending my handlebars if you recall all of that brouhaha) and enquired about bending some 1.375" thin wall mild steel tubing into the correct radius. "No problem" they said, as long as the correct centre line radius is 101mm (I think they meant 4" but I didn't argue).

By a staggering stroke of good fortune, that is exactly the dimension I require, which was nice. 

So starting with a 180 degree bend, the first thing to do is to make an indent on the bottom of the guard. This is so that the guard sits vertically when bolted to the upper and lower fork legs. The upper legs are angled in towards the head and the difference is taken up by this little indent.

Note the little cut out opposite the hole to allow a screwdriver access.

I've mentioned before that I don't like hitting stuff, I prefer squeezing in a controlled fashion so I made a little hard wood insert to go up inside the bend, this has the indent cut into it. All I need to do is then squeeze it in the vice with an external form of a suitable shape.

An indented hardwood plug...

...getting squished in the vice.

Next I need to chop out the inner part of the bend. This is not easy as you can't use a hacksaw, so I bolted a guide to the drill table and drill a series of holes around both sides. A combination of a junior hacksaw and a cut off wheel in the Dremel soon parted the two halves. I was mildly concerned that the radius would change when I removed the inner half of the bend but it stayed exactly the same.

I tried but couldn't get a tune out of this.

At this point the guard is very difficult to hold in the vice without damaging the shape. The answer is to make a suitable clamp from some scrap MDF, this has the curve of the guard cut out with a coping saw and then the inner part radiused slightly so that it sits inside with altering the shape when it is clamped up in the vice.

Cleaning up the edge with an angle grinder back to the marked line.

Then to finish the actual shape of the guard just profile the ends and tidy up with files.

Now to mark out, cut and bend the top mount, this is a reasonable simple affair.

The shape of the top mount.

Bent to shape.

Next job is to establish where the guard is going to sit on the fork legs, it has to be concentric with the sun gear so that the planet is always equidistant when purring round. Once again a little scrap of MDF with the outer radius of the sun and the inner radius of the guard cut out proved jolly useful.

The hole and the cut out are to allow me to scribe positions on the fork legs

The top mount gets riveted to the guard in the correct marked position, I use nails for rivets. My son is 12 and is now taller than me, has much bigger hands and feet and is estimated at current rates to stop at 6'6". I figured it was time he learnt how to rivet, hammering being really bad for my tendonitis at the moment.

The original riveted top mount.

My son's attempt.

I cleaned up this side.

Not bad for a tyro. He already has dibs on this bike, "When you die, can I have this?" Charming isn't it? Just because I've got a gammy hand and fewer teeth than he has, he's already started putting labels on my stuff. Sounds familiar eh Dad?

Then using the MDF jig I can mark out the holes for the screws to bolt the guard to the fork legs. The steel of the fork legs is pretty thin and even with BA screws, the thread count in use would be tiny if I just tapped the threads directly into the tubes. So I didn't, I made some little bosses, just like water bottle bosses, and silver soldered them in.

That's Boss as my kids say when describing something which meets with their approval. 
Honestly, I'm so down with the kids it scares me sometimes.

Make the holes a loose fit and braze them in. I needed to dismantle the bike to do this, it took me an hour and a half and I had quite a pile of bits on the work bench at the end.

I bolted the legs up to prevent movement as the heat is applied.

File flush so that when it's painted only you and I will know.

Finished, and no I'm not going to put it all back together just for a photo. 

I have two more holes to drill for the trouser guard, which I'll do next week.

While I've got it all apart I'm going to harden, plate and paint what I've made so far, studying the photos and my notes of the original, relatively little was plated. Each side of the handlebars, the brake components, the two gears and all the nuts and bolts are plated. Everything else was painted including the crank, con rods and levers. More later.

In other news, we've had a little storm this week. I read on the interweb (so it must be true) that we had 250 kph winds, the strongest on record. Apparently the storm was the worst since 1975 and the second worst ever. I thought our house was going to flat pack itself, we lost power and our trees lost limbs. The morning dawned beautiful, calm and smelled fresh and clean. Commuting in to work took ages due to the many trees down across roads. My lovely wife teaches at a rural school and she's still not able to get to work. They have no electrickery yet anyway.


  1. So much work for a gear mudguard!
    This reminds me of someone new on the first day at a job being told "Go to the stores and get me a couple of holes" - except they really would be!


    1. Yes, it is a lot of work. But then it has to be right, I'm not interested in an approximation. I want to be able to ride something that rides exactly like an original. I have no deadline and I enjoy doing it.

      "Go to the stores and ask for a long weight".

  2. Absolutely :)