Monday, 2 September 2013

Purring Gears

You didn't know that gears could purr did you? Neither did I until my daughter came into the shed whilst I was idly playing with the fruits of this weeks labours. She told me that they sounded just like her cat, Flabby Tabby, when she's purring really loudly. "That sounds just like Flabby Tabby when she's purring really loudly" she said. But we're getting ahead of ourselves.

So clearly, this shedweek I've been finishing off all the little bits and pieces needed to complete the gear assembly.

The first job is to drill and ream the holes through the cranks and live axle for the taper pins. I found a local company that had a taper reamer of the right size and upon enquiry sold me a handful of matching taper pins. Hoorah. The taper on these imperial sized pins is 1:48 or 1" in 4'. In practise this means that a hole goes from too small and you can't get the pin started to too big and the pin falling through very quickly. It is very important not to mix and match imperial and metric pins as metric tapers are 1:50 and the two are not compatible.

The first hole is the easy one as it is in left hand crank which is tightened up to a shoulder on the axle so there is no adjustment needed. Drill through with the appropriate size drill and then hand ream the taper, checking periodically that the hole isn't getting too big. I need enough of the small end poking through that I can cut a thread on to secure the pin.

Another shockingly bad photo, this time of hand reaming a tapered hole.

The hole through the right hand crank required a little more thought as the cranks need to be exactly at 180 degrees to each other. By fiddling around with shims and scrap plate steel I was able to come up with a combination that sat flat in both orientations thus guaranteeing that the cranks were aligned correctly.

The right hand crank was locked with a lock nut and the hole drilled and reamed.

Fitting the taper pins.

Next mark the taper pins to cut the thread and shorten to length. Which raises an interesting problem. How do you grip a taper in the chuck? My solution was to make a little doo hickey to assist me. I drilled and reamed another tapered hole in some scrap bar and then split it with a hacksaw. Each taper pin can then be inserted, lightly tapped in and when the chuck is tighten up, it grips the taper very well but still makes it easy to get out again.

A split doo hickey with a tapered hole, yesterday.

Trim the big end and cut the thread on the little end.

Next make the locking tab for the live axle bearing adjuster. As before I only briefly considered machining it before I came to my senses and hand filed it. The recess is milled, it turned out that this was the last time I used my Myford machine vice...

Hand filed locking tab.

Myford machine vice shortly before it died.

Next drill and tap the hole for the oiler in the left hand crank arm. The placement of this is critical, too far inboard and it will foul the planet gear and too far outboard and the thread will break through to the bearing surface.

A little care with the edge finder and then using the mill as a drill.

Before tapping the hole at 2BA for one of my oilers I made previously.

Note I had to use a different machine vice as my lovely Myford had an unfortunate accident. When tightening it up the screw just kept turning until the end popped off.

You can see from the oil ingress that it has been cracked for a long time. 

I will mourn this, it was in almost new condition when I got it, I even still have the box for it. Now that the original Myford company is no more, my chances of replacing it are slim and none. Anybody have an unmolested one they'd like to sell me. Seriously, I'll pay a fair price for one. And btw, I didn't make those holes in it either, that was a previous owner.

Finally, I just need to stamp the patent info into the left hand crank arm as per the original.

I used my same techniques as before and it went well...

...although the N on the second line is double struck for some reason. 
I'm unconcerned as it shows the hand made nature of these things.

Then I can reassemble everything again for a photo shoot.

Right hand side compared to the original.  
Use your skill and judgement to spot which is which.

Left hand side not compared to the original as I don't have a photo of this assembly. 
I've jammed a wedge into the gears to stop the crank hanging down, just so the text is visible.

A gratuitous photo of the complete progress so far. 

Total weight at this point is 37.7lbs which is possibly very slightly heavier than an original as per the catalogue. Although I read an interesting comment from 1879 today. Henry Sturmey was complaining that manufacturers weren't truthful with their quoted weights and from now on he was going to weigh each machine he reviewed himself. Nothing changes I guess.

Next week, I'll start work on the gear guard. I need the gear assembly to be complete for this, then I can dismantle it all again and get all the components hardened. I seem to be rapidly running out of bits to make. I'm still unsure how to do the levers though.

In other news, I've caught tendonitis in the back of my right hand. It is most painful and I'm unable do anything with it, even the simple action of using a screw driver is out of the question. Fortunately the pain from my removed wisdom teeth is mostly masking this. My hand does mean that I can't even ride a bike at the moment, I'm going insane. And getting fat.

In more other news, this last week my father acknowledged a rather unusual anniversary. It was 50 years ago that he was knocked off his Matchless G3LS by a less than attentive driver. His injuries have caused him much trouble over the intervening years. This is clearly where I get my excessive grumpiness from.

Exactly 50 years previously, to the minute apparently, this spot was a less than happy scene. 
Hey, I pinstriped that tank.

Last weekend I took the family down to Lake Tekapo for an end of winter break. the kids loved the snow tubing which is a little like an icy Brooklands negotiated on large inner tubes.

Apparently it was just as bumpy too. 

We did some excellent local walks which the kids were less keen on. However a quick game of rabbit poo snow balls soon encouraged them along. This is an unfortunate side effect of making snow balls at the end of winter when the snow cover is very thin.


  1. Excellent progress so far!

    Sympathies with the wisdom teeth, i've been there myself.


    1. Hi Stephen,

      Yep coming on well. I'd like to be able ride it this year some time.