Thursday, 9 January 2014

King Cnut - con rods part 3

What with Christmas and New Year and going away and having to make an appearance in the house every once in a while, it's only now that I can get back in the shed and continue work. I did manage a few solid days before Christmas though so I need to update you with the latest progress. I've got lots of photos to describe the steps to finish the con rods. Now then, where did we get to?

Mark the centre of the planet gear hole...

...and drill it out to enable me to...

...get the boring head into it and bore it to tears within 10 thou of size.

Then using a spiffy new adjustable reamer, take it out to the final dimension...

...which is a tight fit on the planet gear shaft.

Then without changing the set up, drill the hole for the locking wedge so that it just grazes the edge of the bore. 
This is the same locking mechanism as for the sun gear.

Then mill the hole into the bore.

Use your skill and judgement to work out what shape the wedge will be.

Then finish off the last part of the lap joints...

...and drill and tap them through.

Then using this new hole mount to the mill and create the top and bottom tapers.

Next round the end in the mill, with such a long handle I could manually feed this around.

Then mark out the shape of the end...

...and start to file the shape...

...until it's done.

Then take it all over to Kung Fu Pete's shed and borrow his gas set to braze them up.

Give the brazed joints a few minutes with a file.

Nearly there. Next machine the flats on the back of the planet mount for use with a puller when disassembling.

Then mill the slot for the planet bearing adjustment locking dog.

Finally, drill and tap the hole to hold the dog in place.

Oh yeah, drill and tap for the oilers and stamp the serial number on each one.

I told you there was a lot of photos.

Compare with the original con roads and you can see that the wedge has failed at some point and the owner has drilled through to use a pin to wedge the gear. This is one of the areas where the original bike has suffered at the hands of an excitable man with a large hammer.

Now that I have them finished, I'm aware that they seem very slender in profile even though they match the original. Conservative calculations on the yield strength of 4140 and the small cross sectional area indicate they are well able to stand my full weight but I'm not sure if the brazed joints will hold up to repeated stress cycles. Normal riding will be fine, but I worry about when I'm grinding away up hills and such like. I'll fit them and if they break, I'll make some more a little differently. As with so much on the bike, it's all a new learning experience for me. We'll just have to see.

Next shedweek I'll make the wedge and the planet bearing locking dog and possibly start on the pivots if my lovely wife can spare me from house duties.

In other news we have been away for Christmas, we usually do. We went up to the far north of the north of the North Island and very nice it was too. We skillfully managed to avoid the wet Christchurch weather and exchanged it for sub tropical humidity and heat. The whanau played in the sea while I went and poked around in a bloke's shed that he playfully liked to call a museum. Actually, it was quite good and I took the kids for a look, giving them a point for every exhibit they found that was also in my shed, my Dad's shed, Mr. Middleton's shed(s) or Kung Fu Pete's shed. I lost count but the game did cost me a round of ice creams.

My son doing his very best King Cnut impression, it was just as effective and he got hammered moments later. 
And you thought it was a typo, shame on you.


  1. I spotted the red angle iron, do I win five pounds?

    1. That's twice now so it must be 10 at least. Can I owe it to you?

  2. I like the idea of tasteful and dignified improvement to the original if the rods should break.