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.

Teenagers - Con Rods Part 2

This shedweek I have mostly been playing with my milling machine. If you recall from last time I had made three of the four con rod ends, I now need to make the middle bits to join them up. I had initially intended to get Kung Fu Pete to weld up the joints but having investigated welding 4140 and then having it nitrided afterwards I've had second thoughts. The weld in such a thin section would be hard and possibly brittle so I had a chat with the man at the SSM and he said that in theory there is no reason why I can't braze the assemblies and then have them hardened. The brazed joints and indeed the entire centre sections can be masked using a special high temperature paste. Nitriding takes place at 570 degrees celsigrade which is a little too close to the melt temperature of the silver solder I have been using, so I'm going to braze them with CZ6 Silicon bronze instead. This melts between 875 and 895 degrees which will give me a bigger margin. A brazed lap joint will be as strong as the parent metal if I follow best practice and make the overlap 4 times as long as the thinnest section.

First thing to do is to sneak into Pete's shed and "borrow" a section of rigid angle to use as a brazing jig. The centres of the con rods are 8.5" and each side must be the same otherwise the levers will have a different  range of movement per side.

The holes can be accurately drilled to be 8.5" apart on the mill table by moving the bed along on the dials.

I've made a series of accurate buttons to take up the gaps between the con rod bearings and the 

bolts so that when the con rod ends are bolted down the centres will still be accurate.

Use them to bolt the ends down and mill the first part of the lap joint.

Then with  the ends bolted down I can accurately measure the gap... 

...and turn a bar  between centres of the correct diameter and length.

Mill the top flat.

Mill the corresponding part of the lap joint.

And finally mill the bottom to thickness.

The middle part then sits nicely in the gap ready for brazing. 

I'll probably put a bolt through the lap joints beforehand. 

The oiler holes still need to be drilled and tapped and I'll file the correct profile after brazing. The gear side con rod is different in that it holds the planet gear rigidly without allowing it to turn. I can make this in two pieces instead of three using one of the ends already made.

Starting from bar stock of the correct size centre drill each end and mill the bar to thickness again.

Then mount between centres and thin down to size...

...before turning the taper. My topslide only has 3" of travel so I had to take two bites at this. 

I'd like a taper turning attachment, sigh.

Next week, I'll finish off the drive side side and get them brazed up.

In other news, we now have a teenager in the house. My son turned 13 today. I took him and some equally excited friends paint balling this morning. I can now report with a high degree of accuracy that getting hit by multiple paint balls simultaneously from several directions is fairly uncomfortable. Having a group of young teenagers gang up on you with mildly offensive weapons is one way to spend a morning I suppose. Actually it was really good fun and I gave as good as I got.

In more other news, this thing arrived yesterday. One of my friends in San Francisco will know exactly what I'm going to make out of it.

Happy Christmas to both of my readers once again.

Lacking Wisdom and Getting Cranky

My lovely wife celebrated a very significant birthday this week and she is no more grumpy than usual. But that's not what I mean anyway. This shedweek I have started work on the right hand crank arm, this is a far simpler affair than the planet gear carrier but I'm not going to mention that in case I screw something up again. What with arranging the lavish parties and the parking for the convoy of trucks carrying her presents, I haven't had a great deal of free time (as usual). My brother has prompted to me update the blog though, so I'll have to take some time out from my hugely busy social life and post an entry.

The original right hand crank arm.

As before, I'm going to start with round billet and machine off one face

And then flip it over and machine the other.

Next I can saw off the thinned section and remount parallel to the ways. 

Using the same techniques as last time I can space the centre holes and 

also thin down the end of the crank to near final size.

Bolt down using the new hole and thin the centre section.

Remount on the faceplate and machine the back of the boss. 

Of course I forgot to take photos of the faceplate set up so you'll have to take my word for it.

Now mill the angled face at the back of the crank.

Then using this new angled surface as a reference, I can start to mill the relief into the front of the crank. 

This cut is at full depth so I can now get in with the ball nose cutter...

...to make the correct shape of the relief.

Mark out the shape of the crank...

...and chop it out with the hacksaw.

Finish off with hand files.

Finally mill the slot for the locking tab.

I now need to finish off a lot of little jobs on the geared assembly. The cranks need to be attached to the axle with taper pins, the locking tab needs to be made, the hole for the oiler needs to be drilled and tapped in the left hand arm and finally the patent information still needs to be stamped into the crank. All little jobs but I'll start on those next week.


In other news, my lovely wife's sister has just gone back to England after coming over for the birthday celebrations. We all had a fantastic time together and she has very warm memories of the visit. She's also pretty much back to normal after her operation a few weeks ago which is a huge relief for us.

Last Thursday I had my bottom two wisdom teeth taken out, they've been border line for the last 20 years and they finally got bad enough to need some action. I now look like a grumpy hamster but less cute. I have an interesting drug cocktail to take, some of which I'm not supposed to operate machinery with. Ho hum...

In more other news, my brother has sent me a link to a video he made of this years Benson run. The Benson run is one of my all time favourite antique bikes rides and I couldn't make it this year. If you are ever in Benson, Oxfordshire, UK on the first Sunday of July and you happen to have a pre 1928 bicycle about your person, I strongly recommend you try it.