Sunday, 4 August 2013


Do you recall that last shedweek I mentioned that making the live axle was going to be trivial? Well, it wasn't, it should have been but it turned into an epic waste of time and materials. In the end I got there after 3 attempts. The turning was easy, as it should have been, but the threading was the hard part.

Top two are scrap, the bottom one is good.

The difficulty is that the threads need to be a very tight fit with no measurable play between the male and female parts. Try this test, pick a brand new, matched nut and bolt and thread them together. Then wiggle the nut about, I guarantee that it will have some play, however slight. Now imagine that that nut is the adjuster that takes the slack out of the bearings. Any measurable play will cause uneven wear on the bearing surfaces. The 5/8" cycle thread die, taper and plug tap that I used cut a set of threads with measurable play despite best practises. On the first attempt I used the die on it's own, on the second attempt I screw cut the thread to 90% of depth and finished off with the die spread wide, this climbed slightly out of true and cut a poor thread, On the final attempt, I screw cut the entire thread which is what I should have done from the start. We learn from our mistakes.

Finally with a decent axle, I could assemble the left hand arm and adjuster into the hub.

I need to do this to measure the gap between the sun gear and the crank arm with feeler gauges. I'd calculated this to be 0.050" and it was extremely close. I need this dimension so that I can machine the gap to be the same on the planet gear to ensure that both gears are aligned.

Next step is to retrieve the planet gear from the oily rag where it's lived for the last 14 months
 I'd deliberately machined the planet between centres so I can easily machine the bearing surface concentric to the teeth. I can repeatedly remove the work and check the fit manually without loss of accuracy.

The original planet gear.

First job is to hollow out the gear and rough out the bearing surface. 

I wondered why the original has the second, larger, outer recess into the gear. It isn't used for anything other than possibly a felt washer. The answer becomes obvious when you try to machine it, you need clearance for the cutting tool. The hollow is 0.350" deep and even with custom ground and relieved tools, clearance is exceedingly tight.

Polish the bearing and cut the thread. Screw cut the thread. Check the thread depth after every pass using the three wires method. Ruining the planet at this stage would have caused a shallow earthquake in my immediate vicinity.
The size of the wires is important, in this case pins proved suitable.

Now machine off the thread from the end of the planet gear for the fixed connecting rod...

...and machine the angled ramp for Renouf's patent wedge, 
this is the same size and shape as that used to hold the sun gear to the hub.

Next machine off the temporary boss that facilitated so many of the machining operations...

...and machine the decorative relief into the rear of the gear

Done. Hoorah.

Finally I can do a trial fit up and check that the gears are aligned and more importantly that the centres aren't too tight.  Everything appears to be spot on and the planet orbits happily around the sun, the centre spacing is good with just a little backlash as there should be. The gears are perfectly aligned, but you knew they would be didn't you? <cough> OCD </cough>

In other news, my lovely wife has been most unwell. She complained of abdominal pain one night last week and the following morning she was unable to get out of bed. Despite protests, we went to the doctor who promptly sent her straight to hospital. Two hours later and she had been relieved of her appendix. She has the tiniest set of scars, mine are huge but I had mine out when I was 13, over a hundred years ago now. Sadly her recovery has not been straightforward, and her complications now have complications. My boss has been very supportive since I've had a lot of time off work. On the plus side though, the house is full of flowers from good friends. Thank you.


  1. I don't know much about machining, but reading your blog has been fascinating

    1. Thank you, I don't know much about machining either really. I'm strictly an amateur but I do enjoy writing about my adventures discovering all this stuff.

  2. I hope your wife is now well.

    All this stuff make one think about how seriously skilled the Victorians were!


    1. Thanks Stephen, she's well on the mend now I'm very pleased to report.

      The Victorians were very highly skilled indeed and they were also figuring this stuff out for the first time. I'm merely copying it, easy in comparison. It's a mistake to assume that us as modern humans are more intelligent than our ancestors, in most cases we are not.