Monday, 29 October 2012

Braking News

These past few shedweeks, I've been making a couple of pivotal components for the geared facile.

Specifically the two pivot mounts for the brake lever and the spoon brake. As mentioned last time, these were almost certainly off the shelf items supplied by Snell & Brown. I'm slowly making all the bits necessary for the handlebars to be brazed up, without actually making the handlebars, I'm still pondering on that chewy little problem. The success of a project like this is in the small details and as mentioned last time, I enjoy small details. Little bits like the lever mounts have to be accurate for the machine as a whole to be accurate.

The lever pivot would originally have been a casting and most likely from gun metal rather than steel. The original I am copying has traces of verdigris on this pivot indicating a copper content. Mine will be machined from 4140 steel, mostly because I have a suitable lump handy but also because machining this from solid will be quite wasteful and anything containing copper isn't cheap right now. Or probably ever again.

In contrast the original spoon pivot is certainly made from steel, it is a tricky little thing and while I don't need it in order to finish of the handlebar assembly, it makes sense to make it at the same time.

Notice the greenish verdigris on the lever pivot and the rust on the spoon pivot.

As usual here is a photographic recipe for cooking your own lever pivots.

Start with a suitable lump of 4140 and mount it eccentrically in the 4 jaw to bore the off centre 0.75" hole.

Then shape the sides to form the start of the convex bulge and define the width of the clamp.
Flip it around, re centre on the bore and machine the other side.

Then saw away the excess, this is the bit that would have been wasteful if using gunmetal.

Mill the upper and lower bounds.

Mill the clamp height and the excess from the round bulge.

Drill a pair of holes, one being threaded, the other just to help with metal removal.

Rough out the slot in the clamp with a saw.

Mill out the clamp slot and finally finish off with a hand file

The spoon pivot is based upon a 0.75" steel ball. On my latest trip back to Blighty just a few months ago, I purchased a ball turning lathe attachment for exactly this job and I've been itching to use it since.

Turn a piece of 4140 bar down to the rough shape.

Start turning the ball, my word, this was fun.

Thin down the threaded section to 0.25" and rough out a 26tpi thread,
this is so that the die will start straight as I'm unable to use the die in the lathe.

Then without removing from the chuck, remount in the dividing head 
and drill and tap the cross through hole at 0.25" cycle thread.

Counterbore for the screw.

Then index a quarter turn and rough mill out the slot from either side. 
Also mill through at the base of the slot.

Remove from the chuck, and saw out the narrow bridge remaining.
Saw off from the barstock and run a 0.25" cycle thread die down it.
Remount in a suitable fixture and mill the slot to final size.

Finally make the two screws for the pivots, first rough out the screw before cutting the thread.

Make a suitable arbor to hold the screw whilst the head is machined, 
first cut the dome, this is cut using the same settings as for the round ball so that it matches the profile.

Then cut the slot with a slitting saw.

The completed pivots.

Phew, that was a lot of pictures.

In other news, I've been exorcising my demons these past few weekends. Last Monday was labour day here in NZ which means a long weekend. Hoorah. The whanau decided to spend the weekend in Akaroa doing exciting holiday things. I decided to ride over following the route of Le Race. Now, I'm not as fit as I usually am at this time of year. This sorry state is due to a number of things that I'm not going to go into, but suffice to say I've been drinking a little too much as a result.

The climb up from Little River to Hilltop was OK and then the summit road was OK to. The steep bit around the back of Duvauchelle was hard but then it always is, the difficulty came on the final descent down Long Bay Road. If you recall, the last time I rode this, I liberally smeared a percentage of my skin down parts of the tarmac. I had no desire to repeat the experience and descended like a very slow descending person. I was pleased to get to the hotel in one piece.

Then this last weekend, we headed up to Hanmer Springs for the night. I usually take an offroad bike and do the loop straight up Jack's Pass, along the Clarence River and then back down Jollie's Pass. Riding up Jack's Pass was relatively hard due to the strong Nor'Wester headwind, I was blown to a stop and then forced backwards three times on the way up. Remounting on such a  steep hill into a headwind proved quite difficult, the whole time getting sandblasted by the gravel. Just before the summit of Jollie's Pass my seat post snapped clean off at the point where it enters the frame, it was a typical aluminium fracture with no prior warning. I rode the final 11km including the steep descent and back into town standing up, my thighs were burning when I got back. Nothing that a quick dip in the hot pools couldn't sort out though.

A breaked aluminium seat post, yesterday.


  1. I've really appreciated reading your blog over the last couple days. The level of detail in your work and writing has helped take my mind off an impending bankruptcy.

    Signed a broke bicycle mechanic from America.

    1. Thanks for the feedback. I'm really sorry to hear about your situation. I understand about the trauma of personal tragedy through my own current experiences. It's partly why I do this blog. I hope that things pick up for you in the future. Chin up.