Wednesday, 5 October 2011

Shaving my head - part 1

I haven't troubled a barber for at least two decades, but that's not what I mean. This week I've been back in the shed inconveniencing a billet of hot rolled 1045 steel.

If you squint and use a little imagination there is a head
for a geared facile inside this lump. I just need to get it out
Originals use castings for this part and I did consider going down this route, however the cost of making or having a pattern made and then cast would be excessive for a one off. Economies of scale dictate that I start from a relatively cheap billet ($50) and spend extra time machining from scratch. The billet is 3.5" (~90mm) diameter and 6.5" (165mm) long. It weighs a very hefty 18lb 3.5oz (8.26kg). Interestingly the original castings were almost certainly provided to Ellis & Co. Ltd.(the manufacturers of the facile) by the Abingdon Works Co. The higher spec. later versions of the Facile and the Geared Facile all featured an Abingdon Ball Head, first patented in 1886. Most of the examples I have seen for myself have this ball head and stamped into the casting is:

No. 3294
I'll be reproducing this ball head, more later.

The first operation is to centre drill each end, every subsequent operation will then use these as the reference to ensure concentricity. Mounted between centres I can then skim the scale off with a carbide tool.

Carefully centred, this ran very smoothly at top speed.
The OD is far wider than the shoulder of the forks at 2.75" however I need the extra width to give me enough material to carve the handle bar mount. A little trig. to calculate this width gave me the 3.5", this will become clear later when I remove the excess.

Thinning down the billet to 3" and then machining in the correct angle for the fork legs is the next process, this took a long time and my little Myford ML7 was pushed to it's limits.

The swarf factory has been at full production this week
The shoulder is now at 2.75" and I can now thin down the centre of the head to nearly the final dimension. This centre section will be tapered but as I need to use a fixed steady on it for later operations, I'm going to leave it plain and slightly oversize for now.

Taking shape
Profiling the shoulder to the correct shape is the last of the operations on the outside of the work piece at this stage.

Now I can remount in the four jaw and fixed steady to bore away unwanted material from the underside, between the fork legs. Reminds me a little too much of a certain procedure from a few weeks ago. The underside of the head is flat with radiused fillets to the fork legs. I'll remove as much material as possible by machine and then file to shape by hand.

In other news, I'm now back on the bike and enjoying the magpie attacks again. Fortunately, I've been out for most of the magpie season but I have at least a month left. I did have one half hearted attack from behind at the weekend, but it wasn't a proper job and he flew off as soon as I looked at him. The really aggressive ones keep coming in even when you get off and confront them. For this reason I usually carry a handheld catapult and a pocket of gravel with me when venturing out of town. I haven't hit a magpie yet in three years of trying but it certainly helps the mental state to have a go.

We have royalty coming next week which means my shed time will be restricted. My good lady wife having given me a list of chores to be done before the in laws arrive. She's realised that I work best from lists since I get to check things off one at a time. Which reminds me of a joke.

Q. Why do women multitask?
A. Because they can't f...... prioritise.

I didn't just say that.

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