After a lot of fumbling around with some redesigns I’ve gone back over the axle muffs and opted against raiding more of my limited supply of delrin rod in favour of epoxy-filled steel gear muffs. The idea for the latter came from Tom Hammond, 2mm aficionado and model engineer, in the hours I spent watching his Jacobs gear hobber last year at the Portland, Oregon GEARS show. Space, as ever, is tight but .100″ mild steel can be bored for enough epoxy to isolate .0625″ W-1 drill rod. The first op doesn’t require any more precision than a 3 jaw will grant but for the second I needed something better. My four jaws don’t hold down that small and I don’t have a .100″ WW collet yet. In any event I wanted an interior shoulder to act as a stop until I work out which method of mounting the gears to the muff I intend to use. The work holding answer was the ubiquitous ring collet turned up from what ever steel was to hand and slit to collapse around the loco axle under pressure of the scroll chuck jaws . Once I’m satisfied that steel muffs are the way forward I guess I’ll consider a home made WW collet.
To make the collet I had two options as I saw it: I could set the hole with a D-bit hoping that the D-bit could be set true in the tailstock (or modify one of the tool holders for my under construction bed turret to do the job) or I could bore to a moderate depth and call it a day. Having just made up some small silver steel boring bars I went with the path of least resistance. The photo below shows a George H Thomas designed eccentric tool holder with a boring bar that’s good to about .05″ diameter and scaled down to fit my Taig and Sherline tool posts. GHT knurled and drilled his for tommy bars on the “top” of the eccentric to set tool height but I don’t always get my tools the right way round when machining them and decided to leave the tommy bar holes off until I play around with the setup a bit more. Eventually I’ll probably put four equidistant holes around the circumference to allow for all eventualities – finger pressure for now! The tool is W-1 drill rod roasted a tad too long – it should be a light straw at the tip.
And here is the collet being bored. With the help of an appropriately sized piece of stock to use as a plug gauge it came out dead on. The collet was then marked for No.1 jaw (the jaw was also marked) and the collet removed from the chuck to be slit.
With the collet ready .125″ stock was turned down, drilled and parted to rough length before insertion in the above manifold. I didn’t have any pipe cleaners small enough to fit the axle muff so I made one of floral wire and some alpaca wool. It works. Once cleaned thoroughly epoxy was mixed and injected with a broken syringe of the type I use for cementing styrene together. I gave it a day before cleaning up the ends and loading them into the collet for finish boring/reaming facing.
Up next: Axles.