Winter build. Atom Minor MK III

[Basil]

I've got quite a few long term builds on the go at the moment and I was looking for a nice little engine I could finish up over the winter. The casting kit and plans are from Hemmingway. I have previously built the Westbury Seal Major 30cc from their castings. Something about just following through instructions and plans and making parts to the best of your ability attracts me to these kits.
After deciding on the first part to make (Ignition bracket) It looked like a no brainer! I spent a few hours working through the best way to go about the machining. Per plans the bracket has a 29/64th hole through it which was going to be very tight with the raw casting material available.
To cut a long story short a couple of hours in the worst happened. A hairline crack between the large hole and the front of the casting. I had gone to great lengths to center everything within the available casting. I could have ordered another casting, this one did have an undercut that made it very thin in one area. Kirk is very good about this kind of thing and I am sure he would have swapped it out.
Because this bracket is designed to be adjustable and be pinch clamped to the front housing I thought it sure would be better to make it out of some good old 6061. I have lots from my machining days in the states. Luckily this component is fully dimensioned on the plans. Sweet!
A day later and it is complete. No need to worry about this one cracking one day from a little over torqueing.
On to the next part......

 

[ShopShoe]

Good Save

I'm following this build.

--ShopShoe

 

[Basil]

I spent today machining the block for the Atom. I had a choice, either chuck the casting in a 4 Jaw and machine on the lathe or rig something up on the mill. I felt I had more control and room for adjustment as I was working up to the final crank hole diameter on the mill. Not an easy item to hold on to, I did not want to put pressure on the casting length, deciding to hold under the mounting lugs instead.
The wood might look sketchy but with a bit of grinding it fitted very well and was solid. Once I was happy with the positioning I firmed everything up with super glue. The casting does not leave much room for error and I was happy when this first cut was over. Now I could mount on a mandrel and cut the flange surfaces.
The only material I could find of a close size for the Mandrel was a piece of nice EN24. I decided not to be wasteful by cutting it, hence the steady rest. Back over to the mill to work on the cylinder diameter, deck height and mounting holes. The cylinder bore is 1/16th offset to the crank centerline which could definitely catch you out.
Turned it over and dialed in an accurate 180degrees and worked on the mounting lugs. Then onto the 10 degree exhaust port. Went for a 7/16 thread in this. I have converted all the other threads to metric.
A full day with some nice resting time. I find taking a good break every hour or two helps keep parts out of the junk bin.
A good day and happy with the result.

 

[Basil]

On to the front and rear housings. Front housing just consists of doing some preliminary machining and making a very slightly tapered spigot to assist with the rest of the machining processes.
With not much to hang onto with the rear housing I got the first part of the machining gingerly out of the way in the 4 jaw. Matched the holes up with the main case in the mill then made a jig for the rest of the machining. The making of the jig was well worth while allowing for easy setup in the mill and 4 Jaw in the lathe. Chose the bore the tapered intake tracts on the lathe instead of making D bits. Then onto some casting clean up. Cheers