Making a new Flywheel nut

When the old flywheel got stuck on the crankshaft, the nut ended up getting damaged removing it. I'm not actually sure what happened as I wasn't there but a new one was required so I ordered some material and a tap and die and got to work. First up was a CAD model so I knew what I was working towards

Basically it's a 24mm nut with a plain section to fit inside the extraction threads of the flywheel, with an M12 x 1.25 thread through the centre. Nothing particularly difficult but it's the first time I've milled flats on anything. 

Here's everything ready for some fun in the lathe. I started with a 30mm bar of EN8 steel, bottom left,  as I've been lead to believe that can be heat treated relatively easily (more on that later). 

Now here I have to own up to a bit of an error, you may notice that the piece of steel in the next pic is rusty, when I've just shown you a piece of bright bar. Well, this pic is from my first attempt which ended in a parting disaster on the lathe and I only took video of this stage on my second attempt which as we know from my last post, I am too stupid to get on the internet properly. This step was exactly the same though, turn down the relevant diameters, including a long narrow section that could be held in a collet for the next step. After this pic it was parted off leaving a little extra length for facing after the flats have been machined

Using a hex shaped collet block in the horizontal mill, the first flat was machined while checking the dimension from the flat to the opposite round edge. Once the first edge was in the correct place, a note was made of the y-axis so each subsequent flat would be in the same place. Each face was done in a couple of passes, checked, then the block was rotated to the next face

I did take a time lapse of the process on my phone and I also have the mental capacity to get that on the internet so here's that process in all it's glory

I have to say I was relieved when I first slipped the socket on and this happened! My first attempt hadn't been so successful and had needed extra passes on a couple of faces to get the socket to fit, second time round I must have been more careful and it just worked out right

Next it went back in the lathe held by the stub to be drilled and tapped and have a chamfer machine on the outer face. Then the stub was cut off by hand (didn't want another parting disaster!) and a mandrel machined with the matching thread so the nut could be threaded on the wrong way round and the last remaining face machined true to the thread. Again, this is all on video that will never see the light of day!

Next it was heated to a cherry red and held there for about 10 minutes before being plunged into old engine oil. I know this won't have been a perfect process but hopefully it's enough. Worst case scenario I'll be making another one! After a quick sand blast it looked like this:

Then a quick sand with some 240grit. I decided to leave the faces 'as machined' as I don't think a perfect nut would look right on the bike. After this it was tempered in the oven at home.

The nut and electronic ignition module are back with the bike at the shop so fingers crossed it will run soon!