A fellow Gauge O Guild member asked if I would tell him how I made the form tool for the whistles. Because I am a bit impatient* I was planning to make another one to turn Globe lubricators (if I could).
So, I made another form tool and took photos as I went along.
Using a second cut file I filed away approximately half the thickness of the bar (in the event it was nearer to 35/40% than half).
Then I used a centre drill to drill a 1.5mm starter hold which I opened out to 2mm. I think my 2mm drill bit must need sharpening because I struggled to get it to go through the last bit.
I had drilled quite close to the end so I put the rod drilled end upwards in my vice and tilted it forward to file away until I had just over half the hole exposed.
Then I transferred it to the lathe. I put my cone shaped grind stone in the collet chuck and ground the inside of the hole to put my rake on it. The black pen mark on the stone was at the 2mm diameter mark so I didn’t inadvertently make the hole bigger.
Next, I used the diamond cutting disk to grind back the outer edges to refine what I had filed and get it nearer to final size. But before removing the tool from the cross slide I marked with a pencil the angle which I had ground at to make replacing the tool at the right angle easier should it need regrinding.
Then I hardened and tempered the cutting end. I did this by heating the end using my Microflame to a red heat then I quenched it in a jar of water. I repeated the process but only heating until it changed to a blue colour before quenching again in water.
I tried cutting a globe but I made a couple of mistakes:
The material I was trying it on was too thin (2.5mm diameter) and I had predrilled the centre thinking that I was going to thread a rod through it.
The ‘globe’ broke off long before it remotely resembled a globe and I realised that even with thicker material I needed to grind more off the tool to make the forming half circle shallower. At this point I used thicker material but still predrilled it.
Another try; another failure and another regrind.
The last go was cut from 4mm bar and no predrilling and I also took some of the edge of the ‘globe section with a diamond file prior to applying the form tool.
Having done all this I now think that I may get away with thinner rod now that I have refined the form tool and my technique.
Of course, the law of sod dictated that not 15 minutes after finishing the successful lubricator the postie came with some brass bearings that I had ordered from China and wasn’t expecting for another three weeks or so.* I an Middleditch in his original advice had suggested buying brass ball bearings and drilling them to make the globes from
The subject of those will make another posting at some point.