All, I've not posted here for a while, mainly due to health issues, which are hopefully now receding into the distance. So thoughts have been turning to getting back in the garage when weather permits.

I've got the Princess Royal on the go, but I thought this little project would ease me back into it: I need to make four very small cones out of aluminium. They are inlet cones for a small scale model:

Dimensions in mm.

The drilled end may have to be ditched (it's to mount a small brass tube, but may be too much of an ask). I suppose the starting 'point' (ha ha) would be to face-off the end of some aluminium rod, lightly centre with a 1mm drill, then try and drill the 0.25mm hole? I could then gradually turn the cone until I hit the drilling o/d. Then a case of measuring the length somehow, and parting off.

So question is how would you suggest I do this? I need 4 identical parts.

I've got an ML7, collet chuck, and a pin drill holder which might be useful. I suppose GT inserts would be best for this?

Cheers.

Thanks Ramon, it may be about time I tried grinding another HSS tool. Worked OK for the boring bar, but seems like decades ago.

Thanks I'll have a look at that after tea.

Thanks Ramon. Yes, Master Model brass parts are incredible – I’ve used loads of their machine guns and cooling jackets in 1:72, plus a few pitot and AoA probes. They usually have a stall at Telford, and I’m often tempted to buy a particular kit based on what detail parts they have available. How they make them for the money is brilliant.

So just to wrap things up – it was fairly warm today up here, so I made the cones this morning. Pretty straightforward in the end, but I still couldn't figure out a quick and easy way of parting to identical lengths. In this case it doesn't matter, but it would be good to know. I ended up parting off by feeding the GT insert into the shank, and eventually it broke free. OK there's a pip left, but again, irrelevant for this application.

They are for a 1960's vintage Airfix kit I'm building and refining – a 1:76 Bristol-Ferranti Bloodhound missile. They are shock cones for the Thor ramjets. According to a few references they are 24 degree cones, which by the look of the real things means a 48 degree apex angle (yes, my o/p drawing was wrong in this respect).

They were fitted with air pressure sensors at their tips, so I began by facing some aluminium rod, and drilling to 0.2 mm. I thought the smallest drill I had ws 0.25 mm, but not so. I used the technique mentioned on the other thread of lightly gripping the shank in the smallest chuck I had, and manually feeding it into the work:

I only broke 1 out of the three drills I had…Then machined the cone with a very sharp GT type insert:

Should really be a double cone angle, but at this size it would be invisible – the transition is pretty much in the inlet. Then machined the spigot to 1.6 mm:

The result:

After sawing off the original plastic one (actually represents a FOD cover I think), and hollowing the inlet, I Blu-Tacked one in place, with some 0.15 mm wire representing the air pressure probe:

The much smaller turbo pump intakes below the main ones will probably be replaced with brass tube for the surround, and a cut-off pin for the cone.

After congratulating myself on a job resonably well done, with the loss of only one drill, I closed the drill box lid, not realising the holder strip had come loose, and subsequently snapped my entire set of remaining PCB drills cean off.

Anyway, it was nice to get back in the garage, clean and lube the lathe, and make something from metal again. Cheers.

Edited By Dr_GMJN on 29/01/2022 16:11:49