Making a series of small aluminium cones

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.

Whilst I can't help with your cones, Can I say welcome back, I wondered where you were

Roy

Using stock larger than 1.8mm dia preferably in a collet

Keep the centring drill as deep in the chuck as possible and spot very gently at high speed

Drill the 0.25mm to depth - again with minimum drill projection from the chuck

Turn taper at 25degrees incl.

Turn od down to 1.8 mm

Part off to length - touch parting tool on tip of cone - move topslide required amount plus thickness of parting tool.

The final diameter will define angle length

Given the small diameter, the fastest top speed on an ML7 and the softness of aluminium, a razor sharp HSS tool bit would be much the better option - well it would for me 

Good to see you back on the tools Doc

Edited By Ramon Wilson on 26/01/2022 16:06:44

Edited By pgk pgk on 26/01/2022 16:12:30

For something that small I would use a form tool.

Drill the end then use form tool. If you make it so the thick end has an extra stick out it will make the stock for parting at the same time

Dave

Maybe I am just thick but I cannot see an overall length, taper is 3.5mm but how long is parallel 1.8 dia length? Also how deep is the hole ?

Edited By Baz on 26/01/2022 17:40:52

Thanks Roy - appreciated.

The daftest issue was breaking my foot on Christmas day, while carrying a huge box of Lego up to the house for the kids...2 weeks to go now before I can try walking properly again.

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

Sorry Baz - it's 4.5 mm long.

The hole depth isn't critical - it's just a location for some tube that will be glued in.

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

I've not watched the video yet, so this may be answered in there, but I've often wondered how you batch produce parts like this?

This is fairly simple, and for a model aircraft, but stuff like, say, model car hubs with multiple features - and they all need to be exactly the same.

Do you do one machining process at a time, and somehow keep swapping the stock in a fixture, or is it just one at a time with very careful measurement, or what?

.

THEY do it like this:

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The rest of us probably don’t

MichaelG.

Yep they do Michael but did you not notice anything - Not a Myford in sight

'How- ever' did they make batch parts before CNC

A matter of dead stops and gauges Doc - as many ops on one set up as possible, and extremely high tolerance fixtures for secondary ops.

Many items made now would not have been possible on conventional machining. A good example are the 'Master' aircraft probes etc for plastic models that you must be familiar with. Search out the aerial for the 1/48 Apache helicopter for a fine specimen.

It's all too easy to forget that CNC as we know it today was a very rare commodity not that long ago.

All fascinating stuff though

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.

.

Yes, I think that’s the essence of it

… The early history is briefly summarised here : **LINK**

https://www.precipart.com/blog/need-know-swiss-turning/

MichaelG.

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Edit: __ I’ve just found this: https://wisconsinmetaltech.com/swiss-machining-faqs/

which gives a little more description.

Edited By Michael Gilligan on 26/01/2022 20:33:37

Edit: __ I’ve just found this: **LINK**

which gives a little more description.

Edited By Michael Gilligan on 26/01/2022 20:33:37

Interesting links - thanks. Couldn't help but notice this in the second one-

With the addition of CNC, Swiss machine tooling areas began to include turrets, gang slides, and secondary spindles, improving speed and accuracy. When parts are rotating at a speed of up to 15,000 RPM with live tooling up to 10,000 RPM and tolerances anywhere between ±0.0002” (±0.00508 mm) and ±0.0005” (±0.0127 mm), Swiss machines have the ability to support high volume requirements with just a single skilled machinist.

A far cry from a Myford for sure!

Ha, I'm a sucker for that aftermarket stuff Doc, especially the resin !!

Master don't do the aerial as a separate item - it's in with the chain gun parts

Without checking it I would say the thinner part is no more than .3mm and yes it's turned along it's full length. As you say some remarkable items at very reasonable prices considering what it would entail to do like wise even if able to!

Edited By Ramon Wilson on 26/01/2022 21:55:14

That aerial is just insane if it’s turned. Some of their 1:72 machine gun cooling jackets are unbelievable too.

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