How would you make this part?

[JellyParticipant @jelly]

So I was looking for something on one of my external HDD's and happened across the 3d model of the main body of something I made as a gift for a friend years ago (there are some other parts which turn it into a little bird).

I've just produced a little drawing of it as it's a really interesting part, which produces lots of challenges:

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The one I made was actually ½ scale, and turned from a cylindrical piece of brass on a M6 threaded arbour, the curves roughed in with chamfers, and the final shape generated with a (gigantic) carbon steel form tool shaped to produce the full profile.

That very direct approach was easy on the work-holding front, but an absolutely bonkers way to go about it in just about every way…

Something which I came to fully appreciate as the process resulted in innumerable scrapped parts, several snapped arbours and at least one malformed brass bird being launched bodily across the workshop.

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I quite fancy making another full-size one for myself, but learning from the previous failures, I can recognise that there's a risk of having a 1kg hunk of brass launched at me, which I'm not really up for.

Thankfully in the intervening years since I made the last one, I have also become slightly more imaginative (to go with the risk aversion) and have been able to come up with a few different approaches using to try which I think would result in a decent outcome, all of which involve making a jig/chuck which can hold onto a sphere securely, and pose their own problems in terms of driving the workpiece and/or marring the surface of a finished part due to clamping pressure

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I am however curious how others would approach this, because on first inspection it's far from simple to even hold on to the thing.

[JellyParticipant @jelly]

A work-holding challence par excellence!

[SillyOldDufferModerator @sillyoldduffer]

Am I allowed to make it in two parts, super-glued together? If so, I think access to the flat between the head and body would reduce the weight and simplify the holding problem. The angled holes suggest a rotary table and milling machine.

I agree it's a challenge though, every time I make things like that there's high-scrappage!

Dave

[Dave SParticipant @daves59043]

Start with bar, bosh in m12 thread, thread onto m12 arbour, turn features.

use m12 to fixture in mill for odd angled holes

Dave

[Tony Pratt 1Participant @tonypratt1]

I was thinking the same as Dave S, the M12 thread makes it not too difficult using a radius turning attachment.

Tony

[JellyParticipant @jelly]

Posted by Dave S on 16/03/2023 17:54:08:

Start with bar, bosh in m12 thread, thread onto m12 arbour, turn features.

use m12 to fixture in mill for odd angled holes

Dave

In fairness actually, the M12 thread would be substantially stronger than the M6 thread used to turn the half-sized one and not using a full profile form tool would also reduce the cutting forces substantially…

I don't think I've seen a ball turning attachment with a 60mm capacity before though, but once one was built, it would be substantially more useful than a fixture to hold 60mm spheres or 40mm hemispheres.

Edited By Jelly on 16/03/2023 18:24:09

[JasonBModerator @jasonb]

Thread end of stock, stick it on an arbor and two setups of my ball turner and that's the lathe work dine. Transfer arbor to ER block and setup on mill for beak and tail holes. My ball turner is OK for those sizes and more.

easier if it were wood, I've done a few birdies like that simple hand turning so I suppose you could use a graver on metal after roughing out with a few CAD derived co-ordinates. It's quite easy to do

Edited By JasonB on 16/03/2023 18:47:36

[JasonBModerator @jasonb]

Regarding the weak M6 arbor. Best option would probably have been to form the "head" while holding by the OD of the stock in a 3-jaw chuck. Then mount on the 6mm arbor and use a female ctr to add support to the "head" while the "body" is machines.

Or you could leave a pip on his head for a small ctr drilled hole for use with the rotating ctr and machine off the pip once the larger parts have been machined

[Anonymous]

Hydraulic copy unit:

Turn the larger ball and a parallel section first, and drill/tap the M12 hole, and part off. Locate larger ball in an aluminium cup chuck held with an M12 bolt. Turn the smaller hemisphere. For drilling/tapping the smaller holes use a universal dividing head with item mounted on a cylinder with an M12 bolt.

Andrew

[Howard LewisParticipant @howardlewis46836]

The Repton Radius Turning tool claims that it can accomodate up to 60 mm diameter.

Howard

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