Best Way to Create These Radii

I wonder if someone could advise me on the best way to shape the complex radii on the part illustrated - this may not have worked, as I can't see any means of attaching the pix!

It’s another of my Austin Seven foolishnesses, this one being the fan pedestal. Replicas have just come on the market but I thought making one would be a challenging project and I’ve bought the aluminium now!

The trickiness is obvious and I really can’t afford concave (or is it ‘convex’, never sure whether you describe the shape of the cutter or the shape you want to make !) to form the spindle barrel. In any case, I don’t think those kind of cutters are really suitable for a vertical mill, lending themselves more to a horizontal machine.

I think a large endmill followed by a bit of judicious filing ought to make a fair rendition of the big rebate that rises vertically through the base and finishes beneath the barrel. But I think the way forward for most of this, once the basic shape is milled out, is riffler files. Would that be a sensible approach?

I did think it might be possible to cut the barrel radii on a rotary table. I.e. secure the work to the table and turn it against an endmill. The experts’ view on this would be helpful.

As always very many thanks in advance for any thoughts.

Martyn

Edited By martyn nutland on 27/07/2015 16:09:58

Edited By martyn nutland on 27/07/2015 16:10:35

Yes rotary table will be your best bet, take the majority off with a standard milling cutter and then finish with a ball or radius corner cutter. You will have to do some of it in stepps and then finally blend by filing.

Put all the holes in first while its easy to hold and mark out on a rectangular block.

It can be done, for example these two lumps

Became these

MartynThanks Jacob. Beautiful pump. Hope I can get a result half as good.

Martyn,

This is probably no help, but I think you could produce all, or most, of that 3D shape using a small CNC vertical mill. Do you have dimensioned drawings (or even your own sketches with approximate sizes)?

You could certainly produce the curved section as you suggest, using an end mill and a rotary table, or using a boring head or boring bar, even though it is only a part-circle.

The bores should be no problem either.

The top curved sections might be possible using the bore holes as a pivot point, and the side of an end mill to get some or all of the curves. Then blend with files. Coarse files, well-chalked work best with aluminium, at least for removing bulk. As JasonB's post shows, you can get a really nice finish on aluminium.

Mind you; if you are not too fussed about the exact detail of the outside of the shape (i.e. you don't need an exact replica) it may be possible to simplify the shape and make machining easier. Anything that eliminates the filing would be a bonus.

Marcus

Some very helpful thoughts there also for which I'm grateful.

And I do have a factory-produced example to work from - to measure etc. And as you rightly say, it's not necessary to worry too much about and exact replica. It only needs to hold the fan spindle which is static. The blade is mounted on an eccentric (for adjusting the belt) on the end of the spindle and that's where the rotation takes place.

But the reason the big rebate is there is to circumnavigate an oiler on the base on which the pedestal sits. So that shape is necessary.

Thanks again.

Martyn