Re: [CAD_CAM_EDM_DRO] Re: DIY probing

> Hi Chris,
>
> Why can't you just work from the outside of the bell, aren't they still
> raised from sheet brass? I think my first approach would be to try a
> shadowgraph technique - literally. Hang a big piece of graph paper on the
> wall then shine the light of a slide projector on this with the horn in
> between. By moving the horn back and forth you could adjust the size to a
> known scale and then just mark the shape on the graph paper and take all the
> relevant dimensions from that. I realise a 'technical' solution might be
> more aesthetically pleasing but I doubt the guy who hammered the brass in
> the first place worried too much about that!! <G>

It may be that I should further investigate the shadow technique. It
needs to a be a good point light source and the light->horn path needs
to be absolutely perpendicular to the tracing surface. After tracing,
a few referemce measurements must be taken to scale the drawing.

Also, due to the manufacturing process the wall thickness is not
consistent on older horns. But the inside shape is very accurate
since it is spun over a mandrel after all the hammering is done
(today, the tendancy is to do it all by spinning).

Besides, I get all worked up to build a CMM and someone suggests I go
play with a flashlight?

;-)

Chris

(Another approach I've cconsidered would be a manually Z-adjustable
guide table on which oversize dial calipers could be manipulated to
directly measure the outside - the usual error with calipers on a
large tapered object is not measuing in the intended plane)