Drilling Bronze?

[Chris TriceParticipant @christrice43267]

If tubes expanded inwards when heated, you'd never be able to shrink fit a tube on a shaft or heat a track rod ball joint taper socket to release a stubborn one.

Edited By Chris Trice on 26/10/2018 16:13:26

[Neil WyattModerator @neilwyatt]

I think it's more likely to be a process related to the release of locked in stresses.

Imagine a bock of foam, squash it into a rather smaller cardboard box.

Now cut a hole though the foam and it will 'expand inwards' to reduce the size of the hole.

Obviously a lot less distortion can be locked into a metal, but you only need a small reduction to grab a tool.

Neil

[CHARLES lipscombeParticipant @charleslipscombe16059]

Posted by Chris Trice on 26/10/2018 16:12:26:

If tubes expanded inwards when heated, you'd never be able to shrink fit a tube on a shaft or heat a track rod ball joint taper socket to release a stubborn one.

It's pretty hard to get past Chris's logic here!

Neil's suggestion might have merit but it does not explain why this behaviour is unique(?) to phosphor and aluminium bronze.

Best wishes, Chas

[Mick B1Participant @mickb1]

Well, I don't know I'm sure. I've turned, drilled tapped and died the stuff (PB1) without noticing much difference from good BDMS. The tools need to be sharp, a bit of extra top-rake seems to help and the swarf comes off in ductile, helical ribbons, but I've not met any of the grief some seem to be describing. Maybe it's just that the components I've made in it are small? For example the acorn cups in my album pics.

I have seen some very high-copper bronze (or perhaps it is effectively just copper) that does exhibit all the difficulties described – to me it seems pretty much unmachineable. Taps stuck in it almost irretrievably, even with a hole 15 thou over tapping size. But it's the wrong colour for anything I've ever thought of as phosphor bronze.

Edited By Mick B1 on 26/10/2018 21:34:49

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 26/10/2018 17:37:10:

I think it's more likely to be a process related to the release of locked in stresses.

…

Or is it that the properties of bronze allow the end of the drill to wedge into the metal (rather than cutting chips as it should) causing the drill's helix to simultaneously screw into the metal while being forced open to jam at the sides? Behaving a bit like an expanding masonry bolt. I image it's the same effect that causes drills to snatch as they break through sheet metal.

Dave

[not done it yetParticipant @notdoneityet]

It is more likely temperature at the cutting tip and just behind it. Differential cooling and no cutting on the flutes of the drill, so hot tip=bigger hole and cooler after the cut=smaller hole. Difference =drag or jam.

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