Is LBSC correct

[Michael GilliganParticipant @michaelgilligan61133]

Posted by john kennedy 1 on 04/02/2013 15:18:12:

Thank you for that link Michael .. So a taper or bellmouth is down to the condition/allignment of the lathe and nothing to do with the tool springing.

 

John,

I don't think that's quite what he says.

This bit is important: "The shape of the boring bit should offer adequate front clearance otherwise the tool will rub and form a bell-mouth hole." 

MichaelG.

.

Added quote

 

Edited By Michael Gilligan on 04/02/2013 16:54:35

[Roderick JenkinsParticipant @roderickjenkins93242]

It is an interesting question. The received wisdom is that the bore will be tapered if the tool is insubstantial. As has been suggested though this seems unlikely. A component of the cutting forces will tend to push the tool towards the centre but I would imagine that equilibrium will be established pretty quickly. This would seem to lead to bell mouthing but not a tapered bore. On the second cut at the same setting the depth of cut will be much less and consequently the forces bending the tool will be less and the tool will remove some more material and so on. Depending on the sharpness of the tool, the final cut may be so small that the tool merely bends out of the way without removing any material. I think a better finish on the return journey is likely because the shape of most boring tools is such that a much wider cut is being taken – a bit like having a well rounded nose.

I don't think that the above detracts from the general advice to use as stiff a boring tool as you can.

Does that make sense?

Rod

[Sub MandrelParticipant @submandrel]

My mate Xeno says that no matter how many passes you take you'll never get a perfectly cylindrical bore

Neil

[colin hawesParticipant @colinhawes85982]

Boring tools need to be very sharp ; you can't rely on a tool with 1/2 thou wear damage on its cutting face to take a reliable 1/2 thou cut. It will deflect instead and you will keep on increasing the cut until it takes too much off or leaves a torn surface. Colin.

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