On Fri, 02 Oct 2020 10:25:19 +0100 (BST), "Dave Liquorice"
wrote:

On Fri, 02 Oct 2020 00:23:35 +0100, T i m wrote:

There are formulae for the right speed for cutting all sorts of
materials, with and without lube and so to answer that we may need to
know the thickness of the steel and the pitch of the blade (which I
think ideally needs to be 'matched' (or within certain criteria)).

Ideally I think you need at least three teeth to be within the
thickness of the material being cut at all times. This prevents the
material dropping deeper between the teeth as it moves along the
blade, thus giving each tooth more to cut than it should have.
Remember you can increase the "thickness" by cutting at a shallow
angle.

Yeah and where a saber saw might be 'easier' than a jigsaw in this
instance. Probably cheaper to buy an angle grinder though. ;-)

Rate of cutting and speed of blade is "common sense" coupled with
"let the tool do the work".

True, but outside of a bit of trial and error, that isn't something
that is (or can be) always obvious to everyone.

I was helping a mate rebuild the engine from his VW Campervan remotely
(he would phone me for 'next step' advice and progress update /
observations etc). Unfortunately, whilst he was following the HBOL for
the actual steps, he wasn't that familiar with torque wrench settings,
set it on the wrong scale and because he had no experience of what
sort of torque might be appropriate for a long cylinder stud in an
ally crankcase, ripped the thread out. ;-(

Broadly the soft/ductile materials
(acrylic, aluminium, lead) cut best at low speeds. Harder ones faster
but brittleness come into it as well...

Yes, lead is especially strange to saw. ;-)

Cheers, T i m