[TheForge] Which Drill Rod?

[David E. Smucker]

Yes to Kim George,  adding a large hub -- large in diameter and spanning
most of the width would make the assembly much much stiffer.  A narrow
pulley with minimal hub would act almost like a point load.

Jerry,  The flexing of a piece of steel, in this example heat-treated O1 vs.
as purchase O1 is the same -- it depends only on the modulus of the material
-- not the strength.  The heat-treated will be much stronger but have no
difference in stiffness.  Now if this "shaft" was heat-treated 2024 aluminum
it would be roughly as strong as the annealed O1 but only 1/3 the stiffness
because aluminum has a modulus 1/3 that of steel.  It is very important not
to confuse modulus of elasticity with strength.  OK what has a higher
modulus than steel?  Tungsten is about twice that of steel, so the
suggestion to make the shaft from a 1/8 dia tungsten TIG welding electrode
is a great idea.

Of course the cheapest way to make a stiffer shaft is to increase its
diameter.  The polar moment of inertia goes up by the 4th power.  So a 1/4
inch shaft of the same width and same loading is 16 times stiffer than a 1/8
shaft.  It is also stronger but that goes up only by the cross sectional
area.

Detailed design of such shafts is basic to many machine designs and is key
for example to the design of a gearbox where shaft deflection under load is
a huge factor in the mesh and wear of the gear teeth.

Dave Smucker
Brasstown, NC

-----Original Message-----
From: theforge-bounces at mailman.qth.net
[mailto:theforge-bounces at mailman.qth.net] On Behalf Of Jerry Frost
Sent: Saturday, November 30, 2013 1:55 PM
To: 'Blacksmithing List Sponsored by ABANA'
Subject: Re: [TheForge] Which Drill Rod?

Yes it would. Unless I'm seriously mistaken the heat treat would have an
effect as well. Quench a piece of O1 in water and try flexing it.

Frosty
-----Original Message-----
From: theforge-bounces at mailman.qth.net
[mailto:theforge-bounces at mailman.qth.net] On Behalf Of Kim George
Sent: Saturday, November 30, 2013 6:21 AM
To: Blacksmithing List Sponsored by ABANA
Subject: Re: [TheForge] Which Drill Rod?

Wouldn't the deflection change depending on the width if the hub of the
pulley? If you have a pulley with a 3" hub on a 4' shaft wouldn't the
deflection be only over 1" of the shaft?

--
Kim George

"Why for you try to bury me in cold,cold ground?"
     Taz
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