[TheForge] Which Drill Rod?

[David E. Smucker]

It is always an area of great confusion, stiffness vs. strength and
hardness.  It just doesn't seem right but stiffness is closely related to
the position of the metal on the periodic chart.  Lead being a poor example
of this as it has a rather low modulus, but then it is highly malleable.
Aluminum, titanium, iron (steel), tungsten being good examples of this.
(Alloy does make a difference, cast iron have a lower modulus than steel by
about something like 8 percent.)

 Having been a rolling mill engineer most of my adult life the search for
stiffness under high loads is a big deal.  A lot of rolling mill
advancements has been in trying to find ways to use smaller rolls (more
effective in reduction) vs. ways to make them functionally stiffer.  Hence
the early development of the 4 high rolling mill.  The smaller work rolls do
the reduction while the backup rolls provide the stiffness.  The backup
rolls are really just rotating beams, while the work rolls do the work.  

Dave Smucker
-----Original Message-----
From: theforge-bounces at mailman.qth.net
[mailto:theforge-bounces at mailman.qth.net] On Behalf Of Bruce .
Sent: Saturday, November 30, 2013 7:55 PM
To: Blacksmithing List Sponsored by ABANA
Subject: Re: [TheForge] Which Drill Rod?

Dave,

I don't doubt your expertise, but my intuition (like Pete's and Jerry's) is
screaming otherwise!

I suspect I know why:  Take a dead soft wire -- it bends real easy.  Take a
hardened music wire of the same diameter -- it doesn't bend nearly so
easily.  What's the catch? -- We typically exceed the elastic limit of the
dead soft wire -- very easy to do.  I learned relatively recently that it is
not so hard to exceed the elastic limit of hardened music wire:  Springs are
wound from hardened wire, not from the annealed wire!

Anyway, I may still need hardened wire or rod, but now I can calculate that
a 3/16" rod will be five times the stiffness of the 1/8" rod.  This may not
help for the pulley shaft, unless I choose to drill out all the pulleys, but
it should do fine for the other application.

I plan to start with what's on hand for this latter case and see whether a
problem develops.  McMaster won't be open till Monday anyway.  (Eat your
hearts out, those of you who can't "will call" from McMaster!)

Bruce

Bruce
NJ


On Sat, Nov 30, 2013 at 3:42 PM, David E. Smucker
<davesmucker at hotmail.com>wrote:

>
>
> 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
>
>
______________________________________________________________
TheForge mailing list
Home: http://mailman.qth.net/mailman/listinfo/theforge
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:TheForge at mailman.qth.net

TheForge mail list group photo site is
http://www.shutterfly.com
Login: blacksmithblacksmith at hotmail.com
Password: anvil

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html