Re: Re: VP-mechanism: geometry symmetry and bearing fri...

From: <themaxout_at_aol.com>
Date: Mon, 25 Jul 2011 23:44:11 -0400 (EDT)

All,
 
A way to stretch wire to make it straight and keep it's properties is to
clamp one end and pull the other end to about yield stress. This makes it
take a "set" of a straight wire. As a former millwright, the usual tactic
was to use a "C" clamp on the fixed end and an "over pull" lever on the
other end, the wire being wrapped around a 2' long rebar about 6" up from the
pivoted end. No need to pull at your best Conan the Barbarian pull, just
enough to give it some yield. Letting up on the pull and noticing the wire
staying straight is a good indicator.
 
One could do calculations based upon the tension force required to yield
the wire. The wire diameter and the yield stress of the particular wire
used if need be are the parameters. I'm sure someone will reply with this
info. This also works for small diameter coiled copper tubing when used for
hydraulic line applications. That is why the tubing looks so straight on
those big machines!
 
FYI: Stress = (Applied tension force) / (Area of the wire) and should be
larger than the yield stress of the wire. Typical yield stresses of wire
are in the 60,000-80,000 #/in-2. For a .010" dia ("pi" x "r"squared) =>
60,000 #/in-2 (PSI) wire...that's about a force required of (Yield
Stress)*(Cross Section Area) => 60,000psi x .00007854in-2= 4.71#...not much so you have
to be careful.
 
Pulling to just better than 5# should do the trick, but find out the wire
yield stress and do a similar calculation. It's not necessary to let the
weight hang for a day or so...just bringing it above the yield stress works.
 
Rick
 
Rick Pangell
Editor of "The Max-Out" Newsletter of
The Magnificent Mountain Men FF Club of Colorado

 
In a message dated 7/25/2011 9:14:24 P.M. Mountain Daylight Time,
laflyer100_at_yahoo.com writes:




on the machinist blog they straightening music wire but chucking one end
in a drill motor with the wire running through a hole in a 1/4" plate or
piece of wood. the tool is held at a 45 degree angle starting next to the
chuck. Run the motor at a fairly slow speed and move the tool away from the
chuck towards the end of the wire. I was amazed how well it worked.



  
____________________________________
 From: Benjamin Saks <bensaks_at_gmail.com>
To: Indoor_Construction_at_yahoogroups.com
Sent: Monday, July 25, 2011 4:10 PM
Subject: Re: [Indoor_Construction] Re: VP-mechanism: geometry symmetry and
bearing friction


 

It's worthwhile to straighten your music wire or guitar string before
making prop shafts. Most strings come packaged in a coiled loop in a paper
envelope. The coiled wire has a memory and I've found props wobble from this.
How do I straighten mine? Well stringing them on a guitar works great if
you have one but hanging a weight off the end will do fine. I let mine
stretch for a week or so.
On Jul 25, 2011 4:37 PM, "John Kagan" <_john_kagan_at_hotmail.com_
(mailto:john_kagan_at_hotmail.com) > wrote:
> --- In _Indoor_Construction_at_yahoogroups.com_
(mailto:Indoor_Construction_at_yahoogroups.com) , Tapio Linkosalo <tapio.linkosalo_at_...> wrote:
>>
>> Looking at Treger's drawing (in INAV 125) I find that he uses 0.35mm
>> (0.0138") wire for the axis. Mine is 0.30 (0.0118"), as that size is
>> readily available, but maybe that is too thin and bends in an
>> uncontrolled manner? What size are other D fliers using?
>>
>
> If you are talking about the prop shaft (the part the rubber connects
to), I'd say .0118" is too small. I use .013" marked, which measures more
like .0135"
>
> The material will also make a difference. Guitar strings work for me -
and are cheap and readily available. I tried some stainless steel wire from
Small Parts once that didn't work well.
>
Received on Mon Jul 25 2011 - 20:44:22 CEST