[AT] O.T. Woodruff vs straight keys

[charlie hill]

Larry, you reminded me of something.  Years ago I had buddies who raced go 
carts.
They often ran souped up 5hp B&S engines.  One of the tricks was to run a 
3HP flywheel
on the 5HP engine to reduce weight.  In order to do that they had a special 
crank key
with a slight offset in it to get the timing back to the correct setting.

Have you ever run into that?

Charlie

-----Original Message----- 
From: Rena Glover Goss
Sent: Saturday, August 12, 2017 11:42 AM
To: Antique tractor email discussion group
Subject: Re: [AT] O.T. Woodruff vs straight keys

A key can be used as a safety limiter on torque so that it shears instead of 
breaking gear teeth, etc.  In that case, the length of the key can be used 
to adjust the break-away torque load.  Some small engines (like Briggs) use 
a particular metal for the key to get this type of safety.  In the lawnmower 
repair shop business, I often ran into engines where the owners had replaced 
the OEM key with a steel one.  I presume they thought that "any ol' key" 
would do the job.  Never mind that when they hit a gas pipe with their 
lawnmower, they twisted off the crank shaft!


Larry
---- Dennis Johnson <moscowengnr at outlook.com> wrote:
> I think there are 2 main reasons for woodruff keys
> 1 - these keys are contained from side to side so they cannot slip. You 
> can also use other types of key ways that enclose the keys, but the most 
> common is to cut keyway to the end of the shaft.
> 2 - the woodruff keys may take less material out of the shaft. This might 
> weaken the shaft slightly less.
>
> Dennis
>
> Sent from my iPad
>
> > On Aug 11, 2017, at 8:13 PM, "joehardy at epix.net" <joehardy at epix.net> 
> > wrote:
> >
> > My brother is rebuilding a corn chopper and having difficulty replacing 
> > bearings on the pick up head. Couldn't get to slide the bevel gears off 
> > drive shaft. He asked me why woodruff keys were used instead of straight 
> > keys. Thought I'd throw his question out to our group. Ref: Read 
> > discussion on Practical Machinist. Joe Hardisky, Ryman Farm, Dallas, PA
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