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MMD > Archives > January 2012 > 2012.01.13 > 02Prev  Next

Testing a Key Striking Pneumatic
By John A. Tuttle

Hi All,  Simple question: How much weight (in grams) should it take
to collapse a striker pneumatic at least 90% of its travel?  I ask
because I've been shooting a series of YouTube videos about removing,
recovering, and installing strikers and it dawned on me that I hadn't
included any information about testing.  So, in figuring out what sort
of tests one could run to determine the quality of the workmanship,
the only one that eluded me was 'how much effort it should take to
fully collapse the pneumatic'.

Along the same line, I considered using vacuum to make the
determination, but how many people are going to have a vacuum source
that's controllable and accurate down to one inch or less.

Having recovered more strikers than I care to remember, I consider
myself somewhat of a pro.  I'm keenly aware of all the possible problems
and how they can be avoided.  So, when I got done making one while
shooting a recent video, I decided to test it using precise Ohaus
weights.  I didn't know what to expect, so I started at one ounce.

Considering that the total operating area of the pneumatic is one inch
(the total span minus the thickness of the two pieces of wood), if the
bellow was collapsed 90%, that would be 0.9 inch.  I found that one
ounce collapsed the pneumatic 93%, and it took 20 grams of weight to
close it 90%.

Unfortunately, I don't have a vacuum gauge that's accurate down to
1/2 inch, but at what registers as one inch on the gauge closed the
pneumatic quite smartly down to 95% of its total travel.  By the time
I turned the vacuum pump down to the point where the pneumatic was
closed 90%, the gauge wasn't even moving a hair off the zero setting.

While I realize that the pneumatic is probably 'great' by most
standards, I'm still left wondering how a novice can easily determine
if they've done a satisfactory job without running some sort of a test.
And, it seems to me that applying a weight is about as easy as it gets.
Question is: what's the right size weight?

John A Tuttle
Brick, New Jersey, USA

(Message sent Fri 13 Jan 2012, 16:09:33 GMT, from time zone GMT-0500.)

Key Words in Subject:  Key, Pneumatic, Striking, Testing

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