Re: Cams, John L.

[Doug Rasmussen <DougRasmussen@domain.elided>]

John L wrote:
> In retrospect, it's clear now that all FM did was make a master cam for
their production by copying a stock factory cam.  They probably took a few
cursory measurements for verification purposes and made a print.  <

 and Joel B wrote:
>Cam grinders can 'copy' cams just like Home Depot copies your house key.
 The one side has the original cam and the other side has the 'blank' cam.<

Guys,

  I was reading a book on performance cams at Barnes & Noble the other day.
 It appears from this book that production camshafts are generally not
ground by copying a master camshaft(as in a key machine).  But, instead
they use large flat plates machined in the shape of the respective intake &
exhaust camshaft lobes.  It looked like the "master" lobe pattern was on
the order of an 8-10 times enlargement of the camshaft.  The grinding
machine would have some type of pantagraph mechanism to follow the flat
pattern and translate and reduce that to appropriate motion of the grinding
wheel.  Of course, this is in the pre-cnc grinder days.  

  The advantage of using an enlarged master is obvious, it makes achieving
tolerances on the finished product easier.   If the enlarged lobe pattern
is made 10 times size and it's machined to "print" within a resonable
tolerance of .002"+/- the actual cam theoretically will have a tolerance of
.0002"+/-.   The enlarged lobe pattern is easy to machine on a cnc machine,
whereas making a 1:1 master cam to those tolerances wouldn't be easy.

  Now, unless Federal-Mogul is a completely hokey outfit they would not
make the "master" lobe patterns by just mechanically copying off a stock
cam.   That could introduce all kinds "accumulation of error" factors into
the situation.   So, I'm betting they have the actual specifications
somewhere.  Whether a consumer could ever have access to those is a
different matter. 

Doug