Drawing symbol - a letter inside a circle

[lawriemcf]

I am building an opposed piston engine which I downloaded. It has its origins in the December 1977 issue of Popular Science.

On the drawings it has a number of letters inside a small circle. These paper adjacent to dimensions. they are (separately) a C, an S, and a P.

Can anyone enlighten me as to what these letters are referring to.

Thanks

Lawrie

View attachment opposed piston engine.pdf

 

[Cogsy]

I can only guess based on having a look. Possibly the C refers to 'centre-line' or something like that. I guess this based on some of the drawings, such as the flywheel, gudgeon pin and connecting rod which don't have full dimensions for the holes. Really just a guess though. The P and S I have no idea but I'd be tempted to ignore them myself.

 

[ruzzie]

P
Projected Tolerance Zone - applies to a hole in which a pin, stud, screw, etc., is to be inserted. It controls the perpendicularity of the hole to the extent of the projection from the hole and as it relates to the mating part clearance. The projected tolerance zone extends above the surface of the part to the functional length of the pin, stud, and screw relative to its assembly with the mating part.
S
Regardless of feature size

 

[Jasonb]

It is in the appendix of Elmer's book, see pdf

http://www.john-tom.com/ElmersEngines/ShopWisdomRevNov07.pdf

 

[bazmak]

I have been a draftsman all my working life and never come across
these symbles.Dont think they are in modern british standards
but have been used in this instance by the engine designer to replace
BS refs to limits and fits and surface finishes.Lot less complicated for the
model engineer

 

[lawriemcf]

Thanks guys

There's no doubt about the knowledge that is out there in our community.


Much appreciated


Lawrie