In my concrete sectional garage, used as a workshop, is a manhole
cover some 8" below the surface of the concrete floor. The edges
of the hole are rounded over, from when whoever installed the
garage and floor, something like this:


##### #####
###### ######
####### ####### # = concrete floor.
####### #######
#######------ --------####### - = cast iron cover.
*******= =******* * = hardcore, I imagine.
*******= =*******
%%%%%%%= =%%%%%%%
%%%%%%%= =%%%%%%% % = subsoil, I should think.
%%%%%%%= =%%%%%%%
%%%%%%%= =%%%%%%%
%%%%%%%= =%%%%%%%
%%%%%%%= =%%%%%%%
%%%%%%%=######V#######=%%%%%%% V = drain
%%%%%%%=##############=%%%%%%%


Anyway, the cover is cracked, and the deep hole in the middle is
dangerous. Sometimes, the smell is unpleasant. I want to bodge this,
not spending money. If I stitch-drill around the top, or zap it with
my Stihl saw, break out some concrete, and put in a frame of 4x2
treated, muck up behind the frame, batten and cut a piece of
shuttering ply to fit, will that do the job? Any better (cheap) ideas?