Is this what you want?
dh = 2; %0.5; % adjust this to see more detains
a = 42;
h = 20;
R = 45;
N = h/dh;
m = 1;
for n = 0:1:360*N
z(m)= 0-((dh/360)*n) + .4*cosd(60*n); % add oscilation about z
r = R -(((dh/360)*n)/tand(a));
x(m)=(r)*cosd(n);
y(m)=(r)*sind(n);
m = m+1;
end
plot3(x,y,z,'b')
axis equal
