Performance was much better in BlockSCAD on the MacBook (though I got a warning about excessive RAM usage in Safari).

Unfortunately things bogged down again in OpenSCAD after I exported the code, and even when I manually reduced the number of passes to get a rendering things look rather rough.

Suggestions on improving the performance of:
https://www.blockscad3d.com/community/projects/973519
(see attached)

would be welcome.
William

Two changes seem to have helped:
 - adding render() before the Endmills definition - increasing the height of the subtracted cylinders
module endmillcut(emd) {  render() {cylinder(r1=(emd / 2), r2=(emd / 2), h=(radius * 2), center=false);}}
module annulus(od, id, ht) {  difference() {    cylinder(r1=(od / 2), r2=(od / 2), h=(ht * 1.1), center=false);
    cylinder(r1=(id / 2), r2=(id / 2), h=(ht * 1.2), center=false);  }}
The rendering is still painfully slow though, pretty much unusable on a 1.4GHz quad-core i5 w/ 16 GBs RAM.
Does BlockSCAD offload rendering to a server or something?
William