Added the 'extra_short' option

README.md

@@ -10,7 +10,7 @@ Currently supported router models:
 You will also need:
 
 * 3/8" collet (only when using Makita router, part #763619-3)
-* 3/8" boring bar with indexable carbide inserts, 3.75" long or more for Makita, 2.5" long for DRILL MASTER
+* 3/8" boring bar with indexable carbide inserts, 3" long or more for Makita, 2.55" long for DRILL MASTER
 * 13/16"-20 trim dies made by Dillon, Lyman, Whidden, etc; one per caliber
 * 13/16"-20 nut (comes with Lyman dies, can also be found at automotive stores, they are thread axle nuts); one per caliber
 * 4 M4x16 bolts (Makita) or 2 M5x20 bolts (DRILL MASTER)
@@ -29,9 +29,9 @@ And one-time requirements:
 
 3. Measure your boring bar and trim it if necessary.
 
-   For Makita: The optimal length is 2.75" below the base of the router. That would make a 3.75" or a 4" bar a perfect fit. The least expensive options on the market are 6" long boring bars, but while they will work, it's better to have them trimmed to 3.75" or 4" to decrease vibration and make more compact adapters. Don't trim your bars less than 3.75", but if it's shorter, you can use "short_threads" set to 1 to make a shorter adapter. 2.8" is the shortest you could go. Shorter bar means less vibration.
+   For Makita: The optimal length is with 3.5" bar but it can be longer, or shorter like 3". The least expensive options on the market are 6" long boring bars, but while they will work, it's better to have them trimmed to 3" or 3.5" to decrease vibration and make more compact adapters. Don't trim your bars less than 3", but you can use "short_threads" set to 1 to make a shorter adapter if your length is less than 3.2". 2.8" is the shortest you could go unless you use "extra_short = 1", in which case, you could go as low as 2.55" but it wouldn't be really convenient and most likely, you won't be able to use any other station. Shorter bar means less vibration.
 
-   For DRILL MASTER: Your boring bar should be at least 2.5" long. Again, shorter bar means less vibration.
+   For DRILL MASTER: Your boring bar should be at least 2.55" long. Again, shorter bar means less vibration.
 
 4. (Optional) Use OpenSCAD to generate two models, one with "is_body_only" set to 0, another set to 1. Or download pre-rendered ones. 
 

TrimmerAdapter.scad

@@ -21,7 +21,7 @@
  */
 
 // total length of the boring bar with a bit attached in millimeters
-bar_length = 95.25; // in mm; 3.75" boring bar
+bar_length = 3.5 * 25.4; // in mm; 3.5" boring bar
 
 // set "is_body_only" if you want to generate the main tube which you can print
 // with higher density as described in documentation
@@ -39,45 +39,60 @@ short_threads = 0;
 
 // if you set it to 1, threads would be a little tighter so the router won't
 // turn the adapter when starting as easily. A downside, you must not share
-// one adapter among multiple dies because threads will get destroyed. 
+// one adapter among multiple dies because threads will get destroyed.
+// If your filament shrinks too much, set to 0.
 tight_threads = 1;
 
 // You can use "additional_height" parameter to adjust the final length of the
 // adapter if default calculations don't work for you for some reason. Negative
 // to shorten, positive to elongate.
 
 // For example, Makita router allows to raise the lower level by 20mm so you
-// can specify "additional_height = -20" and save some filament
+// can specify "additional_height = -15" and save some filament
+// But it's always better to use a shorter boring bar
 additional_height = 0; // in mm
 
+// Setting "extra_short" to 1 will allow to use really short boring bars with
+// Makita routers. It will not work with Drill Master (but its design already
+// allows shorter bars).
+extra_short = 0;
+
 /*****************************************************************************
  * NO SERVICEABLE PARTS BELOW. ENTER AT YOUR OWN RISK
  ****************************************************************************/
 
 mm_in_in = 25.4;
 fn = 120; // slower rendering once, nicer look every day
 threads_size = 13 / 16 * mm_in_in; // 20.6375mm
-threads_length = short_threads ? threads_size * 0.5 : threads_size; // not less than the length of threads on the trim die
+threads_length = short_threads || extra_short ? threads_size * 0.5 : threads_size; // not less than the length of threads on the trim die
 max_bar = 14; // how long the bar extends below the threads. May depend upon the trim die and your preferred trim length
 
 is_makita = router_type == "makita" ? 1 : 0;
 is_dm2hp = is_makita ? 0 : 1;
 
+if (is_dm2hp) {
+    assert(! extra_short, "extra_short will not work with Drill Master");
+}
+
 bolt_hole_height = 30; // for mounting holes, should be more than the base_height
-center_hole = 44; // the opening at the very bottom, can be increased if more clearance is needed or decreased if your boring bar is too short. 
-main_body_inside_diameter = 32; // 
+center_hole = extra_short ? 30 : 44; // the opening at the very bottom, can be increased if more clearance is needed or decreased if your boring bar is too short.
+main_body_inside_diameter = extra_short ? 30 : 32;
 
-base_height = 10;   //  
-body_diameter = 40; // outer diameter of the tube
+base_height = 10;   //
+body_thickness = 2;
+body_diameter = main_body_inside_diameter + 2 * body_thickness; // outer diameter of the tube
 
 spaces = "                "; 
 
+// DM2hp router needs more space to fit the chuck nut, change the angle of the top cone
+taper_cone_angle = is_dm2hp ? 60 : 45;
+
 // minimum body height is base_height + threads_length 
 // minimum_body + max_bar should be equal to bar_lenght - holder_depth assuming the bit holder is completely below the base_height line
 
-holder_depth = is_makita ? 30 : is_dm2hp ? -1.5 : 0;
+holder_depth = is_makita ? 34 : is_dm2hp ? -1.5 : 0;
 
-min_height = (center_hole - threads_size) / 2 + threads_length;
+min_height = (center_hole - threads_size) / 2 / tan(taper_cone_angle) + threads_length;
 
 echo(str("min height = ", min_height, spaces));
 
@@ -121,9 +136,6 @@ dm2hp_minimum_hole_height = 37; // how long is the chuck
 slope_cone_height = 2;
 slope_cone_angle = 45;
 
-// DM2hp router needs more space to fit the chuck nut, change the angle of the top cone
-taper_cone_angle = is_dm2hp ? 60 : 45;
-
 use <./contrib/threads-library-by-cuiso-v1.scad>;
 
 module embossed () {