+// hinge plan
+hp_rn = hingescrew_nut_dia;
+hp_r2 = hp_rn + hinger_th;
+
+hppU = lpp13;
+hppS = epp2o[1] + [0,-1] * case_th_bottom;
+hp_k = 0.5 * (hppU[1] - hppS[1] + foldover_gap);
+
+hppM = [ epp4[0] - foldover_hinger_gap - hp_r2,
+ 0.5 * (hppU + hppS)[1] ];
+hppT = hppM + 0.5 * [0,+1] * hp_k;
+hppB = hppM + 0.5 * [0,-1] * hp_k;
+