diff --git a/sim-test/rigid-test/rearAxle-mod/config.json b/sim-test/rigid-test/rearAxle-mod/config.json
index 4e98b13..9fb800c 100644
--- a/sim-test/rigid-test/rearAxle-mod/config.json
+++ b/sim-test/rigid-test/rearAxle-mod/config.json
@@ -4,21 +4,21 @@
 
     "DBC": [
         {
-            "min": [-0.1, 0.4, -0.1],
-            "max": [0.6, 0.6, 1.1]
+            "min": [-0.01, 0.4, 0.3],
+            "max": [0.07, 0.6, 0.6]
         }
     ],
 
     "NBC": [
         {
-            "min": [-0.1, 0.8, -0.1],
-            "max": [1.1, 1.1, 1.1],
-            "force": [1, 0, 0]
+            "min": [0.3, -0.01, 0.2],
+            "max": [0.6, 0.05, 0.6],
+            "force": [0, 1, 0]
         },
         {
-            "min": [-0.1, -0.1, -0.1],
-            "max": [1.1, 0.2, 1.1],
-            "force": [1, 0, 0]
+            "min": [0.3, 0.95, 0.2],
+            "max": [0.6, 1.01, 0.6],
+            "force": [0, -1, 0]
         }
     ]
 }
diff --git a/sim-test/rigid-test/rearAxle-mod/config.json.in b/sim-test/rigid-test/rearAxle-mod/config.json.in
index db267c8..ab4783e 100644
--- a/sim-test/rigid-test/rearAxle-mod/config.json.in
+++ b/sim-test/rigid-test/rearAxle-mod/config.json.in
@@ -4,21 +4,21 @@
 
     "DBC": [
         {
-            "min": [-0.1, 0.4, -0.1],
-            "max": [0.6, 0.6, 1.1]
+            "min": [-0.01, 0.4, 0.3],
+            "max": [0.07, 0.6, 0.6]
         }
     ],
 
     "NBC": [
         {
-            "min": [-0.1, 0.8, -0.1],
-            "max": [1.1, 1.1, 1.1],
-            "force": [1, 0, 0]
+            "min": [0.3, -0.01, 0.2],
+            "max": [0.6, 0.05, 0.6],
+            "force": [0, 1, 0]
         },
         {
-            "min": [-0.1, -0.1, -0.1],
-            "max": [1.1, 0.2, 1.1],
-            "force": [1, 0, 0]
+            "min": [0.3, 0.95, 0.2],
+            "max": [0.6, 1.01, 0.6],
+            "force": [0, -1, 0]
         }
     ]
 }
diff --git a/src/static_sim/StaticSim.cpp b/src/static_sim/StaticSim.cpp
index d3d8ac9..51bb387 100644
--- a/src/static_sim/StaticSim.cpp
+++ b/src/static_sim/StaticSim.cpp
@@ -361,6 +361,10 @@ namespace ssim {
         );
 #endif
 
+        for (int dofI = 0; dofI < nDof; ++dofI) {
+            linSysSolver->addCoeff(dofI, dofI, 1e-5);
+        }
+
     }
 
     void StaticSim::solve() {
@@ -470,6 +474,63 @@ namespace ssim {
         }
     }
 
+    // BC only apply on surface nodes
+    // void StaticSim::setBC() {
+    //     spdlog::info("set Boundary Conditions");
+    //
+    //     // DBC
+    //     int nDBC = 0;
+    //     DBC_nI.resize(nN);
+    //     isDBC.setZero(nN);
+    //     int DBCNum = (int) DirichletBCs.size();
+    //     for (int svI = 0; svI < SVI.size(); ++svI) {
+    //         int vI = SVI(svI);
+    //         Eigen::Vector3d p = TV.row(vI);
+    //         for (int _i = 0; _i < DBCNum; ++_i) {
+    //             if (DirichletBCs[_i].inDBC(p)) {
+    //                 DBC_nI(nDBC) = vI;
+    //                 isDBC(vI) = 1;
+    //                 ++nDBC;
+    //
+    //                 break;
+    //             }
+    //         }
+    //     }
+    //     DBC_nI.conservativeResize(nDBC);
+    //     // Utils::writeOBJ(outputPath + "DBCV.obj", TV(DBC_nI, Eigen::all),
+    //     //                 Eigen::VectorXi::LinSpaced(nDBC, 0, nDBC-1));
+    //     // NBC
+    //     load.resize(0);
+    //     load.setZero(nDof);
+    //     int nNBC = 0;
+    //     Eigen::VectorXi NBC_nI(nN);
+    //     int NBCNum = (int) NeumannBCs.size();
+    //     for (int svI = 0; svI < SVI.size(); ++svI) {
+    //         int vI = SVI(svI);
+    //         Eigen::Vector3d p = TV.row(vI);
+    //         for (int _i = 0; _i < NBCNum; ++_i) {
+    //             if (NeumannBCs[_i].inNBC(p)) {
+    //                 load.segment<DIM_>(vI * DIM_) = NeumannBCs[_i].force;
+    //                 NBC_nI(nNBC) = vI;
+    //                 ++nNBC;
+    //
+    //                 break;
+    //             }
+    //         }
+    //     }
+    //     NBC_nI.conservativeResize(nNBC);
+    //     // Utils::writeOBJ(outputPath + "NBCV.obj", TV(NBC_nI, Eigen::all),
+    //     //                 Eigen::VectorXi::LinSpaced(nNBC, 0, nNBC-1));
+    //
+    //     spdlog::info("#DBC nodes: {}, #NBC particles: {}", nDBC, nNBC);
+    //
+    //     // ensure (DBC intersect NBC) = (empty)
+    //     for (int i_ = 0; i_ < DBC_nI.size(); ++i_) {
+    //         int nI = DBC_nI(i_);
+    //         load.segment<DIM_>(nI * DIM_).setZero();
+    //     }
+    // }
+
     Model StaticSim::get_mesh() {
         if (mesh_.NumVertex() == 0) {
             // fill mesh_