# Symmetry & MPC's **URL:** \ **Category:** General Questions\ **Created:** [May 19, 2026, 4:08pm UTC](https://prepomax.discourse.group/t/symmetry-mpcs/3483 "2026-05-19T16:08:37Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![alpha-beta](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/alpha-beta/32/8109_2.png) [@alpha-beta](https://prepomax.discourse.group/u/alpha-beta)\ **Post date:** [May 19, 2026, 4:08pm UTC](https://prepomax.discourse.group/t/symmetry-mpcs/3483/1 "2026-05-19T16:08:37Z")
Hi all, Pretty basic question, I’ve been using abaqus & hypermesh/optistruct for about 6 years but am looking into prepomax and I’m having some trouble with setting up a model for axisymmetry and using MPC’s. It seems to be really challenging to apply a symmetry constraint (across say the X plane [Ux=0]) and apply MPC’s to faces adjacent to the symmetry plane at the same time without overconstraining the model. In other software I would usually select a face to select most of the nodes for the MPC/rigid and then use an edge of that face to deselect the nodes that are already constrained by the symmetry constraint (or vice versa). Hopefully this makes sense - Is there some trick I am missing? Thanks! ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/d/dcd28590112eb19d4da43e6f3c8e26117ac7067b.jpeg) ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [May 19, 2026, 4:15pm UTC](https://prepomax.discourse.group/t/symmetry-mpcs/3483/2 "2026-05-19T16:15:50Z")
I assume that by MPCs, you mean rigid body constraint. Indeed, it can’t be applied to nodes with boundary conditions. And a way around it is exactly what you described - create a node set including surface nodes and deselect an edge/face on which overconstraint would occur. This is often done for cyclic symmetric models too in order to avoid conflicts between rigid body constraints (used e.g. to apply torsion) and slave nodes of the cyclic symmetry tie constraint - see this thread: [Cyclic symmetry](https://prepomax.discourse.group/t/cyclic-symmetry/58) ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/c/cb94ac1961957dfa480d951ab85d2d4c6c2610bb.png) ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/0/0e2a15eba840adcc6708ab3346cd57ef57a69f31.png) So the key is to create a node set first and then select it for boundary condition definition: ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/c/c99c7caa349f0fc886e8a2f42644641fa182991c.png) The same approach is sometimes used in Abaqus too. ---
**Author:** ![alpha-beta](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/alpha-beta/32/8109_2.png) [@alpha-beta](https://prepomax.discourse.group/u/alpha-beta)\ **Post date:** [May 19, 2026, 4:31pm UTC](https://prepomax.discourse.group/t/symmetry-mpcs/3483/3 "2026-05-19T16:31:36Z")
Hi, thanks for the fast response! Yes this is exactly the way I am used to dealing with it in abaqus & optistruct! I tried creating the node sets first, but couldn’t seem to select the edge to remove just those nodes. I don’t know if I am doing something wrong but I am doing the following: 1. Select the face to add all symmetry nodes (holding shift to select multiple faces if required) 2. Release shift, press and hold ctrl, hover over the edge I want to deselect, when it highlights orange, I click (whilst still holding ctrl). 3. Rather than just deselecting the edge nodes, everything is deselected. ---
**Author:** ![alpha-beta](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/alpha-beta/32/8109_2.png) [@alpha-beta](https://prepomax.discourse.group/u/alpha-beta)\ **Post date:** [May 19, 2026, 4:34pm UTC](https://prepomax.discourse.group/t/symmetry-mpcs/3483/4 "2026-05-19T16:34:59Z")
having written this, I have tried again and found that it does work exactly as expected - perhaps I was just being impatient / imprecise with my clicks earlier! Thanks again and sorry for the pointless post 🤦‍♂️ ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [May 19, 2026, 5:25pm UTC](https://prepomax.discourse.group/t/symmetry-mpcs/3483/5 "2026-05-19T17:25:34Z")
Yeah, Ctrl removes items from the selection. Sometimes you may want to change the selection filter to avoid accidentally picking other entities, such as faces instead of edges. But the default “Surfaces, edges and vertices” mode is usually sufficient. ---
**Author:** ![alpha-beta](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/alpha-beta/32/8109_2.png) [@alpha-beta](https://prepomax.discourse.group/u/alpha-beta)\ **Post date:** [May 19, 2026, 11:22pm UTC](https://prepomax.discourse.group/t/symmetry-mpcs/3483/6 "2026-05-19T23:22:29Z")
Yes having played with it a bit more it looks like I was de-selecting another surface (that wasn’t selected) that shared an edge with the surface I had originally clicked to select most of the nodes.