diff --git a/assets/locales/en.json b/assets/locales/en.json
index 79c32e881b..7cc72175af 100644
--- a/assets/locales/en.json
+++ b/assets/locales/en.json
@@ -1366,6 +1366,7 @@
   "settings.reset_intro": "These settings don't work on this computer and would keep SolidCraft from starting, so they were changed:",
   "settings.reset_title": "Settings were changed",
   "settings.supersampling_note": "Draws the view at a higher resolution and filters it down: smoother edges, lines and grid on screens below 4K. It costs GPU time: about 2.25× the pixels at 1.5× and 4× at 2×.",
+  "sheet.no_body": "there is no sheet metal body: start one with Flange > Base, or turn a plate into sheet metal with Convert to Sheet Metal (pick its large flat face)",
   "shortcut.json_error": "parameters must be JSON: {error}",
   "shortcut.no_command": "no command `{id}`; the text before the JSON must be a command id",
   "shortcut.pin": "Pin to the top of the S box",
diff --git a/assets/locales/ja.json b/assets/locales/ja.json
index 86af4e4458..51cb6e5d0c 100644
--- a/assets/locales/ja.json
+++ b/assets/locales/ja.json
@@ -1366,6 +1366,7 @@
   "settings.reset_intro": "次の設定はこのコンピューターでは使用できず、SolidCraft が起動できなくなるため変更されました:",
   "settings.reset_title": "設定が変更されました",
   "settings.supersampling_note": "ビューを高い解像度で描画してから縮小します。4K 未満の画面でエッジ、線、グリッドが滑らかになります。GPU の負荷が増えます（1.5× で約 2.25 倍、2× で 4 倍のピクセル）。",
+  "sheet.no_body": "板金ボディがありません。フランジ > Base で作成するか、板金に変換でプレートを板金に変換してください（広い平面を選択）。",
   "shortcut.json_error": "パラメータはJSON形式で指定してください: {error}",
   "shortcut.no_command": "コマンド`{id}`がありません。JSONの前のテキストはコマンドIDである必要があります",
   "shortcut.pin": "Sボックスの先頭にピン留め",
diff --git a/assets/locales/zh.json b/assets/locales/zh.json
index 409307fe80..75ed0d74e6 100644
--- a/assets/locales/zh.json
+++ b/assets/locales/zh.json
@@ -1366,6 +1366,7 @@
   "settings.reset_intro": "这些设置在此计算机上无法正常工作，会导致 SolidCraft 无法启动，因此已更改：",
   "settings.reset_title": "设置已更改",
   "settings.supersampling_note": "以更高分辨率绘制视图再缩小：在低于 4K 的屏幕上边、线和网格更平滑。会消耗 GPU 时间：1.5× 时约 2.25 倍像素，2× 时 4 倍。",
+  "sheet.no_body": "没有钣金实体：请使用法兰 > Base 创建，或使用转换为钣金将板材转换为钣金（选择其较大的平面）。",
   "shortcut.json_error": "参数必须采用 JSON 格式：{error}",
   "shortcut.no_command": "没有命令 `{id}`；JSON 前的文本必须是命令 ID",
   "shortcut.pin": "固定到 S 框顶部",
diff --git a/crates/engine/src/cmd/sheet.rs b/crates/engine/src/cmd/sheet.rs
index 9d693d3deb..fb01531518 100644
--- a/crates/engine/src/cmd/sheet.rs
+++ b/crates/engine/src/cmd/sheet.rs
@@ -206,6 +206,9 @@ fn flange(s: &mut Session, p: &Value) -> Result<Value> {
             if !matches!(position.as_str(), "inside" | "outside" | "middle") {
                 return Err(bad(cmd, "`position` must be inside, outside or middle"));
             }
+            if s.model.state().sheets.is_empty() {
+                return Err(no_sheet_body(cmd));
+            }
             let body = str_(p, "body").map(str::to_string);
             // The corner relief these flanges make, in place of the rule's; null is not given.
             let corner_relief_shape = match p.get("corner_relief_shape").filter(|v| !v.is_null()) {
@@ -451,11 +454,18 @@ fn list_rules(s: &mut Session, _p: &Value) -> Result<Value> {
     Ok(json!({"rules": rules, "active": active}))
 }
 
+fn no_sheet_body(cmd: &str) -> EngineError {
+    bad(
+        cmd,
+        "there is no sheet metal body: start one with Flange > Base, or turn a plate into sheet metal with Convert to Sheet Metal (pick its large flat face)",
+    )
+}
+
 fn sheet_of(s: &Session, p: &Value, cmd: &str) -> Result<SheetBody> {
     let st = s.model.state();
     match str_(p, "body") {
         Some(b) => st.sheets.iter().find(|x| x.body == b).cloned().ok_or_else(|| bad(cmd, format!("`{b}` is not a sheet metal body"))),
-        None => st.sheets.last().cloned().ok_or_else(|| bad(cmd, "there is no sheet metal body")),
+        None => st.sheets.last().cloned().ok_or_else(|| no_sheet_body(cmd)),
     }
 }
 
@@ -816,7 +826,7 @@ fn export_dxf(s: &mut Session, p: &Value) -> Result<Value> {
         }
         let sheets = &s.model.state().sheets;
         if sheets.is_empty() {
-            return Err(bad(cmd, "there is no sheet metal body"));
+            return Err(no_sheet_body(cmd));
         }
         // Every file is made before the first is written.
         let texts = sheets
diff --git a/crates/engine/src/cmd/sheet_tests.rs b/crates/engine/src/cmd/sheet_tests.rs
index 174ed75922..797824ff3b 100644
--- a/crates/engine/src/cmd/sheet_tests.rs
+++ b/crates/engine/src/cmd/sheet_tests.rs
@@ -37,6 +37,27 @@ fn rectangle_tool(s: &mut Session, name: &str, p0: [f64; 2], p1: [f64; 2]) {
     run(s, "sketch.finish", json!({}));
 }
 
+#[test]
+fn plain_solid_sheet_operations_explain_how_to_start_sheet_metal() {
+    let mut s = Session::default();
+    run(&mut s, "solid.box", json!({"length": 100, "width": 60, "height": 2.5}));
+    let before = s.doc.to_json();
+    for (command, params) in [
+        ("sheet.flange", json!({"type": "edge", "edges": [[50, 0, 2.5]], "height": 15})),
+        ("sheet.flat_pattern", json!({})),
+        ("sheet.export_dxf", json!({"per_body": true})),
+    ] {
+        let error = s.execute(command, &params).unwrap_err();
+        let crate::EngineError::BadParams { cmd, msg } = error else { panic!("{error}") };
+        assert_eq!(cmd, command);
+        assert_eq!(
+            msg,
+            "there is no sheet metal body: start one with Flange > Base, or turn a plate into sheet metal with Convert to Sheet Metal (pick its large flat face)"
+        );
+        assert_eq!(s.doc.to_json(), before);
+    }
+}
+
 #[test]
 fn side_edge_flanges_across_a_bend_keep_their_relief_through_rebuild_and_reopen() {
     use solidcraft_geom::Vec3;
diff --git a/crates/ui-egui/src/dialogs.rs b/crates/ui-egui/src/dialogs.rs
index 762879b809..22bea0b6f1 100644
--- a/crates/ui-egui/src/dialogs.rs
+++ b/crates/ui-egui/src/dialogs.rs
@@ -2078,7 +2078,7 @@ fn error_rows(app: &mut SolveApp, ctx: &egui::Context, d: &mut Dialog, ui: &mut
             return;
         }
         ui.vertical(|ui| {
-            crate::ui_kit::text(ui, &error, crate::ui_kit::Text::Report("error", true));
+            crate::ui_kit::text(ui, &shown_error(&error), crate::ui_kit::Text::Report("error", true));
             let response = crate::ui_kit::button(ui, "Create Issue…", crate::ui_kit::Button::Normal);
             crate::scenario::publish_handle("dialog:create_issue", response.rect.center());
             if response.clicked() {
@@ -2088,6 +2088,14 @@ fn error_rows(app: &mut SolveApp, ctx: &egui::Context, d: &mut Dialog, ui: &mut
     }
 }
 
+/// A refusal as the dialog shows it: without the engine's "invalid parameters for `id`: "
+/// prefix (the dialog already names the command), and in the interface language when the
+/// message is in the catalogs.
+fn shown_error(error: &str) -> String {
+    let msg = error.strip_prefix("invalid parameters for `").and_then(|rest| rest.split_once("`: ")).map_or(error, |(_, msg)| msg);
+    crate::i18n::tr_label(msg).to_string()
+}
+
 /// Find the Boundary Fill cells again when the tool bodies changed (keeping the choices of
 /// cells that are still there).
 fn update_fill_cells(app: &SolveApp, d: &mut Dialog) {
@@ -4944,6 +4952,15 @@ mod refused_ok_tests {
         assert_eq!(h.app.dialog.as_ref().and_then(|d| d.error.as_deref()), Some("hole depth must be positive"));
     }
 
+    #[test]
+    fn a_refusal_is_shown_without_the_engine_prefix() {
+        assert_eq!(
+            super::shown_error("invalid parameters for `sheet.flange`: there is no sheet metal body: start one with Flange > Base"),
+            "there is no sheet metal body: start one with Flange > Base"
+        );
+        assert_eq!(super::shown_error("hole depth must be positive"), "hole depth must be positive");
+    }
+
     #[test]
     fn the_error_stays_while_the_inputs_do() {
         let mut h = hole_dialog();
diff --git a/crates/ui-egui/src/i18n.rs b/crates/ui-egui/src/i18n.rs
index 33c18873bc..cc10d39814 100644
--- a/crates/ui-egui/src/i18n.rs
+++ b/crates/ui-egui/src/i18n.rs
@@ -500,6 +500,17 @@ mod tests {
         }
     }
 
+    #[test]
+    fn missing_sheet_metal_guidance_uses_the_message_catalog() {
+        let _scope = scope("ja");
+        let message = "there is no sheet metal body: start one with Flange > Base, or turn a plate into sheet metal with Convert to Sheet Metal (pick its large flat face)";
+        let error = format!("invalid parameters for `sheet.flange`: {message}");
+        let translated = tr("sheet.no_body");
+        assert_ne!(translated, "sheet.no_body");
+        assert_ne!(translated, message);
+        assert_eq!(crate::friendly_error("sheet.flange", &error), format!("{}: {translated}", tr_label("Flange")));
+    }
+
     #[test]
     fn keys_and_engine_labels_translate_with_english_fallback() {
         let ja = Locale::for_language("ja");
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index 8c90ae6d8d..91ef3eb28b 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -1908,12 +1908,13 @@ pub fn command_label(id: &str) -> &str {
     solidcraft_engine::find_command(id).map_or(id, |c| c.label)
 }
 
-/// An engine error with the command's label instead of its id: "Shell: offset must be …". The
-/// label follows the interface language; the engine's sentence stays as the engine wrote it.
+/// An engine error with the command's label instead of its id: "Shell: offset must be …".
+/// The command label and catalogued engine messages follow the interface language.
 pub fn friendly_error(id: &str, e: &str) -> String {
     let label = i18n::tr_label(command_label(id));
     let msg = e.replace(&format!("invalid parameters for `{id}`: "), "").replace(&format!("{id}: "), "").replace(&format!("`{id}`"), label);
-    if msg.starts_with(label) { msg } else { format!("{label}: {msg}") }
+    let msg = i18n::tr_label(&msg);
+    if msg.starts_with(label) { msg.to_string() } else { format!("{label}: {msg}") }
 }
 
 pub fn now_ms() -> f64 {