feat(machines): assign each nest a machine and keep the support grid per machine

The support grid was one shared support-grid.json, off by default, and a nest
had no machine at all, so a plasma table and a fiber laser could not have
different grids, and nothing could pick machine-specific behavior later
(lead-ins differ between laser and plasma; tabbing depends on the grid).

- Nest.Machine (id + name) persists as top-level `machine` in nest.json;
  malformed values load as none.
- MachineConfig.SupportGrid holds each machine's grid; a machine without one
  still falls back to the legacy support-grid.json.
- New and BOM import assign the Tools > Nest Defaults machine (first by name
  when none is chosen) and give the nest that machine's grid.
- Nest > Machine reassigns a nest and swaps in the new machine's grid;
  Nest > Support Grid saves machine defaults to the nest's machine.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest.Core/Nest.cs

@@ -57,6 +57,9 @@ namespace OpenNest
 
         public Units Units { get; set; }
 
+        /// <summary>The machine this nest is cut on, or null when none is assigned.</summary>
+        public NestMachine Machine { get; set; }
+
         public DateTime DateCreated { get; set; }
 
         public DateTime DateLastModified { get; set; }

OpenNest.Core/NestMachine.cs

@@ -0,0 +1,21 @@
+using System;
+
+namespace OpenNest
+{
+    /// <summary>
+    /// The machine a nest is cut on: the id of its machine configuration plus the name it had,
+    /// so a nest still says which machine it was made for on a PC without that configuration.
+    /// </summary>
+    public sealed class NestMachine
+    {
+        public NestMachine(Guid id, string name)
+        {
+            Id = id;
+            Name = name ?? string.Empty;
+        }
+
+        public Guid Id { get; }
+
+        public string Name { get; }
+    }
+}

OpenNest.Data/MachineConfig.cs

@@ -14,6 +14,12 @@ public class MachineConfig
     /// <summary>Acceleration limits; null until entered, when <see cref="GetMotionOrPlaceholder"/> stands in.</summary>
     public MotionConfig? Motion { get; set; }
 
+    /// <summary>
+    /// The support grid nests assigned this machine rest on; null until saved from
+    /// Nest &gt; Support Grid, when the legacy shared support-grid.json stands in.
+    /// </summary>
+    public SupportGridSettings? SupportGrid { get; set; }
+
     public MotionConfig GetMotionOrPlaceholder() => Motion ?? MotionConfig.Placeholder(Units);
 
     public ThicknessConfig? GetParameters(string material, double thickness) =>

OpenNest.Data/NestDefaults.cs

@@ -46,6 +46,12 @@ public sealed class NestDefaults
 
     public Spacing EdgeSpacing { get; set; } = new(1, 1, 1, 1);
 
+    /// <summary>
+    /// The machine configuration new nests are assigned, or null to use the first machine
+    /// by name. An id with no configuration on file falls back the same way.
+    /// </summary>
+    public Guid? MachineId { get; set; }
+
     /// <summary>
     /// The built-in defaults used when no file exists and for every field
     /// that is missing or invalid. Matches the historical
@@ -149,6 +155,10 @@ public sealed class NestDefaults
         )
             defaults.EdgeSpacing = new Spacing(left, bottom, right, top);
 
+        if (dto.MachineId is { ValueKind: JsonValueKind.String } machineId
+            && Guid.TryParse(machineId.GetString(), out var machine) && machine != Guid.Empty)
+            defaults.MachineId = machine;
+
         return defaults;
     }
 
@@ -166,6 +176,7 @@ public sealed class NestDefaults
             Quadrant = plate.Quadrant,
             PartSpacing = plate.PartSpacing,
             EdgeSpacing = plate.EdgeSpacing,
+            MachineId = nest.Machine?.Id,
         };
     }
 
@@ -203,6 +214,7 @@ public sealed class NestDefaults
             PartSpacing = Convert(PartSpacing),
             EdgeSpacing = new Spacing(Convert(EdgeSpacing.Left), Convert(EdgeSpacing.Bottom),
                 Convert(EdgeSpacing.Right), Convert(EdgeSpacing.Top)),
+            MachineId = MachineId,
         };
     }
 
@@ -239,6 +251,7 @@ public sealed class NestDefaults
                 Right = EdgeSpacing.Right,
                 Top = EdgeSpacing.Top,
             },
+            MachineId = MachineId is { } machineId ? JsonSerializer.SerializeToElement(machineId.ToString()) : null,
         };
 
         var json = JsonSerializer.Serialize(dto, JsonOptions);
@@ -319,6 +332,9 @@ public sealed class NestDefaults
         public int? Quadrant { get; init; }
         public double? PartSpacing { get; init; }
         public SpacingDto? EdgeSpacing { get; init; }
+        // Raw JSON for the same reason as Units.
+        [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+        public JsonElement? MachineId { get; init; }
     }
 
     private sealed record SizeDto

OpenNest.IO.Tests/NestMachinePersistenceTests.cs

@@ -0,0 +1,104 @@
+using System.IO.Compression;
+using System.Text;
+using System.Text.Json.Nodes;
+using OpenNest.Geometry;
+
+namespace OpenNest.IO.Tests;
+
+/// <summary>
+/// The nest's assigned machine persists as top-level <c>machine</c> (<c>id</c> and <c>name</c>);
+/// a nest without one writes no key, and a malformed one loads as none.
+/// </summary>
+public class NestMachinePersistenceTests
+{
+    private static readonly NestMachine Machine = new(Guid.Parse("6f1a3c2e-5b7d-4e8f-9a0b-1c2d3e4f5a6b"), "Fiber 1");
+
+    private static Nest NestWith(NestMachine machine)
+    {
+        var nest = new Nest("machine") { Machine = machine };
+        nest.PlateDefaults.Size = new Size(48, 96);
+        nest.CreatePlate();
+        return nest;
+    }
+
+    private static MemoryStream Write(Nest nest)
+    {
+        var stream = new MemoryStream();
+        Assert.True(new NestWriter(nest).Write(stream));
+        stream.Position = 0;
+        return stream;
+    }
+
+    private static JsonNode NestJson(MemoryStream zip)
+    {
+        zip.Position = 0;
+        using var archive = new ZipArchive(zip, ZipArchiveMode.Read, leaveOpen: true);
+        using var reader = new StreamReader(archive.GetEntry("nest.json")!.Open(), Encoding.UTF8);
+        var json = JsonNode.Parse(reader.ReadToEnd())!;
+        zip.Position = 0;
+        return json;
+    }
+
+    private static MemoryStream Rewrite(MemoryStream zip, Action<JsonNode> edit)
+    {
+        var json = NestJson(zip);
+        edit(json);
+        var copy = new MemoryStream();
+        zip.Position = 0;
+        zip.CopyTo(copy);
+        using (var archive = new ZipArchive(copy, ZipArchiveMode.Update, leaveOpen: true))
+        {
+            archive.GetEntry("nest.json")!.Delete();
+            using var writer = new StreamWriter(archive.CreateEntry("nest.json").Open(), new UTF8Encoding(false));
+            writer.Write(json.ToJsonString());
+        }
+        copy.Position = 0;
+        return copy;
+    }
+
+    [Fact]
+    public void MachineRoundTrips()
+    {
+        var reopened = new NestReader(Write(NestWith(Machine))).Read();
+
+        Assert.Equal(Machine.Id, reopened.Machine!.Id);
+        Assert.Equal("Fiber 1", reopened.Machine.Name);
+    }
+
+    [Fact]
+    public void NestWithoutMachine_WritesNoKeyAndLoadsWithoutOne()
+    {
+        var zip = Write(NestWith(null));
+
+        Assert.False(NestJson(zip).AsObject().ContainsKey("machine"));
+        Assert.Null(new NestReader(zip).Read().Machine);
+    }
+
+    [Theory]
+    [InlineData("\"Fiber 1\"")]
+    [InlineData("{\"id\":42,\"name\":\"Fiber 1\"}")]
+    [InlineData("{\"id\":\"not-a-guid\",\"name\":\"Fiber 1\"}")]
+    [InlineData("{\"id\":\"00000000-0000-0000-0000-000000000000\"}")]
+    [InlineData("{\"name\":\"Fiber 1\"}")]
+    public void MalformedMachine_LoadsAsNone(string machine)
+    {
+        var zip = Rewrite(Write(NestWith(Machine)), json => json["machine"] = JsonNode.Parse(machine));
+
+        var reopened = new NestReader(zip).Read();
+
+        Assert.Null(reopened.Machine);
+        Assert.Equal("machine", reopened.Name);
+    }
+
+    [Fact]
+    public void MachineWithoutName_LoadsWithEmptyName()
+    {
+        var zip = Rewrite(Write(NestWith(Machine)),
+            json => json["machine"] = JsonNode.Parse($"{{\"id\":\"{Machine.Id}\",\"name\":7}}"));
+
+        var reopened = new NestReader(zip).Read();
+
+        Assert.Equal(Machine.Id, reopened.Machine!.Id);
+        Assert.Equal("", reopened.Machine.Name);
+    }
+}

OpenNest.IO/NestFormat.cs

@@ -28,6 +28,15 @@ namespace OpenNest.IO
             public string AssistGas { get; init; } = "";
             public string Status { get; init; } = "Quote";
             public string MadeBy { get; init; } = "";
+
+            /// <summary>
+            /// The machine the nest is cut on. Omitted when none is assigned; older files and
+            /// older readers simply have none.
+            /// </summary>
+            [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+            [JsonConverter(typeof(LenientMachineConverter))]
+            public MachineDto Machine { get; init; }
+
             public double Thickness { get; init; }
             public MaterialDto Material { get; init; } = new();
             public PlateDefaultsDto PlateDefaults { get; init; } = new();
@@ -63,6 +72,43 @@ namespace OpenNest.IO
             public SupportBedDto SupportBed { get; init; }
         }
 
+        /// <summary>A machine configuration's id and the name it had when the nest was saved.</summary>
+        public record MachineDto
+        {
+            public Guid Id { get; init; }
+            public string Name { get; init; } = "";
+        }
+
+        /// <summary>
+        /// Reads a malformed or wrongly typed machine, or one without a valid id, as none instead
+        /// of failing the whole nest. A missing or wrongly typed name reads as empty.
+        /// </summary>
+        public sealed class LenientMachineConverter : JsonConverter<MachineDto>
+        {
+            public override MachineDto Read(ref Utf8JsonReader reader, Type typeToConvert,
+                JsonSerializerOptions options)
+            {
+                using var document = JsonDocument.ParseValue(ref reader);
+                var machine = document.RootElement;
+                if (machine.ValueKind != JsonValueKind.Object
+                    || !machine.TryGetProperty("id", out var id) || id.ValueKind != JsonValueKind.String
+                    || !Guid.TryParse(id.GetString(), out var guid) || guid == Guid.Empty)
+                    return null;
+                var name = machine.TryGetProperty("name", out var nameElement) && nameElement.ValueKind == JsonValueKind.String
+                    ? nameElement.GetString()
+                    : "";
+                return new MachineDto { Id = guid, Name = name };
+            }
+
+            public override void Write(Utf8JsonWriter writer, MachineDto value, JsonSerializerOptions options)
+            {
+                writer.WriteStartObject();
+                writer.WriteString("id", value.Id);
+                writer.WriteString("name", value.Name ?? "");
+                writer.WriteEndObject();
+            }
+        }
+
         /// <summary>
         /// A support bed layout. <see cref="Type"/> names the layout: only <c>grid</c>, a regular
         /// grid of contact points, so far. Lengths are in the nest's units.

OpenNest.IO/NestReader.cs

@@ -539,6 +539,7 @@ namespace OpenNest.IO
                 ? status
                 : NestStatus.Quote;
             nest.MadeBy = dto.MadeBy ?? "";
+            nest.Machine = dto.Machine is { } machine ? new NestMachine(machine.Id, machine.Name) : null;
 
             // Nest-level material and thickness (fall back to PlateDefaults for old files)
             var pd = dto.PlateDefaults;

OpenNest.IO/NestWriter.cs

@@ -105,6 +105,9 @@ namespace OpenNest.IO
                 AssistGas = nest.AssistGas ?? "",
                 Status = nest.Status.ToString(),
                 MadeBy = nest.MadeBy ?? "",
+                Machine = nest.Machine is { } machine
+                    ? new MachineDto { Id = machine.Id, Name = machine.Name }
+                    : null,
                 Thickness = nest.Thickness,
                 Material = new MaterialDto
                 {

OpenNest.Tests/Data/LocalJsonProviderTests.cs

@@ -166,4 +166,44 @@ public class LocalJsonProviderTests : IDisposable
         Assert.NotNull(loaded);
         Assert.Equal(1, loaded.SchemaVersion);
     }
+
+    [Fact]
+    public void SaveMachine_RoundTripsTheSupportGrid()
+    {
+        var provider = CreateProvider();
+        var machine = new MachineConfig
+        {
+            Name = "Plasma",
+            SupportGrid = new SupportGridSettings
+            {
+                Enabled = true,
+                Units = Units.Millimeters,
+                PitchX = 50,
+                PitchY = 40,
+                OffsetX = -5,
+                StabilityMargin = 6,
+            },
+        };
+
+        provider.SaveMachine(machine);
+        var grid = provider.GetMachine(machine.Id)!.SupportGrid!;
+
+        Assert.True(grid.Enabled);
+        Assert.Equal(Units.Millimeters, grid.Units);
+        Assert.Equal(50, grid.PitchX);
+        Assert.Equal(40, grid.PitchY);
+        Assert.Equal(-5, grid.OffsetX);
+        Assert.Equal(6, grid.StabilityMargin);
+    }
+
+    [Fact]
+    public void MachineWithoutSupportGrid_LoadsWithNone()
+    {
+        var provider = CreateProvider();
+        var machine = new MachineConfig { Name = "Laser" };
+
+        provider.SaveMachine(machine);
+
+        Assert.Null(provider.GetMachine(machine.Id)!.SupportGrid);
+    }
 }

OpenNest.Tests/Data/NestDefaultsTests.cs

@@ -307,4 +307,49 @@ public class NestDefaultsTests : IDisposable
         Assert.Equal(1, loaded.PartSpacing);
         Assert.Equal(new Spacing(1, 1, 1, 1), loaded.EdgeSpacing);
     }
+
+    [Fact]
+    public void MachineId_RoundTrips()
+    {
+        var id = Guid.NewGuid();
+        new NestDefaults { MachineId = id }.Save(_path);
+
+        Assert.Equal(id, NestDefaults.Load(_path).MachineId);
+    }
+
+    [Fact]
+    public void MachineId_Unset_IsNotWrittenAndLoadsAsNull()
+    {
+        new NestDefaults().Save(_path);
+
+        Assert.DoesNotContain("machineId", File.ReadAllText(_path));
+        Assert.Null(NestDefaults.Load(_path).MachineId);
+    }
+
+    [Theory]
+    [InlineData("42")]
+    [InlineData("\"not-a-guid\"")]
+    [InlineData("\"00000000-0000-0000-0000-000000000000\"")]
+    public void MachineId_Invalid_LoadsAsNullAndKeepsOtherFields(string machineId)
+    {
+        File.WriteAllText(_path, $"{{\"partSpacing\": 4, \"machineId\": {machineId}}}");
+
+        var loaded = NestDefaults.Load(_path, out var status);
+
+        Assert.Equal(NestDefaultsStatus.Ok, status);
+        Assert.Null(loaded.MachineId);
+        Assert.Equal(4, loaded.PartSpacing);
+    }
+
+    [Fact]
+    public void FromNest_AndConvertedTo_KeepTheMachine()
+    {
+        var id = Guid.NewGuid();
+        var nest = new Nest { Units = Units.Inches, Machine = new NestMachine(id, "Plasma") };
+
+        var defaults = NestDefaults.FromNest(nest);
+
+        Assert.Equal(id, defaults.MachineId);
+        Assert.Equal(id, defaults.ConvertedTo(Units.Millimeters).MachineId);
+    }
 }

OpenNest/Forms/BomImportForm.cs

@@ -415,7 +415,7 @@ namespace OpenNest.Forms
             var importErrors = new List<string>();
             // Read when the nests are created, warning (once per session) like New does.
             var clamps = MachineSettings.LoadClampSettings(this);
-            var supportGrid = MachineSettings.LoadSupportGridSettings();
+            var machine = MachineSettings.DefaultMachine(_defaults, MachineSettings.LoadMachines());
 
             foreach (var group in groups)
             {
@@ -439,10 +439,10 @@ namespace OpenNest.Forms
                     jobName,
                     nest =>
                     {
-                        // As New does: saved defaults, then the machine clamps in those units.
+                        // As New does: saved defaults, then the machine clamps and grid in those units.
                         _defaults.ApplyTo(nest);
                         clamps.ApplyToNewNest(nest);
-                        supportGrid.ApplyToNewNest(nest);
+                        MachineSettings.AssignMachine(nest, machine);
                     }
                 );
                 importErrors.AddRange(result.Errors);

OpenNest/Forms/MachineSettings.cs

@@ -79,9 +79,57 @@ namespace OpenNest.Forms
             return settings;
         }
 
-        /// <summary>The persisted machine support grid; never throws, and loads as off when unreadable.</summary>
-        public static SupportGridSettings LoadSupportGridSettings() =>
-            SupportGridSettings.Load(SupportGridSettings.DefaultPath);
+        /// <summary>
+        /// The machine new nests are assigned: the nest defaults' machine when it is on file,
+        /// otherwise the first by name, or null when there are none.
+        /// </summary>
+        public static MachineConfig DefaultMachine(NestDefaults defaults, IEnumerable<MachineConfig> machines)
+        {
+            var sorted = machines.OrderBy(m => m.Name, StringComparer.CurrentCultureIgnoreCase).ToList();
+            return sorted.FirstOrDefault(m => m.Id == defaults?.MachineId) ?? sorted.FirstOrDefault();
+        }
+
+        /// <summary>The configuration of <paramref name="machine"/>, or null when none is assigned or it is not on file.</summary>
+        public static MachineConfig FindMachine(NestMachine machine)
+        {
+            if (machine == null)
+                return null;
+            try
+            {
+                return CreateMachineProvider().GetMachine(machine.Id);
+            }
+            catch (IOException) { }
+            catch (UnauthorizedAccessException) { }
+            return null;
+        }
+
+        /// <summary>
+        /// Assigns <paramref name="machine"/> to <paramref name="nest"/> (null for none) and gives
+        /// every sheet that machine's support grid, or none when the machine gives nests no grid.
+        /// </summary>
+        public static void AssignMachine(Nest nest, MachineConfig machine)
+        {
+            nest.Machine = machine == null ? null : new NestMachine(machine.Id, machine.Name);
+            var grid = LoadSupportGridSettings(machine);
+            nest.SetSupportBed(grid.Enabled ? grid.GridFor(nest.Units) : null);
+        }
+
+        /// <summary>
+        /// The support grid of <paramref name="machine"/>; a machine without one saved yet, or no
+        /// machine, uses the legacy shared support-grid.json. Never throws, and loads as off when unreadable.
+        /// </summary>
+        public static SupportGridSettings LoadSupportGridSettings(MachineConfig machine) =>
+            machine?.SupportGrid ?? SupportGridSettings.Load(SupportGridSettings.DefaultPath);
+
+        /// <summary>Saves <paramref name="settings"/> as the support grid of the machine with <paramref name="machineId"/>.</summary>
+        public static void SaveSupportGridSettings(Guid machineId, SupportGridSettings settings)
+        {
+            var provider = CreateMachineProvider();
+            var machine = provider.GetMachine(machineId)
+                ?? throw new IOException("The machine configuration is no longer on file.");
+            machine.SupportGrid = settings;
+            provider.SaveMachine(machine);
+        }
 
         /// <summary>The single desktop entry point for the persisted machine clamp settings.</summary>
         public static ClampSettings LoadSavedClampSettings(out ClampSettingsStatus status) =>

OpenNest/Forms/MainForm.Designer.cs

@@ -93,6 +93,7 @@ namespace OpenNest.Forms
             mnuNestEdit = new System.Windows.Forms.ToolStripMenuItem();
             mnuNestClamps = new System.Windows.Forms.ToolStripMenuItem();
             mnuNestSupportGrid = new System.Windows.Forms.ToolStripMenuItem();
+            mnuNestMachine = new System.Windows.Forms.ToolStripMenuItem();
             mnuNestImportDrawing = new System.Windows.Forms.ToolStripMenuItem();
             mnuNestShapeLibrary = new System.Windows.Forms.ToolStripMenuItem();
             mnuNestDrawingLibrary = new System.Windows.Forms.ToolStripMenuItem();
@@ -600,7 +601,7 @@ namespace OpenNest.Forms
             // 
             // mnuNest
             // 
-            mnuNest.DropDownItems.AddRange(new System.Windows.Forms.ToolStripItem[] { mnuNestEdit, mnuNestClamps, mnuNestSupportGrid, mnuNestImportDrawing, mnuNestShapeLibrary, mnuNestDrawingLibrary, toolStripMenuItem7, mnuNestFirstPlate, mnuNestLastPlate, toolStripMenuItem6, mnuNestNextPlate, mnuNestPreviousPlate, toolStripMenuItem12, runAutoNestToolStripMenuItem, autoSequenceAllPlatesToolStripMenuItem, mnuNestRemoveEmptyPlates, mnuNestClear, mnuNestValidate, mnuNestPost, toolStripMenuItem19, calculateCutTimeToolStripMenuItem, toolStripMenuItem22, mnuNestAutomaticCutOff, mnuNestPlanCutting, mnuNestRemoveLeadIns });
+            mnuNest.DropDownItems.AddRange(new System.Windows.Forms.ToolStripItem[] { mnuNestEdit, mnuNestMachine, mnuNestClamps, mnuNestSupportGrid, mnuNestImportDrawing, mnuNestShapeLibrary, mnuNestDrawingLibrary, toolStripMenuItem7, mnuNestFirstPlate, mnuNestLastPlate, toolStripMenuItem6, mnuNestNextPlate, mnuNestPreviousPlate, toolStripMenuItem12, runAutoNestToolStripMenuItem, autoSequenceAllPlatesToolStripMenuItem, mnuNestRemoveEmptyPlates, mnuNestClear, mnuNestValidate, mnuNestPost, toolStripMenuItem19, calculateCutTimeToolStripMenuItem, toolStripMenuItem22, mnuNestAutomaticCutOff, mnuNestPlanCutting, mnuNestRemoveLeadIns });
             mnuNest.Name = "mnuNest";
             mnuNest.Size = new System.Drawing.Size(43, 20);
             mnuNest.Text = "&Nest";
@@ -612,6 +613,12 @@ namespace OpenNest.Forms
             mnuNestEdit.Size = new System.Drawing.Size(205, 22);
             mnuNestEdit.Text = "Edit";
             mnuNestEdit.Click += EditNest_Click;
+            //
+            // mnuNestMachine
+            //
+            mnuNestMachine.Name = "mnuNestMachine";
+            mnuNestMachine.Size = new System.Drawing.Size(205, 22);
+            mnuNestMachine.Text = "Machine";
             // 
             // mnuNestClamps
             // 
@@ -1378,6 +1385,7 @@ namespace OpenNest.Forms
         private System.Windows.Forms.ToolStripMenuItem mnuNestEdit;
         private System.Windows.Forms.ToolStripMenuItem mnuNestClamps;
         private System.Windows.Forms.ToolStripMenuItem mnuNestSupportGrid;
+        private System.Windows.Forms.ToolStripMenuItem mnuNestMachine;
         private System.Windows.Forms.ToolStripMenuItem mnuPlateEditClamps;
         private System.Windows.Forms.ToolStripMenuItem mnuNestImportDrawing;
         private System.Windows.Forms.ToolStripMenuItem mnuNestShapeLibrary;

OpenNest/Forms/MainForm.Nest.cs

@@ -4,6 +4,7 @@ using System.Linq;
 using System.Threading;
 using System.Windows.Forms;
 using OpenNest.Collections;
+using OpenNest.Data;
 using OpenNest.Engine.Fill;
 using OpenNest.Forms.Commands;
 
@@ -45,6 +46,56 @@ namespace OpenNest.Forms
             mnuNestDrawingLibrary.ToolTipText = databaseMode ? "" : NestStorage.DatabaseModeOnly;
             // Parts can be added without a plate change, so refresh the clear state on open.
             mnuNestClear.Enabled = activeForm?.PlateManager.CanClearAll ?? false;
+            BuildMachineMenu();
+        }
+
+        // Lists the machines on file, checking the active nest's; one assigned but no longer on
+        // file is shown checked and disabled so the nest still says what it was made for.
+        private void BuildMachineMenu()
+        {
+            mnuNestMachine.DropDownItems.Clear();
+            var nest = activeForm?.Nest;
+            mnuNestMachine.Enabled = nest != null;
+            if (nest == null)
+            {
+                mnuNestMachine.DropDownItems.Add(new ToolStripMenuItem("(no nest open)") { Enabled = false });
+                return;
+            }
+
+            var machines = MachineSettings.LoadMachines()
+                .OrderBy(m => m.Name, StringComparer.CurrentCultureIgnoreCase)
+                .ToList();
+            foreach (var machine in machines)
+            {
+                var item = new ToolStripMenuItem(machine.Name) { Checked = machine.Id == nest.Machine?.Id };
+                item.Click += (_, _) => AssignMachine(machine);
+                mnuNestMachine.DropDownItems.Add(item);
+            }
+            if (nest.Machine is { } assigned && machines.All(m => m.Id != assigned.Id))
+                mnuNestMachine.DropDownItems.Add(new ToolStripMenuItem($"{assigned.Name} (not on file)") { Checked = true, Enabled = false });
+            if (mnuNestMachine.DropDownItems.Count == 0)
+                mnuNestMachine.DropDownItems.Add(new ToolStripMenuItem("(no machines; see Tools > Machine Configuration)") { Enabled = false });
+        }
+
+        // Assigning a machine also puts every sheet on that machine's support grid.
+        private void AssignMachine(MachineConfig machine)
+        {
+            var editForm = activeForm;
+            if (editForm == null || editForm.Nest.Machine?.Id == machine.Id)
+                return;
+
+            var nest = editForm.Nest;
+            var views = ViewsOf(nest);
+            if (IsPlateWorkBusy(views))
+            {
+                MessageBox.Show(this, "Finish or cancel the current nesting or plate action first.",
+                    "Machine", MessageBoxButtons.OK, MessageBoxIcon.Information);
+                return;
+            }
+
+            MachineSettings.AssignMachine(nest, machine);
+            foreach (var view in views)
+                view.Invalidate();
         }
 
         private async void EditNest_Click(object sender, EventArgs e)
@@ -100,7 +151,12 @@ namespace OpenNest.Forms
                 return;
             }
 
-            using var form = new SupportGridForm(nest.SupportBed, nest.Units, MachineSettings.LoadSupportGridSettings());
+            var machine = MachineSettings.FindMachine(nest.Machine);
+            Action<SupportGridSettings> save = machine == null
+                ? null
+                : settings => MachineSettings.SaveSupportGridSettings(machine.Id, settings);
+            using var form = new SupportGridForm(nest.SupportBed, nest.Units, MachineSettings.LoadSupportGridSettings(machine),
+                machine?.Name ?? nest.Machine?.Name, save);
             if (form.ShowDialog(this) != DialogResult.OK)
                 return;
 

OpenNest/Forms/MainForm.Tools.cs

@@ -171,7 +171,7 @@ namespace OpenNest.Forms
 
         private void NestDefaults_Click(object sender, EventArgs e)
         {
-            using (var form = new NestDefaultsForm(MachineSettings.LoadSavedNestDefaults(out _)))
+            using (var form = new NestDefaultsForm(MachineSettings.LoadSavedNestDefaults(out _), MachineSettings.LoadMachines()))
             {
                 if (form.ShowDialog(this) == DialogResult.OK)
                     form.GetDefaults().Save(NestDefaults.DefaultPath);
@@ -183,9 +183,10 @@ namespace OpenNest.Forms
             if (activeForm == null)
                 return;
 
-            NestDefaults
-                .FromPlate(activeForm.Nest.Units, activeForm.PlateView.Plate)
-                .Save(NestDefaults.DefaultPath);
+            var defaults = NestDefaults.FromPlate(activeForm.Nest.Units, activeForm.PlateView.Plate);
+            // The nest's machine becomes the default; a nest without one keeps the saved choice.
+            defaults.MachineId = activeForm.Nest.Machine?.Id ?? MachineSettings.LoadSavedNestDefaults(out _).MachineId;
+            defaults.Save(NestDefaults.DefaultPath);
         }
 
         private void MachineConfig_Click(object sender, EventArgs e)

OpenNest/Forms/NestDefaultsForm.Designer.cs

@@ -47,6 +47,8 @@ namespace OpenNest.Forms
             this.edgeTopBox = new OpenNest.Controls.NumericUpDown();
             this.quadrantLabel = new System.Windows.Forms.Label();
             this.quadrantSelect1 = new OpenNest.Controls.QuadrantSelect();
+            this.machineLabel = new System.Windows.Forms.Label();
+            this.machineCombo = new System.Windows.Forms.ComboBox();
             this.saveButton = new System.Windows.Forms.Button();
             this.cancelButton = new System.Windows.Forms.Button();
             ((System.ComponentModel.ISupportInitialize)(this.widthBox)).BeginInit();
@@ -82,19 +84,22 @@ namespace OpenNest.Forms
             this.tableLayoutPanel1.Controls.Add(this.edgeTopBox, 1, 7);
             this.tableLayoutPanel1.Controls.Add(this.quadrantLabel, 0, 8);
             this.tableLayoutPanel1.Controls.Add(this.quadrantSelect1, 1, 8);
+            this.tableLayoutPanel1.Controls.Add(this.machineLabel, 0, 9);
+            this.tableLayoutPanel1.Controls.Add(this.machineCombo, 1, 9);
             this.tableLayoutPanel1.Location = new System.Drawing.Point(12, 12);
             this.tableLayoutPanel1.Name = "tableLayoutPanel1";
-            this.tableLayoutPanel1.RowCount = 9;
-            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 11.11111F));
-            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 11.11111F));
-            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 11.11111F));
-            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 11.11111F));
-            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 11.11111F));
-            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 11.11111F));
-            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 11.11111F));
-            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 11.11111F));
-            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 11.11111F));
-            this.tableLayoutPanel1.Size = new System.Drawing.Size(410, 260);
+            this.tableLayoutPanel1.RowCount = 10;
+            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 10F));
+            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 10F));
+            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 10F));
+            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 10F));
+            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 10F));
+            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 10F));
+            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 10F));
+            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 10F));
+            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 10F));
+            this.tableLayoutPanel1.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 10F));
+            this.tableLayoutPanel1.Size = new System.Drawing.Size(410, 288);
             this.tableLayoutPanel1.TabIndex = 0;
             //
             // unitsLabel
@@ -286,11 +291,30 @@ namespace OpenNest.Forms
             this.quadrantSelect1.Size = new System.Drawing.Size(120, 28);
             this.quadrantSelect1.TabIndex = 17;
             //
+            // machineLabel
+            //
+            this.machineLabel.Anchor = ((System.Windows.Forms.AnchorStyles)((System.Windows.Forms.AnchorStyles.Left | System.Windows.Forms.AnchorStyles.Right)));
+            this.machineLabel.AutoSize = true;
+            this.machineLabel.Location = new System.Drawing.Point(3, 263);
+            this.machineLabel.Name = "machineLabel";
+            this.machineLabel.Size = new System.Drawing.Size(100, 16);
+            this.machineLabel.TabIndex = 18;
+            this.machineLabel.Text = "Machine:";
+            //
+            // machineCombo
+            //
+            this.machineCombo.Anchor = ((System.Windows.Forms.AnchorStyles)((System.Windows.Forms.AnchorStyles.Left | System.Windows.Forms.AnchorStyles.Right)));
+            this.machineCombo.DropDownStyle = System.Windows.Forms.ComboBoxStyle.DropDownList;
+            this.machineCombo.Location = new System.Drawing.Point(109, 259);
+            this.machineCombo.Name = "machineCombo";
+            this.machineCombo.Size = new System.Drawing.Size(298, 24);
+            this.machineCombo.TabIndex = 19;
+            //
             // saveButton
             //
             this.saveButton.Anchor = ((System.Windows.Forms.AnchorStyles)((System.Windows.Forms.AnchorStyles.Bottom | System.Windows.Forms.AnchorStyles.Right)));
             this.saveButton.DialogResult = System.Windows.Forms.DialogResult.OK;
-            this.saveButton.Location = new System.Drawing.Point(243, 285);
+            this.saveButton.Location = new System.Drawing.Point(243, 313);
             this.saveButton.Name = "saveButton";
             this.saveButton.Size = new System.Drawing.Size(90, 28);
             this.saveButton.TabIndex = 1;
@@ -301,7 +325,7 @@ namespace OpenNest.Forms
             //
             this.cancelButton.Anchor = ((System.Windows.Forms.AnchorStyles)((System.Windows.Forms.AnchorStyles.Bottom | System.Windows.Forms.AnchorStyles.Right)));
             this.cancelButton.DialogResult = System.Windows.Forms.DialogResult.Cancel;
-            this.cancelButton.Location = new System.Drawing.Point(339, 285);
+            this.cancelButton.Location = new System.Drawing.Point(339, 313);
             this.cancelButton.Name = "cancelButton";
             this.cancelButton.Size = new System.Drawing.Size(90, 28);
             this.cancelButton.TabIndex = 2;
@@ -313,7 +337,7 @@ namespace OpenNest.Forms
             this.AcceptButton = this.saveButton;
             this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.None;
             this.CancelButton = this.cancelButton;
-            this.ClientSize = new System.Drawing.Size(434, 322);
+            this.ClientSize = new System.Drawing.Size(434, 350);
             this.Controls.Add(this.tableLayoutPanel1);
             this.Controls.Add(this.saveButton);
             this.Controls.Add(this.cancelButton);
@@ -358,6 +382,8 @@ namespace OpenNest.Forms
         private OpenNest.Controls.NumericUpDown edgeTopBox;
         private System.Windows.Forms.Label quadrantLabel;
         private OpenNest.Controls.QuadrantSelect quadrantSelect1;
+        private System.Windows.Forms.Label machineLabel;
+        private System.Windows.Forms.ComboBox machineCombo;
         private System.Windows.Forms.Button saveButton;
         private System.Windows.Forms.Button cancelButton;
     }

OpenNest/Forms/NestDefaultsForm.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Windows.Forms;
 using OpenNest.Data;
 using OpenNest.Geometry;
@@ -11,10 +13,26 @@ namespace OpenNest.Forms
     /// </summary>
     public partial class NestDefaultsForm : Form
     {
-        public NestDefaultsForm(NestDefaults defaults)
+        private sealed record MachineChoice(MachineConfig Machine)
+        {
+            public override string ToString() => Machine.Name;
+        }
+
+        private readonly Guid? savedMachineId;
+
+        /// <param name="machines">The machines new nests can be assigned.</param>
+        public NestDefaultsForm(NestDefaults defaults, IEnumerable<MachineConfig> machines)
         {
             InitializeComponent();
 
+            savedMachineId = defaults.MachineId;
+            var sorted = machines.OrderBy(m => m.Name, StringComparer.CurrentCultureIgnoreCase).ToList();
+            foreach (var machine in sorted)
+                machineCombo.Items.Add(new MachineChoice(machine));
+            var selected = MachineSettings.DefaultMachine(defaults, sorted);
+            machineCombo.SelectedItem = machineCombo.Items.Cast<MachineChoice>().FirstOrDefault(c => c.Machine == selected);
+            machineCombo.Enabled = machineCombo.Items.Count > 0;
+
             unitsCombo.SelectedIndex = defaults.Units == Units.Millimeters ? 1 : 0;
             widthBox.Value = Clamp(widthBox, defaults.Size.Width);
             lengthBox.Value = Clamp(lengthBox, defaults.Size.Length);
@@ -42,6 +60,8 @@ namespace OpenNest.Forms
                     (double)edgeRightBox.Value,
                     (double)edgeTopBox.Value
                 ),
+                // With no machines on file there is nothing to choose, so keep the saved choice.
+                MachineId = (machineCombo.SelectedItem as MachineChoice)?.Machine.Id ?? savedMachineId,
             };
         }
 

OpenNest/Forms/NewNestFactory.cs

@@ -10,7 +10,7 @@ using OpenNest.Properties;
 namespace OpenNest.Forms
 {
     /// <summary>
-    /// Creates File > New nests: machine defaults and clamps, then the year's next name
+    /// Creates File > New nests: nest defaults, clamps, the default machine and its support grid, then the year's next name
     /// (<see cref="NestNames"/>). In Database mode the nest server allocates the number so
     /// every PC shares one sequence; when it cannot, <see cref="Settings.NestNumber"/> is the
     /// local fallback, kept above every number the server handed out and reset each year.
@@ -39,9 +39,9 @@ namespace OpenNest.Forms
             var nest = new Nest();
             var defaults = MachineSettings.LoadNestDefaults();
             (units is { } converted ? defaults.ConvertedTo(converted) : defaults).ApplyTo(nest);
-            // After the defaults so the rail is converted to the new nest's units.
+            // After the defaults so the rail and grid are converted to the new nest's units.
             MachineSettings.LoadClampSettings(owner).ApplyToNewNest(nest);
-            MachineSettings.LoadSupportGridSettings().ApplyToNewNest(nest);
+            MachineSettings.AssignMachine(nest, MachineSettings.DefaultMachine(defaults, MachineSettings.LoadMachines()));
             return nest;
         }
 

OpenNest/Forms/SupportGridForm.cs

@@ -11,13 +11,13 @@ namespace OpenNest.Forms;
 /// Nest > Support Grid...: edits the laser grid of contact points every sheet of the current
 /// nest rests on, used to judge whether cut parts stay level and where support tabs go (see
 /// docs/support-tabs.md). OK applies it to the nest; Cancel discards the edits. Save as Machine
-/// Defaults writes support-grid.json immediately and is not undone by Cancel.
+/// Defaults writes the grid to the nest's machine configuration immediately and is not undone by Cancel.
 /// </summary>
 public sealed class SupportGridForm : Form
 {
     private readonly Units units;
     private readonly SupportGridSettings machineDefaults;
-    private readonly string settingsPath;
+    private readonly Action<SupportGridSettings> saveMachineDefaults;
     private readonly CheckBox useGridBox;
     private readonly NumericUpDown pitchXBox;
     private readonly NumericUpDown pitchYBox;
@@ -28,11 +28,16 @@ public sealed class SupportGridForm : Form
     private readonly CheckBox applyToNewNestsBox;
     private readonly Label savedLabel;
 
-    public SupportGridForm(SupportBed bed, Units units, SupportGridSettings machineDefaults, string settingsPath = null)
+    /// <param name="machineName">The nest's machine, or null when none is assigned.</param>
+    /// <param name="saveMachineDefaults">
+    /// Saves the grid as that machine's; null disables saving, when the nest has no machine on file.
+    /// </param>
+    public SupportGridForm(SupportBed bed, Units units, SupportGridSettings machineDefaults, string machineName,
+        Action<SupportGridSettings> saveMachineDefaults)
     {
         this.units = units;
         this.machineDefaults = machineDefaults ?? new SupportGridSettings();
-        this.settingsPath = settingsPath ?? SupportGridSettings.DefaultPath;
+        this.saveMachineDefaults = saveMachineDefaults;
         var grid = bed as SupportGrid;
         // A nest without a grid starts from the machine defaults, so enabling it is one click.
         var initial = grid != null
@@ -86,7 +91,12 @@ public sealed class SupportGridForm : Form
         AddRow(values, "Stability margin:", marginBox, unit);
         layout.Controls.Add(values);
 
-        var defaultsGroup = new GroupBox { Text = "Machine defaults (support-grid.json)", AutoSize = true, Padding = new Padding(8) };
+        var defaultsGroup = new GroupBox
+        {
+            Text = string.IsNullOrEmpty(machineName) ? "Machine defaults (no machine assigned)" : $"Machine defaults ({machineName})",
+            AutoSize = true,
+            Padding = new Padding(8),
+        };
         var defaultsLayout = new FlowLayoutPanel
         {
             Dock = DockStyle.Fill,
@@ -96,7 +106,7 @@ public sealed class SupportGridForm : Form
         };
         applyToNewNestsBox = new CheckBox
         {
-            Text = "Give new nests this grid",
+            Text = "Give nests on this machine this grid",
             AutoSize = true,
             Checked = this.machineDefaults.Enabled,
         };
@@ -109,8 +119,12 @@ public sealed class SupportGridForm : Form
         {
             AutoSize = true,
             MaximumSize = new Size(410, 0),
-            Text = "Save as Machine Defaults writes the file immediately; Cancel below does not undo it.",
+            Text = saveMachineDefaults == null
+                ? "Assign this nest a machine on file in Nest > Machine to save its grid."
+                : "Save as Machine Defaults writes the machine configuration immediately; Cancel below does not undo it.",
         };
+        applyToNewNestsBox.Enabled = saveMachineDefaults != null;
+        saveDefaultsButton.Enabled = saveMachineDefaults != null;
         defaultsLayout.Controls.Add(applyToNewNestsBox);
         defaultsLayout.Controls.Add(defaultsButtons);
         defaultsLayout.Controls.Add(savedLabel);
@@ -172,14 +186,14 @@ public sealed class SupportGridForm : Form
         var settings = Read();
         try
         {
-            settings.Save(settingsPath);
+            saveMachineDefaults(settings);
             savedLabel.Text = settings.Enabled
-                ? $"Saved {DateTime.Now:t}: new nests get this grid. Cancel does not undo this."
-                : $"Saved {DateTime.Now:t}: new nests get no grid. Cancel does not undo this.";
+                ? $"Saved {DateTime.Now:t}: nests on this machine get this grid. Cancel does not undo this."
+                : $"Saved {DateTime.Now:t}: nests on this machine get no grid. Cancel does not undo this.";
         }
         catch (Exception ex) when (ex is IOException or UnauthorizedAccessException or ArgumentException)
         {
-            MessageBox.Show(this, $"The machine defaults could not be saved:\n{settingsPath}\n\n{ex.Message}",
+            MessageBox.Show(this, $"The machine defaults could not be saved:\n\n{ex.Message}",
                 Text, MessageBoxButtons.OK, MessageBoxIcon.Error);
         }
     }

docs/nest-file-format.md

@@ -13,6 +13,12 @@ Status and made-by are additive: files written before them load as Quote with an
 empty maker, and an unrecognized status value likewise falls back to Quote. Builds
 before `Draft` therefore open a Draft nest as Quote, and saving it there keeps Quote.
 
+`machine` optionally names the machine the nest is cut on: `id` (its machine
+configuration's GUID) and `name` (the configuration's name when assigned, so the nest
+still says what it was made for on a PC without that configuration). The key is omitted
+when no machine is assigned. A non-object, a missing, non-string, unparseable or empty
+`id` loads as no machine; a missing or non-string `name` loads as empty.
+
 ## Programs and placements
 
 - `programs/program-N` is drawing N's clean G-code program; optional

docs/support-tabs.md

@@ -23,9 +23,14 @@ Every bed also carries:
 
 The bed belongs to the nest (`Nest.SetSupportBed`); every plate follows it, including plates
 added later. It is display, analysis and tab placement only: never material, spacing or a
-keep-out. Nest > Support Grid... edits it; Save as Machine Defaults writes
-`%APPDATA%\OpenNest\support-grid.json`, which new nests receive while it is enabled. The
-nest file stores it in `plateDefaults.supportBed` (see [nest file format](nest-file-format.md)).
+keep-out. Nest > Support Grid... edits it; Save as Machine Defaults writes it to the nest's
+machine configuration (`MachineConfig.SupportGrid`), which nests assigned that machine receive
+while it is enabled: File > New and BOM import assign the Tools > Nest Defaults machine (the
+first by name when none is chosen), and Nest > Machine reassigns a nest and replaces its grid
+with the new machine's (none when that machine gives nests no grid). A machine with no grid
+saved yet uses the legacy shared `%APPDATA%\OpenNest\support-grid.json`. The nest file stores
+the bed in `plateDefaults.supportBed` and the machine in `machine` (see
+[nest file format](nest-file-format.md)).
 
 ## The support check