Saancha mould design guide: from STL to your first mould

Start here: what Saancha actually makes

Example applications include decorative candles, resin keepsakes and figurines, flexible silicone parts, concrete coasters and ornaments, and soap or plaster shapes. Begin with your own STL: these are example uses, not built-in article templates. Soap and plaster use General casting and require your own verified process settings. Hollow forms may need a separately designed core; the tool does not automatically design one.

Saancha (साचा) is a free browser tool that creates mould tooling around an existing 3D model. A mould is a container with the shape of your object inside it. You pour a suitable material into that space, let it set, and remove the copy. Saancha creates the digital pieces; you still need to print, assemble and test the tooling.

There are two workflows. For a flexible rubber mould, Saancha exports a master (a positive copy of your object) and a box. Print them, secure and seal the master inside the box, then pour your actual silicone or polyurethane rubber around it. For directly printed rigid tooling, Saancha exports the negative cavity as one open-face piece or two mould halves.

The tool is an engineering preview, version 0.4. A model passing a digital solid check is not proof that it can be removed from a mould, printed successfully or used with hot or heavy material. Start with the sample cube and a small physical trial.

What you need before starting

Use a current browser with JavaScript, WebGL, WebAssembly and module workers enabled. A desktop or laptop is recommended for large files. Model processing happens on your device; Saancha does not upload the STL to a model-processing service. Normal website requests still load the page and its assets.

Prepare a closed binary or ASCII STL of the object you want to reproduce. The input limits are 1,000,000 triangles AND 200 MB as shown in the tool (200 MiB, exactly 209,715,200 bytes). Both limits must be satisfied. More triangles usually mean more memory and waiting time; a file within the limits is not a guarantee of success on every device.

STL describes a surface with many small triangles. It does not specify units. Know whether the original model uses millimetres, centimetres or inches, and know the size the object should be. The compensated part must have nonzero dimensions and fit within 1,000 mm along every axis. OBJ, 3MF and STEP cannot be imported here; export STL from your design application first.

Your first exercise: a 30 mm two-part mould

This exercise uses the included sample, so you do not need a model file. It teaches the buttons without choosing a real casting formulation. These numbers are demonstration settings, not universal manufacturing settings.

1. Open Saancha from the Tools page. Under 01 / Part, click Try a 30 mm sample cube. Wait until the status says Model ready.
2. Keep Source units as Millimetres. The design check should show 30 × 30 × 30 mm and about 27 ml of part volume.
3. Under 02 / Tooling, choose General casting, Directly printed rigid tooling and Two-part negative mould. Keep Pull axis Z, wall 8 mm, shrinkage 0%, split height 50%, four keys and key fit gap 0.2 mm. Set the pour channel to 8 mm at X 0 / Y 0. Keep vent 0 and external support None for this demonstration.
4. Click Generate tooling and wait for Tooling generated. Use Tooling, Explode, Fit and Top to inspect both halves, the central cavity, pour channel and registration keys. With this cube and 8 mm walls, the assembled block is approximately 46 × 46 × 46 mm; the keys extend above the lower half's split plane.
5. Read the design and material checks. Tick the review checkbox only after reviewing them. Download lower-half STL, upper-half STL and Design notes. Each download is a separate file.
6. Open both STLs in a slicer as millimetres and confirm their size. Review orientation, walls, supports and the layer preview before printing. Changing a setting removes the previous download buttons; generate and review again.

Understand the three selections

Casting material means what the finished copy will be made from: General casting, Candle wax, Concrete / cement mix, Silicone part or Casting resin. Choose Candle wax for a candle, not Silicone part merely because you intend to make a silicone mould. Silicone is the flexible rubber; silicon is a different substance.

Finished mould material means the material surrounding that copy. Silicone rubber and Polyurethane rubber require Master + rubber mould box. Directly printed rigid tooling means you print the cavity itself and use an open-face or two-part negative construction.

Construction means the shape and assembly of the tooling. Changing a rubber material selects the box workflow. Choosing a negative mould switches the finished mould material to printed tooling. Review all three selections after changing one; the tool keeps their combinations consistent.

Soap and plaster do not yet have dedicated profiles or automatic process checks. Select General casting, then use verified temperatures, shrinkage, release and curing instructions for your actual products. Saancha does not automatically assign safe wall thickness, channel sizes or shrinkage from any material name.

Choose a construction that can release your part

Master + rubber mould box creates a positive master and a separate open container. Rubber gap determines the space around and above the master. There is no automatic two-part rubber mould, seam or cut line. Plan how you will remove the master and casting from the cured rubber. Bond and seal the master to the inner floor before pouring so rubber does not seep underneath or move it.

Open-face negative mould creates one rigid cavity open at the top. It is useful when the intended casting has a suitable flat open face and can be removed along the chosen axis. Opening depth deliberately cuts below the highest point of the part, so the open-face casting will not reproduce the removed top section. This is not a complete closed copy of the STL.

Two-part negative mould creates a lower and upper rigid half with one planar split. Cylindrical registration keys help the halves align; they are not clamps or seals. Use an accessible inlet and external clamping and sealing appropriate to your process. Saancha does not create bolts, gaskets, automatic multi-part moulds or a physically validated assembly.

An undercut is a hook-like or overhanging feature that traps a rigid casting when you try to pull it straight out. Imagine trying to pull a mushroom through a hole smaller than its cap. A different axis, split, flexible mould or redesigned part may be required. Saancha does not automatically find undercuts or prove demouldability.

Import your own STL and confirm the size

Click Choose or drop an STL or drag your STL onto the marked area. Wait for the import check before generating. The tool checks whether the mesh is accepted as a closed, consistently oriented solid by its geometry engine. It cannot comprehensively certify self-intersections or manufacturing suitability.

Select Source units from the original design, then compare Part dimensions with a known measurement. For example, an STL intended as 3 cm wide becomes 30 mm when centimetres are selected. Choosing inches multiplies dimensions by 25.4. Choosing the wrong units can make your tool enormous or tiny.

After changing units, axis or shrinkage, Saancha rechecks the part. Use Fit if it leaves the view. There is no general resize-to-width control: resize in your CAD software if you need a different nominal part size. Keep your original STL and work on a copy when repairing or simplifying.

Check disconnected shells and internal surfaces in CAD or a slicer. Some STL files contain hidden little voids or overlapping inner shells. Subtracting those shapes can produce tiny loose cores inside a mould even when the overall mesh is accepted. Saancha does not yet automatically identify every floating core. Do not print and use such a result without resolving the core design.

Pull axis, wall thickness and shrinkage

Pull axis X, Y or Z chooses a source-model direction to become the preview's vertical Z direction. Splitting and vertical channels follow that transformed axis. The displayed red, green and blue lines represent preview X, Y and Z; they are not a guarantee of release direction suitability. Channel X/Y coordinates are measured after this rotation.

Wall / bottom is the nominal extra material around the cavity or container, from 3 to 100 mm. In the box workflow it controls container wall and floor thickness; Rubber gap separately controls rubber space. This input does not establish minimum wall strength around every feature. Check the printer, material, loading and physical assembly.

Linear shrinkage accepts 0–10%. It enlarges the master or cavity using 1 ÷ (1 − percentage/100). At 5%, a 30 mm dimension becomes about 31.58 mm, not 31.50 mm. Enter the compensation justified for your process; keep 0 when learning. This is uniform scaling, not a surface clearance or separate corrections for printer, rubber and casting shrinkage.

Output STL coordinates are always millimetres. Part dimensions shown after compensation describe the enlarged design; they are not a prediction of the measured cooled or cured casting.

Settings for a rubber mould box

Choose Silicone rubber or Polyurethane rubber and Master + rubber mould box. Rubber gap accepts 1–100 mm. It adds space to both sides in X/Y and above the part. Wall / bottom adds printed container material outside that rubber space.

For a 30 mm cube, 10 mm rubber gap, 8 mm walls and no shrinkage, the box exterior is approximately 66 × 66 × 48 mm. The estimated rubber space is 73 ml. This is a geometric estimate excluding spillage, mixing-container residue, process allowance and material density. Measure and mix actual rubber according to its supplier instructions.

Download both mould-box and master. Their preview shows the master touching the inner floor; they are separate exports. Print them separately, verify fit, bond and seal the master, and use the required release and preparation. The tool does not pour, cure or split the rubber for you.

For Silicone rubber choose Mould silicone cure independently: Unknown, Platinum / addition cure or Tin / condensation cure. Use your rubber data sheet. An unknown choice produces a warning. Test the actual printed master, sealer and release system with the rubber before committing a full batch.

Settings for open-face and two-part moulds

Open-face: Opening depth below part top accepts 0.1–100 mm but must be less than the part height along the selected axis. The mould top is lowered by this amount to expose the cavity. Inspect that opening and understand which part of the intended object is removed.

Two-part: Split height accepts 5–95% of part height. A 50% split lies halfway between the part's lowest and highest points, not necessarily at its widest section or the best release line. Choose 0, 2 or 4 cylindrical keys. Key fit gap accepts 0–1 mm and enlarges the sockets for assembly; confirm the actual printer fit with a small test.

Pour channel is the hole through which material enters the upper half. Diameter accepts 0–50 mm; 0 disables it. X and Y are offsets from the transformed part centre in millimetres. A positive or negative offset moves the channel to either side of centre. The channel must intersect the part, otherwise generation is rejected. This check alone does not prove complete cavity access or good flow.

Manual air vent diameter accepts 0–10 mm; 0 disables it. Position it independently with X/Y. It must intersect the part. Only one manual vent is available, rising through the upper half along preview Z. There is no automatic air-trap detection or multi-vent layout. Review high points and the actual filling method with someone familiar with your process.

Candle wax: temperature and wick provisions

Choose Candle wax as casting material, then decide whether to make a flexible rubber mould or use printed rigid tooling. Enter Wax pour temperature and Tool service rating from the actual products, 0–300 °C. Zero means unknown. A temperature below the entered service rating only passes a basic comparison; it does not validate repeated heating, distortion or material compatibility.

With printed negative tooling, Wick passage diameter accepts 0–10 mm. Zero turns it off. X/Y position the wick relative to preview centre. The path must meet the part. When enabled, Saancha cuts a through passage and adds a separate wick-centering-bridge STL. The bridge is shown in its assembled position above the mould.

For a sample exercise, use the 30 mm cube, Candle wax, printed tooling, Two-part, wick 2 mm at 0/0, and pour channel 8 mm at X 8 / Y 0. The offset keeps the inlet away from the wick. These are geometry demonstration values, not a wick recommendation. Choose actual wick and bore sizes for your wax, candle size and sealing system.

The inlet and wick must have at least 1 mm between their edges; overlapping selections are rejected. Seal the bottom wick exit before pouring. The bridge does not seal the exit or determine safe candle burning. For a rubber mould box, no ready-made wick passage or bridge is generated: plan and form the wick passage after the rubber cures and provide a suitable holder.

Concrete, cement and support jackets

Choose Concrete / cement mix. Maximum aggregate means the largest solid grain in your mix, from 0–50 mm; 0 means unknown. For a split mould, an inlet diameter no larger than the entered aggregate raises a warning. A larger inlet is only a basic screen: narrow cavity features and mix flow can still prevent filling.

Wet density is kilograms per litre, 0.1–5 kg/L. The default 2.3 is an editable estimate, not a universal concrete property. The tool estimates part mass from volume and entered density. It also estimates static pressure from full part height. Waste, channels, extra pouring head, vibration and handling can add loads; these figures are not strength calculations.

External support can be None or Two-piece rectangular jacket. Jacket thickness accepts 3–30 mm and Assembly gap 0.1–5 mm. The exported support-left and support-right pieces surround the printed tooling or container with clearance. Keep rubber inside its box if you intend to use that box-sized support.

Clamp the support externally. Saancha does not design fasteners or certify support strength. Inspect the jacket, mould base, seams, print direction, release and abrasion resistance. Follow the mix supplier's actual curing and demoulding instructions.

Silicone parts, casting resin, soap and plaster

For a finished silicone part choose Silicone part as casting material, then choose the actual mould material separately. Select Casting silicone cure (Unknown, Platinum or Tin) from the casting product's data sheet. This is different from Mould silicone cure when the mould itself is silicone.

Read cure compatibility warnings. Silicone can adhere to silicone, and contaminants or inadequately cured printed resin can interfere with curing. Test a small sample with your actual mould, sealer and release system. Saancha does not establish chemical compatibility. Review air escape, viscosity and working time; no selected vent can leave trapped air.

For Casting resin, confirm working time, reaction heat, release compatibility and shrinkage for the actual resin and tooling. Saancha does not simulate resin curing or temperature. For soap and plaster use General casting and verify the full process independently; dedicated soap/plaster presets are not implemented.

No profile certifies food contact, skin contact, candle burn safety or other regulated use. Choose materials and processes appropriate to your intended application and follow supplier documentation.

Preview and review before downloading

Drag the preview to orbit, scroll to zoom, and right-drag to pan. On touch devices use supported orbit and pinch gestures. Part shows the transformed source. Tooling shows generated pieces. Explode separates halves and accessories for inspection. Fit recentres everything and Top looks down preview Z.

Read Part dimensions, volume, triangles and each output's dimensions. Volume is geometric volume, not a quotation or a slicer's printed-material estimate. The design check should say generation succeeded before you proceed. Read every material check, especially items marked Needs attention.

Inspect cavity shape, opening, channels, keys, separate islands, bridge, support halves, wall thickness and intended release. A successful solid check does not detect every undercut, air trap, weak wall, hidden shell or disconnected core. For complex parts seek a mould designer's review.

Tick the checkbox acknowledging your review to enable downloads. This is an acknowledgement, not an approval certificate. Any settings change invalidates the generated output and resets the checkbox. Generate again rather than using files downloaded for old settings.

Download, slice, print and assemble

Download every required STL separately: mould-box and master for rubber tooling, open-face mould for one-piece tooling, or lower-half and upper-half for two-part tooling. Accessories add wick-centering-bridge, support-left and support-right. Design notes downloads JSON containing the current settings, output names, dimensions, volumes and process checks.

STL stores geometry without reliable units, colours or printer instructions. Import the files into a slicer as millimetres, confirm each size, inspect separate components, orient parts, check supports and review the full layer preview. Choose print material and parameters suited to the intended process. Do not send an STL straight to a printer as if it were machine code.

Print a small fit or representative section first when keys, sockets, seals or fine details matter. Check the printed cavity surface, leaks, registration and assembly before filling. Rubber masters may need finishing or sealing. For split rigid tooling, secure the halves and plan the inlet, vent, leakage control and release sequence.

Keep the original STL, exported parts and JSON notes together with a revision name. JSON notes document settings but are not an editable project that Saancha can reopen. Closing or refreshing the page clears the working model. To revise later, import the original STL and re-enter the recorded settings.

Troubleshooting: import or generation fails

Maximum file size / triangle limit: simplify a copy of the mesh in CAD or a mesh editor and re-export STL. A small file can still contain too many triangles; a low-triangle ASCII file can still exceed the byte limit. Binary STL is usually smaller for the same triangles. Reducing triangle count can remove fine details, so compare with your original.

Not a closed, consistently oriented solid: repair holes, inverted faces, overlapping shells and stray internal surfaces in a suitable mesh editor, then export and retry. Saancha does not automatically repair your file. If the wrong model remains visible after a rejected file choice, check the filename and status; do not assume the rejected file was imported.

Part must fit within 1,000 mm / zero dimensions: check Source units, intended dimensions and shrinkage. A flat sheet has no solid thickness; give it thickness in CAD. A model intended in millimetres can become far too large if interpreted as inches.

Pour channel or vent misses the part: move X/Y towards the cavity, change split height or revise diameter. After axis changes, the channel coordinates refer to the rotated preview. Wick overlaps inlet: separate their centres enough for both radii plus 1 mm. Wick misses part: move its X/Y onto the intended candle region.

Opening depth error: reduce it below the part's full height along the selected axis. Rubber construction error: use a rubber material with Master + rubber mould box, or printed tooling with a negative construction. Material and support values must stay inside the displayed numeric ranges.

Blank preview or stalled operation: confirm browser WebGL/hardware acceleration and available memory; close heavy tabs, use a smaller test model and reload. Allow a large model time to finish. If the geometry engine cannot start, check browser support and network access for the page's engine assets. Record the exact error and settings when requesting help.

Download buttons missing: finish generation and tick the review checkbox. If you edited a setting, generate again. If the browser blocks multiple downloads, download the parts one at a time and check its Downloads list. The files do not automatically appear in your slicer.

What is not automated, and when to ask for help

Saancha currently makes one cavity with a manually selected planar split. Automatic parting, multi-cavity layouts, multi-part rubber moulds, pressure/vacuum mould design, draft analysis, flow or air-trap simulation, thermal analysis, strength certification, automatic mesh repair, printer-fit checking and floating-core diagnosis are not implemented.

Avoid treating a visually attractive preview as proof of a usable mould. Deep recesses, mushroom shapes, tunnels, tiny internal shells and fragile appendages may require flexible tooling, separate cores, a different split or professional redesign. Review release and assembly before buying material or printing a large tool.

For help from IRIS, prepare your original STL, dimensions and units, casting and mould materials, construction, settings JSON, intended quantity, printer/material details, and the exact error or screenshot. Use the Contact page to discuss design or 3D printing. Preparing an email or WhatsApp draft is not the same as sending it; complete Send in your chosen application.