{"id":74,"date":"2026-09-12T05:00:51","date_gmt":"2026-09-12T05:00:51","guid":{"rendered":"https:\/\/redstonemanufacturing.com\/resources\/articles\/investment-casting-typical-tolerances\/"},"modified":"2026-09-12T05:00:51","modified_gmt":"2026-09-12T05:00:51","slug":"investment-casting-typical-tolerances","status":"publish","type":"post","link":"https:\/\/redstonemanufacturing.com\/resources\/articles\/investment-casting-typical-tolerances\/","title":{"rendered":"Investment Casting Typical Tolerances: A Decision Guide"},"content":{"rendered":"<h2>Key Takeaways<\/h2>\n<ul>\n<li><strong>Standard Linear Tolerance And Surface Finish:<\/strong> Standard normal linear tolerances for investment castings are <a href=\"https:\/\/www.stainlessfoundry.com\/investment-casting-foundry\/investment-casting-foundry-tolerance\/\" target=\"_blank\" rel=\"noindex nofollow\">\u00b10.010&#8243; up to 1 inch, \u00b10.003&#8243; per inch for each additional inch up to ten inches, and \u00b10.005&#8243; per inch for dimensions greater than ten inches<\/a>. As-cast surface finish typically runs Ra 1.6\u20136.3 \u00b5m (about 63\u2013250 \u00b5in RMS), which corresponds to surface quality classes N7\u2013N9. The 125\u2013250 \u00b5in (3.2\u20136.3 \u00b5m Ra) band represents the rougher end of that range.<\/li>\n<li><strong>What ISO 8062-3:2023 Covers:<\/strong> ISO 8062-3:2023 is the international standard for casting dimensional and geometrical tolerances. Annex A recommends investment casting dimensional casting tolerance grades (DCTG) of 4\u20139 depending on part size and shell process. Silica sol shell systems typically fall in CT4\u2013CT7, while water glass systems fall in CT7\u2013CT11.<\/li>\n<li><strong>Shell System Impact:<\/strong> Silica sol investment casting usually achieves CT4\u2013CT6 tolerance grades under ISO 8062, with many foundries routinely holding CT5\u2013CT6 on suitable parts. Sodium silicate (water glass) shells typically achieve CT7\u2013CT9, so shell selection directly affects how tight you can hold dimensions.<\/li>\n<li><strong>Design And Cost Decision:<\/strong> The real cost decision is knowing which features to hold as-cast and which to machine. Tolerances tighter than CT4 or surface finishes below Ra 1.6 \u00b5m require secondary machining or finishing.<\/li>\n<li><strong>How Redstone Helps:<\/strong> Redstone Manufacturing manages overseas casting and domestic machining under one accountable company. You get one team responsible for both the casting and the machining. <a href=\"https:\/\/redstonemanufacturing.com\/contact-us\/#quote-form\" target=\"_blank\">Request a tolerance review<\/a>.<\/li>\n<\/ul>\n<h2>Investment Casting Tolerance Chart By Dimension Range<\/h2>\n<p>The table below shows how the tolerance band widens as part dimension increases, with specific values for normal and premium grades. Use it to quickly compare your critical dimensions to typical investment casting capability before you finalize a drawing.<\/p>\n<p>Per ISO 8062 casting tolerance (CT) grade tables, tolerance bands widen non-linearly beyond the 250 mm size step. For example, CT6 grows from 1.0 mm at 160\u2013250 mm to 1.1 mm at 250\u2013400 mm. Wax pattern shrinkage and ceramic shell thermal behavior become harder to control across larger surfaces, which drives this widening.<\/p>\n<div class=\"table-scroll\" tabindex=\"0\" role=\"region\" aria-label=\"Scrollable data table\"><table>\n<thead>\n<tr>\n<th>Dimension Range<\/th>\n<th>Normal Grade Tolerance<\/th>\n<th>Premium Grade Tolerance<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Up to 0.5 in (12.7 mm)<\/td>\n<td>\u00b10.007&#8243; (\u00b10.18 mm)<\/td>\n<td>\u00b10.003&#8243; (\u00b10.08 mm)<\/td>\n<\/tr>\n<tr>\n<td>0.5\u20131 in (12.7\u201325.4 mm)<\/td>\n<td>\u00b10.010&#8243; (\u00b10.25 mm)<\/td>\n<td>\u00b10.005&#8243; (\u00b10.13 mm)<\/td>\n<\/tr>\n<tr>\n<td>1\u20132 in (25.4\u201350.8 mm)<\/td>\n<td>\u00b10.013&#8243;<\/td>\n<td>\u00b10.008&#8243;<\/td>\n<\/tr>\n<tr>\n<td>2&#8243;\u20133&#8243; (50.8\u201376.2 mm)<\/td>\n<td>\u00b1.016&#8243;<\/td>\n<td>\u00b1.010&#8243;<\/td>\n<\/tr>\n<tr>\n<td>3\u20134 in (76.2\u2013101.6 mm)<\/td>\n<td>\u00b10.019&#8243;<\/td>\n<td>\u00b10.012&#8243;<\/td>\n<\/tr>\n<tr>\n<td>Up to 5 in (127 mm)<\/td>\n<td>\u00b10.022&#8243; (\u00b10.56 mm)<\/td>\n<td>Tighter than normal grade<\/td>\n<\/tr>\n<tr>\n<td>5\u20136 in (127.0\u2013152.4 mm)<\/td>\n<td>\u00b10.025&#8243; (\u00b10.64 mm)<\/td>\n<td>Confirm with foundry<\/td>\n<\/tr>\n<tr>\n<td>6\u20137 in (152.4\u2013177.8 mm)<\/td>\n<td>\u00b10.035&#8243; (\u00b10.89 mm)<\/td>\n<td>\u00b10.025&#8243; (\u00b10.64 mm)<\/td>\n<\/tr>\n<tr>\n<td>7&#8243; to 8&#8243; (177.8\u2013203.2 mm)<\/td>\n<td>\u00b10.031&#8243;<\/td>\n<td>\u00b10.017&#8243;<\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n<p>Tighter-than-standard tolerances often require special procedures and secondary operations that add cost and time. Reserve premium tolerances for the three to five dimensions that truly drive function, and keep the rest at normal grade.<\/p>\n<figure style=\"text-align: center\"><img decoding=\"async\" src=\"https:\/\/cdn.aigrowthmarketer.co\/1787254105794-5abe8b51bbfd.webp\" alt=\"Hands using a caliper to measure a precision-machined metal component during inspection\" style=\"max-height: 500px\" loading=\"lazy\"><figcaption><em>Every part is measured and verified \u2014 tight-tolerance quality control on the shop floor.<\/em><\/figcaption><\/figure>\n<h2>Geometric Tolerances In Investment Casting<\/h2>\n<p>Geometric tolerances control shape and orientation, not just size, so they behave differently from linear tolerances. The figures below are practical as-cast guidelines, not guaranteed drawing values. Confirm each one with the foundry during the request for quote (RFQ) stage.<\/p>\n<figure style=\"text-align: center\"><img decoding=\"async\" src=\"https:\/\/cdn.aigrowthmarketer.co\/1787254147220-2c73ec1dadee.webp\" alt=\"Metal casting dies and valve-body castings in a foundry setting\" style=\"max-height: 500px\" loading=\"lazy\"><figcaption><em>Cast parts and tooling \u2014 the dies and patterns behind repeatable casting.<\/em><\/figcaption><\/figure>\n<ul>\n<li><strong>Flatness:<\/strong> A common rule of thumb is 0.005&#8243; per inch (0.127 mm per 25 mm) of length. Actual capability depends on configuration, wall thickness, and alloy, and many foundries express it as allowable dish per 6 square inches of surface area. Surfaces over 4 inches across usually need a machining allowance.<\/li>\n<li><strong>Straightness:<\/strong> Typical as-cast straightness is about \u00b10.005&#8243; per inch. Long unsupported sections often need post-cast straightening.<\/li>\n<li><strong>Angularity:<\/strong> Standard as-cast angularity tolerance is about \u00b10.5\u00b0 unless otherwise specified. \u00b11.0\u00b0 applies only to certain castings that can be reworked to that level, depending on alloy.<\/li>\n<li><strong>Parallelism And Perpendicularity:<\/strong> Industry-standard investment casting parallelism and perpendicularity tolerances are about \u00b10.003\u20130.005 per linear inch.<\/li>\n<li><strong>Concentricity:<\/strong> As-cast diameters are typically concentric within about 0.005&#8243; per inch of separation between diameters.<\/li>\n<li><strong>True Position:<\/strong> For stainless steel investment castings, as-cast true position tolerance is about \u00b10.5\u20131.5 mm. Requirements tighter than about \u00b10.3 mm need post-machining. Precision features should reference machined datums.<\/li>\n<li><strong>Roundness:<\/strong> Roundness is a natural strength of investment casting. The exact relationship to the linear tolerance band depends on geometry, so confirm it with the foundry.<\/li>\n<\/ul>\n<p>Roundness is usually the strongest geometric characteristic in investment casting, while true position is the weakest. A bearing bore can be perfectly round yet still fail if it sits 1.2 mm away from its nominal location. Machined datums solve this structural limitation on precision parts.<\/p>\n<h2>ISO 8062 CT Grades For Investment Casting<\/h2>\n<p>ISO 8062-3:2023 defines dimensional casting tolerance grades (DCTG), geometrical casting tolerance grades (GCTG), and machining allowance grades (RMAG) for castings. It replaces ISO 8062-3:2007. The dimensional casting tolerance grade scale runs from <a href=\"https:\/\/standards.iteh.ai\/catalog\/standards\/iso\/a81124cb-4642-44e5-b033-fea28950e687\/iso-8062-3-2023\" target=\"_blank\" rel=\"noindex nofollow\">DCTG 1 (tightest) to DCTG 15 (coarsest), with a special DCTG 15wt grade for wall thicknesses on castings generally specified to DCTG 15<\/a>. Annex A recommends investment casting in the DCTG 4\u20139 range, depending on part size and shell system.<\/p>\n<p>The CT value represents the total tolerance band, not the bilateral \u00b1 value. By default, this band is centered on the nominal dimension, with half on each side, unless buyer and manufacturer agree on an asymmetric band. For a CT6 dimension in the 0\u201310 mm nominal size range, a 0.52 mm total band means \u00b10.26 mm. Divide the CT band by two before you compare it to a bilateral drawing tolerance.<\/p>\n<p>ISO 8062-3:2023 applies by largest overall dimension as follows. Parts up to 100 mm can achieve DCTG 4 to 6. Parts from 100 to 400 mm can achieve DCTG 4 to 8. Parts above 400 mm can achieve DCTG 4 to 9. For castings with a largest overall dimension above 100 mm and up to 400 mm, DCTG 4 is only defined for dimensions up to 160 mm. Larger dimensions within that range use coarser minimum grades. For nominal dimensions above 400 mm and up to 630 mm, DCTG 4 to 9 apply. Wall thickness is toleranced one grade coarser than the general DCTG unless the drawing specifies otherwise.<\/p>\n<p>The table below summarizes the key differences between silica sol and sodium silicate shell systems. It highlights achievable CT grades, typical as-cast surface finishes, and common alloys so you can match your tolerance and finish needs to the right process.<\/p>\n<div class=\"table-scroll\" tabindex=\"0\" role=\"region\" aria-label=\"Scrollable data table\"><table>\n<thead>\n<tr>\n<th>Shell System<\/th>\n<th>Achievable CT Grade<\/th>\n<th>As-Cast Surface Finish<\/th>\n<th>Typical Alloys<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Silica sol<\/td>\n<td>CT4\u2013CT6<\/td>\n<td>Ra 1.6\u20133.2 \u00b5m<\/td>\n<td>Carbon\/low-alloy steel, 304\/316L stainless, 17-4PH, duplex 2205<\/td>\n<\/tr>\n<tr>\n<td>Sodium silicate (water glass)<\/td>\n<td>CT7\u2013CT9<\/td>\n<td>Ra 6.3\u201312.5 \u00b5m<\/td>\n<td>Carbon steel, lower-grade stainless, general industrial alloys<\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n<p>The difference between the two shell systems is significant. At a 50 mm nominal dimension, silica sol investment casting achieves about \u00b10.18\u20130.32 mm, which corresponds to ISO 8062 CT4\u2013CT6. Sodium silicate investment casting at the same size typically falls in CT7\u2013CT9, which corresponds to a linear tolerance deviation of about \u00b10.25\u20130.75 mm. That range is roughly 3\u20135 times wider than silica sol. For steel or stainless parts that need better than about \u00b10.5 mm, silica sol is the practical casting choice.<\/p>\n<h2>What Drives The Investment Casting Tolerance Number<\/h2>\n<p>Five variables drive the tolerance number: alloy, shell system, wall thickness, part size, and feature geometry. Knowing which variable dominates on your part helps you specify a casting that meets function without unnecessary cost.<\/p>\n<p><strong>Alloy.<\/strong> Solidification shrinkage is alloy-specific and sets the achievable CT grade. Carbon and low-alloy steel has a shrinkage allowance of about 2.0%\u20132.5%. Silica sol investment casting of these steels typically achieves CT5\u2013CT7 per ISO 8062, with CT4\u2013CT5 possible on high-precision parts. SS304 (CF8) and SS316L (CF3M) stainless steels show solidification shrinkage of about 2.0\u20132.5% by volume. CT4\u2013CT6 is routinely achievable on well-designed components, and CT4 is realistic on simple, symmetric SS316L parts.<\/p>\n<p>Duplex 2205 (CD3MN) investment castings show higher dimensional scatter than austenitic grades because ferrite and austenite solidify together. Practical as-cast tolerance for duplex parts usually falls in CT5\u2013CT7. For 17-4PH stainless steel, total shrinkage from pattern to final dimension is typically 2.0%\u20133.0%. That total includes about 1.5%\u20132.0% from solidification, 1.0%\u20131.5% from cooling, and 0.5%\u20131.0% from post-heat-treatment or aging. Achievable casting tolerances for 17-4PH are usually CT5\u2013CT7, with CT4\u2013CT6 possible on well-designed parts. Nickel superalloys are more challenging for dimensional control, so confirm CT grades with the foundry for each alloy and geometry.<\/p>\n<p><strong>Shell System.<\/strong> Silica sol shells usually achieve CT4\u2013CT6 with Ra 1.6\u20133.2 \u00b5m. Sodium silicate shells usually achieve CT7\u2013CT8 with Ra 6.3\u201312.5 \u00b5m. Shell system choice is often the single largest lever on tolerance and surface finish, and you lock it in before the first pour.<\/p>\n<p><strong>Wall Thickness.<\/strong> ISO 8062-3:2023 assigns wall thickness a tolerance one grade coarser than the general DCTG unless the drawing states otherwise. Thin walls are harder to control dimensionally than solid sections, so they naturally carry a wider band.<\/p>\n<p><strong>Part Size.<\/strong> Small parts up to about 25 mm can reach CT4, the tightest grade routinely achievable in investment casting, but they require tight process control. CT5 is the most common grade for commercial investment castings from about 25 to 100 mm, with typical bilateral tolerances of roughly \u00b10.2\u20130.4 mm. This range balances precision and cost. For large castings above about 50 kg or 300 mm, CT4\u2013CT5 becomes difficult. CT6\u2013CT7 is more realistic, so parts from 100 to 400 mm usually target CT6 or CT7.<\/p>\n<p><strong>Feature Geometry.<\/strong> Dimensions across the die parting line, long thin features that can distort in wax, and features formed by ceramic cores all run looser than the general DCTG. Wax injection parameters alone can shift a pattern\u2019s dimensions by about 0.5\u20131.0% before metal is poured. Die temperature control and storage conditions matter as much as the casting step itself.<\/p>\n<h2>When To Machine After Investment Casting Instead Of Holding As-Cast Tolerance<\/h2>\n<p>The basic rule is simple. When the required tolerance is tighter than typical investment casting capability for that dimension and alloy, plan a machining operation on that feature instead of trying to hold it as-cast.<\/p>\n<figure style=\"text-align: center\"><img decoding=\"async\" src=\"https:\/\/cdn.aigrowthmarketer.co\/1787254086993-0a7949c65682.webp\" alt=\"Close-up of a metal part being turned on a CNC lathe with coolant, CNC machining\" style=\"max-height: 500px\" loading=\"lazy\"><figcaption><em>Precision CNC turning on a live lathe \u2014 one of Redstone&#8217;s core machining capabilities.<\/em><\/figcaption><\/figure>\n<p>Every extra dimension called out at CT4 instead of CT6, or marked for machining, adds cost. However, machining a feature that truly needs it usually costs less than scrap, rework, and inspection failures from an over-toleranced casting. The table below sorts common features into three categories so you can see which ones usually need machining.<\/p>\n<div class=\"table-scroll\" tabindex=\"0\" role=\"region\" aria-label=\"Scrollable data table\"><table>\n<thead>\n<tr>\n<th>Feature Type<\/th>\n<th>As-Cast Capability<\/th>\n<th>Machined Capability<\/th>\n<th>Recommendation<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Bearing seats and bores<\/td>\n<td>Position tolerance varies with geometry; confirm with foundry<\/td>\n<td>Machined to tight tolerances from a machined datum<\/td>\n<td>Machine when tight functional tolerances are required. Mark [M].<\/td>\n<\/tr>\n<tr>\n<td>Sealing faces (O-ring, gasket)<\/td>\n<td>With silica sol and zircon face coats, typical as-cast surface finish is Ra 1.6\u20133.2 \u00b5m (63\u2013125 \u00b5in)<\/td>\n<td>Static O-ring surfaces often run Ra 0.4\u20131.6 \u00b5m. O-ring grooves are commonly turned to Ra 0.8\u20131.6 \u00b5m. Gasket faces are often specified at Ra 1.6\u20133.2 \u00b5m.<\/td>\n<td>Machine when a fine finish is required. Mark [M].<\/td>\n<\/tr>\n<tr>\n<td>Threaded holes and dowel pin holes<\/td>\n<td>Threaded and dowel pin holes are not reliably holdable as-cast. Internal threads are practical only at about M6\/M8 and above with coarse pitch. Precision dowel holes need drilling and reaming.<\/td>\n<td>For press-fit ground dowels and straight pins, SPIROL specifies total hole tolerances between 0.0002 in and 0.0005 in (about 0.005\u20130.013 mm), which aligns with a machined capability of about \u00b10.01 mm or better.<\/td>\n<td>Machine when precision is required. Mark [M].<\/td>\n<\/tr>\n<tr>\n<td>Datum surfaces for inspection<\/td>\n<td>Unreliable as-cast reference<\/td>\n<td>Consistent, repeatable reference<\/td>\n<td>Machine at least one primary datum.<\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n<p>Some features are negotiable with the foundry rather than assumed as-cast. For steel investment castings, flatness tolerances on large flat surfaces with nominal lengths of 100\u2013300 mm typically range from about 0.6 mm to 3.0 mm, depending on the casting geometrical tolerance grade (CTG 4\u20138) per SFSA Supplement 3 and ISO 8062-2. Tighter flatness requirements should be discussed with the foundry.<\/p>\n<p>Long-span dimensions over about 250 mm that need \u2264\u00b10.5 mm also deserve a discussion. Thin-wall areas over large surfaces need review as well, because large areas dump heat quickly into the ceramic shell and often require added wall thickness to avoid mis-fill. An early design for manufacturability (DFM) review before tooling helps catch these issues.<\/p>\n<p>Tolerance is a design decision with a direct cost impact. Treating it as a generic foundry capability statement often leads to expensive first-article failures.<\/p>\n<p><a href=\"https:\/\/redstonemanufacturing.com\/contact-us\/#quote-form\" target=\"_blank\">Discuss your casting project<\/a>.<\/p>\n<h2>Limitations Of Investment Casting As They Relate To Tolerance<\/h2>\n<p>Investment casting is a near-net-shape process that reduces, but does not remove, dimensional variation. It holds much tighter tolerances than many other casting methods, yet it still has clear limits. Knowing where those limits sit helps you decide when to cast and when to machine.<\/p>\n<p>The practical limits include:<\/p>\n<ul>\n<li><strong>True Position:<\/strong> True position is the biggest geometric weakness at about \u00b10.5\u20131.5 mm as-cast. Precision features should reference machined datums.<\/li>\n<li><strong>Long, Thin Ceramic Cores:<\/strong> Long, thin cores can deflect under molten metal and drive wall thickness variation in valve bodies and manifolds.<\/li>\n<li><strong>Minimum Hole Diameter:<\/strong> Holes below about 2 mm in aluminum and about 3 mm in carbon and stainless steels should be drilled rather than cast. For blind holes without preformed ceramic cores, practical depth is about one times the diameter for smaller holes and up to about two times for larger holes. For through holes without preformed ceramic cores, practical depth is about three times the diameter for small bores in the 0.091&#8243;\u20130.200&#8243; range. Smaller holes in the 0.060&#8243;\u20130.090&#8243; range are usually limited to about two times the diameter, while larger holes can be cast deeper.<\/li>\n<li><strong>Slots:<\/strong> Slots narrower than about 2 mm, or deeper than about three to four times their width, should be reviewed with the foundry. The ceramic shell may not form reliably, which risks ceramic inclusions or positive metal fins.<\/li>\n<li><strong>Very Fine Surface Finish:<\/strong> Surface finishes below about Ra 1.6 \u00b5m need post-processing. Investment casting typically achieves Ra 1.6\u20133.2 \u00b5m as-cast. Ra 0.8\u20131.6 \u00b5m is the finest reliably achievable on shell-facing surfaces of small silica sol parts. Surfaces that need Ra below 0.8 \u00b5m must be machined or otherwise finished.<\/li>\n<li><strong>Tolerances Tighter Than CT4:<\/strong> CT4 is the tightest tolerance grade achievable with investment casting under ISO 8062. That grade corresponds to about \u00b10.13 mm for a 10 mm dimension or about \u00b10.25 mm for a 50 mm dimension. Tighter tolerances require CNC machining. When a feature needs tighter than CT4 or a finish below Ra 1.6 \u00b5m, machining becomes part of the process, not an optional extra.<\/li>\n<\/ul>\n<p>Investment casting holds linear tolerances roughly four times tighter than green sand casting. SFSA comparative data shows about 0.8 mm total tolerance for investment casting versus about 3.4 mm for green sand on a 100 mm steel feature. That precision makes investment casting the most accurate casting option for many steel and stainless parts. CNC machining still holds tighter tolerances, so drawing a casting as if it were a machined block usually creates unnecessary cost.<\/p>\n<h2>How Redstone Manufacturing Fits<\/h2>\n<p>Redstone manages investment casting production at its own overseas facilities and selects the country and process based on part geometry, volume, and landed cost. Redstone Manufacturing produces castings at facilities in China and other locations. Every program includes a design for manufacturability (DFM) review that flags tolerance callouts the process cannot hold before tooling is cut, when a change costs an email instead of a new die.<\/p>\n<figure style=\"text-align: center\"><img decoding=\"async\" src=\"https:\/\/cdn.aigrowthmarketer.co\/1787254276576-d9e2e07e8b5b.webp\" alt=\"Container ship loaded with cargo at port, representing managed overseas production and global supply chain\" style=\"max-height: 500px\" loading=\"lazy\"><figcaption><em>US-managed overseas production \u2014 global supply, domestic accountability.<\/em><\/figcaption><\/figure>\n<p>Redstone also operates a 5-axis computer numerical control (CNC) machining facility in Seattle. A casting produced at a Redstone facility in China can be machined domestically under one accountable company. Many CNC shops avoid castings and ask customers to source them separately. Redstone handles both casting and machining.<\/p>\n<p>Some features should still be held as-cast when the process can support them. The bridge between overseas casting and domestic machining exists for features that genuinely need tight control in the United States. Typical examples include bearing seats, sealing faces, precision datums, and threaded interfaces on parts where domestic accountability matters.<\/p>\n<p>Parts are manufactured at ISO 9001 certified facilities.<\/p>\n<p><a href=\"https:\/\/redstonemanufacturing.com\/contact-us\/#quote-form\" target=\"_blank\">Get a DFM review<\/a>.<\/p>\n<h2>Frequently Asked Questions<\/h2>\n<h3>What Are The Standard Tolerances For Investment Casting?<\/h3>\n<p>Standard normal linear tolerances for investment castings are <a href=\"https:\/\/www.stainlessfoundry.com\/investment-casting-foundry\/investment-casting-foundry-tolerance\/\" target=\"_blank\" rel=\"noindex nofollow\">\u00b10.010&#8243; up to 1 inch, \u00b10.003&#8243; per inch for each additional inch up to ten inches, and \u00b10.005&#8243; per inch for dimensions greater than ten inches<\/a>. As mentioned in the key takeaways, typical as-cast surface finish runs Ra 1.6\u20136.3 \u00b5m, and investment casting usually falls in the CT4\u2013CT9 range under ISO 8062-3:2023, depending on shell system and part size. The CT value is the total tolerance band, so divide it by two to get the bilateral \u00b1 figure for a drawing.<\/p>\n<h3>How Accurate Is Investment Casting?<\/h3>\n<p>Investment casting holds linear tolerances roughly four times tighter than green sand casting. SFSA comparative data shows about 0.8 mm total tolerance for investment casting versus about 3.4 mm for green sand on a 100 mm steel feature. At a 50 mm nominal dimension, silica sol investment casting typically achieves about \u00b10.18\u20130.32 mm as-cast, which aligns with ISO 8062 CT4\u2013CT6. For comparison, under ISO 8062-3, a 50 mm dimension in green sand casting (nominal &gt;40 to \u226463 mm) runs about \u00b11.0 mm at DCT9, \u00b11.4 mm at DCT10, \u00b12.0 mm at DCT11, and \u00b12.8 mm at DCT12.<\/p>\n<p>Post-cast CNC machining can tighten specific high-precision features to about \u00b10.01 mm or better. Examples include hole diameters to about \u00b10.03 mm, reamed pilot holes to about \u00b10.015 mm, and multi-plane features to about \u00b10.03 mm on 5-axis machines. General machined faces typically hold about \u00b10.02 to \u00b10.05 mm, which is why combining casting with machining is the standard approach for precision parts.<\/p>\n<h3>What Are The Limitations Of Investment Casting?<\/h3>\n<p>True position is the weakest geometric characteristic at about \u00b10.5\u20131.5 mm as-cast. Long thin ceramic cores can deflect and drive wall thickness variation. Holes below about 2 mm in aluminum and about 3 mm in carbon and stainless steels should be drilled rather than cast. Slots narrower than about 2 mm or deeper than about three to four times their width need foundry review. The process stops being the right choice for a tolerance callout when the required tolerance is tighter than CT4 or when the feature needs a surface finish below about Ra 1.6 \u00b5m. Both cases call for secondary machining.<\/p>\n<h3>What Are The Common Factors To Consider Before Designing A Casting?<\/h3>\n<p>Key factors include alloy shrinkage, shell system selection, wall thickness uniformity, part size, feature geometry, parting line location, and which features will be machined versus held as-cast. Alloy choice matters because shrinkage is alloy-specific and sets the achievable CT grade. Shell system choice matters because silica sol and sodium silicate differ by several times in tolerance band. Wall thickness uniformity matters because abrupt section changes create hot spots and shrinkage porosity.<\/p>\n<p>Parting line location matters because dimensions across the parting line consume more of their tolerance budget than dimensions within one die half. Deciding which features to machine before tooling is cut is one of the most cost-effective DFM steps available.<\/p>\n<h3>When Should You Machine After Casting Instead Of Holding As-Cast Tolerance?<\/h3>\n<p>Plan to machine a feature when the required tolerance is tighter than typical investment casting capability for that dimension and alloy. Bearing seats, sealing faces, threaded holes, dowel pin holes, keyways, splines, and datum surfaces used for inspection usually need machining when they carry tight functional tolerances or fine surface finishes. Investment casting alone typically holds about \u00b10.1\u20130.25 mm as-cast and cannot reliably meet those precision levels.<\/p>\n<p>These features are marked [M] on the drawing, with machining stock added per face. For steel investment castings, flatness tolerances on large flat surfaces with nominal lengths of 100\u2013300 mm typically range from about 0.6 mm to 3.0 mm, depending on casting geometrical tolerance grade (CTG 4\u20138) per SFSA Supplement 3 and ISO 8062-2. Tighter flatness requirements, long-span dimensions over about 250 mm at \u2264\u00b10.5 mm, and thin-wall areas over large surfaces should be negotiated with the foundry during the RFQ stage rather than assumed as-cast.<\/p>\n<h3>How Do I Know If My Part Is A 5-Axis Part?<\/h3>\n<p>Unless someone has real machining experience, they usually cannot tell whether a part requires 5-axis machining. Some parts that can run on a 5-axis machine can also be produced on a 3-axis or 4-axis machine, depending on fixturing and tolerance stack-up.<\/p>\n<section data-read-next=\"true\">\n<h2>Read Next<\/h2>\n<ul>\n<li><a href=\"https:\/\/redstonemanufacturing.com\/resources\/articles\/sand-casting-tooling-cost\" target=\"_blank\">Sand Casting Tooling Cost: A Complete Pricing Guide<\/a><\/li>\n<li><a href=\"https:\/\/redstonemanufacturing.com\/resources\/articles\/best-die-casting-companies-mexico\" target=\"_blank\">Die Casting Companies in Mexico: A Buyer&#8217;s Guide for 2026<\/a><\/li>\n<li><a href=\"https:\/\/redstonemanufacturing.com\/resources\/articles\/5-axis-cnc-industrial-machinery\" target=\"_blank\">How to Choose a 5-Axis CNC Machine for Industrial Parts<\/a><\/li>\n<li><a href=\"https:\/\/redstonemanufacturing.com\/resources\/articles\/section-232-tariffs-still-effective\" target=\"_blank\">Are Section 232 Tariffs Still in Effect? (2026 Update)<\/a><\/li>\n<li><a href=\"https:\/\/redstonemanufacturing.com\/resources\/articles\/section-232-tariffs-steel-aluminum\" target=\"_blank\">Section 232 Tariffs on Steel and Aluminum: 2026 Guide<\/a><\/li>\n<\/ul>\n<\/section>\n","protected":false},"excerpt":{"rendered":"<p>Redstone Manufacturing helps engineers hit tight tolerances with precision investment casting. Get our tolerance chart and expert guidance today.<\/p>\n","protected":false},"author":118,"featured_media":73,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"inline_featured_image":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-74","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/redstonemanufacturing.com\/resources\/articles\/wp-json\/wp\/v2\/posts\/74","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/redstonemanufacturing.com\/resources\/articles\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/redstonemanufacturing.com\/resources\/articles\/wp-json\/wp\/v2\/types\/post"}],"replies":[{"embeddable":true,"href":"https:\/\/redstonemanufacturing.com\/resources\/articles\/wp-json\/wp\/v2\/comments?post=74"}],"version-history":[{"count":0,"href":"https:\/\/redstonemanufacturing.com\/resources\/articles\/wp-json\/wp\/v2\/posts\/74\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/redstonemanufacturing.com\/resources\/articles\/wp-json\/wp\/v2\/media\/73"}],"wp:attachment":[{"href":"https:\/\/redstonemanufacturing.com\/resources\/articles\/wp-json\/wp\/v2\/media?parent=74"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/redstonemanufacturing.com\/resources\/articles\/wp-json\/wp\/v2\/categories?post=74"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/redstonemanufacturing.com\/resources\/articles\/wp-json\/wp\/v2\/tags?post=74"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}