Measure, choose, and calculate. Before requesting a quote.

If you do not specify tolerances, Proto&Go! applies the general ISO 2768-f tolerance for metals and ISO 2768-m for plastics. For a 25 mm dimension in metal, that means ±0.10 mm, the thickness of two sheets. This is sufficient for most functional parts, housings, supports, and prototypes.

A tighter tolerance than the general one requires slower finishing passes, more careful measurement, and more rejected parts. That is why it is best reserved for dimensions that truly need it, such as a bearing housing. For the rest, the general tolerance is already very fine and keeps the price low.

For specific functional dimensions, Proto&Go! can reach an IT7 quality in metals, about 21 microns for a 25 mm dimension, and IT11 for plastics. Plastics expand and absorb moisture, so it is not advisable to demand metal-level precision. If a part needs such a fit, mention it to the engineering team when requesting the quote.

A machined part shows fine tool marks. At Proto&Go!, surfaces up to Ra 1.6 µm are achieved, about forty times finer than a hair. If you are looking for a uniform appearance, sandblasting or anodizing masks the marks.

H7 defines the size tolerance of a hole. The letter H fixes the lower deviation at zero: the minimum size matches the nominal. The grade 7 determines the tolerance range according to the diameter. For example, a Ø25 H7 hole accepts sizes between 25.000 and 25.021 mm.

Uppercase letters identify hole tolerances and lowercase letters identify shafts. In H7, the hole can be equal to or larger than the nominal size; in h6, the shaft can be equal to or smaller. For the same nominal diameter, the H7/h6 combination has a minimum clearance of zero. Grades 7 and 6 determine the range of each tolerance.

In the Proto&Go! tolerance calculator, select shaft or hole and enter the nominal size, position, and tolerance grade. You will obtain the maximum and minimum sizes in millimeters and the deviations in microns. The table allows comparing the available grades for that position. The tool covers nominal sizes greater than zero up to 500 mm.

H7/g6 is a clearance fit: the g6 shaft is smaller than the H7 hole for the same nominal diameter. At Ø25 mm, the diametral clearance ranges from 7 to 41 µm, that is, from 0.007 to 0.041 mm. For another diameter, recalculate the limits of both parts.

In a clearance fit, the hole is equal to or larger than the shaft. In an interference fit, the shaft is equal to or larger than the hole, and assembly may require pressure or a temperature difference. In a transition fit, clearance or interference may occur depending on the actual measurements. Parts with the same nominal size are always compared.

In the hole-basis system, a hole with H tolerance position is maintained, and the shaft tolerance is selected to obtain the required fit. For example, H7/g6 provides clearance, H7/k6 may provide clearance or interference, and H7/p6 provides interference for a nominal diameter of 25 mm. The choice depends on how the joint must function and be assembled.

ISO 2768 sets general tolerances for dimensions that do not have a specified tolerance. Part 1 covers linear and angular measurements with four classes: f (fine), m (medium), c (coarse), and v (very coarse). Part 2 covers general geometric tolerances with classes H, K, and L. Thus, the drawing only needs explicit tolerances on functional dimensions.

Class f (fine) is tighter than class m (medium). For linear dimensions:

• Over 6 up to 30 mm: ±0.1 mm in f and ±0.2 mm in m.
• Over 30 up to 120 mm: ±0.15 mm in f and ±0.3 mm in m.
• Over 120 up to 400 mm: ±0.2 mm in f and ±0.5 mm in m.

If you do not specify tolerances, Proto&Go! applies ISO 2768-f for machined metal parts and ISO 2768-m for plastic.

±0.3 mm: the dimension can measure between 49.7 and 50.3 mm. For the same dimension, the fine class (f) allows ±0.15 mm and the coarse class (c), ±0.8 mm. All dimensions over 30 up to 120 mm share these values.

It combines the two parts of the standard: «m» is the medium class for linear and angular dimensions (ISO 2768-1) and «K» is the intermediate class for general geometric tolerances, such as straightness, flatness, perpendicularity, or symmetry (ISO 2768-2). It applies to all dimensions and geometries that do not have a specified tolerance.

ISO 286 IT grades define the tolerance width according to the nominal size, from IT01 to IT18: the lower the number, the tighter the tolerance. For a 25 mm dimension, IT7 is 21 µm; IT6, 13 µm; IT8, 33 µm, and IT11, 130 µm. In machining, Proto&Go! achieves IT7 for functional metal dimensions and IT11 for plastic.

An Ø20 h6 shaft allows measurements between 19.987 and 20.000 mm: upper deviation 0 and lower deviation −13 µm. The letter h fixes the maximum measurement at the nominal size and grade 6 provides a width of 13 µm for diameters over 18 up to 30 mm. You can calculate other measurements with the tolerance calculator.

An Ø25 g6 shaft measures between 24.980 and 24.993 mm, with deviations of −20 and −7 µm. It always stays below the nominal size; therefore, with an H7 hole, it forms a clearance fit of 7 to 41 µm.

An Ø10 H7 hole allows measurements between 10.000 and 10.015 mm. The letter H sets the minimum measurement at the nominal size and grade 7 provides a width of 15 µm for diameters over 6 up to 10 mm.

They have the same width but in opposite directions. An H7 hole can be equal to or greater than the nominal size; an h7 shaft, equal to or less than. For Ø25 mm, H7 ranges from 25.000 to 25.021 mm and h7, from 24.979 to 25.000 mm.

In the hole-basis system the usual starting point is H7/p6, a light interference fit for fixed bushings pressed in. For a permanent joint, pressed or shrink-fitted, H7/s6 gives more interference. At Ø25 mm, H7/p6 has an interference of 1 to 35 µm and H7/s6, of 14 to 48 µm. Check it for your diameter with the fit calculator.

For precise and smooth sliding, H7/g6 is typically used, with a clearance of 7 to 41 µm for Ø25 mm. For shafts rotating at medium speed with lubrication, H8/f7 allows more clearance: 20 to 74 µm for Ø25 mm. If the part only needs to be centered and removed by hand, H7/h6 has a minimum clearance of zero.

It depends on which ring rotates relative to the load, the size, and the bearing manufacturer. In the most common case, a rotating shaft with a rigid ball bearing and normal load, SKF, NTN, and Schaeffler recommend the shaft in k5 for diameters of about 18 to 100 mm; j6 or js6 for light loads, and m5 or m6 for larger diameters or high loads. The housing, with the outer ring fixed relative to the load, is usually H7; if the load changes direction, J7 or K7. Qualities 5 and 6 of the shaft usually require grinding. Confirm the fit in the manufacturer's catalog and indicate it on the part PDF drawing.

In the shaft-basis system, the shaft maintains position h, with the maximum size equal to the nominal, and the hole tolerance is changed to achieve clearance, transition, or interference. In the hole-basis system, the hole is fixed in H and the shaft is selected. The hole-basis system is the most common, because holes are manufactured and verified with fixed measuring tools and gauges, and it is simpler to vary the shaft.

Dimensional tolerance limits the size of a dimension, for example Ø25 H7 or 40 ±0.1 mm. Geometric tolerance limits the form, orientation, or position: flatness, cylindricity, perpendicularity, parallelism, or position of a drilled hole, according to ISO 1101. Proto&Go! calculators solve dimensional tolerances; geometric tolerances are indicated on the part PDF drawing.

Attach a PDF drawing assigned to the part and mark only the dimensions that need it, with their tolerance, for example Ø12 H7 or 30 ±0.02 mm. The rest of the dimensions are machined with the general tolerance. Reserving tight tolerances for functional dimensions avoids increasing the part cost.

The standard tolerance for vacuum casting is ±0.3 mm for dimensions up to 100 mm and ±0.3 % for larger dimensions. Polyurethane shrinks by approximately 0.15 %, and precision also depends on the master, the silicone mold, the polyurethane resin, and the geometry: thick walls and long, flat parts warp more. If a dimension requires higher precision, indicate it in the PDF drawing, and the engineering team will confirm feasibility when preparing the quote.

A micron (µm) is one-thousandth of a millimeter: 0.001 mm. A sheet of paper measures about 100 µm in thickness, and a hair, about 70 µm. Therefore, an IT7 tolerance of 21 µm on a 25 mm diameter is less than one-third the thickness of a hair.

Yes. The tolerance calculator and the fit calculator are free and do not require registration. They cover shafts and holes with nominal sizes greater than 0 up to 500 mm, including ISO 286-1 positions and qualities.

On the Proto&Go! resources page you can download the CNC machining design guide as a free PDF, in Spanish, English, French or Italian. It explains how the part is machined, how much tolerance to ask for, seven illustrated rules (inside radii, walls, drilled holes, threads, slots, undercuts and through holes), materials and finishes, and how to lower the cost.

The free PDF guide explains how an HP Multi Jet Fusion printer works, when to choose PA12 or TPA, size and tolerances, six illustrated rules (wall thickness, hollowing, holes, printed threads, inserts and text) and how to redesign, finish and assemble the part. You can download it in Spanish, English, French or Italian on the Proto&Go! resources page.

Yes. On the Proto&Go! resources page you can download the design guide for sheet metal cutting and bending as a free PDF, in Spanish, English, French or Italian. It explains how the part is laser-cut and bent from your 3D model, six illustrated rules (inside radius, minimum flange, holes near the bend, hole diameter, bend reliefs and fasteners), tolerances, materials and finishes, and which file to send.

The free PDF guide explains how the master and the silicone mold are made, which polyurethane to choose (rigid, flexible or transparent), tolerances, five illustrated rules (wall thickness, uniform thickness, ribs, undercuts and demolding, inserts and threads), color and finish, and how many parts each mold yields. You can download it in Spanish, English, French or Italian on the Proto&Go! resources page.

Proto&Go! accepts one 3D model per part in STEP (.stp, .step), SLDPRT, X_T, X_B, IPT, CATPART, PRT, SAT, or 3DM. STL files are accepted only for 3D printing. A 2D file does not replace the 3D model; you can attach a PDF to indicate threads, inserts, tolerances, or other requirements.

At Proto&Go! you can send an STL for 3D printing. For CNC machining, silicone molds, or sheet metal, send STEP or one of the supported native formats. STL represents the surface via triangles; for those other processes, export the original model from your CAD software.

STEP (.stp, .step) is a neutral format that preserves the exact geometry of the part and opens in any CAD software. That is why it is the safest option to quote and manufacture via CNC machining, silicone molds, or sheet metal. If you work with SolidWorks, Inventor, CATIA, Creo, NX, or Rhino, you can also upload the native file.

No. Export the 3D model to STEP or upload a supported native format: SLDPRT, X_T, X_B, IPT, CATPART, PRT, SAT, or 3DM. A 2D drawing in DXF is also not suitable for sheet metal: the part is uploaded already bent in 3D and the development is calculated from the model.

No. Each file must contain a single part. If your design is an assembly, export each part you want to manufacture to an independent file and upload them separately, without screws or commercial elements. If the parts must fit together, indicate the fit dimensions in a PDF drawing.

Attach a PDF drawing assigned to the part when there is information not shown by the 3D model: threads and their metric, inserts, welds, or tolerances tighter than the general tolerance. If there are no special requirements, the 3D model is sufficient and the general tolerance applies.