Feature Control Frame Builder

A feature control frame is a rectangle split into compartments: the geometric characteristic symbol, then the tolerance with any diameter symbol before it and modifiers after it, then up to three datum references in order of precedence, primary first (paras. 6.4.1 to 6.4.3). The 2018 edition has twelve characteristics; concentricity and symmetry were removed, and position or profile now does their job.

What it refuses, and why. A datum on a form tolerance (para. 8.4). An orientation or runout tolerance with no datum (9.3, 12.2). MMC or LMC on a plain surface, which has no size (5.9), or on runout, profile, circularity or cylindricity at all (the Note to 5.9.1, Rule #2). A diameter symbol on anything but an axis (6.6). A projected zone off position and orientation (6.4.7) or off the axis of a hole (10.4.1), the unequally disposed symbol off profile (6.3.22), and a tangent plane off orientation, runout and profile of a surface (9.4). A runout datum at MMB or LMB (12.2). The single letters I, O and Q as datums (6.3.2), a datum used twice, or an empty compartment before a filled one (6.4.3). One refusal is drafting practice rather than a paragraph: a zero tolerance at RFS, which asks for a perfect feature (the standard describes zero at MMC and at LMC, 5.9.5 and 5.9.7, with 9.3.4 and 10.3.4 for orientation and position). Some frames are legal but worth a second look, such as position with no datums (10.6.2.3); those are drawn with a note.

How it is drawn. In units of the lettering height h: the frame 2h high and each symbol at the size Appendix C's Fig. C-2 gives it. Appendix C gives no compartment widths, so the symbol's compartment is the symbol plus 1h and never under 3h, about as wide as Figs. 6-24 and 6-25 draw it, and each datum compartment is at least 2h. Switching units carries a value over at drawing precision (four inch places, three in millimeters). Values follow the drawing rules: millimeters with a zero before a value under 1 and no trailing zeros (4.3.1), inches with no leading zero and the digits as typed (4.3.2). The text is set in Arial so a file opens the same in a document or a slide. The SVG is black on a clear ground; the PNG is black on white, four times the size shown.

Not covered: composite and multiple single-segment frames, datum targets, tabulated tolerances, unit-basis callouts (0.1/25), the between, all-around and all-over symbols, nonuniform and dynamic profile, the continuous feature and independency symbols, and datum translation. The builder checks the frame itself, not whether it suits the part.

Reference: ASME Y14.5-2018, Section 6 (symbology) and Nonmandatory Appendix C (form and proportion of symbols); Sections 8 to 12 for each characteristic. Each refused combination names its paragraph, or is marked as drafting practice; a value that cannot be read as a number is refused without one.

Background on the Drafter blog: Feature control frames.