Decimal Point Input: Is X1000 1000 mm or 1 mm?

.Two ways of reading: calculator-type and standard type

• Calculator-type (pocket calculator type): a number without a decimal point is read as mm, inch or degrees as it is.X1000 is 1000 mm^[1].
• Standard type: a number without a decimal point is multiplied by the least input increment (the smallest amount the machine can command) to get its value. There are two kinds of least input increment, IS-B and IS-C. With IS-B, X1000 is 1000 × 0.001 = 1 mm, and with IS-C it is 1000 × 0.0001 = 0.1 mm^[1].
• FANUC-compatible NCs are standard type by default, and some models can be switched to calculator-type by a setting. A number written with a decimal point (X1000.) is 1000 mm under either reading^[1][3].

Where it is set and how to check it

• How a number is read is set by a machine parameter. The Siemens ISO dialect selects it with machine data MD 10884, and Mitsubishi Electric with parameter #1078 (decimal point input type I = read in least input increments, type II = read in mm)^[2][3]. Even NCs from the same maker may be set differently from machine to machine.
• Do not move the machine to find out. Moving an axis with a value that has no decimal point is itself an accident. First look at the parameter screen, or ask the machine builder.
• The fix on the programming side is simple: always put a decimal point on lengths, angles and feeds. That way, the program behaves the same on a machine with either setting.

Units by address (standard type, in mm)

What the number 1 without a decimal point stands for. Compiled from the table in the Siemens ISO dialect manual^[1]. In this table, the addresses whose reading changes are X Y Z U V W A B C I J K Q R F.

For inch, a linear axis is 0.0001 inch with IS-B and 0.00001 inch with IS-C^[1]. Example with dwell: G04 X1000 is 1 second in standard type and 1000 seconds in calculator-type (it stops for nearly 17 minutes)^[2].

×Addresses where the decimal point has no effect

The Mitsubishi Electric manual lists D H L M N O P S T as “addresses where the decimal point is invalid”; even if you add a decimal point, the fractional part is dropped and the value is read as an integer^[3]. These are numbers (N, O, T, H, D), counts (L), spindle speed (S), M-codes and so on. Even if you write S1000.5 , it is still read as 1000.

Exceptions within the same NC (easy to get wrong here)

• Thread start angle Q: In Haas G32, Q is an integer in units of 0.001°, and you must not add a decimal point (180° is Q180000). The Siemens ISO dialect, by contrast, adds a decimal point and writes Q180. (in degrees)^[4][2]. Even for the same “second start of a multi-start thread”, the way of writing is the exact opposite.
• P and Q in line 2 of G76 (thread height and first depth of cut): write them as integers in least input increments, with no decimal point (P1534 Q450 is 1.534 mm and 0.45 mm). For details, see G76 of the lathe multiple repetitive cycles.
• P of dwell:G04 P500 , the P is an integer with no decimal point (milliseconds). When you write it with X or U, add a decimal point: G04 X0.5.
• Mitsubishi Electric threading F: F without a decimal point is also read as the integer part in mm, not in least input increments (F1 is 1 mm)^[3]. This is read differently from F for feed per revolution.

Expressions, variables and macro arguments

• Values made with expressions or variables are treated as having a decimal point. Mitsubishi Electric reads X123+0 as 123 mm, and all variable values carry a decimal point^[3].
• Conversely, when you call a macro, the Argument may be read in the least increment if they have no decimal point. According to the Haas manual, with an mm setting, writing A1 makes #1 0.001^[5]. Write arguments like A1. — in other words, always include the decimal point. For details, see G65 in the introduction to custom macros.

Differences between NCs

Shop-floor checklist

• Put a decimal point on every X, Y, Z, U, W, I, J, K and R (X30 rather than X30.)
• Put a decimal point on F too (F0.2, F150.)
• Wrote P and Q in cycles (line 2 of G76, G04 P) as integers without a decimal point, as the manual specifies
• Matched Q for multi-start threads to the way that machine writes it (with or without a decimal point)
• Put a decimal point on macro arguments (A1.)
• When reusing a program from another machine or from CAM, searched it for numbers left without a decimal point
• Confirmed the machine's decimal point input setting (calculator-type or standard type, IS-B or IS-C) on the parameter screen or with the machine builder

Related: Introduction to NC Lathe Programming (try forgetting a decimal point in the simulator), Canned cycle list (sign and decimal point of Q), G32 threading, Codes with clashing numbers