Definition
Fixturing is holding the workpiece in the machine, with a vice, a chuck, a vacuum table or a purpose-built fixture. The fixture has to take the cutting forces without deforming the part, and has to align the workpiece to the datums on the drawing.
What it means for the calculation
Fixturing decides the number of setups, and on small batches that number is often the largest cost item. A purpose-built fixture is a one-off investment that only pays back over enough pieces or on a repeat order. A thin-walled or slender part needs extra support or a lighter cut, which raises the run time. And a fixture that does not align to the datums moves the problem to the inspection room.
Where this comes up
Not as a word on the drawing. It follows from the datums, from which faces have to be machined, and from how stiff the part is.
Common mistakes
Booking the full cost of a purpose-built fixture on the first order, which makes that order look unaffordable and the repeat orders too cheap. Also pricing a thin-walled part as if it were as stiff as a solid block.
Fixturing decides the number of setups, and on small batches that number is often the largest cost item. A purpose-built fixture is a one-off investment that only pays back over enough pieces or on a repeat order. A thin-walled or slender part needs extra support or a lighter cut, which raises the run time. And a fixture that does not align to the datums moves the problem to the inspection room.
See how Blake reviews a partFrequently asked questions
Is fixturing the same as clamping?
Clamping is one part of it; fixturing also covers aligning, supporting and repeatable relocation.
When does a purpose-built fixture pay off?
Over enough pieces, or on an expected repeat order, where the one-off cost is spread across more parts.
Why does the drawing not name the fixture?
Because the drawing sets the requirement, not the way you meet it; the datums do steer the fixture.