Stroke broaching on a CNC lathe or machining center is simple until the first program: where does the tool start, how many strokes, how long does it take. This calculator turns bore, keyway width and depth into the start and end position, the stroke count and the cycle time, with the chord height of the bore included.
Starting values only. Insert-type broaching systems differ a lot: one published chart works at 0.015 to 0.05 mm per stroke, a published worked example from another maker uses 0.08 mm. Use your tool maker's infeed, lock the spindle (M19 or C-axis clamp) and run the first part with the feed override down.
The insert starts at the bore centerline and moves outward. It first meets material at the two corners of the keyway, not at the bore surface on the centerline. Those corners sit lower by the chord height of the bore, so the insert has to cut through that segment before the nominal depth t2 even begins.
Check with a published worked example: bore 32 mm, keyway 8 mm gives a chord height of 0.508 mm. With 0.2 mm safety the start position is X30.584 and the total radial travel for a 2.9 mm deep keyway is 3.608 mm, 45.1 strokes at 0.08 mm. Enter the same numbers above (spring passes 0) and you get the same chord, start position and travel; the calculator rounds the air and cutting strokes up separately, so it shows 46.
X is programmed on diameter, so every value above in X is doubled: the X step per stroke is twice the infeed. On a machining center with radial Y moves use half the X values.
It depends on the tool system, insert width and material. One published insert chart runs 0.015 to 0.05 mm per stroke (about 0.0006 to 0.002 in), deeper in aluminium and free-cutting steel, lighter in hardened steel and nickel alloys. Another maker's worked example uses 0.08 mm. Start from the tool maker's value, then raise it only if the turret, the spindle lock and the part stay quiet.
Published starting values for insert-type broaching sit around 5 to 14 m/min (about 200 to 550 in/min) on the cutting stroke, faster in aluminium, slower in hardened steel, stainless and nickel alloys. A slower final pass helps the finish.
The last strokes take almost nothing, so the insert and holder spring back less on the following pass. Two zero-infeed strokes at final depth bring the width and the wall finish closer to the drawing.
The stroke and cycle math is the same. A blind keyway needs a relief groove for the insert to finish in and for chips to collect, so set the keyway length to end in the relief and keep the overrun small.
This page sizes the program. Which grade and edge for your material, and what an alternative brand would be, is the advisor's job, grounded in catalog data across 15 brands, brand-neutral.