Wire EDM shop guide

Simple Operating Steps for Wire Cutting Machine Tools

A shop-floor routine for wire EDM: how to set up, verify the program, run the first cut, hold size, and shut down without losing your settings. Written for machinists and process engineers who need parts off the table, in tolerance, the first time.

Get Instant Quote Talk to an Engineer

±0.005 mm toleranceRa 0.8–1.6 μm finishFirst cut + skim passes100% inspection on request

Operating steps for wire cutting machine tools on a wire EDM machine

On this page

Key takeaways

Zero the machine, not the partTouch off X, Y and Z on the same datum the CAM post used, or the first cut will miss by the skim offset.

First cut is roughing onlyLeave 0.03–0.05 mm per side for skim passes. Trying to finish in one pass burns the wire and shifts the corner radii.

Check the wire path on dry runStep through the program at low speed with the generator off before you commit a workpiece.

Watch flush pressure, not just the displayLow water pressure shows up as wire breakage, not as an alarm, on most machines.

Log the offsetsWrite down the X/Y shift and taper values so the next setup starts from a known point.

Before you press start

Machine and workpiece checks before the first cut

Wire EDM is slow enough that a bad setup costs an hour before anyone notices. The checks below take about ten minutes and catch most of the problems that would otherwise show up as a tapered wall or a scrapped corner. Do them in order. Skipping the dielectric check is the most common shortcut, and it is the one that breaks wires.

Start with the wire itself. Check the spool diameter and the remaining length against the program length plus 10 percent. A brass wire of Ø0.25 mm is the usual choice for general work; drop to Ø0.20 mm when the inside corner radius is under 0.3 mm, and go to Ø0.30 mm when you are cutting 150 mm or thicker stock and want fewer breaks. Measure the wire tension if the machine has a gauge. Slack wire whips in the kerf and cuts an hourglass.

Next, confirm the workpiece. Verify the material grade against the drawing, because some grades behave very differently in the tank. Aluminium 6061 and 7075 cut fast but need higher flush pressure to clear swarf. Stainless 316 and 17-4PH cut slower and tend to leave a recast layer if the flush is weak. Tool steel and carbide need lower peak current to avoid micro-cracking at the edge.

Clamp the part so it cannot move in X or Y, and check that the top and bottom surfaces sit parallel to the table within 0.02 mm. Taper cutting multiplies any tilt you leave in the setup. If the part is thin, back it with a support plate instead of relying on clamps alone.

Finally, look at the dielectric. The tank should be full, the resin bottle should still have capacity, and the water resistivity should read in the normal band for your machine. Dirty water lowers breakdown voltage, and the machine answers with unstable cuts rather than a clean alarm.

1
Wire sizeØ0.25 mm general, Ø0.20 mm for tight radii, Ø0.30 mm for thick stock.
2
WorkpieceGrade verified, faces parallel to the table within 0.02 mm, clamped against X/Y movement.
3
DielectricTank full, resin active, resistivity in the machine's normal band.
4
ConsumablesSpool length at least program length plus 10 percent.

Offsets and datum

Setting the datum and the wire offset

The datum is where most first-cut failures come from. Pick one corner or one bore on the part, touch off in X, Y and Z, and write those values into the work offset the program calls. If the CAM post assumed the top face as Z zero and you touched off the bottom, every taper value is wrong by the part thickness.

Set the wire offset from the machine's own offset table, not from memory. The offset is the sum of half the wire diameter plus the spark gap, and it changes with wire size, workpiece material and the number of skim passes. For a Ø0.25 mm wire roughing cut in steel, a typical offset sits near 0.19–0.21 mm per side. Confirm it against the machine's table before you run.

If the job needs taper, enter the taper angle and the Z reference heights for the top and bottom guides. The machine needs to know where the pivot point is. A wrong Z reference gives a part that measures correct at the top and out of tolerance at the bottom, which is hard to diagnose after the fact.

On parts with a start hole, check the hole diameter against the wire plus offset. A start hole that is too small forces the machine to thread at an angle, and the wire will break on the first move. A safe rule is start hole diameter at least wire diameter plus 0.3 mm.

1
Work offsetTouch off the same corner or bore the CAM post used, including Z.
2
Wire offsetRead it from the machine table; roughly 0.19–0.21 mm per side for Ø0.25 mm wire in steel.
3
TaperEnter angle plus top and bottom guide Z heights, or the taper will not match the drawing.
4
Start holeAt least wire diameter plus 0.3 mm so the wire threads cleanly.

Program and dry run

Loading the program and running the dry check

Transfer the program and read the first twenty blocks on screen before you do anything else. Check the work offset number, the wire offset number, the taper flag and the cutting conditions code. Most machines show these as separate fields, and a mismatch between the offset number in the program and the one you set by hand is a silent error.

Run a dry pass with the generator off and the wire threaded. Watch the path on the display and listen to the machine. The wire should travel the contour without touching the part. If the display shows the path crossing a clamp, stop and fix the fixture before you cut.

Set the cutting conditions from the machine's recommended table for the material and thickness. As a starting point for steel around 20 mm thick with Ø0.25 mm wire, a roughing cut runs with peak current near 4–6 A and a pulse-on time in the 20–30 μs range. These are starting values, not targets. Adjust from the cut behaviour.

Note the estimated cutting time the control gives you. It is usually optimistic by 10–20 percent on a first run. Use it for planning, not for promising a delivery time to the customer.

1
Read the headerWork offset, wire offset, taper flag and condition code all match the setup sheet.
2
Dry runGenerator off, wire threaded, path clear of clamps and fixtures.
3
ConditionsStart from the machine table; steel at 20 mm with Ø0.25 mm wire runs near 4–6 A.
4
Time estimateTreat the control's estimate as 10–20 percent optimistic on a first run.

Shop routine

Operating steps for wire cutting machine tools, start to finish

Follow in order. Each step names the parameter to watch and the mistake to avoid.

1
Power up and home the machineRun the reference return on X, Y, Z and U/V if the machine has independent taper axes. Let the dielectric reach working temperature if the room swings more than 3 °C overnight. Skipping the home leaves the offsets from the last job in memory.
2
Load the wire and set tensionThread a new spool if the remaining length is under program length plus 10 percent. Set tension to the machine's recommended value for the wire diameter, usually in the middle of the range for Ø0.25 mm brass. Avoid running at the top of the range on thin wire; it snaps at corners.
3
Clamp and indicate the workpieceSeat the part on clean parallels, clamp it against X and Y movement, and indicate the top face within 0.02 mm of the table. Use a support plate under thin parts. Do not rely on the vise alone for a tapered cut.
4
Set the work offsetTouch off X, Y and Z on the datum the CAM post used and store it in the offset number the program calls. Write the values on the setup sheet. Re-check Z after any clamp change; it moves more often than people expect.
5
Enter the wire offset and taper dataRead the wire offset from the machine table for your wire size, material and pass number. Enter taper angle plus top and bottom guide Z heights. A wrong Z reference shows up as a taper error at the bottom of the part.
6
Run the dry checkGenerator off, wire threaded, single block for the first ten moves. Confirm the path clears every clamp. Then run the full dry pass at reduced speed and watch for any axis reversal that looks wrong.
7
Cut the first pass and measureRun the roughing cut and measure the part before the skim passes. Expect 0.03–0.05 mm of stock per side. If the roughing cut is off by more than 0.02 mm from the expected position, stop and recheck the offset rather than compensating in the skim.
8
Run skim passes and inspectRun the skim passes in the programmed order. Measure size and surface finish, then log the offset values and the actual cutting time on the setup sheet so the next run starts from known numbers.

Setup reference

Setup values and what each one controls

Starting ranges for a Ø0.25 mm brass wire on steel. Confirm against your machine's own tables.

Setting	Typical range	What it controls
Wire diameter	Ø0.20–0.30 mm	Corner radius and cutting speed
Wire tension	Middle of machine range	Straightness and break frequency
Roughing offset	0.19–0.21 mm per side	Position of the roughing cut
Stock for skim	0.03–0.05 mm per side	Final size and finish
Peak current, rough	4–6 A at 20 mm steel	Cutting speed and recast layer
Pulse-on time	20–30 μs	Surface finish and wire wear
Flush pressure	Machine setting for thickness	Swarf removal and wire life
Top face parallelism	Within 0.02 mm	Taper accuracy over part height

FAQs

Questions that come up on the floor

How many passes should a wire EDM cut use?

For most parts, one roughing pass plus two or three skim passes. The roughing pass removes the bulk of the material and leaves 0.03–0.05 mm per side.

Add more skim passes only when the drawing asks for a finer finish or a tighter tolerance than the standard run gives. Extra passes cost time and wire without improving size if the roughing cut was already correct.

Why does the wire break during the first cut and not later?

The first cut moves the most material, so flush pressure and current are at their highest. Breaks at this stage usually come from low water pressure, a wire tension set too high for the diameter, or a start hole that is too small.

Check the flush nozzles for swarf build-up and confirm the start hole diameter is at least wire diameter plus 0.3 mm before you change any electrical settings.

Can I skip the dry run to save time?

No. A dry run costs a few minutes. A crash into a clamp costs a wire, a fixture and sometimes the workpiece.

Run it in single block for the first ten moves at minimum, even on a program you have run before. Fixtures move between jobs.

What tolerance can wire EDM hold in normal production?

At GreatLight we hold ±0.005 mm (±0.0002 in) on wire EDM work, with surface finish down to Ra 0.2–0.8 μm on fine work and Ra 0.8–1.6 μm on standard runs.

Holding that band depends on the setup checks above, not on the machine alone. A part that is not parallel to the table will not hold tolerance at the bottom of a taper.

When is wire EDM the wrong process for a part?

Skip wire EDM when the feature is a blind pocket with no start hole, when the part is a simple through slot that a mill can cut in a tenth of the time, or when the material is a soft plastic that a CNC router handles better.

Wire EDM earns its cost on hardened steel, tight inside corners, thin walls and features that a cutter cannot reach.

Do I need to log the offsets after every job?

Yes, if the same family of parts comes back. Log the work offset, wire offset, taper values and actual cutting time. The next setup then starts from known numbers instead of from a dry run and a guess.

It also makes it obvious when a machine has drifted. A wire offset that keeps moving is a sign of a worn guide or a dirty dielectric.

Send the drawing, get a wire EDM plan

Upload your part and we will return a quotation plus a free DFM analysis within 12 hours, with the wire size, pass count and setup notes for your geometry.

12-hour quote±0.005 mm toleranceNo minimum order quantityNDA on request

Get Instant Quote Talk to an Engineer

Follow our shop