Detailed operating steps and precautions for the double-axis CNC razing machine
This guide walks through power-up checks, workholding, axis referencing, first-cut verification and shutdown for the double-axis CNC razing machine. It is written for machinists and process engineers who already run CNC equipment and now need a repeatable procedure. By the end you will know which checks catch scrap before the first pass, and which numbers to record so the next run repeats.
In this article
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Key takeaways
What the double-axis CNC razing machine actually does
A razing machine removes material with two independent tool spindles that travel on separate axes, usually one vertical head and one horizontal head, or two opposed heads facing the same work zone. The part sits on a table or rotary table while both heads cut in sequence or at the same time. That arrangement is why setup discipline matters more than on a single-head machine: an error in one head shows up as a step, taper or mismatch on the same surface.
The two axes are not interchangeable. Typical configurations give each head its own Z travel and its own tool offset, so the machine can face a top surface with one head and cut a side wall with the other without re-clamping. On a rotary-table version, the table indexes between passes and the heads work on different features. Understand which head cuts which feature before you touch an offset.
Razing sits between roughing and finishing. It flattens a face, removes a parting line or blends a weld, and it usually holds tighter flatness than a mill would on the same part. Typical work is die plates, weldments, castings and large flat components where flatness across the whole face matters more than the surface profile.
Where it does not fit: deep pockets, small internal radii and thin walls under 1.5 mm. A single-spindle mill or a 5-axis center handles those better. If your part needs both a flat face and a tight internal corner, split the operation rather than forcing one machine to do both.
Pre-run checks that prevent most scrap
Before power-up, check the coolant level, way lube reservoir and air pressure. Low way lube shows up as stick-slip on the axis and a wavy finish that looks like chatter but is not. Confirm the pressure gauge sits inside the range on the machine plate; most machines run between 0.5 MPa and 0.7 MPa. Drain the water trap on the air line if the shop runs humid.
Clean both wheel and tool interfaces. A chip trapped between the wheel flange and the spindle nose produces a runout error of 0.02 mm or more, which the finish will show as a repeating mark. Wipe the taper, wipe the flange, then seat the tool and pull it by hand before clamping. Check the wheel for cracks under good light; a ring test with a light tap tells you whether the bond is sound.
Verify the program against the drawing before the first cycle. Check work coordinate origin, tool numbers, offsets and the safe Z height. The most common crash on a two-head machine is a head change written at a Z that clears head one but not head two. Walk the toolpath in single block with rapid override turned down to 25 percent.
Clamp the part and check it again after clamping. Thin plates bow when the vise closes. Set a dial indicator on the top face, loosen and retighten the clamps, and watch the needle. If the face moves more than 0.02 mm, shim the low corner or change the clamping points before you cut.
Setting offsets and workholding on two heads
Reference the machine first: home Z, then X, then Y. Write the work offset only after the axes are referenced, otherwise the controller stores numbers against a position that will move on the next power-up. Touch off head one on the part face, then head two on the same face. The difference between the two Z offsets is the machine's head match error, and you should know that number before the first cut.
For flatness work, hold the part on three points or a magnetic chuck, not on a full bed. A full bed copies the bed's own error onto the part. Three-point support lets the part settle, and you can measure the gap at each point with a feeler gauge. On large plates, add two adjustable supports under the middle and bring them up until they just touch.
Set spindle speed from the wheel or cutter diameter and the material, not from habit. For a 180 mm vitrified wheel on mild steel, a surface speed around 30 m/s is normal; that puts spindle speed near 3,180 rpm. Feed per pass on a razing cut usually falls between 0.05 mm and 0.15 mm for finishing, and cross feed between 2 mm and 5 mm per table stroke.
Do not skip the dress. A freshly dressed wheel cuts cooler and quieter. Dress with a single-point diamond at 0.02 mm per pass, two passes, then a spark-out pass with no infeed. If the machine has a rotary table, check runout at the part radius, not at the table edge. A 0.01 mm error at Ø400 mm becomes roughly 0.03 mm at the rim.
Precautions that keep the operator and the machine intact
Never start a cycle with a guard removed or a door interlock bypassed. On a two-head machine the second head is often outside the operator's line of sight, which is exactly why the interlock matters. Keep hands out of the work zone until the spindle reads zero rpm, not until the door opens.
Wheel breakage is the highest-energy failure on this machine class. Stand to the side of the wheel plane, not in front of it, during the first cut after a dress. Check the wheel for cracks before mounting, use the correct flange diameter, and never exceed the maximum rpm marked on the wheel. Vitrified wheels rated for 35 m/s should not run at 40 m/s to save cycle time.
Keep the floor dry and the chip conveyor clear. Razing produces fine swarf that packs into the coolant tank and reduces flow, which shows up later as burn marks on the part. Clean the tank screen at the end of each shift. Use a chip hook, not gloved fingers, to clear a jam.
Lock out the machine for any maintenance inside the enclosure, including wheel changes and coolant tank cleaning. Two-head machines store energy in the axis drives and in the wheel spindle; an accidental start during a wheel change is a serious injury. Tag the disconnect and keep the key with the person doing the work.
Step-by-step operation of the double-axis CNC razing machine
Follow the order. Skipping step 4 is the most common cause of a scrapped first part.
- 11. Power up and referenceTurn on main power, release E-stop, then home Z followed by X and Y. Let the spindle warm up for 10-15 minutes at half speed before any cut. Cold spindles grow 0.01-0.02 mm during the first hour.
- 22. Verify air, coolant and lubeCheck air pressure 0.5-0.7 MPa, coolant flow at the nozzle, and way lube level. Confirm the lube pump cycles when the axes move.
- 33. Load and indicate the partClamp on three points where possible. Indicate the top face and one side; keep face runout under 0.02 mm and side alignment under 0.03 mm over 300 mm.
- 44. Touch off both headsTouch head one on the face, store Z. Touch head two on the same face, store Z. Compare the two numbers and note the head match error before continuing.
- 55. Load and check the programConfirm work offset, tool numbers and safe Z for both heads. Run single block with rapid override at 25 percent for the first cycle.
- 66. Air pass firstRun the full path 50 mm above the stock. Watch both heads through the whole cycle and listen for the spindle loading up on a rapid move.
- 77. Take the first cut and measureCut 0.05-0.10 mm, stop, and measure flatness and size. Adjust offset by the measured error, not by half of it, when the machine is repeatable.
- 88. Run production and logRecord spindle load, dress count and parts per dress. Stop at the first chatter mark and re-dress before continuing.
When to raze, when to mill
Use this to decide the operation before you write the program.
| Part condition | Razing | Milling | Reason |
|---|---|---|---|
| Flat face, large area | Yes | Possible | Razing holds flatness across the whole face |
| Deep pocket, small radii | No | Yes | No clearance for the head body |
| Weld blend on a plate | Yes | Possible | Cooler cut, less heat into the plate |
| Thin wall under 1.5 mm | No | Yes | Clamping and wheel force deflect the wall |
| Cast surface cleanup | Yes | Possible | Handles interrupted cuts better |
| Tight bore or slot | No | Yes | Needs a single controlled tool path |
| Prototype, one or two parts | Possible | Yes | Milling needs less setup time |
Run the checks, then cut
Most scrap on a double-axis razing machine comes from an unreferenced axis, a dirty flange or a skipped air pass, not from the machine itself. Fix the sequence and the finish follows.
Questions we get about this operation
How do I know the two heads are matched well enough to run production?
Touch both heads on the same reference face and compare the Z offsets. A difference under 0.01 mm is good for most flatness work.
If the difference exceeds 0.02 mm, re-check the tool seating and the flange before you adjust anything in the controller. Most head match errors come from a chip or a worn flange, not from the machine geometry.
What spindle speed should I start with on a 180 mm wheel?
Work from surface speed. For mild steel, 30 m/s is a normal starting point, which puts a 180 mm wheel near 3,180 rpm.
Reduce it for stainless and for interrupted cuts. Listen to the cut: a rising pitch means the wheel is loading, not that the speed is too low.
How much material can I take in one razing pass?
On a finishing pass, 0.05 mm to 0.15 mm is typical, with cross feed between 2 mm and 5 mm per stroke.
For cleanup of a cast or welded surface, take two lighter passes rather than one heavy pass. One heavy pass on an interrupted cut is how wheels break.
When should I re-dress the wheel?
Dress on a part count, then adjust the count from the finish you measure. Start with a conservative number and log every dress.
Two signals mean dress now: the finish develops a repeating mark, or the spindle load climbs more than 10 percent at the same parameters.
Can I run both heads at the same time to save cycle time?
Only if the program and the fixture allow it without the heads entering each other's clearance zone. Check the collision envelope in the controller simulation first.
For most flatness work, running the heads in sequence gives a better face and a safer cycle. Simultaneous cutting is worth it on long plates where the cycle is dominated by table travel.
What flatness can I expect after a good setup?
It depends on the part, the fixture and the wheel condition more than on the machine. Measure the first part and use that number as the baseline.
If the first part is out of flatness by more than your allowance, check clamping distortion before you touch the machine geometry.
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