Operating guide

What are the operating techniques of five axis tool grinders?

Five axis tool grinders cut flutes, reliefs and end geometry on carbide and high-speed steel tools in one setup. This guide covers the sequence we follow on the shop floor, the numbers that matter, and the mistakes that scrap a tool.

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Carbide and HSSØ3–20 mm toolsRelief and flute grinding

Grinding angle adjustment on five axis tool grinders

On this page

1
What matters most on five axis tool grinders
2
Setting up five axis tool grinders before the first pass
3
Choosing and dressing the grinding wheel
4
Grinding parameters that hold flute geometry
5
Coolant delivery on five axis tool grinders
6
Step by step: grinding a 4-flute carbide end mill
7
Parameter ranges by tool material

Key takeaways

What matters most on five axis tool grinders

Dress before you trust the wheelA wheel dressed 0.02 mm off true shows up as runout on every flute.

Grind in one setupFive axis tool grinders keep the tool in one clamp, so flute and relief share the same datum.

Coolant pressure beats flow6–10 bar directed at the contact zone clears chips better than a wider, softer flood.

Check the first and last fluteIf flute 1 and flute 6 differ, the problem is workholding or thermal drift, not the program.

Measure before unclampingRunout and diameter checks on the machine catch drift while the tool is still recoverable.

Setup

Setting up five axis tool grinders before the first pass

Everything that goes wrong on a ground tool usually starts before the wheel touches carbide. On five axis tool grinders the workpiece stays in one clamp for the whole cycle, so the datum you set at minute one is the datum you finish with. If the collet has 0.01 mm of runout, every flute inherits it.

Start with the blank. Measure shank diameter at three points along its length. A ground shank from a good supplier should hold ±0.005 mm. A turned shank that varies by 0.02 mm will not sit concentric no matter how carefully you dial it in.

Clean the collet and the spindle taper with a lint-free wipe and a light oil film. Chips of carbide left from the last job will seat the blank off-axis. It takes thirty seconds and it prevents a scrapped tool.

Check the coolant nozzles before you close the door. Aim them at the contact zone, not at the shank. On a Ø6 mm end mill running at 4,000 rpm, a misdirected nozzle leaves the flute dry for the first 2 mm of grind, and that is where the burn mark appears.

Wheels

Choosing and dressing the grinding wheel

Wheel choice sets the ceiling on what your five axis tool grinders can hold. For carbide tools we run diamond wheels in the 120 to 320 grit range depending on the operation. Flute grinding usually sits around 220 grit. Relief grinding can go finer, 320 grit, when the edge radius has to stay under 0.02 mm.

Bond hardness matters as much as grit. A wheel that is too hard glazes, and the tool rubs instead of cutting. You hear it before you see it, a higher pitch and a change in the sound of the cut. If the spindle load drops while the pitch rises, stop and dress.

Dress with a single-point tool and take 0.01 to 0.02 mm per pass. Two passes is normal. More than four passes on a fresh wheel wastes diamond and does not improve true running.

For high-speed steel tools, aluminum oxide wheels in the 60 to 120 grit range cut cooler and cost less. Do not mix carbide and HSS wheels on the same spindle without cleaning between jobs. Carbide grit embedded in an aluminum oxide wheel will scratch an HSS flute.

Parameters

Grinding parameters that hold flute geometry

Grinding speed for carbide on a diamond wheel sits between 18 and 25 m/s. Above that the bond wears fast and the wheel loses form. Below 15 m/s the wheel rubs and the edge work-hardens.

Feed per pass depends on the flute depth. For a Ø6 mm end mill with a 1.5 mm flute depth, we take 0.05 to 0.08 mm per pass on the flute and 0.02 to 0.04 mm on the relief. Deeper flutes need lighter passes because the wheel contact arc grows.

Table speed runs 150 to 250 mm/min on flute grinding. Push it higher and you trade edge quality for cycle time. The Ra on a ground flute lands around Ra 0.2–0.8 μm when the parameters are right.

Watch the spindle load, not the clock. A steady load within 10 percent of the baseline means the wheel is cutting cleanly. A load that climbs and falls in a rhythm means the wheel is loading up and the coolant is not reaching the contact zone.

Coolant

Coolant delivery on five axis tool grinders

Coolant does two jobs on a tool grinder, cooling and chip clearing. On carbide the second job matters more. A recirculated chip that passes under the wheel will chip a flute edge in one revolution.

Run 6 to 10 bar at the nozzle. That is higher than most milling operations and it is deliberate. High pressure through a small nozzle gives you a coherent stream that reaches the contact zone through the spray shield.

Filter the coolant to 5 μm or better and skim the tramp oil daily. Carbide sludge turns the coolant into a lapping compound. You will see it as a dull grey finish on a flute that should be bright.

For high-speed steel, a lower pressure of 4 to 6 bar works because the chips are softer and longer. Use the same filtration. Long stringy chips will wrap a collet if they get past the guards.

Step by step

Step by step: grinding a 4-flute carbide end mill

Sequence we run on the shop floor

1
Inspect and clean the blankMeasure shank diameter at three points. Wipe the collet and taper. Reject any blank with a visible bend or a chipped end.
2
Clamp and indicateClamp with 20 to 30 N·m on a Ø6 mm shank. Indicate runout at 10 mm and 40 mm from the collet face. Both readings must be within 0.005 mm.
3
Dress the wheelSingle-point dress, two passes at 0.01 to 0.02 mm. Check the wheel edge with a loupe before you start the cycle.
4
Set the wheel and nozzlePosition the wheel so the contact point matches the flute profile. Aim the coolant nozzle at the contact zone, 6 to 10 bar.
5
Rough the flutes0.05 to 0.08 mm per pass on a Ø6 mm tool. Keep the spindle load steady. Dress again if the pitch rises.
6
Grind the relief0.02 to 0.04 mm per pass. Slow the table to 150 mm/min. This pass sets the edge radius and the cutting feel.
7
Check the first and last fluteMeasure flute 1 and flute 4 with a tool microscope. A difference over 0.01 mm means the workholding moved.
8
Measure before unclampingCheck diameter, runout and edge radius on the machine. Log the numbers so the next run has a baseline.

Reference

Parameter ranges by tool material

Typical values for Ø3–12 mm tools

Parameter	Carbide	High-speed steel
Wheel type	Diamond, 120–320 grit	Aluminum oxide, 60–120 grit
Grinding speed	18–25 m/s	25–35 m/s
Flute feed per pass	0.05–0.08 mm	0.06–0.10 mm
Relief feed per pass	0.02–0.04 mm	0.03–0.05 mm
Table speed	150–250 mm/min	200–300 mm/min
Coolant pressure	6–10 bar	4–6 bar
Filtration	5 μm or finer	5 μm or finer
Typical flute finish	Ra 0.2–0.8 μm	Ra 0.4–1.2 μm

FAQs

Questions we hear from engineers

How often should we dress the wheel during a run?

Dress at the start of every job and again whenever the sound changes or the spindle load drifts more than 10 percent from baseline. On a long run of Ø6 mm tools we typically dress every 15 to 25 tools.

If you are dressing more often than that, check the wheel bond grade and the coolant filtration first. Both will shorten wheel life.

Why do the flutes come out different from each other?

Unequal flutes almost always trace back to workholding or thermal drift, not the program. Indicate the blank at two points along the shank and re-clamp if either reading is over 0.005 mm.

Run the machine for 20 to 30 minutes before a tight-tolerance job so the spindle and the table reach thermal equilibrium.

Can five axis tool grinders grind both carbide and HSS?

Yes, with different wheels and different parameters. The machine does not care about the material, but the wheel does.

Keep dedicated wheels for each material and clean the spindle and guards between changeovers. Carbide grit left in an aluminum oxide wheel will scratch an HSS flute.

What runout should we accept on a finished tool?

For a Ø6 mm end mill we hold runout at 0.005 mm or better on the shank and 0.01 mm on the cutting edge. Tighter than that is possible on our 5-axis machines with a good blank.

Anything over 0.02 mm on the cutting edge will show up as a poor surface finish in the customer's cut.

How do we keep the edge from burning?

Burning is a coolant and speed problem, not a wheel problem. Check that the nozzle stream reaches the contact zone, then reduce grinding speed by 10 to 15 percent and see if the discoloration goes away.

If the burn stays, lighten the feed per pass. A 0.02 mm reduction on the relief pass often solves it.

Do we need to measure on the machine or off?

Measure on the machine before you unclamp. The tool is still on the same datum and you can correct drift without a full re-setup.

Offline inspection with a tool microscope still matters for edge radius and surface finish. Use both, but start on the machine.