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Why does a bar of tungsten heavy alloy chew through a carbide insert that would cut a hundred parts in steel? The short answer is density and how the material deforms under a cutting edge. Tungsten heavy alloy runs 17.0 to 18.8 g/cm3, roughly 2.2 times denser than A36 steel, and it work-hardens locally at the cutting edge in a way plain steel does not. Run steel parameters on it and you will glaze the insert, generate heat instead of a clean chip, and finish with a part that measures wrong once it cools. None of that means the material is unmachinable. It means it runs on its own numbers, and those numbers are below.
Why Tungsten Heavy Alloy Cuts Differently
Tungsten heavy alloy is not a single uniform metal under the tool. It is 90 to 97 percent tungsten by weight, sintered into a matrix of nickel and iron or nickel and copper, and that structure is exactly why it machines the way it does. The tungsten grains are hard and abrasive. The metal matrix holding them is comparatively soft. A cutting edge does not shear through one consistent material, it alternates between the two, and that is what produces the short, discontinuous chips the alloy is known for instead of the long curling chip you get in steel.
Hardness typically tests 24 to 32 HRC, inside the 32 to 35 HRC ceiling ASTM B777 sets by class, and TPW’s own certified Class 2 stock runs an 895 MPa ultimate tensile strength with a 640 MPa yield. Combine that with a Young’s modulus around 310 to 365 GPa, about 1.5 to 1.9 times stiffer than steel, and the part barely deflects under load. That stiffness is exactly why heavy alloy gets specified for tight-tolerance work in the first place, and exactly why a soft setup or a dull edge shows up immediately as chatter instead of getting absorbed the way it would in a more forgiving material.
Step 1: Pick Carbide, Not High-Speed Steel
Carbide inserts are the standard recommendation for turning, milling, and drilling tungsten heavy alloy, and premium-grade carbide is worth the cost over a standard grade. C-2 grade carbide is the common call for drilling specifically. Surface-treated high-speed steel twist drills will get through a hole, but they wear fast enough that they only make sense for a one-off or a prototype, not a production run.
Geometry matters as much as grade. Positive rake inserts are the standard choice for turning, and for a finished surface, pair a positive rake with a large nose radius, a higher spindle speed, and a light feed rather than trying to remove more material per pass. That combination controls the segmented chip instead of fighting it.
Step 2: Set Turning Parameters
| Pass | Depth of cut | Feed | Speed |
|---|---|---|---|
| Roughing | 0.030 to 0.125 in | 0.008 to 0.015 in/rev | 200 to 300 SFM |
| Finishing | 0.010 to 0.015 in | 0.004 to 0.010 in/rev | 250 to 400 SFM |
Those speeds sit well below what you would run in steel, and that is by design. Push past them and the segmented chip formation that is normal in this alloy turns into excess heat at the edge instead of leaving with the chip, which is what actually glazes an insert.
Step 3: Set Milling Parameters
| Pass | Feed per tooth | Speed |
|---|---|---|
| Roughing | 0.007 to 0.015 in | 200 to 400 SFM |
| Finishing | 0.003 to 0.010 in | 300 to 700 SFM |
The finishing range runs faster than roughing on purpose. A lighter chip load at a higher spindle speed is what produces a clean finish on this alloy; trying to finish at roughing speeds just reproduces the roughing surface with a smaller stepover.
Step 4: Set Drilling Parameters and Avoid Binding
Tungsten heavy alloy does not clear a hole the way steel does. Increased clearance angles and automatic, consistent feed are what keep a carbide or C-2 drill from binding and seizing partway down the hole. A peck cycle that hesitates gives the bit a chance to rub instead of cut, and rubbing is what work-hardens the wall of the hole and ruins the next pass.
This is also where the density difference actually costs you time. The same drill running in gray cast iron at a comparable surface speed will clear a heavy alloy hole slower, simply because there is more mass to displace per revolution. Budget for it in the cycle time rather than compensating by pushing feed.
Step 5: Manage Coolant, Chips, and Dust
Coolant should be non-alkaline, water-soluble, and formulated for high lubricity rather than straight cooling. The chips themselves are short and discontinuous by nature, which is actually a convenience on a production run: they clear the cut instead of wrapping the tool the way a steel chip can.
The real precaution is dust, not chips. Fine metal dust from grinding or heavy machining can be an inhalation and ignition hazard if it is allowed to accumulate, the same as it is for most dense metal powders. NIOSH recommends keeping insoluble tungsten dust to 5 mg/m3 as an 8-hour time-weighted average, tighter at 1 mg/m3 for soluble compounds (OSHA has no enforceable tungsten-specific limit). That is a tungsten limit specifically, separate from the cobalt exposure limit that applies to WC-Co carbide tooling itself, not to the heavy alloy part being cut. Standard shop dust collection and housekeeping around the machine handle it; nothing about it is a reason to avoid the material.
The swarf and turnings from a production run are not scrap in the usual sense either. Tungsten heavy alloy retains real value at end of life, turnings included, which is worth knowing before a bin of it goes out with the regular metal recycling. Tungsten Buyers buys grinding sludge and turnings from shops running this material, sorted or not.
What This Looks Like in a Finished Part
Everything above is the difference between a part that holds its print tolerance and one that does not. It is also exactly what goes into shaping a tungsten heavy alloy block into a functional tool rather than just a round or square blank. Our sister brand USA Tungsten machines that same alloy into the working end of a bucking bar, and how a straight, angled, offset, or hook bar gets its final geometry comes down to the same speeds-and-feeds discipline covered here, just aimed at a hand tool instead of a machined component.
Tungsten Parts Wyoming presses, sinters, and machines tungsten heavy alloy to print in Laramie, Wyoming, under ISO 9001. Send us your drawing and we will quote it against the actual tolerance, not a rule of thumb. For the density and stiffness numbers behind these cutting parameters, see tungsten heavy alloy vs steel.
