Can HDM machine A36 Mild Steel?

Is the HDM capable of machining mild steel with decent results? I’m expecting it to be really really slow, but with the correct tooling and feeds, is it doable? Thickness will be around 1 1/2 inches, will be cutting and drilling holes. I have a mist coolant setup and I expect to run some kind of coolant appropriate for ferrous metals.


A few folks have done some work in steel. I think @wmoy posted some details a while back.

Here’s a clip from some work I did. I’ll see if I can dig out the details.


It all comes down to math. Given the minimum RPM of the spindle, the “optimal” diameter cutter is about 1/8" or less. I’ve seen Vince @ SMW/ProvenCut push it a little and do 1/4" cutters, but it really comes down to how forgiving the alloy of steel you’re using is.

Without firsthand experience with that particular alloy, I personally wouldn’t go that far and would stick to 1/8" or smaller tooling. But… another thing to balance that against is that if you’re going to be cutting stock 1.5 inches thick, you’re going to need tools that have that much reach. An 1/8" that long will be very fragile, so 1/4" might be all you can manage.

Also, if you’re using an adaptive/trochoidal toolpath I think you can get by with a 1/4" endmill a lot more reasonably. It’s easier on the machine/endmill, and generates less heat. But for doing pure contour cuts/slotting, I wouldn’t recommend it.

There are going to be compromises, you have to see what will work best for you.


As promised, speeds and feeds.
As developed by a woodworker by the seat of his pants.
Please listen to the folks that know what they are doing.
All I know is, it worked for me on my HDM.

End mill - 3/8” 3 flute rougher
15.5 k rpm (8k didn’t sound good so bumped rpm to 15.5 k sweet spot)
50 ipm
Optimal load .0365”
DOC 0.2”

Finished product, a collet wrench


Thanks you all for the replies,

I think I’ll try a 1/4 endmill first for the roughing cut, then move to a 1/8 for details. 1/8 does seem to be too fragile for something this deep.

What coolant/ lubricant are you guys using?

wd40 works great or thread cutting oil but it tends to be more messy

In the video I used a 50/50 water/ipa mix in a squirt bottle which I’m sure is all wrong. But, it

I’ve cut a few more small steel projects using my newly connected mister, air/water.

Water is the universal solvent.

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