Milling tool steel

I am working on a project that involves milling tool steel. I work in an architectural metal fabrication shop and know only the basics of milling. I want to be able to make a series of 1/8" through slots in 1/4" thick tool steel and then round the edges. What kind of tooling will A) be able to handle the tool steel and B) make a small radius all the way around the slot?

Thank you in advance

There's tool steel and there's tool steel. I presume you refer to what's commonly called "ground flat stock" "Starrett stock" etc. Annealed tool steel sold in flat plate about 6" x 18" by nominal thicknessses up to an inch. It comes annealed (soft) in several alloys: water heardening, oil hardening, and air hardening which refers to the quenching medium the material's suited for. All this is background for the noobs.

The preferred way to make slots in flat plates in a slitting saw in a horizontal mill. This has a number of advantages namely strong tooling, a rigid set up using a milling arbor and the overarm support, and you can cut accurate slots in a single cut.

However most small shops have a turret mill with a vertical spindle. This means using an endmill to cut slots. Endmills deflect to an astonishing degree when cutting from the solid. If you use a 1/8 endmill and cut your tool steel plate in 6 passes (probably that safest mode; endmills are delicate and the plate is thick in relation to the endmill diameter) you will find the sides come out a little ragged. The preferred way is to cut the slot undersized with a 3/32 end mill and finish the width with a 1/8 endmill.

You will probably get advise all over the map including cut the slot in one whack but generally you will break ferer cutters (you may break more than one endmill on this job so get extra) if you rough undersized and finish with an on sized cutter.

You will have trouble with chips so keep the slot you're cutting clear. A stready air blast strong enough to blow the chips clear is a good start. A srton cjet of coolant is even better but very messy.

Tool steel can be readily cut with high speed steel endmills but it's tough and somewhat abrasive. I suggest you run the 3/32" and 1/8" endmills about 2000 RPM and figure 0.0015" or a bit more feed per tooth. This will move right along. Watch the cut.

Watch the chip color. Silvery to usat turning color is about the limit for high speed steel. If they start turning blue the cutter is getting dull and it's time to change. Coolant will retard the color change so kepp an eye on the cut quality. If you start plowing up a burr ahead of the cutter or the cutter breaks off it's time to change cutters.

You can use carbide endmills but few turret mills run fast enough to take full advantage of them You need about 6000 RPM in these cutter sizes. If that's what you have go ahead but the cutters will not last much longer thant high speed steel.

Rgw bwstr ans most productive way to radius the corners in tinly slots is to remove the burrs by stoning, then use a Burr Quick, Noga, Vargus or eq casterig deburring tool and a rat tail Swiss pattren file. If you wish smoothly polished radii use a little pad of wet-or-dry 400 grit paper to do the final touches. You can machin the radius but in a manual machine this requires extraordinaly care and luck if you are to avoid overcutting ro accidents. Hand de-burring is surprizingly quick in these instances if a little tedious.

When we have to answer questions such as that it helps to know the following: what grade of tool steel? what machine are you going to cut it on? what is the Rockwell hardness of the steel?

I would go ahead and try to cut it with a solid carbide endmill and see how it goes. The normal problem if the steel is too hard is short tool life evidenced by cratering on the top face of the tool. If the machine is not ridgid enough you'll get edge chipping on the tool.

To round over the edge of the cut use a round-over bit. Simple eh?

"What kind of tooling will A) be able to handle the tool steel and B) make a small radius all the way around the slot?" is confusing me a little.

A radius all the way around the slot, sounds like dulling the cutting edges to extreme negative rake.
....but maybe, you wont be cutting material with this "cutter"? Hard stuff for some other reason?

Bob

The tool steel I have is A-2 in 1" by 1/4". I'm not sure of the Rockwell hardness. I bought it from speedy metals just to play around with and get a feel for as I want to eventually make myself some custom tools. The machine I work with has a vertical spindle, brand I can't recall at the moment. No one at the shop is a machinist and we kind of just guess and pool our limited knowledge together whenever we have to make something new with it, until we get it to work. I've done a lot of slots and holes but only on stainless and mild, nothing as hard as what I've got. I tried a test pass with a 3/8" carbide end mill I have and it didn't seem to like it too much. But for all I know, my speed setting could have been way off. Anyways, I've got some good starting points now so thank you everyone.

By radius all the way around, I meant that I just want to break the edges of the slot so it's not a sharp 90 degrees from the face of the metal.

Also, if you havent noticed, I don't know most of the proper terminology, I'm more of a welder. Thanks again.

A2 has plenty of chrome and some tungsten. Expect some cutter wear. Expect ot change cutters frequently. Don't rush it because a cutter that small is easily broken. OTH keep the cutter feeding so it doesn't rub. A2 will work harden to a certain extent. It's a balancing act.

A little oil will help. I use mineral lard oil (commercially available as Mobilmet Omicron and others) but ATF or hydraulic oil will do just fine. Remember to keep the cutter path clear of chips. Also don't let the cutter dwell because rubbing without cutting will wear the cutting edge.

Why not a slitting saw in the vert. spindle and a angle plate if necessary
You can tell if you see the drawing
Peter from Holland

Monkey Wrench said:

... I bought it from speedy metals just to play around with and get a feel for as I want to eventually make myself some custom tools. ....

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It's annealed then. Very soft. Just chuck it up and mill it. No worries.

Monkey Wrench said:

The tool steel I have is A-2 in 1" by 1/4". I'm not sure of the Rockwell hardness. I bought it from speedy metals just to play around with and get a feel for as I want to eventually make myself some custom tools. The machine I work with has a vertical spindle, brand I can't recall at the moment. No one at the shop is a machinist and we kind of just guess and pool our limited knowledge together whenever we have to make something new with it, until we get it to work. I've done a lot of slots and holes but only on stainless and mild, nothing as hard as what I've got. I tried a test pass with a 3/8" carbide end mill I have and it didn't seem to like it too much. But for all I know, my speed setting could have been way off. Anyways, I've got some good starting points now so thank you everyone.

By radius all the way around, I meant that I just want to break the edges of the slot so it's not a sharp 90 degrees from the face of the metal.

Also, if you havent noticed, I don't know most of the proper terminology, I'm more of a welder. Thanks again.

Click to expand...

If you're jst looking to break the edge, and it doesn't HAVE to be a radius, use a c'sink.

Drop it in until you get the edge break you want and then mill a chamfer on your slot.

If it has got to be a radius get a corner-rounding cutter.