[ruawake]

With the Tormach 770, when milling a pocket in steel or ss 304, using carbide, what would be the deepest
cuts with each pass?
assuming it was a 4 inch thick by 5 inches long and 3 inches wide.. The pocket would be 2 inches deep
and 2 inches long and 2 inches wide.
what would the g code be? are there any canned cycles in g code?
Thanks for any info you may share.

[zero_divide]

Material: 304 Stainless Cold Rolled 225-275 HB
Tool: 0.500in 4FL Carbide TiAlN coated Solid HP End Mill
Speed: 192.0 SFM/ 1467.5 RPM
Feed: 0.0021 ipt/ 0.0086 ipr/ 12.59 ipm
Chip Thickness: 0.0021 in
Reference Chipload: 0.0021 in
Engagement: DOC=0.094 in WOC=0.500 in

Power: 0.5HP
MRR: 0.59 in^3
Torque: 1.82 ft-lb
Max Torque: 7.90 ft-lb

Start there.
Have to use flood coolant.
Up the DOC from 0.094" if it cuts too easy

[nitewatchman]

ruawake -- With the Tormach 770, when milling a pocket in steel or ss 304

zero_divide -- Material: 304 Stainless Cold Rolled 225-275 HB

Careful, Cold Rolled Steel and 304 Stainless Steel are very different animals.

Austenitic Stainless Steels are not typically Cold Rolled, they are HRAP (Hot Rolled Annealed & Pickled). By definition they cannot be a 300 series Stainless unless they are Austenitic in structure and they must be solution annealed to become Austenitic (heated to 2000F and quickly water quenched, hardness 180Hb). Since Austenitic Manganese Steels (AMS) and Austentic Stainless Steels (ASS) are strain hardening, the surface of a Cold Rolled would likely be over 500Hb with the hardness decreasing to the core. In processing AMS we explosive harden it using Plastic Explosives to raise the Surface Hardness to over 425Hb. For railroad frogs the surface hardness will exceed 650Hb after being in service for a short period due to strain hardening.

This characteristic is what gives Stainless Steel and Manganese Steel the reputation of being hard and difficult to machine. The annealed material tends to be soft and gummy making good chip generation difficult. At the same time if the cut is not agressive enough to cut under the work hardened zone for the previous tooth the material hardness will try to approach the hardness of a High Speed Cutter and increase in depth with every rubbing tooth. Even the force required to check the hardness will have an effect, a piece tested with a 10mm Brinell Ball might read 230Hb to 250Hb where if the same piece is tested with a more accurate Vicker Micro Hardness Probe it might read 180Hb to 190Hb.

Cold Rolled Steel on the other hand is a pleasure to machine.

Numbers given don't look bad for SS, the speed may be a little higher than I would start with but remember the tendency for most people is to back off the cut feedrate, with SS this is not necessarily the best thing to do. It starts to rub the cutter to death on a thin layer for extremely hard material. If anything reduce the speed while keeping the feed up.

nitewatchman

[zero_divide]

Nitewatchman,

Can you hook me up with some good info on stainless steels conditions.
I do realize that hot rolled and cold rolled stainless steels are different to machine.

But most of the sources I have come up with put hot rolled 304 at 180 HB and cold rolled to up to 270HB

Also I think general consensus is that cold rolled 304 is basically twice harder to machine than the hot rolled.

Can you drop me a link where cold rolled and hot rolled steels are compared side to side?

[nitewatchman]

Let me see what I can dig up.

nitewatchman

[ruawake]

Thanks Guys, that was very helpful
jon

[Wirecutter]

In processing AMS we explosive harden it using Plastic Explosives to raise the Surface Hardness to over 425Hb. For railroad frogs the surface hardness will exceed 650Hb after being in service for a short period due to strain hardening.

nitewatchman

Ok, I'll bite. What is the application for which you must explosive harden AMS? What are you doing?

I've seen a TV show that details explosive welding. Very cool stuff. This is apparently used to weld sheets of dissimilar metals together. The sheets are then used to make non-reactive chemical tanks. The inside surface is safe to have in contact with some chemical or another, and the outside surface is made of something that is perhaps easier to weld or stronger.

Is your (or your customer's) application anything like that?

BTW, I really appreciate the discussion/explanation of cutting stainless. (More! more!) I've had some 'seat of the pants' experience cutting 304, and I know it can be a real bear and tear up tools. I've also noticed that getting more aggressive with feed sometimes makes life easier, contrary to what I would have thought.

When I got my Tormach, I didn't want to shell out the money for Tormach's lifting bar. I was also wondering whether to keep my old manual Bridgeport. The decision became very easy. I used the Bridgy to drill 1" holes in .250" thick 304 stainless plate that became my lifting bar. I had the spindle going less than 60 RPM, and a fairly hard feed rate. The chips looked like that spiral pasta you see in the grocery store. They were warm, but not hot. It was a thing of beauty. Oh, and the lifting bar worked wonderfully, too.

From your description, I was probably doing exactly what you describe - cutting under the work-hardened surface. Anyway, thanks again for the explanation.

-Mark

[nitewatchman]

We make Railway Special Trackwork ----- switches, frogs and diamond crossings. The primary material for frogs is Austenitic Manganese Steel. To date it is the only economical material that will work harden to more than 60 Rc and still remain tough and ductile.

We rapidly accelerate the pre-hardening of the AMS material using PETN or RDX Explosives. The entire surface that will contact the wheel is blasted and the process is repeated three times to push the depth of the work hardening down to about 1/2". Hopefully the video will play showing the operations from a safe distance. There is approximately 30# of material in the first shot and 60# in the second shot.

My group is responsible for the development and management of the process.

nitewatchman