[ihavenofish]

im helping a guy out setting up his new machine (novakon nm-200) and we have a dilema for one of his products.

he makes punch dies for gold and silver coins and medalions.

his past work flow was to have the steel milled soft then hardened, then ground. now that hes got his own machine, the idea is to try and do as much as possible in house.

im wondering if anyone has recomendations for feeds and speeds to mill pre hardened die steel - likely D2 though given the soft coin material, it could be something weaker. the smallest tool required would be in the 1/8" territory, so we probably need an acessory high speed spindle since the machines one is 4000rpm.

ive only ever cut a hrc 58 vise jaw of unknown material, so i dont know if the feeds i used would apply to D2. what ive found on the web does seem to indicate i was on the right track though, using about 650sfm, very shallow depths and agressive feeds and no coolant.

[roninB4]

I worked as a tool and die maker for many years, one place I worked at chose to use carbide tooling on all repairs. The punch/die material was often D2 and sometimes had details to be mindful of. I never really thought using carbide instead of grinding was a very good choice. The cutting edge never looked as good under magnification and the number of hits between sharpening was much less (a fraction of) than a proper grind would result in. I would certainly not claim to be the last word in anything but I thought milling/turning hardened material was a poor choice for the company. You may have an application where it works just fine to do this so your own results should be taken as the final word for the process. Hey, anything is worth a try and how else would you know if you don't take a chance? Having said that, all the thermal stress that carbide loads into the workpiece, the comparatively poor finish, the inferior cutting edge of the punch/die, and the cost of carbide vs. grinding wheels it just would not be my first choice.

[ihavenofish]

Having said that, all the thermal stress that carbide loads into the workpiece, the comparatively poor finish, the inferior cutting edge of the punch/die, and the cost of carbide vs. grinding wheels it just would not be my first choice.

thermal stress i dont know is an issue with hard milling techniques, as both the tool and work piece stay cold during machining. the chips come off molten. maybe im wrong though.

cost of the carbide tools seems negligable, as it takes the same tool to mill the unhardened steel in the first place, and tool life isnt shortened significantly. we also eliminate coolant, which is another cost savings.

sharpness of the corners is a big concern. the piece i milled (not d2 mind you) left what appears to be a sharp edge, with minimal burr. i havent looked at it under a microscope though. it would obviously need a small amount of hand work though. i dont know if that negates the savings.

[roninB4]

thermal stress i dont know is an issue with hard milling techniques, as both the tool and work piece stay cold during machining. the chips come off molten. maybe im wrong though.

-You may be right, it depends upon how much material you're removing. Any punch/die section I had to make required more material removal than could be done in a single pass. Sure the chip was blue but there was plenty of heat left in the workpiece. Now if you're just sharpening the punch/die section that's only .010-.030 and nowhere near as much material removed as new tool construction. Then again, your die may not require enough material removed to create the sort of heat I'm talking about. You've seen the die so your experience trumps my estimation.

cost of the carbide tools seems negligable, as it takes the same tool to mill the unhardened steel in the first place, and tool life isnt shortened significantly. we also eliminate coolant, which is another cost savings.

-We return to the amount of material removed. The level of detail figures in here but you must have covered that already.


sharpness of the corners is a big concern. the piece i milled (not d2 mind you) left what appears to be a sharp edge, with minimal burr. i havent looked at it under a microscope though. it would obviously need a small amount of hand work though. i dont know if that negates the savings.

-If you haven't milled D2 that's already hardened then you should experience the joy that can only come from milling hardened D2, it's right up there with Ferro-Tic and Waspalloy in terms of sheer machining pleasure. All BS aside, the burr can be tough to remove. If your cutter has rotation into the edge instead of exiting at the edge (does that make sense?) it has less tendency to push/wipe material out over the edge, thereby creating a burr. Hand finishing will depend upon the geometry of the workpiece and the amount of difficulty will be inversely proportionate to the amount of available time. You may also find that some stones will just "skate' across hardened D2 and you'll need to find some that are soft enough to bite into it. You shouldn't need a microsope to examine the cutting edge, a 10x loupe will be good enough unless the die is expected to have production runs of +1,000,000 hits between sharpenings. I applaud somebody trying to explore outside the conventional methods and hope it works out for you, do let me know if you find success with your methods. Good luck.

[ihavenofish]

thermal stress i dont know is an issue with hard milling techniques, as both the tool and work piece stay cold during machining. the chips come off molten. maybe im wrong though.

-You may be right, it depends upon how much material you're removing. Any punch/die section I had to make required more material removal than could be done in a single pass. Sure the chip was blue but there was plenty of heat left in the workpiece. Now if you're just sharpening the punch/die section that's only .010-.030 and nowhere near as much material removed as new tool construction. Then again, your die may not require enough material removed to create the sort of heat I'm talking about. You've seen the die so your experience trumps my estimation.

cost of the carbide tools seems negligable, as it takes the same tool to mill the unhardened steel in the first place, and tool life isnt shortened significantly. we also eliminate coolant, which is another cost savings.

-We return to the amount of material removed. The level of detail figures in here but you must have covered that already.


sharpness of the corners is a big concern. the piece i milled (not d2 mind you) left what appears to be a sharp edge, with minimal burr. i havent looked at it under a microscope though. it would obviously need a small amount of hand work though. i dont know if that negates the savings.

-If you haven't milled D2 that's already hardened then you should experience the joy that can only come from milling hardened D2, it's right up there with Ferro-Tic and Waspalloy in terms of sheer machining pleasure. All BS aside, the burr can be tough to remove. If your cutter has rotation into the edge instead of exiting at the edge (does that make sense?) it has less tendency to push/wipe material out over the edge, thereby creating a burr. Hand finishing will depend upon the geometry of the workpiece and the amount of difficulty will be inversely proportionate to the amount of available time. You may also find that some stones will just "skate' across hardened D2 and you'll need to find some that are soft enough to bite into it. You shouldn't need a microsope to examine the cutting edge, a 10x loupe will be good enough unless the die is expected to have production runs of +1,000,000 hits between sharpenings. I applaud somebody trying to explore outside the conventional methods and hope it works out for you, do let me know if you find success with your methods. Good luck.

thanks alot for the insigt.

i think what we need to do is simply test. i have to end mills already, just need to get some pre hardened stock and see what explodes worst case, we lose $13 tool and know its not a good idea on this machine.

[RICHARD ZASTROW]

My experience dry machining D-2 left an edge that had minuscule chipping on edges. Went back to jig grinding.

Dick Z

[ihavenofish]

as it turns out hes using mild steel for the punches, then hardening. i guess gold and silver really isnt that demanding. will have to run some tests in the near future.

[juergenwt]

Have the punches annealed, rework and than re-harden. D-2 does not change in heat treating.

[ihavenofish]

Have the punches annealed, rework and than re-harden. D-2 does not change in heat treating.

this is not rework, its new punches and as mentioned, it turns out not d2, just 1018 or 1045.

[jimmyjames1981]

They're using cold roll for coin punches dies???? What?? Yeah that will last about 1 hit...... it does sound like doing all in house by machine prehard d2 would be good but.... milling 60rc steel will kill your cutters, you'll have more money in end mills than sending the work out to be heat treated and ground, for delicate profiles they can be hard milled with a die mold ball or bullnose end mill. The only type of steel I machine everyday is a2 and d2 and heat great and grind and hard mill ungrindable profiles. God if we bought prehard d2 and milled everything out of that it would be retardely non cost effective and time consuming...not too mention the stacks of cash spent on inserts and end mills....... and if any of your parts need threads they'd have to be thread milled with $100+ thread mills that don't last for squat on 60rc d2.....

[jimmyjames1981]

Hard being 1018? To what a 20rc? Not enough carbon in mild steel to be worth heat treating, at very least a 4140 or prehard 4142 should be used.... if I built anything out of 1018 the first hit it would turn into a blob of crap.....not to mention cold roll moves after machining like the leaves on a tree....

[ihavenofish]

Umm... This thread is 5 years old

[jimmyjames1981]

Have you hard milled anything? If your chips are coming off as hot lava you have problems.... it chips just like any other steel, use flood coolant and your edges on your end mill won't fry off lickity split... has to be flood coolant though, a little sprits with a spray bottle won't cut it and will shatter your end mill.

[ihavenofish]

Have you hard milled anything? If your chips are coming off as hot lava you have problems.... it chips just like any other steel, use flood coolant and your edges on your end mill won't fry off lickity split... has to be flood coolant though, a little sprits with a spray bottle won't cut it and will shatter your end mill.

Still 5 years old.....