My way to make a mold

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Dan,

HSS can be made to a sharper edge than tungsten carbide.  The latter usually has less acute angles because it tends to chip if shocked.

Brass likes flat top rake angles, but not a dull edge.  Cutting steel and aluminum required more rake angle regardless of tool material.

As long as the drill rod is annealed or at a temper no harder than around 40 Rockwell C, a properly sharpened and angled HHS cutter will do fine.  Annealed drill rod (the way you buy it) cuts very nicely and is not appreciably harder than mild steel.

HSS tools will wear faster than "carbide", but they usually start sharper and produce a better finish.  They are also very easy to  resharpen.

The height of the cutting edge relative to the lathe center line is rather important, as it changes the effective angles of the tool - both cutting and clearance.

You will find typical tool profiles from many sources.  Cross check them to see that they are in fact correct.  Tool angles are more a matter of principle than absolute law.  Here are a few sources I found in a fast search:

https://littlemachineshop.com/images/gallery/instructions/GrindingToolBits.pdf
http://www.steves-workshop.co.uk/tips/toolgrinding/toolgrinding.htm
https://www.practicalmachinist.com/vb/general/first-attempt-grinding-cutter-259588/
http://www.mini-lathe.com/Mini_lathe/Tool_grinding/tool_grinding.htm





Chip breaker tool is for steel.  Definitely not for brass:











"Carbide" tools contain cobalt as a binder.  Breathing cobalt dust is very bad for your lungs.  A little edge honing is OK, but grinding a form tool with lots of dust exposure is a bad idea.  Some HSS may also contain significant cobalt.

Having air flow away from you is a good idea.  As is wet grinding, or wearing a dust mask.  No need to be paranoid, but I would hate for you to develop pneumonia because you were not aware of the risk and precautions: 

https://nj.gov/health/eoh/rtkweb/documents/fs/1960.pdf
https://carbideprocessors.com/pages/technical-info/grinding-carbide-health-and-safety-risks.html

http://www.mitsubishicarbide.com/application/files/2114/5214/0004/sds_hss_en-gl.pdf
https://www.vodex.co.uk/blog/dangers-metal-dust-fumes/

Rather than scare you, just be aware of anything that irritates your nose or lungs.  The scare stuff is the tungsten carbide.  I discovered that after grinding some form tools.  Fortunately I set things up to spray the bulk of dust away from me and don't stand close breathing in the "cloud".  Whatever exposure I had, had no effect on me.

Lathes are more likely to grab your sleeve and rip your hand or arm off.  They seem docile, but I consider them more dangerous than a milling machine.  The latter will just rip the flesh off a finger, rather than feed you into the machine.  The larger the machine, the more it can hurt you...