need to machine a Hardened gear

[monte55]

I need to mill or drill a 1/4" - 3/8" hole into the side of a hardened steel gear. I only have HSS end mills. Will they work if I take shallow passes?
Thanks...Nick

[Geof]

Probably not.

One way to test is try and file the gear. If it is possible to make an imprint with a file it might be soft enough to machine with HSS. If the file just skates over the surface the only tool to use is carbide.

[scadvice]

... it depends on how hard the gear is. The larger percentage of gears are case hardened and this does make it difficult but possible if you can get below the hardened surface. Mark your hole boarder and mount a dremal grinding wheel then at high est spindle speed lightly peck straight down to a depth at which you ca scratch the metal with the sharp edge of a old HS end mill. It you have any carbide tools even very worn you can also peck with that. Case hardened material is about .05 to .075 thou thick.

I routinely machine hardened materials up to RC 62, but this is really a job for a coated carbide. Ridged set ups are a must.
Steve

[blackbeard52]

one other alternative is to drill through the surface with an ordinary masonary bit. it is cheap and will do a great job of breaking through the skin...the you can mill the hole to size if needed.

[monte55]

I want to thank the guys for the input on machining a hardened rear end gear.
I purchaced a solid carbide end mill and with shallow passes...........I got it done. Actually the gear is going into a very small one man helicopter. On U Tube it is under Human Helicopter for any interested people.
Thanks again.

[aaron p]

Id go to your local supply shop and grab a good Garr brand solid carbide drill. Have to turn the rpm up when using carbide tooling compared to HSS. You CAN use a good Parabolic HSS TiN coated or a Nachi Cobalt drill, but you have to run low rpm and keep coolant on it or some sorta of lubricant.