Grinding a Step Drill

One thing I drill a lot are holes for hinge pins in molds. Typically I drill D, then G, (F would work, but G allows for faster work and still not bind) and then deburr the hole.

I was thinking if I grind a 5/16 or 3/8 with a .246 and then .260 step I could drill and deburr every hole in one setup with out swapping drills.

I'm about to go swap out the diamond wheel (normally I make carbide tools) for a white stone and give it a go.

Can you:

1. Tell me what I'm about to do wrong?
2. Off suggestions to make it work better next time?
3. Off some guidance other than ask a tool grinding shop to make some for me?

I'll stick with stub length screw machine drills of course.

Bob La Londe CNC Molds N Stuff

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I've made drills to cut various tapers and curves but never a step drill, and they usually needed a pilot hole.

Supposedly dry diamond wheels won't burn on steel below a speed variously given between 3500 and 4500 SFPM. Is your grinder 3 phase?

I started with a split point screw machine length drill.

Nope. Just a plane old single phase single speed induction motor. I did go ahead and use the diamond wheel. Mostly because I didn't feel like digging for the wheel arbor spanner.

I started with a split point screw machine length drill.

Nope. Just a plane old single phase single speed induction motor. I did go ahead and use the diamond wheel. Mostly because I didn't feel like digging for the wheel arbor spanner. Bob La Londe

---------------------------- Drills I modified to make one or two holes cut aluminum without back relief if pushed hard enough. Your step may be small enough to get away without it. One without side relief jammed in the hole when the corners and/or side edge wore down a little.

I made an edge locating support finger for spiral flute grinding from the end of a dull hacksaw blade, a thin spring with a mounting hole. Grinding toward the end went fairly well because the finger forced the end mill to rotate, grinding toward the shank while maintaining contact was difficult. The finger slipped down if twisted too hard and the wheel damaged the edge if it lifted off the finger.

This is the grinding fixture which is very fussy to set up.

Straight flutes are easier to grind because the finger can be attached to and move with the rotary fixture. I bought large dull taps cheap and resharpened them between centers on the surface grinder tool grinding attachment.