machining holes in hardened steel

[Mad Chipster]

i have some .360 holes that need to be reamed to .371. the material is case hardened 8620. around 58-60 rockwell. the problem is the holes were supposed to be plugged at the heat treater but were not. any suggestions on a method to enlarge these holes. finish tolerance is +/- .0005.

[Cmailco]

Blind or thru? To what depth? Is .360 the actual hole size or pre-cased size?

Regards

[dertsap]

solid carbide reamer or interpolate
interpolation would probably produce the best results with that kind of hardness

[TheBigJW]

Do a search for Hi-Roc drills. They work great in a very rigid setup on 58-60.

John

[MikeZee]

Jig grinding, pure and simple.

[Mad Chipster]

the pieces are 1.2" thick and they are thru holes. .360 is the actual hole size.

[Mad Chipster]

pieces are 1.25" thick. holes are thru holes.

[TheBigJW]

Wire edm would be an option as well.

John

[Cmailco]

A carbide reamer is probably going to be your least expensive option for this.

20-30 SFM, .003-.004 in/rev.

[millgirl]

With that kind of tolerance, I would drop into the hole with a carbide end mill and use a circle mill path (or interpolation move), but sneak up on the wall with wear comp. (I would go with multi-passes to get rid of deflection and taper...i've had the best luck with light, quick cuts). You could probably get away with using a 1/4 EM - if there is enough flute (1/2 depth?)

[Cmailco]

By the way, that recommendation is based on actual experience reaming hardened steels in this range. And, HSS actually works quite well in materials up to 50 HRC. The amount of leave (.011) is ideal for reaming in this situation.