17-4 machining - carbide vs. cobalt

[specfab]

I am selecting either H900 or H1150 grade 17-4 to make some harder wear parts to replace a 303 piece. H900 runs about Rc 40, H1150 is around Rc 28. I'm wondering whether the difference between the two hardness specs means a complete change of tooling required. I need to make some disks about 1" dia. with a precision center bore and a few small holes, and I'm hoping that carbide drills are not required. It's small qty work on my own product, so I have some flexibility based on all the factors involved. Any guidance appreciated.

 

[Milland]

Either hardness you'll be fine with quality cobalt drills. I tend to use them rather than carbide when I have the option. It sounds like limited cutting time, so have at it.

 

[Mtndew]

Cobalt will be fine. Just make sure you run it at the appropriate speeds and feeds.

 

[Zeuserdoo]

Cobalt will work fine for what you are doing. The work where carbide drills are worth the price is when you are drilling hundreds or thousands of holes.

 

[plastikdreams]

Surprisingly Cobalt drills do very well in 17-4...endmills, not so much

 

[BugRobotics]

I prefer cobalt drills in stainless where I have a limited run and don't have the feed/speed dialed in as the cobalt is a bit more forgiving.

 

[plastikdreams]

Honestly, regular hss drills do pretty well in 17-4.

 

[Cole2534]

I prefer cobalt drills in stainless where I have a limited run and don't have the feed/speed dialed in as the cobalt is a bit more forgiving.

Bingo!

 

[specfab]

Thanks, all -- made the parts, using cobalt drills and carbide inserts on lathe work, except for a couple of small (.062) holes through the parts, which are 1/16" thk. Looks like after 2 holes through, a standard HSS drill (what I had on hand) gets the outside corners of the cutting edge worn away, and they are essentially useless for completing a center-drilled hole location. It surprised me after the first part, where the drill seemed to be fine. Went though a few drills for a few parts. Probably need to look more carefully at speed/feed for that size drill. I love that H900 stuff, beautiful finish on the turning and part-off.

 

[Cole2534]

What was your SFM? Id be thinking 30ish.

Just checked, and FS Wizard says 20ish.

 

[trevj]

If I were to guess, I'd say i have made well in excess of my body weight in 17-4PH shims and bushings, mostly with HSS tooling and whatever drills were on sale when the supply guy ordered. It's not really 'that' hard, or miserable to machine.

 

[specfab]

If I were to guess, I'd say i have made well in excess of my body weight in 17-4PH shims and bushings, mostly with HSS tooling and whatever drills were on sale when the supply guy ordered. It's not really 'that' hard, or miserable to machine.

I agree -- just requires a little care. Does seem like cobalt works better than standard HSS, but my sample size is small.

 

[plastikdreams]

I used to drill condition a all day with hss bits. They last surprisingly well.