Debate: Grinding your own HSS tooling vs buying inserts for a manual CNC conversion?

I spent a weekend grinding HSS bits for my bridgeport conversion project and got a surface finish that looked like a mirror, but it took forever to dial in the angles. My buddy just slapped on some CNMG inserts and his parts came out fine in a quarter of the time. Which side do you fall on when you gotta balance setup time versus part quality?

3 comments

3 Comments

jordang321mo ago

Read somewhere that HSS is way better for one-off parts but inserts win for production runs.

sam171mo ago

Rowan nailed it honestly. Had this job once where I needed a weird internal groove in some 304 stainless and figured inserts would be the faster call. Set everything up, first pass chipped the edge on a built up edge that formed from the stringy chips. Swapped to a sharp HSS tool I ground myself and it ran smooth the whole way with just some heavy mist coolant. Took a bit longer to get the speeds dialed in but that one part came out perfect without buying a whole new holder or insert pack. HSS is just more forgiving with those unpredictable materials where you don't know exactly how the cut is going to behave. For something like aluminum or brass though, I'll take inserts every time since they last forever and index quick.

the_rowan1mo ago

Let me chime in here @jordang32, you're on the right track but it depends a lot on what you're cutting. HSS is tough to beat for weird shapes or soft materials where you'd spend more time programming than actually cutting. Inserts are nice for repeat jobs because you just index them and keep going, no need to regrind or anything. That said, I've had jobs where inserts chipped on the first pass and HSS handled it fine, so don't sleep on it for one-offs even if it's slower.