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Drill point wear in stainless

claya

Cast Iron
Joined
Aug 6, 2006
Location
california
What causes this type of drill point wear when peck drilling stainless? Cobalt drills. 15sfm. Peck depth: 0.25D. Hole 7XD deep. 10% rapid retract.
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What specific stainless is it?

The slow rapid retract may be allowing chips to fall back in the hole. If you're pecking at .25 of diameter, that may be too little, leading to short chips that aid falling back into the hole. I also think your SFM may be too low, but that's material/hardness dependent.

What's your coolant situation? Is it running rich or lean (presuming a water-based coolant)?
 
What specific stainless is it?

The slow rapid retract may be allowing chips to fall back in the hole. If you're pecking at .25 of diameter, that may be too little, leading to short chips that aid falling back into the hole. I also think your SFM may be too low, but that's material/hardness dependent.

What's your coolant situation? Is it running rich or lean (presuming a water-based coolant)?

The chips are spiraling up out the hole, and clearing on retract. SS 17-4ph annealed. We don't see this problem with hardened 17-4ph. Coolant is 9-10%.

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Are you spot drilling? Also I drill a lot of 17-4 and 15sfm is insanely low to me.
Yes. Spot drilling. This part is actually Inco 718 (annealed), Hence the much lower 15sfm.

But, we see the same exact issue with 17-4ph annealed and cobalt drills. We normally cut/drill 17-4ph H1150. And use carbide drills for that. This part we did not have that option.

Is the hole tip getting work hardened, due to a too shallow peck, or from <15sfm at the tip?

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Wee bit of difference between 17-4 and 718! Minimize pecking, you want to keep the drill engaged and cutting. Each retract is a chance to start work hardening. I'd up speed a little, maybe 50 SFM.

What's your feed rate?
 
Okay, that's quite a bit different then. In general when I see catastrophic failure like that I crank up the RPMS as a rule of thumb. I'd rather burn em up then break em off. In inconel it could be a lot of different things though and I almost never drill it, just turn it so I can't really help you there. I'm sure someone else will chime in.

If you're seeing this in 17-4 though crank up your RPMs.
 
Wee bit of difference between 17-4 and 718! Minimize pecking, you want to keep the drill engaged and cutting. Each retract is a chance to start work hardening. I'd up speed a little, maybe 50 SFM.

What's your feed rate?
Feed: .34ipm. We see the exact same drill tip problem with 17-4ph annealed and Cobalt. Figured the cause was the same.

With deep hole drilling the rule is reduce the peck. So with Inco its INCREASE the peck depth? 50sfm is not a little from 15sfm, its 150%. Was using the S&F from g-wizard.

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My take on superalloys is drill as deep as you can, keeping the cutting action going. Obviously if you aren't using TSC you're limited, but each retract/return is (as I said) another chance to initiate work hardening as the drill tries to reenter the metal. If you can cut the number of pecks in half you'll be ahead of the game.

Try to balance the speed and feed to keep the chips coming out of the hole, some experimenting is needed. 50 SFM should be within cobalt's range in 718, at least try it.

At .34 IPM and 15 SFM, roughly 190 RPM at guesstimate .3" drill size? That's less than a thou per tooth, I think you're rubbing too much. Try a more aggressive cut, .003/tooth or so. But start with a fresh drill, not one already used on a slower cut. If you can use a stub drill and avoid spotting I'd do so.
 
0.246 drill. At 40sfm @ 1.0ipm, 0.125 peck the new drill started screetching halfway down. Tip was already damaged by then.

Finished the job using the original rates.

I agree the tool is rubbing possibly WH the bottom. And/or the pullout is chipping the tip. Someone was going to post a peck drilling macro that added a bottom dwell, but I have never seen it. I had a really bad experience with drill that welded itself from too high rpm/peck in a one-off 17-4ph part. Since then I have always used shorter pecks in deep holes in SS..

Sounds like 718 has a narrow sweetspot when drilling using Hss/Cobalt. We have always sidestepped that with carbides in high nickel alloys.

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Good, that's additional data. What brand is the drill, is it a jobber? What coolant are you using? Are your numbers what the drill vendor recommended?
Generic C-L. Stub length, 135 splitpoint. Coolant: Trimsol synthetic, 10%
S&F: From G-wizard or Fz-wizard. Both were ~15-25sfm range for Inco 718

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Chicago Latrobe is part of Greenfield Industries Inc., which itself is now owned by a Chinese company. Even though the drill bits themselves may still be made here, there's always a question as to whether standards have been kept in alloys and heat treatment.

Greenfield Tap & Die modern history [Archive] - The Garage Journal Board

If you run these parts again and have the option to try other cobalt drills, check out Titex or Guhring products.
 
Chicago Latrobe is part of Greenfield Industries Inc., which itself is now owned by a Chinese company. Even though the drill bits themselves may still be made here, there's always a question as to whether standards have been kept in alloys and heat treatment.

Greenfield Tap & Die modern history [Archive] - The Garage Journal Board

If you run these parts again and have the option to try other cobalt drills, check out Titex or Guhring products.
Will do. We have probably had those CL drills for 5 years at least.

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Inco is not friendly to drills,
Sounds to me you have multiple
problems going on at the same time. What angle spot drill.
Small window for sweet spot.
I would switch to a better drill.
 
Inco is not friendly to drills,
Sounds to me you have multiple
problems going on at the same time. What angle spot drill.
Small window for sweet spot.
I would switch to a better drill.
140 spot.

What other issues that have not already been covered?

Found out yesterday the previous shop that did these (and all other INCO) parts was using 0.02" pecks @ 50sfm with higher performance Cobalts. We were using 0.062 pecks @ 15sfm. An attempt at 0.125pecks, tool started to fail first hole at 1" deep. So a bit confused at the INCO deeper pecks advice.

We usually use carbides for high nickel alloys. This was a special case where we used Cobalt. Next op was a reamer, so thought cobalt was good enough, as long as we went slow. Did not anticipate the aggressive tool wear, we have not seen/noticed it before on other drilled INCO parts.

Does heat treated INCO drill better (or more consistently), so long as you go slow enough? Does HT INCO have a wider sweet spot for drilling and milling? We have seen this with other materials.

Tool runout was 0.00025" on the last drill.. Previous drills may have been worse Tir.

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718 double age hardened is about the most difficult material you can work with. Tooling just doesn't last long which is one of the many reasons it is so costly to work with. TSC will make a huge difference but you will still go through tools rather quickly.
 
140 spot.

What other issues that have not already been covered?

Found out yesterday the previous shop that did these (and all other INCO) parts was using 0.02" pecks @ 50sfm with higher performance Cobalts. We were using 0.062 pecks @ 15sfm. An attempt at 0.125pecks, tool started to fail first hole at 1" deep. So a bit confused at the INCO deeper pecks advice.

So I got the SFM right, at least... ;)

The deeper peck is based on minimizing re-entry into the material with each pecking event, on the basis that the impact on the edge due to retreat-reentry gives more wear and work hardening opportunities. But circumstance can vary, if the other company made .020 pecks work for them, so be it.

High nickel? Max pain is more like it...
 
HSS in 718 is going to want to be around 10ish SFM, I would be willing to be the only reason the other company got away with 50 SFM is from the peck being so small.

I've worked with the stuff a fair bit in the past and it is slow going with HSS or carbide......ceramics are a different story and although they don't last a long time they are very effective if you compare the cost to the amount of material removed in that short period of time.

Best advice I was ever given when it comes to working with the stuff is to change out tools long before they start showing wear.
 








 
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