Loosing the center of carbide tip drills...

mmurray70 · Apr 20, 2019

Hey guys Im drilling some 7/8" holes, 3.5" deep in steel. Several thousand of them. Using kennametal KTFS carbide tip drills. The inserts are holding up fairly well, but have lost a few a little early with the center blowing out long before insert was worn. See attached pic. I hate loosing tools before they are fully worn out. What do you guys think is causing this? Any suggestions with speed/feed to reduce it?

This is on a Mazak lathe. Coolant through the tool, fairly low pressure but good flow and chips are getting out perfectly. Tool is straight and on center. Running 0.012"/rev and 1500 RPM. Kennametal reccomends something like 0.010-0.019 IPR feedrate. I am facing and then drilling (no spot drill). There is no tit left from facing. One died on entry and 2 more died deeper inside.

Any suggestions? How many holes should I expect from an insert? I need to buy another drill like this soon (around 1.050"), should I look at other brands? What do you guys reccomend?

DMF_TomB · Apr 20, 2019

mmurray70 said:
Hey guys Im drilling some 7/8" holes, 3.5" deep in steel. Several thousand of them. Using kennametal KTFS carbide tip drills. The inserts are holding up fairly well, but have lost a few a little early with the center blowing out long before insert was worn. See attached pic. I hate loosing tools before they are fully worn out. What do you guys think is causing this? Any suggestions with speed/feed to reduce it?

This is on a Mazak lathe. Coolant through the tool, fairly low pressure but good flow and chips are getting out perfectly. Tool is straight and on center. Running 0.012"/rev and 1500 RPM. Kennametal reccomends something like 0.010-0.019 IPR feedrate. I am facing and then drilling (no spot drill). There is no tit left from facing. One died on entry and 2 more died deeper inside.

Any suggestions? How many holes should I expect from an insert? I need to buy another drill like this soon (around 1.050"), should I look at other brands? What do you guys reccomend?

.
1) length of tool and tool holder is the most important factor.
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2) servo oscillation that is if is machine moving back and forth even .001 its hard on any tool especially shorter tools. also grid shift or tool out of expected position can effects things too
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3) metal hard spots or slag. if the metal has hard spots it can be hard on any tool often dulling it in seconds. i have seen hard spots dull 3 tools in a row each within seconds
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4) feed and speed are usually max recommendations. usually tool life goes up if you reduce settings. if it takes 2 seconds longer per hole its often much faster going slower in the long run. often 1% sudden tool failure rate is taking up 400% more time than if you just go slower and get much less sudden tool failure rate
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5) tool life i have seen carbide drills set for 45 minute tool life and if settings are reduced tool life usually gets longer then 100 minutes. depends on what you are drilling of course

spock · Apr 20, 2019

let me beat 50 guys to the first question: what kind of steel? it matters......

mmurray70 · Apr 20, 2019

Its just low carbon mild steel. Probably 44w here in canada, not exactly sure as customer supplied it.

Drill is 5x diameter in length.

Yes im willing to trade cycle time for reliability. I started at 0.010" per rev and after loosing the center on one, my tool rep said try feeding faster. Sort of seems to me slower would be better in terms of the tip crumbling. I am WAY under the maximum though already? Thought I would be safe here. Also, there is no visible wear on the center before this happens.

memphisjed · Apr 20, 2019

I have not found the swoon over the kenmetal drills. Allied inserts/holders are more forgiving. Then gen2 are slower, but are stupid forgiving. 120 fpm at .0075 or 85 ipr (around 4.7 ipm) for 13/16, start feed at .004 ipr, max thrust at 1600 lbs. hole count 2000 to 3000. The gen 3 xt are 1000 rpm (our spindles max at 1200, so detuned accordingly) at near same ipr (around 6.4 ipm) - max thrust at 650 lbs. somewhere near 700 they self destruct holder and all, but at 650 you can partial hole no problems. They say no start feed needed, but it changes hole count from 700-1000 to 5000-7000 per adding it in. 3 or 5d holders we run the same initial settings, I can usually boost 3d a smidge and detune 5 the same (+-.0015 ipr)
I know the ipm numbers off the top of my head, because that is my slider on running screen, the others are close - (stored in about-ish memory).

Spinit · Apr 20, 2019

Shock is my first thought. The tool moving too fast to contact the said material. It is a speed feed issue. Of course depth of cuts and coolant flow weigh heavy in this situation also.

gregormarwick · Apr 20, 2019

That looks like an exceptionally weak geometry at the point. Seems like those inserts must be for something other than steel, but I don't use Kennametal.

If you want a recommendation, Tungaloy's Drillmeister system has proven to be very good for me over the last few years.

metlcutr55 · Apr 20, 2019

once dealing with an issue of low tool life, we had the rep come in. he looked at what we were doing (in titanium), noted we were running very conservatively from their recommendations, and told us to use their recommendations, rather than starting slow and creeping up. the tools ran perfectly where he said they would, and brought us a few spares to replace the ones we had ruined trying to go easy. then he bought us lunch. have you asked Kennametal wtf?

Triaged · Apr 20, 2019

I have seen the same thing on other drills with the same point geometry. I don't think the little swirl at the point cuts as good as a standard split point type of cut. Slowing down the feed at the start will help. So will using a pilot drill.

guest · Apr 20, 2019

mmurray70 said:
Its just low carbon mild steel. Probably 44w here in canada, not exactly sure as customer supplied it.

Drill is 5x diameter in length.

Yes im willing to trade cycle time for reliability. I started at 0.010" per rev and after loosing the center on one, my tool rep said try feeding faster. Sort of seems to me slower would be better in terms of the tip crumbling. I am WAY under the maximum though already? Thought I would be safe here. Also, there is no visible wear on the center before this happens.

What does the chip look like? Is it folding? Is this a long chipping steel like 1018 where you get a bunch of stringy shit?

Just looking at the drill, my first impression was too light a feed. It might help to do a little spot drill so you have a little flank engagement when the point starts cutting. That may help stabilize the cut.

But my gut agrees with your tool rep. Whenever I've killed a drill that way, it's because I was trying to baby it. That's a big drill- lean on that sucker.

Johnhudson · Apr 20, 2019

We had the same problem,
In 316L .875 Dia,
I changed the the retract to a feed rate that took care of our problem.
Good luck

litlerob1 · Apr 20, 2019

Generally tip failure is because the Feed is too low. 343 SFM is pretty conservative.

Right in the middle of the recommendation, I would try 2200 RPM, and .015" IPR. BUT I would get about .5" deep with a low feed, don't retract just change to the higher Feed.

R

Mike1974 · Apr 21, 2019

Can you get a 'regular' (2 insert style?) indexable drill? I've not used the style you have, but have found 'regular' indexable drills to last almost forever in mild steel and/or 4140.

Something like this- 114.459mm Max Drill Depth, 5xD, 7/8" Drill 58148164 - MSC

mmurray70 · Apr 21, 2019

My tool rep suggested higher feed too, and you guys are saying the same so ill give it a shot when I get some more inserts. I was limping along last night with a sharpened up insert and had to feed it slower (not as much clearance now) and the tip seems to be lasting just fine at around 0.007" feed. Much slower though. Im still not so sure about increasing feed to save the center, but I will try it though.

This is on an older mazak. Not very friendly for programming. I would have to do 2 separate drill cycles (with a retract and return to toolchange position) to slow entry feed. Would rather avoid this if possible.

Chips are comming out great at 0.010 and 0.012"/rev. This is stringy mild steel but this drill is breaking them up and spiting out small pieces perfectly. See attached pic, the longer chips are from facing tool.

mmurray70 · Apr 21, 2019

Mike1974 said:
Can you get a 'regular' (2 insert style?) indexable drill? I've not used the style you have, but have found 'regular' indexable drills to last almost forever in mild steel and/or 4140.

Something like this- 114.459mm Max Drill Depth, 5xD, 7/8" Drill 58148164 - MSC

On smaller drills I thought the modular full carbide tip made more sense. Avoid fragile tiny inserts and screws. On bigger holes im sure these would be far more economical.

How fast can you feed the corodrill 880? I need another insert drill 26.5mm (1.043) and im still trying to decide what to get for that one. Thinking of another one of these Kennametal drills or Sandvik 870 or 880. My sandvik rep recommended the 870 over the 880 but it could possibly be related to inserts costing way more.

litlerob1 · Apr 21, 2019

You're using Mazatrol to program. You can still use EIA (G code) as an alternative.

Just dwell for a complete revolution, to clean up the Spot. Don't leave a lip down in there.

Rapid_Tech · Apr 21, 2019

Never used the Kennametal drill personally but I really like the Iscar SumoChams. Mitsubishi TAW's are nice too.

If you go with a flat bottom indexable I'm sure you wouldn't be disappointed with the 880. The Iscar DR drills are nice too and use the same inner and outer insert unlike the Sandvik. If you'll be drilling lots of holes I'd go with a flat bottom 2 insert indexable like the 880. Tooling cost would end up being much less since you'd end up getting the equivalent of 40 cutting edges per 10 inserts for about $200 vs ~$100 for just one indexable tip like the Kennametal.

Whysosharp · Apr 21, 2019

If your looking for a solid drill system the Mits TAW or it’s younger but more refined brother MVX series drill will take a poo on the Sandvik having run them side by side I would always grab the Mitsubishi. Additionally the MVX series drill has collars that allow you to drill holes larger than the stock diameter which is nice.

MoriMillMan · Apr 21, 2019

I use the sandvik insert maybe 75% of the time with spot drilling. never really see wear like that on them. Usually chipped corners or flank wear. But they last forever in mild steel and 4140.

mmurray70 · Apr 21, 2019

litlerob1 said:
You're using Mazatrol to program. You can still use EIA (G code) as an alternative.

Just dwell for a complete revolution, to clean up the Spot. Don't leave a lip down in there.

This a real old Mazak, T1 control, no eia capability. Early 80's, but shes still making chips and making money.

The Mitsubishi TAW drills look nice, where would I buy these from in Canada? Do they have next day shipping?

Morimillman, Are you using the 870 (full tip) or 880 (2 inserts)?

Loosing the center of carbide tip drills...

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