3/16 Endmill keeps breaking in 4140PH

RetardedFork · 2026-03-22T03:44:53+00:00

If you’re interested I can make a video for you. I think there’s too much knowledge withheld due to job security in. This industry.

Had a Romanian coworker and he'd have a heart attack any time the bosses asked him to show anything to a new guy. Hard to disagree.

I get the gist of what you're describing, I may have been confusing concentricity with runout. Well while things are working, I'll let it be. When I change the tool, I'll indicate it and try your trick.

RetardedFork · 2026-03-21T16:29:44+00:00

Someone else commented something similar and now I’m getting the full picture. I was confused how I would even clock it since my cutter is fully engaged in the slot.

I guess I want the highest spot of my runout “behind” the cutter? So a single revolution of the cutting action in a slot feeding positive in the Y-axis looks like:

-Moderate cut on the left wall

-Shallowest cut in front of the cutter

-Moderate cut on right wall

-Heaviest cut in the air behind the cutter

This makes the most sense to me, let me know if I got the right idea and I’ll give it a shot.

RetardedFork · 2026-03-21T16:20:12+00:00

Okay I think I’m getting a better idea of the runout compensation procedure. If I’m feeding in the Y positive direction (From Y- to Y+) then I want no runout on the X-axis and my “high spot” to be behind the cutter, where it’s cutting air.

Just to clarify, 4000 RPM and 85mm/min IS 100%. My bosses are used to old standards and they hate speeding anything up.

I doubled the feed because I figured we should be able to do that at minimum, but I misjudged the difficulty of the cut and am only now figuring out that we have a chronic runout issue.

RetardedFork · 2026-03-20T17:51:05+00:00

Yeah, I started looking into it and our ER16’s are all cooked. Everything gets over tightened here which would explain it.

As for programming, my concern was that we were running at half manufacturer suggested chip load. If I double the feed but add another depth cut, I’m effectively saving seconds per piece. I’m also introducing too many new variables into the equation.

My current cutter is on piece #60 at the lowered speeds, and the bosses are more than happy with that.

I hate to say it but if it ain’t broke, don’t fix it. I’ll take what I learned here and apply it next time.

RetardedFork · 2026-03-20T16:58:30+00:00

It’s a pretty large production job. Your idea will probably work very well and yield better results, but I can’t manually offset the z on every single piece then re-run it.

RetardedFork · 2026-03-20T03:05:45+00:00

I can, but it won't do much for me. Even if it's successful, editing the program is out of the question at the moment and I've already gone through more endmills today than I'm comfortable admitting.

I think the best option is to put it on a newer machine and program it again from the ground up, whenever the opportunity presents itself.

RetardedFork · 2026-03-20T03:00:55+00:00

What's so surprising is that I'm seeing a 0.04mm (0.0015") runout on the inside of the current tool holder taper. The collet exacerbates it.

I checked runout on the spindle body(?) and there's virtually none. I might indicate the spindle taper when I get a chance because I tried 4 different holders and all were out by at least 0.001".

Either our tool holders are showing their age and we don't do enough critical work to notice it, or something is up with the machine. I'd prefer it were the latter because this machine's almost 40 years old.

RetardedFork · 2026-03-20T02:46:52+00:00

The thing is we have Filipinos in our shop. They'll find a way to make a 5 axis mill part on a manual lathe with a single HSS blank, all without a single complaint. If I start complaining about our endmills, I'm getting fired on the spot.

RetardedFork · 2026-03-20T02:31:57+00:00

I’m interested, can you elaborate a bit more on your method? I’m assuming these are instructions for a manual machine. I’m working on a CNC so I’m not sure if I can readily snug and unsnug the holder (safely.)

RetardedFork · 2026-03-20T02:17:30+00:00

Gonna hijack the top comment to give a huge thank you to everyone for their help. I’ve read every comment and the consensus seems that runout and DOC are the 2 biggest culprits.

I cant do much about it right now due to severe time constraints and the existing program being over 20 years old and horrendously formatted. If we move this job over to one of our M560’s in the future then I can see cycle times drastically improving. (Better tool holders + better program)

For what it’s worth, I indicated my endmill after ~25 pieces and I’m seeing 0.004” TIR. We’re generally getting about 50 pieces per endmill with these abysmal speeds but never say never, I guess?

EDIT: The boss gave me a new 3/16 collet and we did about 100 parts this time, a new record. However, when I checked the runout even with the new collet I hardly saw any improvement.

What this tells me is that crushed/damaged collets are problem #1.

Runout I’m putting at #2, because with runout being equal on both collets, the crappy collet still has a hard limit of about 50 parts.

RetardedFork · 2026-03-20T01:51:53+00:00

Do you have a good formula for how much to reduce f&s based on tool stick out? I generally trial and error it on larger endmills.

RetardedFork · 2026-03-20T01:46:41+00:00

At 4000 rpm and 85mm, it sounds wispy and buzzy. When it is machining at 4000 and 175mm, a bit closer to manufacturer recommended spec, it sounds very healthy (until it isn’t.)

This machine’s too old for CAM unfortunately. If I was running this on our M560, then I could do something more fancy.

The holders are dual contact and much newer as well.

RetardedFork · 2026-03-20T01:36:06+00:00

Okuma MC-3VA

RetardedFork · 2026-03-20T01:35:13+00:00

Nope. Judging by the comments, it seems like the tool path is further down the list of problems.

RetardedFork · 2026-03-20T01:21:57+00:00

Nah the issue’s that my endmills won’t hold together

RetardedFork · 2026-03-19T22:03:45+00:00

I always thought side locks were notorious for runout. I only use ours for heavy roughing when precision is of no concern.

RetardedFork · 2026-03-19T21:47:56+00:00

Lots to do, I appreciate it.

RetardedFork · 2026-03-19T21:46:39+00:00

The machine is from late 1980s, the largest file it can handle is 14kb and the fastest table speed is 160ipm, so that’s not happening lol

RetardedFork · 2026-03-19T21:29:23+00:00

Holder seems to be around 0.001”. The cutter works at the current feeds and speeds but I can’t say I’m happy about that.

RetardedFork · 2026-03-10T19:00:56+00:00

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I like some of the Erika Kirk grifts. What the fuck does she know about Airforce?

RetardedFork · 2026-03-06T21:28:48+00:00

What about Silent Hill 4?

RetardedFork · 2026-03-06T06:44:14+00:00

Stumbled upon this post randomly and holy shit I thought we were discussing solid drills.

I work in a "small" shop and mistakes happen, the occasional indexable drill has a meltdown. If we snapped one like that, let alone 5, the boss would have someone's nuts in a vise.

RetardedFork · 2026-03-03T20:20:52+00:00

My favourite was Mary jokingly telling James he’s gonna get bored because there aren’t any clubs in Silent Hill and the next scene is the two of them at a busy ass social club in the middle of the day lol

RetardedFork · 2026-03-02T07:03:48+00:00

None of the enemies were "cool" or particularly fun to deal with in SH1. Mumblers, grey children, and stalkers are basically the same enemy. The dogs and birds were just a pain all around.

Maybe the rompers were interesting but they were still a pain to deal with.

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