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  • Death of an endmill?

    This is probably going to be an obvious question but I'm a little confused. Just looking to learn from my mistakes really. The short story is that I think I trashed an endmill....but I'm not sure which thing killed it.
    Longer story is that I was milling aluminium and having done the side milling fine, I plunged and slotted the two screw holes you can see below. This is with a 10mm uncoated 4-flute HSS endmill - probably not the ideal choice but you work with what you have sometimes and besides, it's "only aluminium, it'll be fine". First plunge (to 6mm depth following a 6mm diameter drilled hole) was fine and then I slotted in 0.5mm DoC passes as I really couldn't be bothered to slot the centre and then clean up both edges....don't judge me too much, it was 90°F in the shop that day with next to no ventilation! These passes went smoothly until the finish pass where I sprayed in a squirt of WD40 to improve the finish. It did seem to make things worse as it stuck all the chips together and made a grey mess rather than silver chips coming out....so I'm wondering if this caused all the chips to get repeatedly re-cut and made an abrasive slurry that killed the endmill. I say killed it because the finish pass, and a subsequent attempt to improve it, were awful. I tried the second hole and the plunge left a very noticeable spiral grove down the hole. Slotting resulted in lots of chatter - which hadn't occurred in the first slot and nothing in the setup had changed. A new endmill (ordered one specifically for aluminium and the finish is great) has fixed the problem both with the chatter and the finish so I'm pretty sure it's the endmill that's toast. There's no chip-welding I can see but under magnification there does appear to be damage to the tips.

    Now here's the part that will probably seem like the obvious cause - and I'd agree but it was working fine for the first part. I managed to run this endmill into the top of my vise jaws - it's the first time I've done anything like that (but probably not the last) and I'm annoyed about it. Not much DoC and not for very long but they are hardened and it did cut. I can see (and accept) this being the cause of killing the endmill; what I'm curious about is why it was fine for most of the first slot? Is the answer that this damaged it and the WD40 was the final nail in the coffin? Should I be avoiding WD40 (or any other lubricant) in slots in future?



    Thanks guys.

    Gareth

  • #2
    Slotting kills endmills because it wedges chips between the sidewall of the part and the endmill as they are recut. Either don't slot full width which you can't be bothered with, run flood coolant, or keep buying more endmills.

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    • #3
      Thanks RB211. So it sounds like in this particular situation the WD40 made the chip re-cutting far worse and probably finished off the already damaged endmill. Ah well, you live, you learn...well, at least sometimes!

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      • #4
        I did slotting in mild steel using mist coolant/lube and a 3/16" end mill. I started out taking .020" DoC in 3/16" stock. I did the first 3-4 slots like that then went full depth with a plunge then slot. That little HSS end mill ate mild steel for lunch. And the setup wasn't all that great either. I fear nothing now!

        I run my mister at around 60-70 psi so it has enough "blow" to keep the chips clear. And the through cut also gives the chips a place to go.

        I'm thinking your end mill wasn't too sharp to begin with and it got hot. You probably welded some swarf to it. That always makes for a bad finish.

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        • #5
          Though flood or mist coolant is best, quite often all you need is an air-jet to flush the chips as they are made. Also, a 2-flute cutter is a good idea for aluminum. I wonder if you were getting a deep enough cut when you refer to a 'grey mess'. Was the aluminum soft or heat-treated (that makes a big difference in chip characteristics)?

          For slotting, I always use a roughing (corn-cob) endmill. They'll cut at least twice as fast, with less effort and the chips are easily blown away. If you need smooth sides in your slot you have to do a finish pass with a conventional mill.
          Last edited by chipmaker4130; 07-25-2019, 09:00 AM.

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          • #6
            Originally posted by CCWKen View Post
            I did slotting in mild steel using mist coolant/lube and a 3/16" end mill. I started out taking .020" DoC in 3/16" stock. I did the first 3-4 slots like that then went full depth with a plunge then slot. That little HSS end mill ate mild steel for lunch. And the setup wasn't all that great either. I fear nothing now!

            I run my mister at around 60-70 psi so it has enough "blow" to keep the chips clear. And the through cut also gives the chips a place to go.

            I'm thinking your end mill wasn't too sharp to begin with and it got hot. You probably welded some swarf to it. That always makes for a bad finish.
            I suspect it may have been sharper before it tried slotting my vise jaw
            Mist is something I'd like but I need to get shop air first....and that entails a complete redesign of the shop, bench, storage etc. Working on it....but slowly.


            Originally posted by chipmaker4130 View Post
            Though flood or mist coolant is best, quite often all you need is an air-jet to flush the chips as they are made. Also, a 2-flute cutter is a good idea for aluminum. I wonder if you were getting a deep enough cut when you refer to a 'grey mess'. Was the aluminum soft or heat-treated (that makes a big difference in chip characteristics)?

            For slotting, I always use a roughing (corn-cob) endmill. They'll cut at least twice as fast, with less effort and the chips are easily blown away. If you need smooth sides in your slot you have to do a finish pass with a conventional mill.
            DoC was 0.5mm per pass (20 thou ish) so fairly conservative as I didn't want the sides to go tottally skewed on me - only for pride and vanity's sake, mind. Originally the chips were chips and a normal colour - you can see a mix of chips from fly-cutting and various milling in the pic. It only turned grey when I added WD40 in the assumption that it would improve things. I think that it kept the chips in-situ rather than letting them escape and made for a lot of re-cutting. The aluminium was listed as "2014 T651" so heat treated I believe. I have a 10mm corncob and they're great - one of the benefits you didn't mention is that the chips they produce are far less splintery, not as sharp - was originally thinking a quick slot wouldn't be an issue (and probably wouldn't have been if the endmill wasn't shot) but I might have to try a quick 10mm rough slot followed by a finisher and see if the serrations clean up without taking the slot larger.

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            • #7
              Lot's of factors when cutting a slot like this --- something else to consider is after a certain depth of cut the flutes start gaining some surface area and can set up a "chatter pattern"

              this along with your re-cutting of old chips may have done the surface finish in,,, im very surprised it got your endmill though

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              • #8
                Originally posted by Cenedd View Post
                I suspect it may have been sharper before it tried slotting my vise jaw
                Mist is something I'd like but I need to get shop air first....and that entails a complete redesign of the shop, bench, storage etc. Working on it....but slowly.
                Something else to consider; I have two of these--One at the mill and one at the lathe. Keeps me from having to run the big compressor just to do a few tasks (or run dedicated air lines). These put out enough air for mist and blowgun duty.

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                • #9
                  Good to know they're enough for the sort of thing I'd currently need it for. My issue is - apart from cash, which is a little tight currently - space. Currently there is enough space to walk in without breaking something or myself IF I tidy up. The floor space reluctantly gets used as workspace as it's the only space available - the bench is full of mill and lathe. I'm working on getting all the stuff I don't need regular access to up in the loft. I've done quite a bit but the temperature in the loft makes it seem chilly outside....and it's looking set to break the all-time high of 101.3 °F (38.5°C) out there today. Might be why I've just downed tools and declared beer O'Clock!
                  Once I can make enough space to replace the workbench with a much longer one (at the cost of half the shelving - I plan to keep the bottom deck as storage) I should have enough space for a compressor. The challenge then is to reconcile my actual need with the "But what if I want to run xyz tool off it in the future?!". This is how I lumbered myself with a massive bench grinder!

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                  • #10
                    Hi,

                    4-flute endmills are never fine for aluminum. Unless you have no other choice, 2 or 3 flute endmills are the proper choice here, (preferably high helix flutes). You need the extra chip clearance to evacuate the soft and gummy chips. Are you sure the endmill you did use was center cutting?

                    The WD-40 is perfectly fine for machining aluminum. Just use liberally.

                    I would have cut the slots full depth through in one pass, it allows even better chip evac. And a 10mm endmill should be fine for that depth of cut. At least the photo seems to show less than endmill diameter.

                    Putting a divot in your jaws is no big, lots of jaws have suffered such assaults. Stone it smooth and consider it character.
                    If you think you understand what is going on, you haven't been paying attention.

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                    • #11
                      One trick we used in the shop where I worked was to drill a set of undersized holes the length of the slot to be cut. Then do a finish cut with the proper size end mill. When making deep slots we also used a vacuum to remove the chips so they didn't constantly get recut.

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                      • #12
                        I don't know about the chips becoming abrasive. That seems a stretch. But if it's the right sort of alloy the edges might not like re-cutting the metal over and over. And yeah, if you use lube you need to use enough to clear stuff out.

                        For small tools a small little compressor is not a bad option. Either on it's own roll around cart or at some central point with a reel style hose. In the wood shop I've got a small little thing connected to a self retracting 50' reel. It's easy to pull out and just as easy to put back. The compressor can live in a little dark unused corner under some other items easily enough.

                        Aluminium does like to be cut quite fast. If your chips off the end mill were not large and turned into grey gum perhaps your feed rate was not high enough? And with the right sort of alloy this would cause the edges to rub more than cut? And that'll take the keen sharpness off in more of a hurry than a proper chip load that produces nice easily seen proper chips.

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                        • #13
                          Originally posted by dalee100 View Post
                          4-flute endmills are never fine for aluminum. Unless you have no other choice, 2 or 3 flute endmills are the proper choice here, (preferably high helix flutes). You need the extra chip clearance to evacuate the soft and gummy chips. Are you sure the endmill you did use was center cutting?
                          Definitely centre cutting. I now have a two and a three flute in 10mm stub length for future escapades but didn't in the required size. I know the correct thing would have been to slot it smaller and then widen to size....but I thought I'd get away without the tool-change and added complication.

                          Originally posted by dalee100 View Post
                          The WD-40 is perfectly fine for machining aluminum. Just use liberally.
                          I think it was the situation here rather than the specific lubricant. After applying it, it completely stopped all chip evac and I think that was the problem. Might have got away with it had it not been for crashing the endmill previously....but at least I'm aware of the issue for the future.

                          Originally posted by dalee100 View Post
                          I would have cut the slots full depth through in one pass, it allows even better chip evac. And a 10mm endmill should be fine for that depth of cut. At least the photo seems to show less than endmill diameter.
                          Depth was 6mm and I'd have loved to have cut them in one pass. I don't think I've got enough power or rigidity (probably more the latter) to get away with it though. Part of the issue, I think, is that as a noob (more clueless than I am now even!) I obviously HAD to have a vise that tiltled and swiveled...cos those features were clearly going to be essential. I think I've used the tilt once and the swivel not at all. The added height - apart from causing me to run out of z travel - means less rigidity as the entire vise acts as a lever against the table. I did try buying a simpler vise but managed to go overboard (again!) and buy one that doesn't really fit on my table. Hence the "sometimes" when I said "You live, you (sometimes) learn". Need to wait a while for that though.

                          Originally posted by dalee100 View Post
                          Putting a divot in your jaws is no big, lots of jaws have suffered such assaults. Stone it smooth and consider it character.
                          Already filed the edges so they're not sharp - it's clearly not ridiculously hard but we're not talking about taking off much, just the burrs. It won't cause any functional issues as it was coming in from the side....it's just annoying as you tell yourself "Oh, I won't be as careless as the people who used the machinery I learned on or the items you see on eBay". It's tough losing your own moral high-ground that nobody knew about and wouldn't care anyway!

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                          • #14
                            And don't drop an endmill endfirst onto the vise. This was a nice 1/2" rougher endmill. Fell out of collet, two bad chips and one small one, will still sidemill. JFLingg

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                            • #15
                              I use WD-40 when making cuts in aluminum, but I do not use "a shot", just on the final cut. I have a couple of the pump bottles (WD brand) filled with it and spray it liberally for the entire cutting process. I adjust the nozzle on the pump bottle for a tight stream and aim it at the end mill. Enough to wash the chips away from the milling cutter. It is also very effective in preventing aluminum build-up on the cutter's edges. It seems to work well. And the hand pump allows me to use the right amount of WD to flood the cutter without the waste you would get with an aerosol spray can. I can use short pulses of WD with short intervals in between them and vary the times as needed to keep the chips washed away.

                              But, of course, it uses a lot more WD. I buy the WD in gallon cans. Some times I have both hands busy, one spraying WD and the other cranking on the X handwheel. God bless power feed on the Y axis.
                              Paul A.

                              Make it fit.
                              You can't win and there is a penalty for trying!

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