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  1. #1
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    Default What did I do wrong?

    Hi all,

    Using a slitting saw (3-1/2" x 1" 1mm thick and approx 140 teeth) on the mill, conventional milling into aluminium (unknown grade) and doing approx 600 rpm using WD40 generously for lube and chip clearance.

    All going reasonably well and the bang!

    Spindle stalled and bits of HSS slitting saw shatters and flies in all directions.

    I never did trust it and so was wearing a full face shield.

    What did I do wrong?



    Sent from a galaxy far far away
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  2. #2
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    No idea but following along. I’m always very cautious with slitting saws, tend to run them around that speed for steel but with very low feed.

    What was your feed rate?

  3. #3
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    Off the top of my head I would hazard this guess.

    Too many teeth and the tooth gullets aren't large enough to remove the waste which then sticks and packs the teeth.

    Subsequently it accumulates and jams up,then breaks. There is something that is used for a particular cutting coolant best suited for aluminum -metho??? - keeps teeth cool maybe???

    From a bloke who has not used a slitting saw.
    Save the broken bits -good for custom made cutting tools.

    Grahame

  4. #4
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    Feed rate was hand fed by "feel". Quite slow and backing out from time to time to aid chip removal when the cutting sounded laboured.

    Simon

    Sent from a galaxy far far away
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  5. #5
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    Sep 2008
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    Riddells Creek, Vic.
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    The release of internal stresses in the material could have nipped the saw blade up in the cut, that combined with it running a bit too fast and getting slightly warm leading to the breakage. I have cut similar chunks of aluminium before with extreme care.

    Die Grinder.jpg

  6. #6
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    I've posted this before, but you know solidarity in numbers..

    I had to pull a sliver of the saw blade out of my forearm, so your decision to wear a full face is probably a wise one.
    Attached Images Attached Images

  7. #7
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    We're you using a belt drive mill?

    How deep was the cut?

    How consistent do you think you were with the feed?

    If the cut was close too or over half thickness of material had or did you use a wedge to hold the cut from closing as already mentioned?

    Had you machined similar before?

    If so what might you have changed this time?

  8. #8
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    Not that I'm an authority on slitting saws, but I've cut a lot of aluminium with TCT circular saws, woodwork bandsaws and also grinders with 1mm discs. As we all know, aluminium expands far more than steel (hence oversized contact tips when mig welding) and is a relatively sticky metal. It wouldn't surprise me if the saw began to get hot (WD40 lubricates but has little cooling effect if any), this combined with the fine tooth blade began to cause loading of the teeth and the kerf, which increased the heat generation until the kerf closed in due to expansion of the material and the loading of the cut, stalling the saw and BANG! A shower of shrapnel.
    I remember that the bandsaw used to become quite temperamental over 20 or 25mm with some grades of aluminium, particularly as the teeth began to dull. Candle wax may be worth trying as a lubricant or better still flood coolant and definitely a lower tooth count.

    Sent from my SM-N976B using Tapatalk

  9. #9
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    Sep 2012
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    York, North Yorkshire UK
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    Hi Simon, Guys,

    Thick aluminium is not a nice material to cut, particularly with a thin high tooth count slitting saw. I use diesel fuel liberally on jobs like this. WD40 and the like evaporate far too quickly to provide lubrication in a deep slot, its great for surface work like turning. One other lubricant I found effective is "Lamp Oil" ! Its quite sticky and like diesel gets dragged into the cut. Unlike diesel it has a nice lemon smell !

    Also I would take multiple shallow cuts, say two or three mm at a time until I got to the depth that I want. A thing to check is to make sure that the mill is as well trammed as it can be. Any out of tram is going to cause the blade to flex more and more as it gets deeper.

    Way back I had almost the same issue ! But when the slitting saw blade jambed it damaged the teeth on the plastic gears in the mill head. New gears were an arm and a leg at the time, so I made a new set of gears using steel ones. I did a thread on here about it.
    Best Regards:
    Baron J.

  10. #10
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    I only ever used a slitting saw on Acetal so I'm certainly not an expert on them. There is info on the internet, but it is a bit hard to find and some of the speeds I seen seem to be contradictory. I agree with with the other comments: too many teeth, stress the metal and lubrication. I will add speed from looking at this Slitting saw speeds | Model Engineer (model-engineer.co.uk) now that is for brass I know, but I have a chart at work and it would be 300 x 4 which is 1200 divide by 3.5 giving you 342 rpm. Karl Robbers is right in what he says about cutting aluminium it gets quite hot. I think that you would be better to use flood coolant. Also kerosene apparently works really well for aluminium. I'm going to make sure that I have a face shield next time I use a slitting saw as that broken saw is scary as.
    All The Best steran50 Stewart

    The shortest way to do many things is to do only one thing at once.

  11. #11
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    Dec 2013
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    I lost 2x 8-12 year old endmills recently machining gummy aluminium for a job for myself.
    One 4mm and one 12mm, the 12mm was the 12 years old dormer and pretty blunt from steel over the years.
    I know better but wanted the job done yesterday.

    Aluminium expands quickly and gums up even easier, I had plenty of Kero going on it, but pushed to hard, to deap to quick.

    I agree with what is said, go shallow cuts and large teeth spacing on aluminium.

    It could of already had some micro damage if it was a used one.

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  12. #12
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    Oct 2007
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    Haven't used slitting saws at all, but plenty of experience with Brobo's and similar cold cut saws using HSS and Cobalt HSS blades, and reasonably familiar with breaks of that nature.

    Typical scenario is some sort of feedrate/chip clearance issue leaving swarf in the saw gullet, which then starts to grab at the material each time it passes through it, producing a cyclic sound as it gets dragged through the kerf. Ultimately, the repeated shock on entering the material and drag passing through starts a crack in the gullet of the blade and the sound intensifies briefly, then the blade explodes.

    Much easier to analyse the process with a cold cut because the the blade is operating at 30-80 RPM depending on saw and blade size, so you can hear each individual time the swarf impacts the material and take preventative action in time. Also fairly common to 'ring' a blade before mounting, (suspend at tap something light and metallic to listen to the sound of the blade, intact blade sounds a pure tone, blade with a crack forming sounds a distorted sound) and also visually inspect for cracks or buildup.

    Slitting saw running at a faster speed would probably disintegrate before you could detect the issue.

    With a cold cut, there are recommendations for the number of teeth in the material at any instant which determine what blade/tooth count you would use for each specific task, a lot of task swapping means a lot of blade swapping. Ali and SS are very prone to sticking swarf in the gullet, MS much less so. I suspect that your depth of cut would severely limit chip clearance.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  13. #13
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    Hi everyone,

    I appreciate all the replies. Lots of helpful info in all that.

    I suspect many of you are dead on with your suspicions;

    Aluminium was quite hot by the end, DOC probably way to optimistic and not flood coolant used. That combined with insufficient chip removal ensured the end result.

    PC, to answer your further questions, the mill is a Pacific (Lagun mill) FT-2 Bridgeport clone, NT40 spindle. The slitting saw had a 12mm arbor which was held with a 12mm ER32 collet. All of which were destroyed in the mishap!

    It was a cheapie slitting saw holder which had terrible run out (even more now!) So looks like I will make my own this time.

    Slitting saw use reminds me of the days when I used to destroy part off blades, before learning how to part off properly!

    Cheers everyone.

    PS. If you live in NSW, GET OUT AND ENJOY! What did I do wrong?

    Simon

    Sent from a galaxy far far away
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  14. #14
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    Default

    Thanks Simon for the great question and thanks too to all the other contributors for the useful info and experience being shared. I have never used a slitting saw either, and would not have considered it any more dangerous than most other milling operations. I will definitely use a face shield when I do use one. I wonder if the use of Metho, (ethyl alcohol for those unfamiliar with this British/Australian term) as a cutting fluid for Aluminium was for its coolant properties, because I doubt that it had much lubrication ability.

  15. #15
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    Quote Originally Posted by simonl View Post
    It was a cheapie slitting saw holder which had terrible run out.
    As I understand it, the slower your feedrate the more this matters. Also deep cuts and conventional milling.
    Assuming my maths is correct. If we take your 600 rpm and 140 tooth, even feeding a 600mm/min(in which case you would have been finished in 15 seconds) I make your feed per tooth 0.007mm that's less than 10% of what it "should be". Add in some runout and I'm guessing a lot less than half your teeth are cutting and there is a lot of rubbing going on.
    Have I misplaced a decimal point?

    Now of course if you tried to meet "feed per tooth" numbers with that depth of cut the result may have been the same

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