oops. mini lathe cutoff blade shattered.

Discussion in 'Mistakes, Blunders and Boo Boos' started by MCRIPPPer, May 22, 2013.

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  1. May 22, 2013 #1

    MCRIPPPer

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    was parting off a .75 inch did. aluminum piece. i kept having an issue of ships welding onto the HSS blade, so i kept retracting it and clearing the chips off. it started welding on chips, i presume, and i began to retract it. im guessing more and more welded on until it seized up in the groove and shattered the blade into three pieces. scary! luckily everything is ok except the cutoff blade. the blade was not even making a cut when it seized up. am i sharpening it wrong or something? it was running at a nice slow speed.

    to grind my parting tool (which has a T shaped cross section, are those P type or something?) i grind only the front face to give it some relief. i also grind it so that it leaves a clean face on the piece i part off, so it has end relief combined with a slight angle. i leave the top alone, becuase it has a little groove that seems to help the chip come out if the cut, but i guess it doesn't work effectively.


    any tips? this only seemed to happen on aluminum. no chip welding with brass or steel.
     
  2. May 22, 2013 #2

    chucketn

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    Try using a small squirt of WD-40 or kerosene when parting aluminum.

    Chuck
     
  3. May 22, 2013 #3

    MCRIPPPer

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    i used a little oil, and it helped, but it quickly got ejected with the chips. maybe i need a continuous flood coolant or something? or maybe i just need to keep oil dripping onto the cut?

    do you guys use some sort of emulsion oil on the mini lathe?
     
  4. May 22, 2013 #4

    chucketn

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    Use cutting or tapping oil on steel, WD-40 or kerosene(parafin in the UK) on aluminum, and nothing on brass or cast iron. In my experience oil does nothing for aluminum.

    Chuck
     
  5. May 22, 2013 #5

    mygrizzly1022

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    Hi



    What are your speed and feed rate like? You may be quite surprised at how fast and aggressive you can be with aluminum. If you are welding: speed and cut rate may be too timid. Increase your rate of cut and increase you speed a bit as you reduce your diameter. Your cut off tools needs to be very sharp, and as others have suggested mist with wd40.



    Regards Bert
     
  6. May 22, 2013 #6

    wildun

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    If you are stuck with the particular grade of aluminium you are using then the above remedies will work, except that it would be preferable to have at least a continuous trickle going on to the tool.
    However, if possible try to use the 'free cutting' grades of aluminium and you'll have no problem at all.
    I have found that aluminium with a high silicon content can often be very troublesome.
     
  7. May 22, 2013 #7

    MCRIPPPer

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    i was cutting 6061 t6.

    i was feeding pretty hard. a big fat chip was coming out, not dust.
     
  8. May 22, 2013 #8

    dieselpilot

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    I keep my blades sharp and square. My steel cut off blades make a nice tight curled chip that winds up into a coil in the slot if things are going smoothly. When the chip(coil) gets large I back out to break it. I part aluminum at a fairly low RPM, this I figured out after several broken blades. Those thin steel blades can't get rid of heat very quickly so not making too much heat in the first place is the right method to use. I use a brush to keep some lamp oil (odorless kerosene) in the groove at all times. I typically use my cross slide feed and the chip is fairly thin, this gives me consistent results. 200-250RPM .0005-.001" IPR feed. smaller than 1" I'll run faster.

    The angled relief on the front of the blade causes the blade to drift to the side and rub. This causes more trouble than facing the parts after cutoff. As soon as you seen galling on the sides of the cut or the sound changes back out and add some kerosene if you're not continuously lubricating it.

    Greg
     
  9. May 23, 2013 #9

    jwcnc1911

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    In my experience, most cut-off/grooving tools break due to tool geometry. Of course second to that is feed/speed ratio. Run it slow and feed it at a constant rate. No more sticking out of the post than absolutely necessary. Since you say you did not relieve the top at all you should cut a little chip breaker relief (at least that's what we call it at work). If I can get out to the shop tonight I'll put a picture up. Been using the same tool for I can't even remember how long. 6061, cold rolled, hot rolled, brass and even some 304. It's cut everything I've charged into. What style of cut-off tool are you using? Give us a picture so we can better apply experiences.
     
  10. May 23, 2013 #10

    CrashedAgain

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    Sharp tool with a squared off tip set truly on center height, slow speed and flooded with cutting fluid (soluble oil). The clue is that you are welding material to the tool tip.....means too much heat is being generated. Flood with coolant which will also help wash out the chips.
    I use soluble oil applied from a squirt bottle.
    Also make sure your slides (gib screws) are tightened so you don't get a sudden grab.....and use a narrow parting tool to reduce tool loading.
     
  11. May 23, 2013 #11

    MarioM

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    Hi mccripper, I have the same T shape parting tool and it is sharpened the same way than yours. I use slow speed and try to constantly feed with aluminum, but stop a lot a use plenty of oil. It seems to work ok. I either use cutting fluid or mix kerosene with lard. To be honest I always hesitate when have to use a parting tool and I do not know if that T shape help or not.

    Mario
     
  12. May 23, 2013 #12

    Tin Falcon

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    Lots of good advise.
    the t-shape is the way to go.
    keep the setup as rigid as possible
    if you have a carriage lock use it.

    use plenty of lube appropriate to the material slow speed heavy feed
    keep the tool on center above center tends to dig.
    tin
     
  13. May 23, 2013 #13

    MCRIPPPer

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    this is the parting blade that came with my mini lathe tooling package. as you can see the ends are not sharpened at all. when i got mine it looked like it was cut from a linger piece and the ends were rough. http://littlemachineshop.com/products/product_view.php?ProductID=1930

    the top of this blade has a rounded grove down the spine. i simply put it on the grinding wheel at an angle to make a front relief.

    i think maybe i just need to put some wd40 or other lube continuously.

    i will double check that it is on center, although im pretty sure it is.
     
  14. May 23, 2013 #14

    Tin Falcon

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    A buddy of mine used to cut a small notch in the end , he called it a snake tongue I have done it seems to stabilize the blade. The groove should be a good thing.
    Tin
     
  15. May 23, 2013 #15

    jack620

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    Another vote for WD40 on ali. It's cheap, easy to apply and doesn't smell too bad. Just give a squirt every few seconds. Greg's idea of backing out to break off the coil of ali before it gets too large is a good one.
     
  16. May 23, 2013 #16

    ShopShoe

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    Cut as close to the chuck as you can. I have found steady feed is best, regardless of speed.

    On my mini-lathe, the flex of the tool was caused by lack of rigidity in the toolpost. If you are using the stock 4-way toolpost, clamp another toolbit or a suitable piece of metal in the toolpost opposite the cutoff-tool holder: It does help some. As has been mentioned, tighten up the compound-slide gibs before cutting-off. I set the compound at 90 degrees, disengage the leadscrew and lock the carriage to the leadscrew to prevent left-right motion. (Be sure to check that the leadscrew is truly disengaged before starting the motor.) The compound can be used to set left-right position of the tool.

    I ultimately found that a QCTP setup added considerable rigidity over the stock 4-way toolpost, even though the cutoff-tool holder for the QCTP acted differently and forced me to re-learn what cutoff techniques work best.

    Also, check to make sure the saddle is not loose on the bed: things will be mostly OK until a cutoff tool digs in, then the force will be strong enough to lift the rear of the saddle off the bed and that will change the tool geometry.

    --ShopShoe
     
  17. May 23, 2013 #17

    gus

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    Hi Mcgripper,

    Just like you,I use same LMS parting tool,to cut 1" aluminium bars at 500 rpm with Tapmatic Aluminium Cuttting Fluid with very good results with no tool breakage.Fluid is applied with a small brush into the groove. Chips comes out smoothly and continously with steady and consistent feed rate.
    But I must watch the cutting edge when it gets dull,trouble begins.Best to keep cutting edge sharp.Cutter is set slightly below centreline.Cross slide must not be too sloppy to prevent tool grab.Slide play the parting tool make groove slightly wider to avoid side friction and tool grab.
    Tapmatic is expensive.Been told kerosene works fine.Will try this sometime
    later.
    Steel bars,
    Parting steel bars ,I also use Tapmatic Tapping Oil formulated for steel.
    Fluid is brushed into groove.

    The UK Eclipse Parting Tool is not user friendly on mini lathes.



    Gus Teng from faraway Singapore.
     
  18. May 23, 2013 #18

    MachineTom

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    Look at the end of the work after being cut. Is it dead square or concave/convex. If not square your not getting the blade 90° to the work. This leads to trouble like you are having.
     
  19. May 23, 2013 #19

    MCRIPPPer

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    thanks for all the tips.

    i am using the a2z cnc QCTP.
     
  20. May 24, 2013 #20

    dieselpilot

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    I sharpen just the tip with a diamond hone or stone. I had inconsistent results until I started doing that. Use an indicator to set the blade perpendicular to the spindle, or at least the front of your work. Make sure the blade is mounted vertically in the holder. It's easy to install the blade at an angle by pushing on the side while clamping.

    This is what I use for lube. http://www.tikibrand.com/Torch-Fuel-Lamp-Oil/UltraPure-Clear-Lamp-Oil-32-oz/60009 No smell, no residue( no heavy oils added), if spilled, it eventually evaporates and is gone.

    Greg
     

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