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Thread: Chip loading

  1. #1
    Join Date
    Sep 2004
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    The Traditional Rocking Horse Co.,
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    Default Chip loading

    In another thread the question of chip loading has again returned.
    Many people swear by the necessity of getting the chip loading right.
    This, as I understand it , is a combination of spindle or router R.P.M., speed of cut (IPS), the bit being used, and the material.
    3 of these are constants, R.P.M.,bit and material. The fourth is a variable. You may well tell the machine to cut at 4"(100mm)ps for instance, but if it is cutting out a shape like
    14550.gif, then it is likely never to reach the dialled in speed, continually ramping up and down, even stopping, or nearly stopping on many occasions.
    Does this mean that, if the 'correct' chip load calculation is needed to get satisfactory cuts, any cut, other than a straight line, is going to be substandard? This is not a Shopbot problem per se, any machine that doesn't adjust the spindle R.P.M. to match the speed (IPS), (do any?) will have this problem.
    In practice I see no difference when cutting, so ignore chip loading calculations, using experience instead.

    .............Mike

  2. #2
    Join Date
    Jul 2005
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    Whispering Pines Innovations LLC, Grand Rapids MN
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    Default

    Mike,
    Lets me give the crank a few spins here and see what happens. Years of sawmill work running band and circle saws (Large high HP) there are a few things that I have found to be a fact.

    1: If you take too small a bite per tooth the sawdust will spill out of the gullet of the tooth and spill between the sawplate and the wood and cause it to heat, run, and dodge.

    2: Taking too big a bite per tooth will overfill the gullet and you will have sawdust forced out of the gullet and between the sawplate and wood with the same results plus you will pull the tension out of the saw.

    Now between the two extreams the saw will do a passable job over a wide range of feed rates. You may find a point that gives you a better board but for the most part you feed as hard as you can and still produce a good product. How hard you can feed is a comdination of your HP, gullet capacity, thickness of you saw plate, good tension in the saw, sharpness of the saw and the individual log you are cutting. And last but not least having your mill set up like it should be. The standard recomended saw speed is 10,000 to 11,000 SFPM and .100" tooth bite. This does not work ALL the time.

    I find the same to be true of milling cutters, router bits and my Bot. I feed at what ever rate works for me. Recomended rates are just that, recomended, a good place to start and you may wish to back off from there. Higher most often has a negative outcome. Even missing, damaged and or nonfunctional body parts. It may even result in your body temp and room temp being the same.

    When cutting a complex shape like you show the rate most of the time is not the set feed rate.
    BTW What is the name of that lake?????

    Ted

    "Minnesota, The Land Of 10,000 Lakes" or is it taxes?????

  3. #3
    Join Date
    Oct 2001
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    2,941

    Default

    ...land of the mosquito. (met some Duluthians last week - seemed fairly normal folk - Kathy and Aziz). That lake is full of sheep.

  4. #4
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    Jan 2004
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    , South Jordan Utah
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    Default

    Mike J,
    When cutting complex shapes, where there is almost no possibility of going faster than the non-ramped speed, you could assume that your feed speed is the same as your non-ramped speed and figure accordingly. On my Alpha, 2-ips is my non-ramped speed. My ramped speed is usually about 6-ips. If I were cutting something like you posted, I would use a 1-flute cutter, figure on 2-ips and set the RPM on my spindle to give the proper chip size. I just ran the calculation and came up with a chip load of 0.015, 2-ips, and a 1-flute cutter. The resulting RPM is 8,000. Although my spindle will run at 8,000 RPM, the torque drops off at speeds below 12,000 RPM. So, most likely, I would first try 12,000 RPM (which would give a chip load of 0.008). The other alternative would be to run the spindle at 8,000 RPM but to make shallower cuts that would be within the torque range of the derated spindle.

  5. #5
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    Default

    The lake is New Zealand with the two Islands joined


    Other Mike, (or am I the other Mike?)
    what you are saying, and I don't disagree, is that the feed rate is a matter of experience and not the feed you have dialed in to the software.
    I started by using a calculator, then realised I was running no where near this speed throughout the cut, adjusted my chip loading.
    Now I have done a bit, I seem to know what I should be doing, wet finger in the air sort of thing
    .

    ................Mike

  6. #6
    Join Date
    Jan 2006
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    Toomey Studios, Orlando FL
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    Default

    I took a tip from the Onsrud rep and use the chipload calculations as a starting point and then look and listen. Look at the chips coming off the cutter, they should be pretty warm and they should be the right size. And listen to the cutter in the material, it'll "tell" you when it's happy. It took awhile but I'm pretty comfortable with listening and telling if I need to speed up or slow down. For Spiral bits in wood I usually listen for a nice smooth buzz and another sound on top, almost like paper ripping. I guess if you're running a PC you may not hear much else besides the motor but with a spindle you can really hear the cutter working.

  7. #7
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    Default

    I agree with Patrick.
    Start from a chipload calculation, then adjust to what sounds and looks the best.

    ...........Mike

  8. #8
    Join Date
    Oct 2000
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    Toms River, New Jersey
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    Default

    Here's another version of a "chip load calculator", this time offered by Robb Jack tools ;
    http://www.robbjack.com/
    They offer very nice bits. Some are expensive, but supposedly worth the extra bucks. I know a few Shopbotters are using their bits out in California...

  9. #9
    Join Date
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    Default

    Bill,
    The robbjack.com site is one of the most informative sites on chipload that I've ever visited. Thanks for the info.

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