Determining Chip Load

This topic contains 8 replies, has 4 voices, and was last updated by  Sheemalakameeda 1 year, 2 months ago.

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  • #15202

    Sheemalakameeda
    Participant

    In determining the feed rate, formulas ask for RPM and chip load. The RPMs is pretty easy to figure out, but what about chip load? When you’re cutting through MDF, you can’t exactly measure the size of your chips, can you?

    I don’t want to post any equations if I am wrong without first clarifying that I am only making a guess here. So please, do not just run with these numbers if you happen to come across this post.

    In my example, I am attempting to clean up and level out my spoil board/work surface. I do not need to take off much and looking to remove 1mm. I have a fairly large work area of 24×35 inches and this can take some time, so I would prefer to do this quickly yet preserve the life of my bits.
    For a bit, I have a 2 flute half inch flat cutting bit (12.7).

    I took this info from http://www.pdsspindles.com/engineering-speeds to get a benchmark of chip loads for different materials and bit sizes. Though I am unclear if depth makes a difference.
    Chip Load

    Going off of the lower value for MDF and a half inch bit, I’d get .025.
    But if I look at http://www.shopbottools.com/mTechShop/files/ChipLoad_inch.pdf I would get a large range of .005mm-.030mm.

    .025 would seem reasonable for such a low depth, but calculators would then give me a feedrate of 1400. This is quite a bit of a jump from the 500 that seems to be a baseline. Now, I would love to increase the speed this much, but is it safe?

    Feel free to jump in and add your two cents.

    #15255

    Ryan
    Keymaster

    Unfortunately for me I have no way to measure RPM, so my chip load is calculated by ear.

    #15265

    Sheemalakameeda
    Participant

    Using the DeWalt 660, I start with 30,000RPMs and estimate after based on the speed controller setting. What’s really getting me is that this number is inches per minute, which is even more greater than the feed rate I’m using. Again, I’d love to go that fast, but this would match the speeds seen in accelerated videos.

    #15269

    Ryan
    Keymaster

    I have not compared to the calc values. It is pretty clear how fast and deep I need to go after a few test cuts. I aim to cut at about 15mm/s and adjust the spindle and depth to match that. Most of those calcs are for extremely large cast iron machines so any numbers you get off that always assume the shallowest, slowest, lowest load. a half inch bit would be very large for this machine, I would stick with 1/4″ or less I use 1/8″ and 1/16″, I do not even own any 1/4″..

    #15271

    Sheemalakameeda
    Participant

    I thought it was worth a try for the price I got it for to resurface my spoil board. Going over a 24×35 inch area with a 1/8 bit would drive me crazy.

    #15276

    Barry
    Participant

    I got one of these and ground off the bearing.
    http://www.menards.com/main/tools-hardware/power-tools-accessories/power-tool-accessories/router-bits-sets-accessories/cmt-1-2-rabbeting-bit/p-1444426664065-c-10080.htm?tid=7586973348430254083

    Haven’t tried it yet though. My current spoil board is plywood, and this wouldn’t work with that very well.

    #15277

    John
    Participant

    I used a cheap (in all senses of the word) harbor freight 1/2 inch straight router bit for surfacing the spoil board. It works just fine in the cnc. I think I got 3 for less than half what Barry paid for his nice rabbeting bit.

    #15284

    Barry
    Participant

    I keep forgetting about Harbor Freight. We didn’t have those in Alaska, so now that I’m back in the states it doesn’t occur to me.

    #15290

    Sheemalakameeda
    Participant

    I didn’t find one at Harbor Freight, but I picked one up at the TrueValue where I live. http://www.truevalue.com/product/1-2-Inch-2-Flute-Carbide-Straight-Router-Bit/20242.uts?keyword=Router%20bit

    It cuts nicely, but with everything being dust, I was wondering if I was going too slow and how much I could kick it up.

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