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Thread: Poor cut quality on solid birch wood

  1. #1
    Join Date
    Dec 2014
    Location
    Los Angeles, CA
    Posts
    41

    Default Poor cut quality on solid birch wood

    I'm cutting some pieces on solid 3/4" birch wood. I've done numerous tests with the feeds/speeds and a climb/conventional cutting, however the cut quality is just not that great. There's chips and coarseness/fibrous shavings left on the side. When the bit reaches the corners, there's a screaming/screeching noise which is very high pitch and irritating.

    Here are my cut settings:
    Onsrud 57-910 1/4" downcut bit
    10,000RPM
    4IPS
    7 passes at around 0.117 depth per pass
    Climb cutting

    Attached are the photos of the piece. The overall size of the piece is around 1.4"x3.5".

    I'm still a newbie to the CNC world, would appreciate the help. Thanks!
    Attached Images Attached Images

  2. #2
    Join Date
    Feb 2013
    Location
    River Fall WI
    Posts
    768

    Default

    You are cutting way too fast for a part that size.
    Try 1ips. or slower
    Kyle Stapleton
    River Falls Renaissance Academy
    Math/Technology Education Teacher


    PRS Alpha 96x60 2.2 hp spindle, Double Air drills, 6" indexer, Fein 5 zone vac table
    Desktop w/spindle
    Potter Pen
    Aspire 8.5, Creo 3.0

  3. #3
    Join Date
    Nov 2006
    Location
    LaGrange GA
    Posts
    590

    Default

    yeah, cutting too fast.
    Take a small sample piece of the wood. Cover the smoothest side with transfer tape. I like "Conform" brand. Squeegee it down.
    Then take some double sided adhesive tape (like banner hem tape) cover a piece of coroplast with it then squeegee it down.
    Then apply wood with application tape to the sticky side of the tape you applied to the coro. Use roller or laminator to smash the two together.

    When you cut on the machine, cut through the wood by about .1

    The transfer tape will hold to the sticky tape and the small letters should not move and cause chatter. the transfer tape will come right off the wood and make it easy to pull out. Also you can walk away from the machine and let it cut letters without worrying about them jumping around after the cut.

    Harbor Sales sells all these products.

    Dave
    Attached Images Attached Images

  4. #4
    Join Date
    Dec 2014
    Location
    Los Angeles, CA
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    41

    Default

    Hi Kyle, I just made a cut with 1IPS. The cut quality of the sides came out better but there were more chipouts than before in the same area as pointed in the photos. Any other thoughts?

  5. #5
    Join Date
    Nov 2006
    Location
    LaGrange GA
    Posts
    590

    Default

    try .7 inch per sec and increase stepdown to .25" or maybe even .376"

    After your cut out is made, you could go back with a profile pass just barely taking off any material. But you got to have them held down securely.

    Dave

  6. #6
    Join Date
    Sep 2008
    Location
    San Jose del Cabo based since 1997
    Posts
    1,242

    Default

    bump up the spindle to 12-13k try a spiral ramp

    welcome to the world of solid wood machining...
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    Vector Studio 22

  7. #7
    Join Date
    Apr 2013
    Location
    Kennebunkport, Maine
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    4,100

    Default

    Try 1.6,.5,10.5K with .125" passes/spiral ramp/last pass .001/ conventional cut.
    IF possible, change design from a sharp angle where tearing out to even the very smallest of radius. Also if possible, flip wood 90 degrees so the tearout section isn't unsupported endgrain.
    Never cut Birch, so I may be talking through my hat
    Bit squeals at corners because the machine slows down for corners just like you do in a car, VR(Virtual Ramping NOT ramping like in a profile toolpath setting) and it's "Hungry".
    Doubt if it was ever getting near 4IPS on a small part like that anyways because of VR.
    If my settings are still "Noisy" reduce RPM slowly while listening to bit. Some woods are "Picky" and even 500 RPM can make a huge difference. Got one wood that likes 9K for RPM. Go figure
    Hope this helps.
    scott
    Scott Plaisted
    2013 Desktop/spindle/VCP 9
    Maine

  8. #8
    Join Date
    Jan 2004
    Location
    iBILD Solutions - Southern NJ
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    7,952

    Default

    Some woods, regardless of what you do, will cut like crapola. Birch and maple come to mind - and it has to do with the way the grain runs through the piece more than anything.

    You can sometimes get good results by using allowance (say .02") and a climb cut stepping down say .125" per pass with a ramped plunge. Leave a .05" onion skin on the bottom. Then come back, FULL DEPTH in one pass, @ zero allowance using a Conventional strategy. You can try Climbing it with no allowance @ .125" pass depth, but you will most likely get climb marks.

    Climb - does just that...It climbs on the material and pushes the wood fibers IN rather than yanking them out.

    -B
    High Definition 3D Laser Scanning Services - Advanced ShopBot CNC Training and Consultation - Vectric Custom Video Training IBILD.com

  9. #9
    Join Date
    Dec 2014
    Location
    Los Angeles, CA
    Posts
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    Default

    Thanks for all the great suggestions/advice! After more tests per your suggestions, I think I came upon a happy medium in terms of noise and cut quality. A lot cleaner edges and fewer/smaller chips.

    Feed: 1 IPS
    Plunge: 0.5 IPS
    7200RPM
    .125" passes/spiral ramp/last pass is .001
    Climb cut

    Thanks for all the help, much appreciated!

  10. #10
    Join Date
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    iBILD Solutions - Southern NJ
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    Default

    Keep in mind you are out of the torque range for your spindle @ 7200 RPM. You can get the same results by doubling both the spindle speed and XY move speed. So...Run 14,500 RPM at 2" per second XY. You'll cut the same exact size chip (chipload).

    -B
    High Definition 3D Laser Scanning Services - Advanced ShopBot CNC Training and Consultation - Vectric Custom Video Training IBILD.com

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