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Thread: Poor Chip Clearance in Slots

  1. #1
    Join Date
    Feb 2016
    Posts
    29

    Default Poor Chip Clearance in Slots

    Hey y'all! I'm finding that I'm getting pretty poor chip clearance when running profile paths that are more than 1x DOC that are essentially slots. For example cutting out the body shape of a guitar from a big square wood blank. Even with upcut bits (1/4" going 1.5IPM, 12k, .17" DOC). The first path seems to work fine, but then subsequent passes leave more and more until I see things like:
    - bit deflecting and gauging the edge
    - lost steps from the bit binding
    - bad noise from the bit
    The machine is obviously struggling and therefore I have to stop and until I figure this out I'll have to not do these operations.
    Thoughts? Should I slow the feed each step down? Should I do two profiles making a wider slot each pass? (Both of those require a lot more paths and programming...) Am I just going too fast overall for slots up to 1" deep after all the passes are finished?
    Thanks,
    Chris

  2. #2
    Join Date
    Apr 2007
    Location
    Marquette, MI
    Posts
    3,250

    Default

    Chris....
    Try a 3/8 compression with a 1 1/8" LOC and try multiple feeds to see which ejects chips better. You may also need to use an air blower to remove chips from the slot
    Gary Campbell
    CNC Training & Technology
    GCnC411(at)gmail(dot)com
    http://www.youtube.com/user/Islaww1


    "We can not solve our problems with the same level of thinking that created them"
    Albert Einstein


  3. #3
    Join Date
    Jul 2005
    Location
    Brookline, New Hampshire
    Posts
    427

    Default

    You might try a single flute bit.

    Paul Z

  4. #4
    Join Date
    Jun 2013
    Location
    Pasadena, CA
    Posts
    891

    Default

    When cutting such deep slots I tend to get similar clogging. Things that help as mentioned in the previous posts
    - single o-flute or at least a steep flute helix angle
    - a directed air jet (I have such a nozzle now as a permanent fixture next to the spindle)]
    - strong dust collection air flow to prevent flying chips from settling somewhere else in the groove
    - making a wider slot than the bit
    - less depth of cut per pass (if you can afford the time) makes it easier for the bit to clear the produced chips
    Box Joint, Dovetail and MazeMaker Software Here

  5. #5
    Join Date
    Jan 2011
    Location
    gleason, wi 54435
    Posts
    376

    Default

    I would use a 3/8 bit with .015-.020 offset for the cut outs so that chatter doesn't reach into the finished part. Follow up with a full depth of cut in a single pass to clean up to the vectors (climb or conventional doesn't seem to matter. Make sure to blow all the chips out of the kerf before that final cut to eliminate deflection.
    Bob

  6. #6
    Join Date
    Feb 2016
    Posts
    29

    Default

    Thanks guys. I have a single O that I'll give it a try with. I'll admit my dust collection likely leaves a bit to be desired. The CNC is in the house as I didn't fancy leaving it out in the non-humidity/AC controlled barn shop... where all the real dust collection is. So right now it runs on a shop vac. Looks like I should look into an air jet.
    As of right now I always do a .020" offset and then finish up with a full depth pass for cleanliness. I just usually don't get that far before running into clogging issues haha.
    Thanks, time to experiment!
    Chris

  7. #7
    Join Date
    Feb 2016
    Posts
    29

    Default

    Burkhardt do you know of an easy way in VCarve to do a slot wider than the bit? The only way I could think of is to:
    - make a path with a large offset to the first DOC
    - repeat that path without the offset
    - repeat both paths to second DOC
    - repeat both as needed for total depth
    - finish with onion-skin full depth pass
    This seems like a LOT of paths. So if there's some secret I don't know about I'd love to hear it.
    Chris

  8. #8
    Join Date
    Feb 2016
    Posts
    29

    Default

    OMG that single flute Super O bit test I just did is like night and day! I did three 0.75" deep slots:
    Top: 1/4" 2 flute upcut at 1.5ips 12k
    Middle: 1/4" 2 flute upcut at 1ips 12k
    Bottom: 1/4" upcut super O at 1.33ips 12k




    Here's what I noticed:
    1- the super O had more "chip" looking results while the 2 flute bit had thinner shaving type chips
    2- the super O had much better chip evacuation
    3- when the super O path ran I was surprised by how quiet it was! I was used to the other bits having this sharp high pitch noise as they ran through material and there was none of that with the super O!
    4- Look that the surface quality that the super O left!!! It's gorgeous! The other two slots have little "hairs" hanging off the sides.
    Chris

  9. #9
    Join Date
    Feb 2013
    Location
    River Fall WI
    Posts
    733

    Default

    You are cutting too slow with the 2 flute bits.
    With your feeds and speeds almost the same for the 1 and 2 flute bit, that means your chip load is double for the o flute.
    That is why it sounds better, cutting slow does not mean you are getting a better cut.
    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

  10. #10
    Join Date
    Feb 2016
    Posts
    29

    Default

    I used to run them faster Kyle, but ran into the problems I discussed in this thread: http://www.talkshopbot.com/forum/sho...-Skipping-Axis
    It seems when I ran them at the speeds that I should have to get good chiploads I encountered other problems.
    Chris

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