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Thread: Smooth Cuts in Hardwood?

  1. #1
    Join Date
    Jan 2015
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    Santa Rosa, California
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    26

    Default Smooth Cuts in Hardwood?

    I hope I'm not already in danger of wearing out my welcome, but I have a question about cut quality in hardwoods. Until today, I've been practicing on various grades of Pine and found a better cut is made in the better grade of Pine. I cut some Cherry this afternoon and got a really rough cut. I hope it's not related to cutting into a hold-down bolt the other day.

    Can someone point me in the right direction to start getting up to speed on the factors related to smooth cuts in various woods?

    Lee
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  2. #2
    Join Date
    Sep 2006
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    Garland Tx
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    Lee…
    What I’m seeing… The watermarks of your three step-downs tells me you’re not cutting with an onion skin strategy.You should cut in climb mode with a .01”-.015” allowance away from your perimeter vector, and then make a final pass, full depth, in the conventional direction, on the line.
    This should help… as will not cutting into hold down bolts! J
    SG

  3. #3
    Join Date
    Jan 2004
    Location
    Cleveland TN
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    369

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    Lee,

    I've cut quite a bit of hardwood, including cherry and have not seen that bad of a problem. A number of factors could be hurting you but will need more information. 1st, cutting into your hold down bolts may have damaged your bit enough to cause this (trust me we have all done that) and we would need your feed rates ( x, y, z). This will help us to see what may be contributing to your problem. Of course Steve has a very good suggestion and I have read this several times on this forum and must admit I keep forgetting to follow it myself.

    Joe
    2005 PRT Alpha 48x96
    2013 Colombo 3hp spindle
    Indexer (converted lathe)
    Aspire 9.0

  4. #4
    Join Date
    Jan 2004
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    iBILD Solutions - Southern NJ
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    Default

    First, check your Z axis to make sure it is truly perpendicular to the table. I see waterline marks & when I see that the first thing to check is router squareness.

    Second, analyze the scrap pieces in comparison to the finished parts. Does the scrap look better? "Don't throw away your best edge." - If it does, reverse cutting direction. If running Climb, change to Conventional in the profile toolpath strategy fill-in sheet - right under where you selected the tool bit - or vice versa.

    Third, experiment with higher RPM. Try running somewhere in the 1.5 to 2 inches per second on the XY and 1 in/sec on the Z. Set your RPM somewhere in the 13,000-15,000 range. See if the cuts improve. Focus on getting the best cut quality. Softer woods require higher RPM. These are just baseline numbers. adjust one or the other until the cut quality is improved.

    Pine is junk & not easy to get a clean edge all the way around. You need good fresh tooling to get your best edge. You should be running a 2-flute upcut spiral (or solid carbide end mill) or straight bit for this job.

    Try it out and let us know how you make out.

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

  5. #5
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    Jan 2004
    Location
    Paris TX
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    Default

    Brady,

    On a 2001 PRT, with a spindle, would there be enough adjustment in the v-rollers of the Z axis, to adjust this problem? You can't access the screws for the spindle mounting to make the adjustment without completely removing the Z axis. If there is another way, please advise. Thanks in advance.

  6. #6
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    Oct 2014
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    La Crosse, Wisconsin
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    here is a nice article about cutter feed speed etc.

    http://makezine.com/magazine/cnc-rou...eeds-n-speeds/

  7. #7
    Join Date
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    iBILD Solutions - Southern NJ
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    Quote Originally Posted by gary_n View Post
    Brady,

    On a 2001 PRT, with a spindle, would there be enough adjustment in the v-rollers of the Z axis, to adjust this problem? You can't access the screws for the spindle mounting to make the adjustment without completely removing the Z axis. If there is another way, please advise. Thanks in advance.
    The adjustment is entirely with the 1/2" bolts that go through the 2x2 'towers'....OR clocking the spindle plate a little bit. Get a good square and see where it is...Dial indicator is the preferred method.

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

  8. #8
    Join Date
    Dec 2008
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    Diamond Lake, WA
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    Default

    I cut hardwood all the time and use the method Steve G recommends. I also use this method for cutting plywood. Very clean cuts perfectly on the line.

    The Shopbot has enough slop in it that trying to cut everything conventional leaves less then desirable results. The climb then conventional method removes this and provides for excellent results. The down side is it takes longer to cut everything. But that's life. If you want super cuts on single passes you will probably need to go with a big-iron machine that is much more rigid.
    Don
    Diamond Lake Custom Woodworks, LLC
    www.dlwoodworks.com
    ***********************************
    Life is not a journey to the grave with the intention of arriving safely in one pretty and well preserved piece; But to skid in broadside, thoroughly used up, worn out, bank accounts empty, credit cards maxed out, defiantly shouting "Geronimo"!

    If you make something idiot proof, all they do is create a better idiot.

  9. #9
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    Quote Originally Posted by dlcw View Post
    The Shopbot has enough slop in it that trying to cut everything conventional leaves less then desirable results. The climb then conventional method removes this and provides for excellent results. The down side is it takes longer to cut everything. But that's life.
    Don - I don't agree with any of these statements. I certainly don't get cuts like that on my machine and only do climb with allowance, then conventional, for acrylics where the edge quality is critical. If I had to go through that nonsense on every job, I would have ditched my machine long ago and bought something else.

    The reason machines 'have slop' in them is because they have not been properly maintained or they are being run 'chipload heavy'. People start to get Scotch with their carbide and run them at 8,000 RPM. That's milling machine territory & not routing territory. Running the same chiploads as heavy iron is going to result in poor cuts on these machines. You can't make any money if you have to do the climb/conventional trick on every job...and you certainly can't send out parts with waterline marks on them - at least I can't/don't.

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

  10. #10
    Join Date
    Apr 2013
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    Kennebunkport, Maine
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    Default

    Also, Lee has a 2 week old Desktop.
    Should be just a feed/speed/damaged bit issue.
    scott P.
    2013 Desktop/spindle/VCP 11.5**
    Maine

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