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  1. #1
    Join Date
    Jul 2013
    Posts
    230

    DRILL VS. END MILL

    I'm making guitar bodies. All wood 1.75" thick

    When I use a drill, the holes are not always too large. So, I have to use a smaller bit. That's ok, but what is happening that makes the hole larger than what it should actually be?

    I use a PECK drill cycle with a .25 drop in Z.
    I have the bit clear the top of the piece hopefully allowing the chips to clear.
    When I use an EM.....no problem. But, I can't go 1.8" deep because I do not have an EM that is long enough to make that depth of cut.

    Any ideas?
    Rob

  2. #2
    Join Date
    Jan 2005
    Posts
    238

    Re: DRILL VS. END MILL

    Well, how fast are you spinning the drill? Also what diameter and how long is it. HSS , Cobalt or maybe Carbide?
    If you spin a drill too fast, it whips around quite a bit. Now being that the wood is softer than the drill, the drill acts as a rotating boring bar, enlarging the hole beyond the drill diameter. Another cause of over size holes can be caused by a drill having an uneven point angle/length(the cutting face that is). This causes the drill to wander when drilling in steel or hard materials as one side of the drill is working/cutting more than the other.
    As for the endmill, I'm sure it is quite a bit shorter than the drill which means unaffected by RPM, or it is made of a better/higher strength material.

    That's all I have for now until you let us know what RPM or drill length(stick out preferably) you are drilling with.

  3. #3
    Join Date
    Jul 2013
    Posts
    230

    Re: DRILL VS. END MILL

    That's great info. Speed is a big part of it .
    I never really got Mach 3 to slow the speed down.


    Sent from my iPhone using Tapatalk

  4. #4
    Join Date
    Jul 2013
    Posts
    230

    Re: DRILL VS. END MILL

    Drill length is 2.25 total
    Diameter is 5/32
    Speed... Don't remember 1800?
    So I switched to a 1/8"
    To try to control the diameter of the final cut


    Sent from my iPhone using Tapatalk

  5. #5
    Join Date
    Jan 2005
    Posts
    238

    Re: DRILL VS. END MILL

    Hmmm...............well 1800 rpm isn't fast enough to make the tip whip, and I doubt you resharpened it by hand. I know that too much pressure and running too slow, can cause drills that small to flex and not clearing the chips often enough, therefore rubbing the flutes of the drill against the wall. You are possibly feeding it too fast into the material.
    A few things I would check, the runout in your drill chuck. Also measure the drill bits to see if they're really the right size. Bad grinds do exist.

  6. #6
    Join Date
    Jan 2005
    Posts
    238

    Re: DRILL VS. END MILL

    Just did a quick calculation for magnesium as wood varies so much, you should be OK with a feed rate of 7.2 inches per minute at 1800 rpm.

  7. #7
    Join Date
    Jun 2004
    Posts
    6618

    Re: DRILL VS. END MILL

    I suggest that you need a longer smaller end mill or router bit. If you need precise holes at that depth, the way I do it is interpolate with an end mill. You can speed up interpolation with a smaller drill bit to remove the bulk of material. Always include a high speed finish pass at depth. That will help negate any flex of the end mill when interpolating.
    Lee

  8. #8
    Join Date
    Jan 2009
    Posts
    68

    Re: DRILL VS. END MILL

    Quote Originally Posted by robwiacek View Post
    I'm making guitar bodies. All wood 1.75" thick
    When I use a drill, the holes are not always too large. So, I have to use a smaller bit. That's ok, but what is happening that makes the hole larger than what it should actually be?
    Any ideas?
    Rob
    Unless the drill is very sharp, there will usually be a small amount of tearing in wood, making a slightly large hole.
    Check your feeds and speeds, and perhaps slow the drilling rpm down a bit.

    Have you checked for run-out at the chuck?
    It is not uncommon for a router to have a few thousandths and the chuck to have a few thousandths and the hole then gets that much bigger.
    Try chucking a piece of drill rod and measuring the run-out.
    Then relocate the chuck at 90 degrees intervals in case the router and chuck are each out to find the worse case run-out.
    Add that to the drill diameter.
    Easiest way to slightly increase the size of a hole for clearance is to add a piece of paper or two under one of the jaws of the chuck.
    This may be what you are inadvertently doing with run-out.
    Dennis

  9. #9
    Join Date
    Jun 2013
    Posts
    1041

    Re: DRILL VS. END MILL

    Try picking up a set of brad point drills. I have had great success with them in wood on my router. How much oversize are your holes coming out? I doubt you will ever get it perfect but you should be able to stay within a few thou.

    Ben

  10. #10
    Join Date
    Jan 2013
    Posts
    263

    Re: DRILL VS. END MILL

    Isn't a peck cycle just to break the chip and allow evacuation? But on wood you don't have nice long chips that will find their way out, you produce more of a mess. You may need to pull the bit clear out of the work after each .25" incremental plunge to ensure you're getting rid of all that material.

  11. #11
    Join Date
    Jun 2004
    Posts
    6618

    Re: DRILL VS. END MILL

    That isn't all it's for. It is to eject the material from the flutes and clear the hole, but it also reduces the temperature. Wood doesn't clear as well as steel and aluminum, so the heat stays inside the hole until cleared. Depending on the depth and type of wood as well as bit type and speed, it can get hot enough to burn quickly. If you peck drill even in wood, for these reasons, you get a cleaner more accurate hole.
    Lee

  12. #12
    Join Date
    Apr 2007
    Posts
    100

    Re: DRILL VS. END MILL

    Very good responses for you here. With drills not running true in the holder and perhaps having the cutting flutes uneven will oversize the holes. With thinner material and also material which is easier to cut than SS the trend is to max out the speeds and peck cut on them. I understand their motive yet sometimes we can just go too darn fast in certain materials. If your peck on drilling is say .1 or more you may want to see what happens when you cut it back. I would do a drastic difference and make it about .03. Really it is just trial and error.

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