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Router Flush Trim Bits

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  • Router Flush Trim Bits

    Well, I think I asked my router to bite off more than the bit could chew today. I had just glued the 4/4 mahogany baffles onto the front of the pair of Tritrix ported bookshelf MTMs I'm rebuilding for my brother, and I guess I left a little too much overhang for the 1/4" shank flush trim bit. The bit was an MLCS 1/4" Spiral Flush Trim Downcut #5089 and it snapped in two about midway only a couple inches into the cut. My router is the Dewalt DW618M and I had it at max speed.

    So my question is ... what to get now and what precautions or tips do you guys have? I already plan on trying to take off as much of the overhang as I can with a jig saw (or my table saw if I can set it up to slice off a sliver or two). My plan is to stay with MLCS and increase the shank size to 1/2" (what I should have been using on 4/4 anyway): 1/2" Spiral Flush Trim Downcut #7389.

    I'm just a little let down because I've seen many people use these flush trim bits with great success with harder and thicker material. Now I need to make some logos for the front of the baffle to cover my gouge of ineptitude.

    Thanks guys!

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  • #2
    Using a 1/2" diameter bit will certainly help. I use 1/2" shank, 1/2" cutting diameter straight-flute flush trim bits, and take multiple small cutting passes. I take only about 1/16" off on each pass to not stress the bit or get chatter.marks on the cuts.

    The bit shown above was cutting way over it's design limit, and overheated. Your idea of using a saw to get a closer fit to begin with is a good one.
    Bill Schneider
    -+-+-+-+-
    www.afterness.com/audio

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    • #3
      Gouge of ineptitude...LOL

      This is a good warning for how I treat my bits. I've been pretty lucky with much cheaper bits than that (but softer wood).
      Electronics engineer, woofer enthusiast, and musician.
      Wogg Music
      Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat

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      • #4
        Originally posted by williamrschneider View Post
        Using a 1/2" diameter bit will certainly help. I use 1/2" shank, 1/2" cutting diameter straight-flute flush trim bits, and take multiple small cutting passes. I take only about 1/16" off on each pass to not stress the bit or get chatter.marks on the cuts.

        The bit shown above was cutting way over it's design limit, and overheated. Your idea of using a saw to get a closer fit to begin with is a good one.
        +1 on this very good advice. Also check to make sure your speed is adjusted appropriately for the task.
        Carbon13

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        • #5
          This looks like user error to me. Is that like 3/8" of overhang that you're cutting into with a 1/4" flush trim bit? You need to do like 1/16" max with those things...Yikes..Did you cut the woofer holes in a single pass too?

          The bit is called "trim". It works well with thick and hard material, but only to shave the edge to clean it up, not to complete the entire cut that a 10" table saw blade should be used for.
          "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
          exactly a Fc 3K for both drivers, anybody can do it." -Xmax

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          • #6
            Originally posted by dcibel View Post
            This looks like user error to me. Is that like 3/8" of overhang that you're cutting into with a 1/4" flush trim bit? You need to do like 1/16" max with those things...Yikes..Did you cut the woofer holes in a single pass too?

            The bit is called "trim". It works well with thick and hard material, but only to shave the edge to clean it up, not to complete the entire cut that a 10" table saw blade should be used for.
            ^This. Way too much material and too small of a bite I have snapped expensive 1/4” flush trim bits on less material. Trim the edge to 1/16” then flush trim.
            "A dirty shop is an unsafe shop, if you injure yourself in a clean shop you are just stupid" - Coach Kupchinsky

            The Madeleine
            The Roxster
            Swopes 5.0
            Acoustic Panels
            Living Room Make Over

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            • #7
              Originally posted by Carbon13 View Post

              .... Also check to make sure your speed is adjusted appropriately for the task.
              +1

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              • #8
                I have a few Yonico 1/2 shank, 3/4 inch wide, 2-1/2 inch long pattern cutting bits. The weight helps me power through any over cutting mistakes. Lately though it has been all hand planes on MDF. It's much easier to flatten a surface vs. sometimes blindly trimming edges. Less messy too.
                John H

                Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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                • #9
                  Thanks for all the feedback guys: I'm glad it's user error. That's correctable. I ordered the 1/2" bit (MLCS #7389) and I'm hoping to finish these up in two weeks.

                  I had wayyyy too much overhang and the poor 1/4" bit was using 50% of its circumference cutting through 4/4 mahogany. What do you mean it was too much?? bahaha
                  To the table saw, I go. Wish me luck. I'll post the finished in the gallery.

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