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Thread: flush trim router bits

  1. #1
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    flush trim router bits

    So, as is typical for my backwards tool buying habits, it would have been nice to have a flush trim router bit for some recent shop shelving units. They're inexpensive enough that I don't really have an excuse not to get one soon. I can definitely foresee myself using the kind with the bearing at the end of the bit. But it would probably be nice to have one of each style. Then I noticed that Freud makes one with a bearing at either end for about twice the price of the one bearing models (a note on this price - the double bearing bit is a 3/4" cutter and the single bearing models were 1/2").

    For a hobbyist, what are the advantages and disadvantages of getting the two-in-one bit vs the two separate bits?

    FWIW my router is a 2 1/4 HP PC8729 plunge router.

  2. #2
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    Mark, both top bearing and bottom bearing bits are useful, and I agree that they're good to have in the arsenal. If the dual bearing bit is about twice the price, I think I'd just buy two separate bits. The way I see it, for about the same amount of money, you get two sets of cutting edges to wear out, not one. The only thing I see you lose is the convenience of having a single bit do two jobs.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
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  3. #3
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    The dual bearing bit would indeed be handy, but...

    If you're using the top bearing on a thick piece - like 6/4 ot 8/4 stock - then the bottom bearing will contact the rough edge first and keep the bit from working. The dual bearing bit will only work if the cutting edge height is greater than the thickness of your stock.

    With a top bearing (only) bit, you can make your first cut using a template, then lower the bit (or raise it if the router is table-mounted) and use the previously routed edge as a continuation of the template.

    Of course, you could always remove whichever bearing you don't need, and use the bit that way.

    Personally, though, I'd rather have the two different bits so that, like Vaughn said, there are two sets of cutting edges to wear out, for about the same overall cost.

    Also - unsolicited advice - think about spending a few dollars more and getting flush trim bits with spiraled cutting edges. The shear the wood instead of 'chopping at it,' and you'll get a cleaner cut and smoother edge that way. They work especially well in plywood, since the shear the face veneer in a downward cut and virtually eliminate splintering.
    Jim D.
    Adapt, Improvise, Overcome!

  4. #4
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    Spiral flush trim bits... they'll probably be twice the cost each, but I'm intrigued, as the inspiration to get these is a plywood project.

    Thanks!

  5. #5
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    For flush bits I find larger diameter bits give better results (someone mentioned this so I tried it, they were right). I used to use nothing but 1/2" bits. Tried 3/8" spirals; worked OK, did give a cleaner edge on ply. A 1/4" spiral was pretty much a waste of time except for light duty in the Colt. A 1" flush bit (Amana) works real well for me on various materials (larger spiral is still better on ply). Live and learn.
    Any sufficiently advanced technology is indistinguishable from magic.
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  6. #6
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    Here's my take
    - Bigger is better.
    - 1/2" shank is better
    - You'll always have to buy another one with a different cutter length or bearing location than the ones you already have.
    - If you're using it in a table, you primarily want the bearing on the end vs bearing near the shank for hand-held, but those aren't absolutes.
    - Template thickness can greatly affect the cutter length you want.
    - You might want a very short bit plus a 3/4" or 1" for doing normal 3/4" ply. I prefer not to cut the full depth in one pass. You're pretty much forced to do that to keep the bearing in contact with the template if all you have is the longer one.
    - If you're following a straight-edge guide you can take the bearing off to avoid the problem of rough edge following that Jim mentioned, but make sure you're trimming well back of where the bearing post would contact the edge.

    I just trimmed a 4" workbench top this weekend with a router, straight edge guides, and an assortment of bearing bits. A standard plunge cut, a couple top bearing (shank end) of increasing lengths to follow the first cut (with one trip to the store for the size I didn't have), and a long bottom bearing bit with the top flipped over to follow the first 3 bits. Flush trim bits are like clamps - you can never have too many.
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  7. #7
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    Would this (Amazon link) be an example of the spiral flush trim bit that people are talking about?

  8. #8
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    i buy my flush cutters from woodline 1/2 dozen at a time.......about the same price as one spiral...
    [SIZE="1"] associated with several importers and manufacturers.[/SIZE]

  9. Quote Originally Posted by Mark Kosmowski View Post
    Would this (Amazon link) be an example of the spiral flush trim bit that people are talking about?
    Yep, that's one type. Here's another:



    In regards to the top/bottom bearing bits, they are ideal for template work and the advantage is that they allow you to flip the workpiece and template for tricky grain (sort of the equivalent of changing feed direction except without climb cutting) without changing bits.

  10. #10
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    Um, I know there's usually no such thing as a stupid question, but... the bit that Charles posted a picture of - is that a bottom-bearing bit?

    The only time I've used my router out of the table has been to cut the hole for the table insert... I get confused with top and bottom.

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