Flush Trim Router Bits

Bits and Bits is a long time partner of Jays Custom Creations. They create high quality router bits and offer them with competitive pricing. Check them out at bitsbits.com and use the code JAYBATES to save 10% at checkout.

In the video, I mentioned I’ll be giving away a few of the duplicate bits I have. Leave a router/cnc related comment below, and you’ll be entered. Leave a tip, trick, learning experience, or whatever bit you plan on adding to your arsenal next. I’ll do a quick video and randomly select a winner in a few days.

The following were provided by Bits & Bits. I’ll select three winners. One bit per winner.

  1. Winner #1 will get an Astra coated RFTD5125 1/2″ diameter spiral down cut flush trim bit.
  2. Winner #2 will get an Astra coated 430-CM250FT 1/4″ diameter compression flush trim bit.
  3. Winner #3 will get an Astra coated 430-SRF250FT 1/4″ diameter up cut flush trim bit.

Below are the notes used for the video:

Up vs. Down?

  • Upcut for router table; Using the downcut on the router table with a gnarlier grain wood can push the workpiece up off the table if you’re not expecting it.
    • Caveat – Down for pushing against a template for reduced tearout. 

Bit Diameter?

  • Avoid an “enveloped cut” where the bit is surrounded on three sides by wood, instead of rough cutting close to the line and trimming off 1/16” or so. 
    • If you’re going to envelope the bit, we recommend a single-direction bit instead of the compression, which can get a little jumpy when it’s buried. The single direction is pulling the chips out quickly and not letting them pack into the cut pocket like a compression would.
  • Interior corners may require a smaller diameter bit. 

Router Speed?

  • Router speed is another issue that comes up, especially in the ¼” bits. Most guys install the bit and turn it up to full speed, but chip load applies to all spiral bits, regardless of CNC or router use. Turning the speed up to 27,000RPM + can make the bit erratic as well as cause it to dull quicker because it’s cutting dust and overheating (rubbing vs cutting). 16,000-18,000 is the recommended speed for all spirals.

Router Size?

  • Router size is also important. A solid carbide bit is more brittle than a standard steel shank tool, we have guys sticking a ¼” bit into a 3HP+ router and over-torquing and snapping the bit after it hits a dense pocket of wood or the user moves the router too fast. The thinner ¼” work really well on the smaller trim routers, but a larger router will do much better with a ½” bit.

Worth Considering…

  • The compression isn’t necessarily the ‘ultimate’ bit for trimming. It may produce the most crisp edges but most of the time, you’re going to round over or chamfer the edge anyways, so a little fuzz doesn’t really matter in the long run.
  • Integrated depth stop on the ⅞” bit. You can’t take a massive bite. It just won’t allow it.


  1. I ordered that 7/8ths bit a month ago but forgot to order from BitsNBits! Ugh still waiting for it to arrive.

  2. Great video – I really enjoyed the practical tips, especially about the compression flush trim, since you’re right, I’ll likely round over or break that edge in some way so a bit of fuzz won’t hurt anything. Won’t stop me from coveting that 7/8 bit, though!

    Thanks again!

  3. Good timing on this. Last night I broke the bearing off the top of my brand new Upcut spiral flush trim bit. Scared the crap outta me! Hit a section of gnarly grain on a piece of purple heart.
    I will probably watch this video several times to make sure I have it down.

  4. As usual, another great video. I always learn something new or at least something I should have thought of. I was concerned about “fuzz” or trying to get the cleanest cut possible. Then turn around and do a quarter inch roundover. Not any more. Thanks.

  5. This is a great guide to the different kind of bits and the decisions that go into choosing one over the other.

  6. Just ordered my first router table, so this was great info. Probably going to grab a set of tongue and groove bits soon.

  7. I just started using template routing in my process flow and it’s a game changer. Slowly amassing a line up bits for different situations

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