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I order this 3/32 slotting bit from Amazon.

Bit

Shank size 1/4, depth of cut up to 9/16. I only need 3/8 depth (slightly over is ok), but I could not find the right bearing. There are router bearing sets sold on the internet, but they are very sparse with descriptions. Can someone recommend the right bearing or a set that will do the job?

The application is to convert tongues to grooves in engineered flooring for this project.

Update: I ended up making my own rip-fence, since the router's rip-fence could not accommodate a bit this wide at a shallow depth that my project required. Certainly not the prettiest thing, but served the purpose well. I was amazed at how smoothly it cut grooves in engineered hardwood flooring. When I first tried it out, I barely felt any resistance. It practically evaporated the material, rather than chipping it away.

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    How much "slightly over" is okay? 9/16" is only 3/16" deeper that 3/8". Is this the Frued 63-106? The pain you'll have is that the bearings are on that cutter 8mm (8mm ID, 22mm OD), so you'd have to try to find another 8mm bearing. You need something close to 1 1/4" bearing, probably along the lines of 8mm ID and 30mm OD (which should give you something like a 7/16" cut), like the Freud 62-128. That is, if my math is correct.
    – Jacob S
    Commented Jul 30, 2013 at 16:10
  • @JacobS: How much over is a grey area, ideally I would prefer not to overshoot at all, in order not to create unnecessary cavities in the flooring, thus weakening it. But probably 1/16 is tolerable. Yes, this is Freud 63-106. Thanks for pointing out the inner diameter, that's a good starting point for my search. Not to doubt your expertise but rather for my own benefit: how did you figure out it's 8mm? The bearing spec page on Freud Tools website lists 62-128 at 5/16" ID, that is slightly less than 8mm. But the Amazon description page for it says 8mm.
    – user443854
    Commented Jul 30, 2013 at 16:51
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    Freud seems to list their stuff in odd ways. I checked their standard 1/4" shank bearing which is 8mm x 22mm (63-106 isn't listed on the bearing page, but all the 1/4" shanks are 9/16" cut which means they all have to use the same bearing). As for the 8mm x 30mm being the 62-128, I admit that I am taking the Amazon description on face, since I'm unsure why Frued would measure IDs of fractional and ODs of mm for ONLY 62-124 and 62-128. As for the match -- 2" diameter cutter - 3/8" radius cut = 1 1/4" bearing (or ~30mm which is about 1 3/16"). But no offense, as I'm no expert.
    – Jacob S
    Commented Jul 30, 2013 at 17:18
  • @JacobS: Yes, Freud's nomenclature seems inconsistent. Do you happen to know if they make even bigger OD bearings, e.g. 32 or 33 mm? I cannot seem to find one. In case they do not exist: do you think I can achieve similar results by using rail guides? I would like to avoid purchasing a router table for this project, but I might end up doing so. What are your thoughts on this? By the way, thanks for the discussion. If you copy/paste your comments as an answer, I will gladly accept it.
    – user443854
    Commented Jul 30, 2013 at 19:32
  • @JacobS: Just found this bearing Freud 62-122 1-1/2-Inch OD by 8mm ID' which should produce 1/4" deep cut.
    – user443854
    Commented Jul 30, 2013 at 20:15

1 Answer 1

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The combination bit/bearing that you pictured in the original post would be particularly useful for routing a slot along a curved edge, such as the rounded corners of a table top in preparation for the vinyl edge moulding held in place with a spline.

Trying to route a slot in something as thin as 3/8" engineered flooring is problematic when depth is controlled by a shank bearing. The upper and lower lips on either side of the groove will be a bout 1/8". For a composite material, that narrow surface makes using a shank bearing technically challenging. In practice though, it is even worse. The gap between the top of the bearing and the bottom of the cutting disc will reduce the effective lip to something less than 1/8", particularly in light of the rounded shoulders on the bearing. My guesstimate is that the bearing will have solid contact on only 1/16" of the 1/8" lip.

With that said, here are a few options ...

  1. Instead of routing the 3.5" ends one by one, route in batches, say 8 or 10 at a time. Mate them up side by side with the ends aligned. Clamp them together using a light weight 36" bar clamp, then use 6" bar clamps and a 2x4 on edge to secure the assembly down to the work surface (this will sandwich the flooring between the 2x4 and the work surface). Place the 2x4 at the correct distance from the ends of the flooring so that the 2x4 serves as a rip fence for the router base. No bearings are needed with this approach. The 2x4 can be aligned with the edge of the work surface, with the ends of the flooring protruding out.

  2. Use the rip-fence that came with the router ... or make your own rip fence by screwing a, say 8"x4" piece of 3/4" plywood to the bottom of the router, with a U-shaped recess cut out of the middle of one edge to accommodate the router bit. Note that this will provide full bearing on both lips.

  3. Make your own donut-shaped adapter to slip over the metal ball-bearing, increasing it's effective outer diameter, making it out of a scrap of 1/4" plywood/lexan or similar. Use a hole saw whose plugs happen to match the desired outer diameter of the bearing. Cut a hole, and retrieve the plug (disc). In the middle of the disc there will be a 1/4 pilot hole made by the hole saw. Enlarge it with a regular drill bit (or spade bit) that matches the existing bearing's outer diameter. Slip the resulting plywood donut onto the bearing, using a wrap or two of duct tape on the bearing to achieve a snug fit. Lots of variations on this idea.

  4. Use a base plate bushing instead of a shank bearing

For a number of reasons (1) is how I'd do it. Second best is (2).

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  • I did not realize that the bearing is intended primarily for routing curved edges. Now that you said it, it totally makes sense. I am going with your suggestion number 1.
    – user443854
    Commented Jul 31, 2013 at 13:01
  • i woke with the thought that unless the slot provides a very snug fit, there is no point to it at all. better to just cut off both tongues for a square butt joint, in my opinion.
    – mike
    Commented Jul 31, 2013 at 13:09
  • This has been suggested to me before. Now that there are two people arguing for it, I am inclined to follow this advice. Since I already ordered the bit, I will experiment with a plank or two to see (1) if the fit is very snug, and (2) whether this will cause chipping or any other issues. I guess one benefit to cutting the groove is not having to cut the opposing tongue.
    – user443854
    Commented Jul 31, 2013 at 13:27
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    Cutting the tongues off of the old flooring could be done with a sharp chisel, or by scoring repeatedly with a utility knife.
    – mike
    Commented Aug 2, 2013 at 5:34
  • Making grooves instead of cutting off both tongues turned out to be the right approach. It was easy enough, so that just cutting the tongues off would not save any time, and would probably take even more time. And it made a world of difference by keeping the planks nicely tucked. Without tong-in-groove, it would be impossible to achieve a perfectly flat surface.
    – user443854
    Commented Aug 9, 2013 at 3:01

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