Rabbeting bits sized for baltic birch plywood

[Ruperto Mendiones]

Is there a rabbeting router bit set sized for baltic birch ply thicknesses? Alternatively has anyone purchased individual bearings to achieve the same? Using imperial sized bearings I get an annoying lip fitting bb into a rabbet.

[George Bokros]

Baltic birch is sized in metric. I have not seen a rabbeting bit for metric but I am not saying one does not exist.

[David Bassett]

Baltic birch is sized in metric. I have not seen a rabbeting bit for metric but I am not saying one does not exist.

I think most plywood is metric these days, certainly it is undersized from it's "nominal" values. Any way, lots of metric bits are available, even in US, e.g. at Woodcraft Metric Router Bits. (Not saying Woodcraft is best source, just a well known main stream one. Several manufacturers and other vendors have been recommended here over the years. Also, Lee Valley has metric shaft (20mm?) in addition to the 1/4" and 1/2" shaft models common for the US market.)

[Charles Lent]

I gave up trying to find bits to cut the exact size dados years ago and now use a smaller bit and a jig built much like this one https://www.google.com/search?q=adju...fRYKG7MPenL-M:

You put the board that you want the dado to fit in this jig and close the jig against the board surfaces. Then remove the board and use the jig and a smaller bit to cut an exact width dado to fit the board. It will fit perfectly every time no matter what the board thickness is.

Charley

[Ron Citerone]

I haven't used baltic plywood, but I cut my dadoes 3/8" for 3/4" stock and then rabbet the joining piece to fit. That way you can sneak up on a piece of scrap until you get the perfect fit. It not only makes a stronger joint, but avoids all the frustration. When I started doing this my case work started coming out square at glue up without much last minute heroics. Try it sometime.

[David Bassett]

I gave up trying to find bits to cut the exact size dados years ago ....

Cool jig idea. I think the way to go if you will be cutting dados with a router often.

For the very occasional dado, you can use the same technique, without the dedicated jig, if you have a guide and measure carefully. E.g. my track saw has a router holder, (so you can route to a line like the saw cuts to a line.) I'm sure it'd be possible without the track, with even more care.

Another thought, you could do this with the track saw, without the router holder, by cutting the dado sides with the saw. Then you can clean out the waste with the router (guided or not.)

[Ted Derryberry]

In my experience with Baltic Birch (several hundred sheets over the last five years) it's not consistent enough to try to find a bit sized for it. I just checked some pieces in the shop and found a range of 0.687" to 0.727". That's 40 thousandths which is more than 1/32". If you're cutting rabbets just use the fence on the router table to set your size. Or let the lip hang over and flush trim and sand it.

[Jim Becker]

Almost all plywood you can buy today is actually in metric thickness...12mm for 1/2" and 18mm for 3/4". Most router bit manufacturers sell bits sized for plywood use in dados and grooves; many list them with Imperial dimensions, but if you measure them... A rabbit, due to the nature of how you cut it along the edge, would probably require you to alter the bearing as you state. I haven't noticed specific bearings for this, but that doesn't mean they don't exist. For rabbits on the edge of a sheet or board that will intersect plywood, there's always the option to cut them using the table saw and a dado blade which you can fine tune "exactly" using a sacrificial fence with the edge of the stack buried in the sacrificial fence.

[Ruperto Mendiones]

I guess setting the fence on a router table is the best way to cut an exact fit rabbet. I wondered if anyone had used a bearing guided rabbeting bit and bought bearings sized to cut the exact thickness of the plywood. However, I did not realize there can be more than 40 thousandths variation in BB thickness.

[Mike Henderson]

I gave up trying to find bits to cut the exact size dados years ago and now use a smaller bit and a jig built much like this one https://www.google.com/search?q=adju...fRYKG7MPenL-M:

You put the board that you want the dado to fit in this jig and close the jig against the board surfaces. Then remove the board and use the jig and a smaller bit to cut an exact width dado to fit the board. It will fit perfectly every time no matter what the board thickness is.

Charley

I do a similar thing. You can see what I did here, a few pictures down. It's similar to what Charles points to, but it's a one time jig.

Mike

[Ted Derryberry]

Almost all plywood you can buy today is actually in metric thickness...12mm for 1/2" and 18mm for 3/4". Most router bit manufacturers sell bits sized for plywood use in dados and grooves; many list them with Imperial dimensions, but if you measure them... A rabbit, due to the nature of how you cut it along the edge, would probably require you to alter the bearing as you state. I haven't noticed specific bearings for this, but that doesn't mean they don't exist. For rabbits on the edge of a sheet or board that will intersect plywood, there's always the option to cut them using the table saw and a dado blade which you can fine tune "exactly" using a sacrificial fence with the edge of the stack buried in the sacrificial fence.

Jim, just because it's "sized" in metric doesn't mean it's actually that metric size. See my post above. 18mm is 0.70861 inches and I have baltic birch (definitely sized and sold as 18mm) which ranges from 0.687" to 0.727". That's pretty much +/- 0.020" which is way more than a properly fitting dado or rabbet.

[Jim Becker]

Understood, Ted. There will always be variance in thickness....nature of the beast. I should have indicated I was referencing nominal dimensions. My bad.

I recently had some "really bad import" birch multi-ply for a shop project that measured in at 17.7mm. Mostly, if you catch my drift...

[Charles Lent]

Take the time to build the jig that I posted. Mine was built 15 years ago and I use it several times a year. It's hanging from my shop ceiling along with my other jigs right now, and ready for the next time that I need to use it. If you have one, you will find that you will use it often and be very glad that you made it every time. I don't have plywood size problems any more. It wvwn works when dadoing odd thicknesses of solid wood.

Charley.

[Edwin Santos]

Almost all plywood you can buy today is actually in metric thickness...12mm for 1/2" and 18mm for 3/4". Most router bit manufacturers sell bits sized for plywood use in dados and grooves; many list them with Imperial dimensions, but if you measure them... A rabbit, due to the nature of how you cut it along the edge, would probably require you to alter the bearing as you state. I haven't noticed specific bearings for this, but that doesn't mean they don't exist. For rabbits on the edge of a sheet or board that will intersect plywood, there's always the option to cut them using the table saw and a dado blade which you can fine tune "exactly" using a sacrificial fence with the edge of the stack buried in the sacrificial fence.

I cut almost all rabbets using a dado set on the table saw. As an alternative to the traditional sacrificial fence with the buried dado blade Jim is describing, look up a jig called the Incredible L Fence from an article in Fine Woodworking by an author named Bob Van Dyke. It is brilliant, easy to make and after using it, you will probably never sacrifice another sacrificial fence for rabbetting again. Plus, the L fence will be useful for several other applications in addition to rabbets.

Here's a link to the video: http://www.finewoodworking.com/2014/...blesaw-l-fence

However if the router is the only option here, and you have a router table available, I see no reason why the L-Fence can't be applied and used in pretty much the same way as demonstrated with the table saw. I think it would be faster to build and more versatile than the other jig for rabbets (though the other jig would be the way to go for dados)

[Jim Becker]

That's a good system, Edwin!