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 (https://www.woodcraft.com/search?q=metric+router+bit&button=search). (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=adjustable+rabbet+jig&rlz=1C1CHMI_en-USUS339US339&tbm=isch&source=iu&ictx=1&fir=wfRYKG7MPenL-M%253A%252CgcN2ZY7NWSQhTM%252C_&usg=__dXfXd_U4FoLoJmRCGWkcmZkLhQY%3D&sa=X&ved=0ahUKEwjxxtnIhojZAhWJo1kKHfIUAuIQ9QEIsAEwAA#im grc=wfRYKG7MPenL-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=adjustable+rabbet+jig&rlz=1C1CHMI_en-USUS339US339&tbm=isch&source=iu&ictx=1&fir=wfRYKG7MPenL-M%253A%252CgcN2ZY7NWSQhTM%252C_&usg=__dXfXd_U4FoLoJmRCGWkcmZkLhQY%3D&sa=X&ved=0ahUKEwjxxtnIhojZAhWJo1kKHfIUAuIQ9QEIsAEwAA#im grc=wfRYKG7MPenL-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 (http://www.mikes-woodwork.com/Box_For_Trays.htm), 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/2014/07/30/versatile-tablesaw-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!

[Bill Fleming]

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=adjustable+rabbet+jig&rlz=1C1CHMI_en-USUS339US339&tbm=isch&source=iu&ictx=1&fir=wfRYKG7MPenL-M%253A%252CgcN2ZY7NWSQhTM%252C_&usg=__dXfXd_U4FoLoJmRCGWkcmZkLhQY%3D&sa=X&ved=0ahUKEwjxxtnIhojZAhWJo1kKHfIUAuIQ9QEIsAEwAA#im grc=wfRYKG7MPenL-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

Charley - I have made several fixed jigs similar to this for specific applications. I’m not sure how the one you linked to works, I.e. if the ears of the angle are used to set the width to the shelf say, what is the guide collar, bit. To get the exact fit?

[Glen Gunderson]

Charley - I have made several fixed jigs similar to this for specific applications. I’m not sure how the one you linked to works, I.e. if the ears of the angle are used to set the width to the shelf say, what is the guide collar, bit. To get the exact fit?

The size of the guide collar and the bit wouldn't matter as long as you used the same setup each time. You just need to attach the upper pieces to the lower ones far enough from the edge so that you'll cut the edge of lower piece the first time you run the router along it. That way the offset between the pieces will match the size difference between the guide and router bit perfectly. Then you set the width of the dado with the gap between the lower pieces but the router is guided by the upper ones.

[Bill Dufour]

I doubt you can buy a precision ball bearing in non metric sizes. They have pretty much all been metric since they were invented and mass marketed in France. There were some inch ID bearings made but not much after 1942 or so. And I think they had something like 3/4' or bigger inner bore. I believe the outer races have always been metric. Kind of like light bulbs and spark plugs, except the ford NPT ones of old.

That said I suppose you could wrap tape around the outer race to make it a slightly larger diameter. It might last long enough to make a rabbit or two if you get lucky.
Bill D.

[Bill Fleming]

I see, clever. You end up with a jig tuned for a specific collar and bit...I can’t forget to mark that on the jig! Thx

[Charles Lent]

No collar/bushing is used. The shoulders of the top layer of the jig guide the router by it's base. Just use the same router bit every time so the distance between the router bit and the shoulders of the jig are always the same with the router bit always being smaller in diameter than the dado that you will be making. It will always take at least two basses to widen the dado to the width that you need. Down the left side shoulder and back the right side, but the resulting dado will match the thickness of the board that you set the jig width to.

When you make the first cut on the new jig with the router you are trimming the lower parts of the jig so that their edge to the upper shoulder of the jig is the distance from the router bit to the outer edge of the router base. Do both sides of the jig this way. Now, when you insert the shelf board in the gap between the two lower boards of the jig you are widening the jig by the width of the desired dado. Lock the jig width to the thickness of the shelf board and the space between the upper shoulders of the jig will be the diameter of your router base, plus the thickness of the shelf board. Run the router base against the shoulders of the jig and the router bit will cut the left side of the dado when you go down the left shoulder of the jig and the right side of the dado when you come back along the right shoulder.

If you put a straight edge on a board and run your router along it, the board being cut will be cut to 1/2 the diameter of your router base minus 1/2 the diameter of your router bit when measured from the straight edge to the edge of the cut. With this jig you are doing the same thing, but from both sides, with two straight edges. Since you trimmed off the excess wood in the lower level of the jig it's width from the shoulder (straight edge) to the edge of the cut will also be the diameter of the router base minus 1/2 of the diameter of the router bit and pushing both sides of the jig together until the bottom pieces touch should result in the space between the two shoulders being the diameter of your router base. When you insert the shelf board between these two freshly cut jig edges you are moving the two sides of the jig apart by the thickness of the shelf board so the dado that you cut by riding the router base against both shoulders (straignt edges) of the jig will only be this added space (shelf board thickness) that you have added to the width of the jig.

(I'm wishing that I had a working video camera as it would be easier to demonstrate this than it is to explain).

Charley