# Router bit for finger joints



## keithet (Jan 29, 2012)

I have a Veritas Router table, fence and right angle sled. I want to make some box joints and need to know if a carbide spiral bit is the way to go to make the best possible clean joint. If so, I would like to try 1/4", 3/8" and maybe 1/2" joints. I will be using 1/2" to 3/4" hardwood (red oak, maple, cherry and other woods) and after using 1/4" regular cut dado bits (carbide and sharp) I seem to get unacceptable tear-out even with a backer. Any help would be appreciated. I realize that the spiral bits are expensive compared to the non spiral bits. What brand would you recommend?


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## Cherryville Chuck (Sep 28, 2010)

I think the ones that LV sells are Onsrud which are as good as you can get in my opinion. Whiteside, Freud, and CMT all have good ones. I used a 1/4" LV in some Douglas fir recently and it went through it like warm butter. The spiral may do a better job since it has a shear angle. The backer should be working unless it isn't tight together with your work. Are you clamping them together?


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## FreeTime (Dec 2, 2012)

I don't have any experience with box joints but I've been using a Whiteside 1/2" down cut spiral on Cherry for dados - it cuts a real clean entry edge but I also used small depth increments (< 1/4"). The up-cut spiral rips up the edge noticeably. ditto on the backer board comment.


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## DesertRatTom (Jul 3, 2012)

I use down cut carbide spiral bits for this since they seem to make a cleaner edge. I got mine from both Rockler and MLCS. Had some trouble with tearout that stopped when I clamped the piece instead of trying to hold it in place by hand as I'd seen Norm do on TV. There is a lot of lateral force being applied to the workpiece by a spiral cutter and the piece wants to walk away. To clamp it tight enough without denting the piece, I added a small, thin block of hardwood to distribute the pressure.


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## whimsofchaz (Jun 6, 2013)

The last two Whiteside bits I have bought have been very sharp and worked well. I would recommend Whiteside


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## Mike (Nov 22, 2004)

I normally use Whiteside spiral up cut bits; I have no complaints about tear out. This one was cut with a straight bit with good results. Make sure you are not forcing the cut... give the bit time to do it's job.


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## CharleyL (Feb 28, 2009)

If you want to do clean tear out free box joints with a router you will need to use a backer board. The backer board is a sacrificial board that is clamped behind the work. It will prevent the router bit from chipping the back side of your cut. If you can align it perfectly you can use it on additional cuts of the same spacing and dimension (multiple identical parts). I prefer a table saw with a dado blade and a zero clearance insert plus my I-Box jig for making clean box joints quickly. The I-Box uses a piece of 1/2" MDF as the sacrificial board, which can be moved or flipped for additional setups before it needs to be replaced. The I-Box can be used either on a router table or a table saw to cut many sizes and types of box joints.

Charley


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## Mike (Nov 22, 2004)

With Oak Park or MLCS box joint jigs the push block is the backer board. Take a look at the first photo in my last post to see how clean the cuts are made... even with straight bits.


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## TangoDown3727 (Oct 13, 2013)

An UPcut spiral bit is the best choice for box joints. The up-cut pulls the stock toward the base of the router or the router table surface as it cuts, so it makes for a very clean dado or groove because it also pulls the chips/dust out of the groove which helps avoid overheating the bit and giving a very clean cut. Not to nit-pick either, but "Finger Joints" and "Box Joints" are two very different things and require very different bits. Unfortunately spiral bits are kinda pricey, but they are worth it and certainly a great way to go for Box joints IMO.


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