# Box joint help



## Dustjunkie (Feb 11, 2020)

I have never tried box joints before so I purchased the PC 4216 kit and I have a Freud 1/4" spiral up cut bit. Today I decided to practice a little to see how things would turn out, the first joint the ends were very proud so I adjusted the router bit which helped. My dilemma is that I constantly get tear out on the work piece, I have tried different speeds with the router but it does not get any better. I am currently playing around with 1/4" ply, any feedback would be greatly appreciated.


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## ArlinEastman (May 22, 2011)

Put a board in front and one in the back any you will never have any tear out.

Also it is good to have your finger joints just a tad proud and then you can plane them off which is much easier then making them to short.


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## Dustjunkie (Feb 11, 2020)

Thank you Arlin. I never throughout about that, I will try that the next time around.


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## Joel_B (Aug 14, 2014)

I make box joints on my TS with a dado blade.
Plywood is the worst for tear out.


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## bandit571 (Jan 20, 2011)

hmmmm..I usually just hand cut mine…









YMMV


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## tvrgeek (Nov 19, 2013)

In addition to hackup boards, you can use a knife or chisel to cut the surface fibers for a cleaner cut no matter which tool you use.


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## therealSteveN (Oct 29, 2016)

Your tear out? Does it appear to be one sided?

Reason I ask is an upcut bit will always leave a rough surface, on the face or entry cut, but the finish, or end of the cuts are usually very clean and smooth. It's my belief they were designed to use so the waste after being cut is more easily ejected from down in the cut. In your case you are blowing through that, so it may have different properties?

A downcutter is the opposite of that.

A best of both worlds thing if it is one sided is to use a "compression bit" they are dual identity, being both an upcut, and downcut. If it was me though I would just use a cheap straight cut bit.

My experience with them is limited solely to Dado's and grooves. An upcut can make for a ragged edge. I cut finger joints on the TS, so I don't know how that will play for what you are doing, but for a trench cut it's a thing. So if your mess is one sided, I'd just use the backer on that fuzzy side.


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## Dustjunkie (Feb 11, 2020)

I tried a cheap straight dual flute and the results were worse, should I use a single flute instead?


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## RichT (Oct 14, 2016)

Since you're cutting across the end grain the spiral direction shouldn't matter. As has been suggested, use a backer board. I have the Incra I-Box and it's designed to allow you to move to a fresh spot on the backer board when needed. You shouldn't need a board in front.

Regarding speed, keep it set at or near the max.

And no, a single flute will not work better than double. A compression bit is not intended for that sort of cut and won't help a thing. Stick with the spiral bit you have and adjust your technique. Go slow into the cut and let the bit do the work.


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## Dustjunkie (Feb 11, 2020)

Thank you for that advice Rich, I need to try using a solid work piece and see if the results are any different since plywood is know to have tear out.


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## RichT (Oct 14, 2016)

> Thank you for that advice Rich, I need to try using a solid work piece and see if the results are any different since plywood is know to have tear out.
> 
> - Dustjunkie


I missed the part about using plywood. Yes, switch to something like poplar or alder. They mill cleanly and you can keep practicing without breaking the bank. It can be frustrating at first, but you'll get there.


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## Lazyman (Aug 8, 2014)

+1. Plywood is awful for router jig box joints and dovetails. It is tough to avoid tear out on the face. Other brittle woods can have the problem too but usually not as bad as PW. One other thing that I found helps is to not just simply plunge in between the fingers. Make a light cut along the front edge first, sort of just grazing the front, and then make progressively deeper cuts until the finger is removed.

EDIT: I just realized you are using 1/4" plywood and presumeably 1/4" fingers. That probably doesn't really allow a grazing pass but it helps on wider fingers.


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