Same as with dovetailing: cut the joints a bit shallow and then
you can clamp them hard if you have to, without fancy cauls.
You need good clamps.

After the glue dries, hand plane off the excess long grain so your
joints are flush.

The difference with box joints (which I never use so I am not
an expert) is with dovetails you only clamp in one direction because
the joint geometry clamps the other. With box joints, to clamp
them tight you'll need to get clamps going in both orientations.

This may not solve your problem, but it's a good method for getting
tighter joints so I recommend you try it.

Also check your dado cuts to make sure the bottoms really are flat.

Scribe a line on either side of your board with a marking gauge and
you'll be able to tell if some of the cuts are coming up shallow for
some reason or other, probably operator error.

 

All I can say is make sure the miter gauge / jig is dead square to the miter slot and the blade is dead square to the slot as well. I think your jig thickness is probably a little thin. When you make your cuts and you move the piece over after each notch is cut make sure your clamping pressure on the stock is the same against the back of the jig and the key whether you hold the stock with your hand or a mechanical clamp. Also make sure your feed rate is constant and make sure your hand position is always the same. Things that may seem minor like hand position on your jig can actually cause influence variations in the joint due to pressure applied changes from one position to another. Dialing in a box joint jig can be frustrating, hang in there you'll get it!

 

DW,
I may not be visualizing correctly but if I read you right, it sounds as if your jig is not square to your table ie: slanted towards or away from the blade. The 1/2 dowel may not actually be 1/2" either.
Hope that helps

 

Thanks for all the replies guys! I really do appreciate it. =0)

Now that you all mention the square to the miter slot/blade issue, I wonder if it is the 1/2" MDF flexing as I push the work piece through the blade that's causing the fit issues? I was amazed while making my test cuts at just how tiny of a tweak made a huge difference. Well…lol…I guess I shouldn't have been amazed but I was. =P

When I get back in the shop I'm going to try glueing two pieces of it together to make a thicker jig base, make sure it's all cleaned up after, and see what happens with take 2 on this jig. During my last test cuts I kept getting the feeling the 1/2" MDF was too flimsy for this jig.

I will post my results with using a thicker fence and double checking the jig's square. I've checked the saw's miter slot-to-blade squareness with a dial guage recently and it was good. It must be the jig and me. I have some smaller 3/4" baltic birch scraps and a couple of spare miter runners. I may try to knock together a small sled to see it that will help too sturdy up the cut some too. If that works I may just stay with the small sled until I pick up a small piece of 3/4" MDF.

Thanks again guys!

dw

 

Your Freud box joint blades should cut perfectly flat bottoms in your notches so that shouldnt be a problem.My next thought is that you are allowing the wood to ride up as you cut the notch.Make sure it stays seated tight to ypur index pin.My final thought is that your saw blade may be creeping down causing shallower notches the further you go.Crank your blade UP to the desired height rather than LOWERING it to the desired height and it will usually stay put better.This pretty much sums up all the problems I had when I first started my box addiction.Hope this helps.

 

I'm wondering at your use of a dowel for a key. I am no expert but i think your key should be square or rectangular like the joint to ensure a good tight fit. Pictures will help. If it makes you feel any better, most of us have problems with box joints. Dovetails, no problem, but ===oh heck, I have problems with butt joints.

Steve

 

Hey everyone. Sorry for not posting back so soon. Had a busy holiday weekend with a little shop time added in too. Hope everyone had a great holiday. =0)

@cr - You're right: definitely easier to see than explain. I will definitely add some pics. I took a few in the shop this weekend.

@gfadvm - I think the board creeping up is a great item to double check too. Thank you for the tip.

@fussy - lol…I have problems with butt joints on occasion myself. Why they seem trickier than cutting joints at times is beyond me. Actually I should have clarified. It was a piece of 1/2" sqauare dowel that I picked up at the home center. I looked to me like it was poplar, but I'm not really sure. I took my caliper with me and it measured right at 1/2" so I grabbed a couple of them because they were cheap.

Box joint education update: This weekend in the shop I broke down and built myself a dedicated sled! I made it similar to an image of one I saw on FWW's website out of some scrap baltic birch in my cutoffs pile. I'm looking forward to making the sacrificial fence and key set this evening if I can, and hopefully give it a test run. I routed a groove for a length of mini track in the back fence to make each sacrificial fence easily adjustable with a couple of jig knobs, and added a clamp surface/thumb-rest bar to the back fence. I will post some of the pics of my sled when I transfer them off my phone. Now, I just hope it works! =0)

 

Sorry it's been a few days since I posted back. Been in busy in and out of the shop. I finally achieved success with the box joints - and learned a TON.

To break it down I'll divide it by miter gauge approach and sled.

Miter Gauge:

The culprit of the inconsistent cuts/ill fit was the 1/2" MDF. It would flex ever so slightly as I fed the work through the blade. That was causing my notches to be different depths and other weirdness. At least that was the best I could determine.

Sled:

I build a small sled and still had issues with the notches being consistent depths. After analyzing it further, I realized the light weight aluminum runners I picked up work too light (at least for this particular application). One of them would "float" up out of the miter slot as I fed it through the blade. I fixed this by changing out to heavier runners. Both sets were Incra. I think I prefer their heavier steel ones after this exercise (not saying the others are bad just not too great for this application).

I also mitigated tear out by purchasing the Freud box joint blade set. They worked great! My dado set is also Freud, but it is their cheaper set sold at home centers. They work great for rabbets and dados and didn't let me down, but for the box joints they were a little fussy getting a smooth cut and good looking joint. I also used a index key made of red oak this time for the sacrificial fence that fits in the sled.

Below are some pics of the sled and the project I'm using it for. Thanks for all the great tips and help everyone! I sincerely appreciate it!! I look forward to learning more and seeing all of your great work. =0)

dw

 

Wow, I am struggling with getting my joints to be day light tight and it is not happening, I am using an Ibox from Incra and it is quite easy to use but the joints do not tighten.
Keep up the good work
Cheers