Tablesaw Box Joint Gap Troubleshooting

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Forum topic by DFlatMinor9 posted 04-22-2011 05:05 PM 4331 views 0 times favorited 9 replies Add to Favorites Watch
View DFlatMinor9's profile


5 posts in 2831 days

04-22-2011 05:05 PM

Topic tags/keywords: box joint troubleshooting tablesaw dado stack poplar jig gaps fit

Hello everyone! I’ve been a long time reader/lurker of Lumber Jocks and this is my first posting. I’ve really learned and enjoyed the content I’ve found on this site, as well as seeing all of the amazing work you all are doing. It’s very, very inspiring. =0) I apologize if this is the wrong forum category to post in. I hope it is the correct one. If not please let me know and I’ll be sure to post to the proper category.

I’ve been practicing box joints in 1×6 Poplar on my table saw using a jig similar to the many seen all over the web (small scrap of MDF with a key and a couple of notches). I have quite a few different box projects that that I want to do, and some are need to do’s. I’d like to make them as beautiful as my skill level and tooling will allow. They’re close to fitting nicely but I’m still having a little trouble. I’m positive it’s something I’m missing with either the making/setup of my jig, my cutting technique, or something ::scratching head::.

Thankfully I solved my tear out issue by using a piece of hardboard backer and slowing my feed after reading some advice given to another person on this forum regarding it. Now if I could just get them to fit nicely and seat all the way…lol.

The problem I’m having is tiny gaps where the pins meet the bottom of the notch. I’ve tried using a piece of the key material as a punch of sorts and tapping them gently to get them down, but they just won’t go all of the way. The gaps are very small but definitely noticable – plus I see small gaps on the inside too. I’ll list a breakdown of my jig materials/setup below for your critique. I’m sorry for the wordy first post, but I don’t have any pictures of the fit issue at the moment. Easy to see, tough to describe succinctly.

The jig
  • 6” wide piece of 1/2” MDF (realize it should be 3/4” but it’s what I had on hand in the shop this might be part of the problem though?)
  • 1/2” dowel purchased from a home center for the index key. It looks like poplar.
  • Dowel glued and screwed to the notch.
  • Using a Freud Dado stack (208 model?) with 2 chippers and a 0.1 shim

They only time I’ve seen my test cuts seat all the way is when the fit was too loose. I’ve been having a devil of a time trying to dial in this jig, do it quickly, and get snug fitting, gap free joints. As a quick aside, and odddly enough at that, I tried some test cuts in some home center grade birch I had lying around to try and slow chewing up what little bit of the Poplar I have left, and the box joints came out flawless! Right fit and noooo tear out. Weird. My joinery experience with ply has been a rocky road, but has been the opposite the past couple of days between the ply and poplar.

Any advice/tips you all would be willing to share to help me troubleshoot my fit/setup would be greatly appreciated.

Thanks everyone and sorry again for the wordy first post! I look forward to seeing more of everyone’s inspiring work as well as learning and improving from all of you.


9 replies so far

View Loren's profile


10477 posts in 3887 days

#1 posted 04-22-2011 07:39 PM

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.

View RetiredCoastie's profile


999 posts in 3422 days

#2 posted 04-22-2011 07:46 PM

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!

-- Proud Supporter of Homes For Our Troops

View FMG's profile


65 posts in 3521 days

#3 posted 04-22-2011 08:18 PM

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

-- FMG- Woodworking is 90% mental the other half is physical

View DFlatMinor9's profile


5 posts in 2831 days

#4 posted 04-22-2011 10:50 PM

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!


View gfadvm's profile


14940 posts in 2930 days

#5 posted 04-23-2011 05:20 AM

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'll try to be nicer, if you'll try to be smarter" gfadvm

View fussy's profile


980 posts in 3290 days

#6 posted 04-23-2011 06:09 AM

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 in KY. 44 years so far with my lovely bride. Think I'll keep her.

View DFlatMinor9's profile


5 posts in 2831 days

#7 posted 04-25-2011 09:39 PM

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)

View DFlatMinor9's profile


5 posts in 2831 days

#8 posted 05-04-2011 07:41 PM

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.


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)


View Jim Ganley's profile

Jim Ganley

54 posts in 3407 days

#9 posted 10-19-2018 06:36 PM

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

-- Jim - Cushing, WI

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