Why are finger joints so difficult?

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Forum topic by Tom posted 08-01-2015 10:50 PM 1658 views 0 times favorited 17 replies Add to Favorites Watch
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178 posts in 1258 days

08-01-2015 10:50 PM

Today it was finally cool enough to try to do some woodwork. All I want to do is make a simple box…and watching Youtube videos it sure looks easy. (But those people have nicer equipment than I do.) Not having much scrap lumber, I dug out some 1/2” ply scrap (cheap Home Depot) and set up my Harbor Freight dado blade and started cutting. It took about 8 passes before I finally got the blade set (so I thought) to give me even cuts that would fit together nicely. I finally accomplished this with a piece of 1/2 ply and 1/2 scrap from some remodel project. So I get out the pieces I’d cut for the box; it was better quality hardwood ply from HD and I cut my joints. For some reason the cuts aren’t quite lining up and I think I’m going to have to either sand or run them through the blade again to trim them.

My question: is it the wood I’m using? The solid piece seems to cut better than both of the ply I used. Also, is there a trick to the jig? The miter on my saw is garbage; it rattles in the table saw slot. I made one..but it wobbles and I’m going to re-make it…again. I have an idea on how to make it not wobble. The videos all seemed to be using 1/2 hardwood…not plywood. I can’t afford to buy a new saw or a $80 dado blade either.

17 replies so far

View johnstoneb's profile


3054 posts in 2371 days

#1 posted 08-01-2015 11:00 PM

Plywood is extremely difficult to impossible to get high quality cuts. Masking tape on both sides seems to help keep splintering down.
Aluminum foil around the slide on the miter guage will tighten it up in the slot. If that tightens it up enough you can get aluminum tape with adhesive on one side and put that on the guage and it will stay on longer.

-- Bruce, Boise, ID

View benchbuilder's profile


284 posts in 2648 days

#2 posted 08-01-2015 11:04 PM

I would say the ply will work just as good, fix the wably saw and mak sure yoursetup is near perfect. Take tour time and learn as you go. you can do this, just think about what your doing as you go. Good luck!!!!

View WoodNSawdust's profile


1417 posts in 1374 days

#3 posted 08-01-2015 11:06 PM

I think you are talking about a box joint not a finger joint.

-- "I love it when a plan comes together" John "Hannibal" Smith

View TheFridge's profile


10705 posts in 1684 days

#4 posted 08-01-2015 11:16 PM

Check out William Ng’s box joint jig on YouTube.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Tom's profile


178 posts in 1258 days

#5 posted 08-01-2015 11:29 PM

After watching some more videos I think the issue is with my jig. I’m going to have to re-make it and try to get it so it’s just better. I may go as far as making a small sled to use just for stability.

I will not be buying another Ryobi table saw…it is fine for ripping laminate flooring for a project and rougher work but too small and the accessories aren’t really good enough for quality/detail work.

Also…dado size. I have it set for 1/2” (biggest that fits on the arbor) and was wondering if a smaller joint would work better? I’m running out of 1/2” scrap and might have to try some 1” (more like 3/4”) boards.

View Redoak49's profile


3661 posts in 2186 days

#6 posted 08-01-2015 11:37 PM

Finger joints/box joints are not as easy as they look. Even with a good saw and jig, you have to carefully adjust it for fit.

View MrRon's profile


5190 posts in 3441 days

#7 posted 08-01-2015 11:39 PM

The first thing you need to know is: Plywood is no good for a box joint , except Baltic Birch ply which is imported in 5’x5” sheets and is measured in metric thickness. Two. When setting up the jig, you have to tweak it by thousands. This takes trial and error to get the spacing right. This is not a slam/bam job. It can take many tries to get it just right. A box joint is actually one of the hardest joints to make, but once set up right-on, you can make box joints all day long as long as you don’t disturb any of the settings. Although a dado blade from HF may not be the best blade to use, it can be used within it’s limitations. There are dedicated box joint blades on the market (Freud is one of them) that makes either 1/4” or 3/8” fingers. This makes it easier to set up the jig.

View gfadvm's profile


14940 posts in 2888 days

#8 posted 08-03-2015 01:21 AM

You can’t have ANY slop or movement side to side in your jig or your box joints will never line up. I cut a LOT of box joints on my little Ryobi TS with a shop made jig and Harbor freight dado set when I first started woodworking so it can be done! Get your jig where it is very stable in the miter slot, set the distance from the blade to the pin very carefully, then cut joints/adjust the jig on some scrap pine until you get a perfect fit. Then save a perfectly cut sample and use it to set up your jig each time you use it.

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

View rwe2156's profile


3163 posts in 1679 days

#9 posted 08-03-2015 11:51 AM

After struggling like you are, I now use the Incra Box jig. I’ve got one jig that works on any size joint.
I don’t have to worry about what my wood jig is doing re: wood movement.

I am suspect of anything labeled “HF” so you may want to consider a quality dado set.
If you have a dial indicator, check the run out in that dado set.

-- Everything is a prototype thats why its one of a kind!!

View Tom's profile


178 posts in 1258 days

#10 posted 08-03-2015 12:47 PM

Thanks for the advice, I’m going to re-do my jig and try again on some scrap pine I have. As for the Incra jig…I don’t have $140 lying around to buy one. I’m pretty sure most of my issues are based on a lack of skill, very crappy test wood, and a poorly constructed jig.

View CharleyL's profile


223 posts in 3562 days

#11 posted 08-03-2015 01:53 PM

I’ve made a bunch of box joint jigs in my life, but now have the Incra I-Box jig. When I was making them it became obvious to me that the key to making a good jig was to make the “key” strip of wood exactly the width of your dado blade or router bit. Then make your jig using pieces of this “key” to get the right spacing and for the pin to increment your cuts. Of course, the jig itself has to be made to fit perfectly in the miter slot so there is no side play. If the pin (key) and the space between the pin and the blade is identical in width your box joints will fit very well. Unfortunately, when you make the jig for pine and then try to cut hard woods you will discover that a slightly different jig is needed, because the dado blade or router bit will not make exactly the same width slot in different woods. The I-Box jig lets me just make one adjustment and a single test cut when getting ready to cut different materials, so I quickly save in time much more than the jig costs. For me, the I-Box has been a huge time saver.


View hairy's profile


2782 posts in 3730 days

#12 posted 08-03-2015 09:05 PM

1/2” plywood isn’t usually 1/2”, your 2 different 1/2” materials may not be the same thickness.

-- My reality check bounced...

View Kazooman's profile


1237 posts in 2150 days

#13 posted 08-03-2015 10:11 PM

Just a comment about making jigs. All of the advice offered above is right on the mark. One potential pitfall is thinking that a jig is just a quick assembly made from scrap wood to get a job done. In reality, you should take as much or even more care in constructing a jig as you do in machining the final project. The end result can never be any more precise than the tolerances of the jig. The runner for a table saw slot has to fit very well. Any slop will show up in the final work. The fence has to be dead on square to the runner. In this case, the index piece has to be exactly the width of the dado blade kerf and spaced just as accurately in the jig. If you take your time and build a jig that has all of these issues covered, then finger joints (box joints) are easy.

View Kvegas's profile


8 posts in 1271 days

#14 posted 08-03-2015 11:26 PM

Check out William Ng s box joint jig on YouTube.

- TheFridge

Couldn’t agree more. I’ve used his jig in his shop with Mr. Ng by my side and my plywood drawers turned out perfect.

View ScottKaye's profile


711 posts in 2151 days

#15 posted 08-03-2015 11:49 PM

I agree with thefridge and kvegas. you should watch William Ng’s you tube video on building box joints. Here is the link to his video. He also has a great video on building a cross cut sled. I used his box joint method to build this grooming box for the barn my kids ride at.


-- "Nothing happens until you build it"

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