Mirco-adjustment Box Joint Jig





Introduction: Mirco-adjustment Box Joint Jig

My home made jig lets me dial in a perfect fitting box joint on either my table saw or router table. The mirco-adjustment and locking feature makes it easy and accurate but I must admit it did make me scratch the bald spot on my head at the start to get use to which adjustment did what. 

All the timber used here was recycled from around the shed or scrap from a building site.

The long face board was sitting on a shelf hiding under a empty fuel can and the rest was left over hard wood Murbou decking pieces  except the Mickey Mouse wood  (MDF) used for the cutting back board insert. I had a piece hiding in the back corner I had kept from a old TV cabinet

Nuts, bolts and washers were a simple purchase for Bunnings.

Step 1: Material List

¾ x5 ½  x 18  hard wood                                    A. Fence        
¼ x1 ½ x5 ½.  Mickey Mouse wood (MDF)        b. Backing Plate
¾ x 1 ½ x 11 3/8 hard wood                               c. Fixed material rest
¾ x 3 x 5 3/8  hard wood                                    d. Moveable material rest
¾ x 2 x 6 ½  hard wood                                      e. Front adjustable piece
¾ x 2 x 5 3/8. Hard wood                                    f. Back adjustable piece
¼ x2 x 2 ¼.   Mickey Mouse wood (MDF)           g. End Plate

Step 2: Tools I Used!

I’m missing my router and level from this picture. Sorry!

Step 3: 1. Making Your Fence/ Back Board

Square your timber on a saw bench if you have access to one.

Cut to length 18 x 5 ½ x ¾ thick

Trim the corners at a 45’ bevel.

Well that’s the easiest part of the whole job done. Congratulations.

Step 4: 2. Cut Out the Recess for the Backing Plate.

Used my router to remove ¼ deep x ¾ wide waist from the Fence using several passes each depth to insure there is little excess pressure on the router bit. I do this because there has been times when I simply could not be bothered with the multi passes and wound the router bit to 12mm and went for it.

When the router bit head snapped off it was nice enough to spit out striking me in the ribs. Luckily for me it was a cold night and I had a thick jumper on.  Just ended up with a very large dark purple bruised rib.  It could have been much worse.  In addition I always work with the opening of the job facing away from me. Life lesions.

The depth of your backing plate recess will depend on the thickness of Mickey Mouse Wood (MDF) you use, I’ve used ¼

The correct position to start marking your fence is 5 ½“in from the left hand side.

At this stage it makes no difference what part of the timber u call the left hand side. Once you measure from it that will be your left hand side and please mark it as (lhs).

Step 5: 3. Making the Fixed Material Rest

Note the thickness of the fence is ¾ not 3/8 as shown

You will need a piece of timber measuring 1 ½ x 11 3/8 x ¾ 

Your fixed material rest should be the same length from the (rhs) edge of your recess for the Backing plate to the end of your fence.

I used my router to remove the waist material routing out the ¾ x ¼

Again if your measurements are correct your fence should fit neatly on the remaining edge not cut out.

If there is over hang on your fixed material rest and your fence is lined up at the back of the fixed material rest then feel free to remove the lip left on the front edge.

The front edge of the fence must line up perfectly with the start of the recess of your fixed material rest as well as being perfectly lined up with the rear of the fixed material rest.


Step 6: 4. Cut the Movable Material Rest.

The overall width is 3”

The length needed is 5 3/8”

The thickness of your material should be ¾

Use the same method to make this piece as you did with the fixed material rest.  STEP 3

 Remove the ¾x ¼ using your router with several passes.

I made several material rests settling on 3 ½” but that will be up to you to play with

Step 7: 5. Glue and Screw the Fence to the Fixed Material Rest

Glue and screw the fence to the fixed material rest measuring 1 ½ x 11 3/8 x ¾ 

Ensure the front edge of the fence is level (spot on) to the lip of the material rest.

Start by lining up the back edge of the fence with the back edge of the fixed material rest.

Now the front edge of the fence should be perfectly level with the lip of the fixed material rest if all your measurements are correct. It took me 3 attempts to get it spot on.

If there is an overhang you need to make it level with your saw or router.

Run your hand down the fence, if your fingers catch a lip from the material rest it is vital you bring it back to be level with the fence.

Turn the job around and look at the back of your job before it is s glued and screwed.

Once you are happy there is no overhang in any direction glue and screw them together.

Step 8: 6. Make the Back Adjustment Piece

We are going to make the back adjustment piece next
you will need a nice piece cut at
5 3/8 x 2 "x 3/4 wide

From the top left hand side of your back adjustment piece   measue down 1 3/8 and in 1 ½”and make a mark with your pencil.  Cut out with your router from your pencil mark back to the left hand side edge.
The thickness of this slot should match the thickness of whatever bolt you are using I used 6mm bolts.

On the right hand side from the top measure down 7/8” and in 2 3/4”. again mark with your pencil and make your slot with your routerto the outer edge of your wood.



Step 9: 7. Secure the Moveable Material Rest to Back Adjustment Piece

Secure the moveable material rest to back adjustment piece.

The back adjustment piece glues and screws to the movable material rest

The movable material rest you just made in step 4 just to clear up which piece to use.

Aligning the back edge of the moveable material rest with the back edge of the back adjustment piece..

I found it easier to lay the back adjustment piece down and stand the moveable material rest against its base.
As ive been stressing it is vital to make these edges square and with no overhang.

Mark your clearance holes and drill, glue and screw the two pieces together from the bottom of the moveable material rest.

Step 10: 8. Secure the L Bracket

Secure the L bracket to the right hand side and make sure it lines up at the top of the moveable material rest.  If your back adjustment piece is out of square as mine is by 1mm you need to ensure the bracket is square to the moveable material rest and not the front of the up right. check your squarness of your work at all times.

Square to the (none cut out flat edge.) of the moveable material rest.  I hope that is clear, because it sounds like thick mud to me lol.

The  top of the moveable material rest is the part of the job u need to allign the top of your L bracket with and not  the bottom of the waist material area you removed with your router. the L brackest is the important guide area, the L brackets are the accurate pieces that matter in the design of this JIG.
clear as mud   sory ill try and clear it up later.  its been a very long day. 

Step 11: 9. Making the Front Adjustment Piece.

I had several problems here, due to really poorly written instructions. Ill try and improve on them and hopefully you don’t make the stupid mistakes I did.

The mistakes happened because I need to understand what I’m doing while I’m doing it. I cannot blindly drill holes or follow instructions I don’t understand what they are for and what purpose they have.

 Using  a piece of hard wood ¾“ thick  2” wide and 6 ½ long

If you don’t have one lying around trim one to size

With the face facing up, Measure  ½”  from one end, place your square across and mark your piece.

Measure  7/8” down and using your square mark along the entire length of the job.

From the ½” mark, measure along the last drawn line a further 2 3/8” and lay your square across the job and mark across the face.

Drop your router in its spot and route out between the two points making a 2 3/8 straight line. Ensure you have a bolt that will fit through your router bit size hole or simply make your slot wider with your straight bit .

the holes come later.





Step 12: 10. Make the End Plate

Make the end plate   2 ¼ x 2” in size. 

Drill 4 holes at 3/16 dia

Find the centre vertically and drag your pencil across it.  Measure 3/8”down and drill your first hole

Flip the small piece around and do the same at the opposite end where you have marked the centre line.

From the top of your piece measure 5/8 down and place your square down and mark a line horizontally (sideways) across your job.  Measure 3/8 in from each end and drill your 3/16 holes

 ( you should be marking out a cross) 

The first two holes are used to secure the end plate to the front adjustment piece

The last two are for the micro-adjustment bolts or thread rods as I have used.

There is no right or wrong wood to use here, if you don’t have any Mickey Mouse wood lying around feel free to make it in pine or even hard wood.

Add your great glue and hay presto, yet another part complete.



Step 13: 11. Odds and Ends to Finish

There are two methods to work out where to place the through bolt that goes from the front of the fence through the front adjustable piece and out the back of the back adjustable piece.

Firstly I moved my two L brackets via the micro adjustment system so they were as far tho the left as possible as long as they were both touching each other.I then located the entire job under the drill press and wacked a 6.5mm drill bit through the lot.
From where on the back did I align up with?
Smack in the middle of the slot.
Turn the job over in the drill press and use a spade bit to lower the head of your bolt below the surface of the fence  but be care full not do drill your spade bit all the way through the fence like i did.

I don’t think I’ll go into the 2nd way but if ppl get stuck ill add it then.

I don’t want anyone getting confused any more than I have already confused them lol.

I think that covers all facets of the project.

Oh!The rear of the fence is secured to the miter gauge of your bench saw.I’m sure u can work out the rest.

If I’ve missed something or a section needs clarification I’m sure some will let me know.
lol yep i still need to add how to insert the threads and micro adjustments, it will have to be done tomorrow or later.

Wow what an effort i dont think id like to make too many of these up.

here is some instruction to help use .


Sorry no video.

How does it work?

Firstly you need to attach the  back of the fence to your miter.


make a test piece the width you want  your fingers to be, either cut by hand or any way you like as long as the width of the timber is the same as your job. once you have your finger cut to width this we are gunna call your test finger.


to make a box joint with perfect fingers you will need to make the blade the same mm above the material rest as the thickness of your timber.     YES!!!!!


take your TEST finger and place on the jig. move it to the left until its over your adjustable L brackets. now move the KNOBS in and out until one is touching the LHS of the FINGER and the other is touching the RHS of the finger.


YOU now have adjusted the thickness of the fingers.


Tighten the two knobs at the rear of the Jig. Nice and tight please.   Very important.


Take your test piece away n toss it anywhere you like.


Find the piece your want to cut fingers in and sit it on the fixed material rest.

Slide it gently along until the left hand side touches the RHS of the L bracket closest to the saw blade.


Cut away with your datto blade.


Once you have cut the first finger lift the piece up and place the finger over the two L brackets  ( as if you were sitting on a horse) sorry first thing that came to mind and yes I love riding.


Once you have finished and are ready to cut the opposite end flip the job over ( top goes to the blade and the finger you just cut are now in the air, repeat above and your are well on your way.


To make fingers that match the slots you just made.  Use the one you just make as a guide flip it around so the waist, (the cut out part) is over the L brackets. Slide the nest piece of wood hard against the side of the already cut piece as if the boards were joined.


And keep cutting


I would advise using some scrap wood first to make a heap of test pieces b4 you use the good wood


You don’t want to make mistakes on good wood.


Good luck and have fun.


I think I might add this to the instructable




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    Woodsmith sells the hardware for these for about $15 US. I just purchased a kit and am glad to see an instructible on the assembly. "Real world" instructions are so much better than the "Nothing can possibly go wrong" sheets that are included with the hardware. Thanks for showing the "Problem areas," I think my assembly will go a bit smoother now.

    What size are the L brackets that come in the kit? thanks!

    The brackets are 3/4" X 4".


    this is great but can anyone list the sizes of the "L" brackets and the studs and such?

    G'Day Mate

    Sorry I’ve never heard of Shopnotes
    Nope, I got the plans from a very old set of "woodsmith" books this one was titled “shop build jigs and fixtures”.
    I build it coz I was going to make a display cabinet for the wife, until she changed her mind.

    If you look around, as I have since I listed it, you will find several jigs like this one. I even found one made of aluminum with all the same movable pieces.
    Whatever tickles your fancy I guess lol

    Good luck and happy playing

    I think Woodsmith and Shopnotes are the same company, different divisions.

    This is a very smart design. Thanks for posting.

    Yeah, that plan is from Woodsmith, the same company that publishes Shopnotes (http://www.woodsmith.com). In fact, they sell that plan on their Plans Now site - here's the link:


    G'Day Mate

    wow small world.
    now no one needs my instructable.lol

    Imust have a very old set of ther books.