Splined Box-Corner Jig From Scrap

Introduction: Splined Box-Corner Jig From Scrap

About: Software geek, electronics enthusiast, musician, artist ... I enjoy making stuff, and discovering new things!

This is another mini-instructable for a table saw jig, and this one is for putting "splined corners" onto wooden boxes.

All you need is three pieces of wood to make this, and you can then safely and accurately cut slots across the corner of boxes, either to strengthen the box, or just for cosmetic reasons.

This one was made from scrap wood offcuts.

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Step 1: Parts List

Sizes are not critical, you can adapt as needed! I used :-

  • Plywood 6mm thick, 13" x 7" (1)
  • Pieces MDF/Wood 9" x 3.5" (2)
  • No 8 x 1" Wood Screws (4)
  • PVA Glue
  • 45/45/90' Square

Step 2: Marking Up

Find (or cut!) a square edge on the board, and place it at the bottom. Mark a 90 degree line straight up the middle of the board.

Then put a 45 degree line either side of this centre line. They should all converge in a point on the bottom edge, as shown.

Place your pieces of wood on these lines, and mark the approximate thickness of the wood.

Put two holes through the plywood, which will secure the wooden pieces with screws later. Keep the lower two holes at least a couple of inches away from the board edge so the screws don't get sawn through!

Step 3: Glue and Screw

Glue and screw the two pieces onto the plywood.

As you go along, make sure that the boards form an exact 90' V shape, and also that both boards are upright and 90' to the plywood.

I found that the first board was slightly angled, and used the second board to "push" it square. The screws will locate the wood in place securely while the glue dries.

Step 4: First Use Adjustments

I set the cutting fence on the table saw to 50mm to the left of the blade. This gives 6mm for the plywood, and about 44mm maximum kerf positioning depth inside the jig.

Lower the blade right down, and pass the jig through, keeping it upright and against the table saw's fence.

Keep raising the blade a tiny amount until you JUST break through the inside of the jig, and stop the saw.

Place the jig alongside the blade and mark the height of the blade onto the back-board. In future, this line is your "zero" line for how deep it will cut into the box corner you are working on.

Raise the blade a couple of millimetres more, and drop in a temporary piece of wood (as shown). KEEPING YOUR FINGERS AWAY FROM THIS BLOCK -- use another block or a clamp to keep it down in the vee, and pushed to the back, run the jig through again.

You now have a measuring block with a little kerf nicked into the corner. This can be used to measure exactly where the saw kerf will end up on your box. You can pack out the back of the jig with scrap wood (inside the VEE) to adjust where the cut falls on the box. e.g. a piece of 18mm MDF will move the cut from 44mm to 26mm. Experiment with pieces of wood/plywood/hardboard as needed -- don't adjust the table saw fence.

Step 5: Done -- Now Use It!

To use the jig: Use the marking stick from above to work out how much packing depth you may need, and place it in the vee guide. Place the box you are cutting into the vee guide and hold it firmly down and inward, and slide the whole thing across the table saw (again, holding it down and IN against the fence).

The blade height of the saw will dictate how deep (and at the same time, how far round the corners) the splines will reach.

Usually you would adjust it until it is just short of breaking through the inside of the box. If you do go further, you will end up with a little "ledge" in each corner of the box on the inside. You might find that useful, e.g. to support a tray or internal layer inside the box

You may need to neaten up the inside of the spline cuts with a file or sandpaper on a narrow stick to get a completely flat base for the slots, especially if you have a table saw with an "alternate bevel tooth" blade.

Now all you need is some thin wood -- for my blade this is about 3mm -- that you can glue into the slots to complete the splines. You use the same colour wood,or a contrasting colour.

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