How To Cut Angled Slots In Wood

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I’m working on a new woodworking project that involved cutting through-slots for bolts in a couple of boards. The two boards will act as adjustable arms to hold a dowel handle for a garden cart.

Cal, I like simple. Cut this on a table saw with an angled dado blade. Better if you have a Wixey or some such electronic angle gauge. Have some stock for sample cuts to check your blade position, height, and angle. Cut the groove the full length of the leg and just fill in the upper part that you don’t need. I happen to have made some cubbies like Jason is describing. I used a three-step process to cut the slots where the shelves intersect: After laying out the slots, saw out most of the material with a jigsaw, but leave a little bit for trimming. Clean up the sides of the slots with a router guided by a straightedge or a jig like this one. Make your first deposit to have your money matched 100% Cutting Angled Slots In Wood up to £100 and 300 spins on Starburst awarded!T & Cs apply.

I have cut shorter and narrower slots using a table-mounted router for a coin bank. These bolt slots were considerably longer and 1/4' wide so I was reluctant to use the same technique. I don’t have a plunge router – which would probably be the fastest and easiest way to do this.

Crowd-sourcing ideas

After checking a couple of woodworking forums for ideas – including one where someone trying this on a router table said the board 'shattered' (yikes!) – the general consensus seemed to be todrill out most of the material and clean up the slot later with a coping saw.

That sounded good (and safe) to me.

Wood

Since my slot was only 1/4' wide, I decided best approach was to use a 1/4' Forstner bit in a drill press to define the slot and remove most of the material, then clean up the slot with a file and sandpaper.

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The shaft on the 1/4' bit was larger than the bit itself so I had to flip the board over to drill all the way through the 3/4' material. It’s probably a good idea to do this anyway to avoid tear-out unless you have a backer board underneath when you’re drilling.

What to do

Drilling

  • Mark the centre points for each end of the slot in the blank and use a nail or awl to punch a small hole for orienting the bit.
  • Set up the drill press with a Forstner bit the same size as the slot you’re cutting. You’ll need to attach a fence to the drill press table to maintain a straight line as you drill along the length.
  • Place the blank against the fence and lower the bit. Adjust the fence and blank so the point of the Forstner bit enters the small punched hole. Clamp the fence in place, slide the blank to the mark at the other end of the slot and check that it’s aligned properly.
  • Put a mark on the edge of the board that’s against the fence. Keep this edge against the fence when you flip the board over and drill the other side. This ensures the holes are in line even if your a hair off centre of the board.
  • Turn on the drill press and drill the each end hole to define the slot – drilling about two-thirds to three-quarters of the way through the board. After that, just keep drilling holes and moving the work piece along the fence, overlapping holes just enough to keep point of the bit entering new wood. The slot will fill up with shavings which you should clear out if they get in the way.
  • Once you’ve drilled the length of the slot, clean it out with a screw driver or something similar. Flip the board over (keeping the same edge against the fence).
  • Repeat the process starting with the end holes. It doesn’t matter which direction you work in.

A COUPLE OF NOTES:

  • If you’re making a wider slot, you may want to make an additional pass to remove the 'peaks' between holes.
  • If you have a mortising chisel & bit you could swap that in once you’ve drilled the end holes.

Cleaning up the slot

  • After the drilling is complete, clean out the shavings with an awl or small screwdriver.
  • Clamp the work piece on edge to your bench and use a flat file to remove the high points left between the drilled holes being careful not to hit the rounded ends of the slots.
  • Wrap a small piece of sandpaper around a drill bit (smaller than the slot) to sand the ends of the slot.
  • After filing off most of the rough surfaces in the slot, wrap some sandpaper around the file and use it to finish cleaning up the slot.

If the slots were 1/2” wide or more, I probably would have used a jigsaw and straightedge to clean up the slots before sanding.

One of the most popular ways to create a 3 dimensional assembly of waterjet cut parts is via the t-nut technique. In this technique, a bolt or screw is passed through a round hole on the faces of one waterjet cut part, and then through a special slot perpendicular to the cut edge of another piece. The bolt is threaded through a nut which is held in place in a perpendicular slot.

The mating edges of both parts are usually cut with tabs and slots to further secure them together. This is similar to the finger joint or comb joint sometimes found in woodworking.

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Illustration : CAD drawing of parts to be joined at their edges with the t-nut technique

Illustration : Waterjet cut pieces joined at the edge with the t-nut technique

Illustration : Another view of the t-nut technique with the same part from the previous photo

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The slots cut into the face can be placed along the edge for maximum space savings. For more stability, the slots should be surrounded by solid material. This is analogous to the mortise and tenon joint of woodworking.

Illustration : Parts to be assembled using the t-nut technique;
the slots are placed in a location which provides more stability.

Illustration : The t-slot technique in a more
stable configuration: the slots in the center of the part

Illustration : Another view of the more stable variation of the t-slot technique

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Note that the slot which holds the bolt extends slightly beyond the nut. This is to make sure that the bolt fully engages all the threads on the nut. It also gives some flexibility in the length of the bolt used.

Angled

You might need to consider making the tabs slightly smaller than the slots or overcutting the corners in order to compensate for rounded inside corners due to the waterjet's kerf, as shown below. (More information on kerf can be found in our article on the limitations of waterjet cutting).

Illustration : Inside corner reliefs on tab section to compensate for kerf

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Illustration : Inside corner reliefs on slot section to compensate for kerf

Since the cut edge of the part is used in contact with a flat face, you should consider the use of low-taper waterjet cutting for this type of construction.

You should decide whether it's more important to have a tight fit or easy assembly.

If you go with 'tight fit', you should design the slots slightly undersized (0.005 or so), and fix it by filing away any excess. Heating the hole section with a torch or heat gun so that it expands will make putting the pieces together easier. You can force the pieces together with a press or even a hammer.

If you want 'easy assembly', you can get the parts to hold together more tightly using retaining compound (Loctite makes a good one) or epoxy.

Here is a complete box made using this technique. The box sides have been laser cut from clear acrylic, which lets you see how the whole thing is assembled.

Illustration : Box assembled with the t-nut technique