Router with a straight cutting bit, and a clamp straight edge. Another option is to drill holes for the shelf supports to put the shelf on, like they use in kitchen cabinets.

Thanks for the quick response. I'll write that down about the bit and clamp, because it's a job I have to find someone to do for me. I'd make a mess of it.

As far as shelf pins, yes - I saw that as an option too. Thanks. Perhaps that's what I might have to end up with.

After calling two different handymen, one didn't have the proper router bit, the other never called back, I scrapped the dado and shelf pin ideas. Instead, I decided to use wooden blocks glued and screwed onto the interior walls on the cabinet to hold a shelf (with lightweight items only). I managed to cut, measure, level everything every which way, and apply glue to the blocks. They are clamped and drying as I type. No turning back now!

For extra stabilizing after removing the shelf in the dado, I am attaching a back to the lower half of the cabinet only. As I will have electronics above. Then a couple cross pieces there. That's my plan anyway. Now if I only had someone to help me take the old TV out of the cabinet - an older analog model - I could proceed with that part of the project. : ) Wish me luck that my DYI turns out well.

I would have used shelf pin.

Al you need to make up is a piece of 1x (like 1x4) with a hole at the distance you want from the other shelf about the middle of the 1x4.

Hold the edge of the 1x4 with the edge of front edge ofthe side of the cupboard and resting on the shelf below. Put the correct drill in the hole and make the part way through holes for the pins 9put a turn of blue painters tape on the drill to mark the depth to stop drilling at, about 1/2 way through the side (depends on the pins you buy).

Use the same positioning of the 1x4 for the other three holes.

Places like Rockler sell the pins, drill bits, and even brass inserts if you plan on making a case you can easily move multiple shelves around.

There are plastic jigs to make multiple holes at varying spacing (some with metal bushings to prevent the drill bit from wearing the hole position).

For just a few holes bare wood should last long enough.

Outside of drilling through it is pretty hard to mess up.

Routing on a finished item is higher risk unless you use two guides to trap the router base (or bushing) and prevent any movement except across the side piece to cut the groove.

If you have only one guide the slightest pulling of the router away from the guide wrecks the cut.

Screws in anything but the largest diameters are not going to hold as much weight as the typical pins (they are around 1/4 inch or 8-10 mm in diameter).

Most yellow glues have 'creep' under long term loading.

Well, it's all finished and shelf is in place. I used self counter sinking screws (learned from watching video online) after waiting two and half hours for the glue to dry enough. I don't think I used enough glue, because when I put the second screw in, the block pulled away. I hammered it back in place and put the remaining screws in. Used three in each block, screwed from outside in.

At first I rejected the idea because i didn't want to ruin the look of the wood, but on inspection I saw that my Uncle (who made the primitive cabinet) had used nails to hold shelves in the dado, pounded from the outside. And in more than one instance, so I didn't feel so bad after seeing that. I will use wood filler to cover the screw heads. Nothing heavy will be put on the shelves, but these blocks are very solid.

Someday I'd like to try my hand at the shelf pins. I notice there is a special bit you can buy that only enables the cut to be made a certain depth, only the depth the pin needs.