The basis is one of not having any machine tools, unless you count a power drill, and needing a high degree of accuracy.
I took ideas from this instructable: https://www.instructables.com/id/Concentric-Drilling-with-a-Radial-Arm-Saw/ and the 'Fonly drill (http://www.btinternet.com/~two.mm/articles/fonly/fonlydr.htm)
to set up my battery drill to make the central holes in my square bits of wood for the headstock of the drilling machine. The details will vary depending on what you have available. I discovered in the process of doing this that my drill is slightly wibbly-wobbly. *Sigh*.
You are going to end up with a long bed, with the drill mounted horizontally at one end, a retaining strip along one edge, and a sliding carriage to hold the stock. I managed to achieve tolerance of 1/32" over about a foot with this setup, though I'm sure you could do better than this.
I eventually used a long piece of wood to make a bed for the whole thing, with a strip attached to the back of it for the stock-holder to slide against. The drill holder was screwed down to this. I was able to work much more accurately this way.
I discovered that when end-boring a piece of wood, especially with a standard twist drill, the drill tends to try and follow the grain rather than the direction you are drilling in. This set up just isn't sturdy enough to overcome this.
I was able to drill out the end of the long 10mm bar shown in some of the pictures by making a stock-holder that could hold another drill chuck, mounting a drill in that one, drilling a mid-point holder to stop the bar wobbling, and mounting the bar in the drill.
The wooden stock I originally intended to use turned out to be diamond shaped rather than square, and impossible to hold consistently in the holder.
Step 1: Materials and Tools
* Strip of wood to make a runner along one edge of the bed
* 4 pieces of plywood - maybe 5mm - to hold the drill and the stock
* Piece of board a bit shorter than the body of the drill
* Thick piece of wood to attach the boards which carry the stock. If using hole saws, this needs to be no longer than the length from the drill collar to the cutting edge of the saw that makes a hole to fit your stock, plus twice the thickness of the plywood.
* Screws and nails to hold it all together.
* Long piece of straight bar or dowel
Step 2: Make Bed and Carriage
Nail or screw 2 pieces of ply to the ends of the thick piece of wood. This is the carriage which will hold the stock. Use 2 rows of nails or screws so that they can't move.
Step 3: Make Drill Holder
Cut a hole big enough to snugly hold the collar of the drill. Screw this piece to the piece of board which is just a bit shorter than the drill body (base board).
If you have one, fit a long straight piece of bar, or dowel, in the drill chuck. This will soon show up any misalignment. Fit the drill collar into the holder you just made. Prop up the drill body with the handle vertical or horizontal so it is held with the long bar parallel to the bed and to the edge with the strip attached. Run the drill (slowly if it has speed control) to check for wobble, so you know to compensate for any.
Measure the height of the top and bottom surfaces of the drill body at the position the second piece of ply is going to be. Draw a vertical centre line down the piece. Mark the exact halfway point between your top and bottom lines and cut a round hole centred on it.
File the hole to fit the shape of the drill body, taking care not to go past the top and bottom limits you marked, and not to make it so the drill is twisted at all.
Fit the drill into the two boards and screw the back board to the base board.
Check the alignment again and secure the base board down to the bench. Re-check the alignment. Adjust any tilt using shims. Gentle application of a hammer to the base board seems to be the best remedy for horizontal misalignment.
I found it necessary to add a couple of wood bars to the top of the drill holder, to stop the drill collar being pushed out of its hole when pressing hard with the workpiece (photo to follow)
Step 4: Make the Sliding Stock Holder
If you are not using a hole saw, drill a tiny centre hole in the nearest piece and use that to centre your compass. After cutting it out, slide the carriage down and repeat for the far piece.
If you intend to bore off centre, or at some angle, drill tiny centre holes as above, and use these to set up your markings.
Step 5: Ready to Bore!
Fit a tiny drill bit in the drill. Fit your piece of stock in the holder, lock the drill on (mine doesn't have a lock so I used a spring clamp) and drill a shallow hole.
Stop the drill and measure the distance from the hole to the edges of the stock. It should be the same for every side/all round.
If all is well, fit the proper drill bit, and get boring!
Tip. As I was drilling the end grain of my piece, I found that a flat bit made for very slow going. Using a large twist drill was much quicker. I then used the correct sized flat bit to ream the hole to the size I wanted - no need to worry about centring as everything is anchored down.