Andy - I keep thinking I need to make one of these too. I stole the following from ontariostrongman.ca :
WOODEN LOG
Materials required:
Log
Pay a visit to your local lumber yard. Ask for a peeled log, about 10" - 13" in diameter and 5' - 6' long. You will usually be charged $2 - $3 per linear foot. Be warned - the log might seem far too heavy when it is green - but it will lose 60 - 70% of its weight as it dries.
Saw
Acquire a chainsaw that can do "plunge cuts"; i.e. has a lubricated sprocket at the end of the cutting arm, enabling cuts with the tip of the saw.
1" Spade drill bit, 12" long
1" pipe, at least 5' long (and a means to cut the pipe - hacksaw, reciprocating saw, pipe cutter)
hammer
My log, after a few years of use and abuse.
Find and mark the log's center of gravity, using a pivot.
Measure and mark 12" out from each side of the center.
Draw a box measuring at least 8" x 8", centered around your two marks and even with each other.
Using a plunge cut, cut out the holes. If you do not want the holes all the way through the log, you will have to cross-hatch your cuts and chip out the remaining wood with a hammer and chisel or hatchet. I thought that the structural integrity of the log might be somewhat compromised if the cutouts were to be punched right through the log, so I only went to a depth of about 85%.
Rotate the log 90 degrees. Drill two holes for the handles - 24" apart. If you have the 12" long bit, you can drill straight through without having to worry about lining up your holes on each end.
Also drill holes at least 6" deep in each end of the log.
Cut your pipe - you will need 2 x 12" handles (depending on the width of your log) and two 16"-18" weight loading bars for the ends. Hammer them into the holes you have drilled.
Slap several coats of deck sealer or stain or paint onto your log. After the paint has dried, wrap about 15' of ¼" rope, or 8' of ½" rope around each end and soak/seal with glue or resin. This should prevent splitting when the log is dropped.