My oak piece for the head is straight grained, but it will work for a mallet and also to show how to make it. I first planed up the rough-sawn facets and didn’t spend too much time worrying about perfect squareness because when done and shaped, there really won’t be much of any visual angular surface to reference. That said, it’s handy to start with two reference faces to use for laying out.
I continued the lines onto the endgrain to guide my axe cut. I split off the excess in two stages, the first to check grain direction, the second to establish the width before planing smooth. The axe works well for this. I use my chisel hammer with the nylon faces for this, but a wooden shaft would work as well and a steel hammer if you like. My eye follows the split and my line feels right.
I lay out the mortise hole lines on the narrow faces roughly. The outside hole is 1 3/4” and the inside 1 1/2” so from the centre line I split the difference. 7/8” each side on the outside and 3/4” on the inside.
I bore about half way through from each side using a brace and 3/4” bit, aligning my bit rim with the two extreme knife lines on the rim of the hole. The important thing when boring is to align the brace with the centre run of the mallet head. This again relies on visual accuracy.
When the hole is complete, I chisel a small chamfer on the short edges of the hole on both sides of the mallet head as shown. Because the taper fit of the shaft in the head is tight, backing out or tightening the shaft in the head can cause a split on these outside faces. the chamfer reduces this possibility.
I rip the taper for the handle using the handsaw. It goes quickly and is easier than setting up taper jigs for table saws and even free-handing on the bandsaw. Two or three whisks with the Stanley smoothing plane gives me exactness and the shaft then gets fitted to the tapered mortise hole so that there is no gap on either side of the mallet head.
I leave a large excess on the shaft because the wood compresses in the hole and there may also be additional shrinkage to take place yet. I will usually leave this for a couple of weeks to make certain there is no major shrinkage that leaves the mallet shaft beneath the rim of the mortise in the head.
Now that the shaft is fitted I can start shaping the head and the handle to what suits me.