I have made a makeshift makiwara, loosely based on designs garnered from the internet, but also from Mike Clarke's book "Hojo Undo". Compared to some of the makiwara out there, it's quite springy, and compared to others, it's a bit woosy. I like to think of it as "my-first-makiwara", and the intention is, once I've broken myself in to using it, I'll replace it with a stronger one.
It is made from a spare mountain ash plank I had lying around. I sawed it into two lengths, one shorter than the other, and dug a hole to put it in. At the base of the hole, I put a large rock just in front of the planks and as I filled it in, I placed another rock about 2/3 of the way up behind the planks. I packed all the dirt down, angling the board a little forward of vertical (about 10 degrees).
The idea behind the two planks was to give me a poor-man's way of angling the wood. In a traditional makiwara, it is made of a single piece of tapered wood - about 4 inches at the ground, to 1/2 an inch at the striking surface. I don't have the tools to do the taper, so I doubled up the thickness of the wood in the hole, and 1/3 up the post. Then, I tied the two together with a couple of cable ties. I thought of using screws, but figured that if they were rigidly joined together it would be more likely to snap than give with a solid blow.
The pad is a thin neoprene stubby holder with the bottom removed, and wrapped with an old coloured gi belt. When I'm not using it, I cover the pad with an upside-down empty paint tin.
I started lightly with it early this year, with only about 20-a-side reverse punches, as that was all my knuckles could take. I'm still not doing much more than 40-a-side, about 3 times a week, but I'm hitting it full-strength each time, with little negative after-effects. Pain-wise, once I developed a better hitting technique and body alignment and allowed my knuckles to heal in mid-February, I have almost no pain from hitting it at all. Visually, my main knuckles are a little darker and redder than the others, but not significantly, and there is no physical "build-up" that can be seen. They feel a little more leathery and thicker, but I have found no pain on cold mornings, or tightness when playing clarinet or touch-typing from them.
Why am I using it? I can hit just as hard on my homemade heavy bag, at different angles and with a greater variety of techniques and without strange looks from my wife. But what the makiwara gives me is feedback on how I am making contact, whether everything is in correct alignment, or whether I'm just flailing away with poor technique. The heavy bag is too forgiving of crappy technique for that. I am punching better, punching harder and my general body structure in day-to-day karate is improving too. Next, to start using different strikes on it.