Pete Stanaitis has designed a really nice drilling and tapping block and you can find the plans for it on his web site. A tapping block is a simple but very useful tool used to make sure a tap is started straight in its hole. The tap is much more likely to break if it’s not, plus you’ll probably get poorer quality threads even if it doesn’t. Pete’s block can be used with 16 different sized taps from size 6 to 1/2-inch (NC & NF threads). It can also be used to drill straight clearance holes. You could make the block using aluminum or another kind of steel, but it will last longer if use 4140.
By the way, Pete is a blacksmith and has a large web site with lots of interesting and useful information.