If you want to go first class, Brownells has a neat tool for engine turning bolts, but you can do the same thing by eyeball and some care. With the bolt in the vise, bring the nib down on it and cut one circle. Then move the vise by x number of handle turns so you move the bolt lengthwise, and bring down the nib again. Do the same number of turns, etc. You want the circles to overlap.
When you reach the end of the bolt, with the first row, turn the bolt an amount equal to about 3/4 the circle and do the next row, and so on. I have done a lot of those, using the tool. It is a bit tedious, but looks good if you like that sort of thing. (I don't, because a little wear can make it look like heck, but it is a matter of taste.)
Jim