Before you start
Make sure your test fabric has been backed with interfacing. You will get a much better result from doing this and even the 1911 book recommends a backing fabric.
Using your automatic patternsI had a look at doing this a while ago on my 320K2 and it seemed to do a really nice job. Things I learned about embroidering on 1950s machines are:
1. Zig-zag is useful when creating a really thick line.
2. So is built-in patterns and pattern cams.
3. So is your machine's ability to do a really short stitch.
4. If you don't have a machine with cams, you really only need zig-zag. You can move the lever as it sews to make just about any pattern.
I have to say that my Pfaffs have been extraordinarily good at all of this, particularly at achieving a very small and accurate stitch length. The idea with all of this is to use the machine to do most of the work. Break the picture you want to make into patterns covered by your machine's cams then just go for it.
The Necchi Supernova is really unbelievably good at patterns, since it will go backwards to achieve the pattern you want. First time I saw the Necchi do this my jaw dropped. It was like an electronic machine, except totally mechanical and 60 years old. What a machine! I just have to fix mine and I'll be happier to experiment some more (transformer blew up).
Using free motion on a straight stitching machineThis needs to be explained first. Free motion refers to placing the work in an embroidery hoop, Removing your machine's presser foot so there isn't one there at all, and sewing slowly while moving the hoop to make the pattern in one hand while using the other hand to press down the fabric right next to the needle.
This technique is described in the Singer embroidery book of 1911 (no longer in copyright so go for it) and it specifically mentions models 66, 15 and 27. It's pretty much accepted that machines with drop in bobbins (the 66) are less satisfactory doing this due to the 90 degree turn the bobbin thread needs to make, leading to loose threads. I haven't experienced this at all and don't have a spare 66 to test, just quoting what I've read on various forums.
I tried this on a 319K (not a straight stitcher and a vertical bobbin machine) and the results were 'mixed'. Stitching in the normal direction worked beautifully, but when I attempted to go any other direction, the thread wouldn't catch. Here is the best I could do with the 319K (the word 'Mike'):
Another problem I had was forgetting to put the presser bar lever down before sewing. The lack of a foot makes it easy to overlook, and if you do the bottom threads will be extremely loopy (because there's no tension at all on the top). Also on the 319, the feed dog was dropped.
The word 'Audrey' was done on my 1891 VS2 ('vibrating' bullet shuttle) and with this machine the feed dog doesn't drop so it needs to be covered (the feed dog interferes with the fabric movement). Any vintage buttonholer will have an appropriate plate, so screw this in place before starting.
I was surprised that the 1891 machine performed so much better than the 1950s vertical bobbin, but it definitely did, so I'll leave the green machine for automatic patterns and the VS2 for free motion work. The VS2 had no trouble at all with anything I tried and didn't skip a single stitch in any direction. I tested both of these machines by sewing a circle and the VS2 did it beautifully.
There are a lot of good instructions in the book, so if you like an older machine, this is for you. I'll be playing a lot more with it in the near future.