There is a wonderful little book for self published authors on how to sell lots of books and build an interested readership fairly quickly using email with an assist from social media. It is by far the most concise and worthwhile book on the topic I've ever found. It is titled "Your First 1,000 Copies."
Although for authors, it applies to almost any business. We used if for years to generate business ourselves, modified it only slightly to apply to our clients practices and a bit of it is in my suggestions for marketing. You use the emails to follow up and send a stream of useful information out to prospects who have signed up to read your email. The method fits the small CNC business to a T. It is inexpensive to maintain and allows you to present your current projects to new prospects. In a way, it allows you to let your prospects know how good you are, and at the same time caution them about picking just any provider when they could get your expert help and production.
The basic principles of marketing are very simple, even if some of the methods are arcane. You are looking to reveal people who want what you want to sell, and over time, to turn them into paying customers. Old sales methods focus on overcoming objections to get someone to buy. New methods focus on providing services and goods that people want, or will want, or preferably will want over and over again. If land a contract with a small, but expanding hotel chain to put their logo on every room number plaque on every door, then as they expand, so will your business with them. Once you have their logo scanned in, it's easy to fit on all kinds of additional signs, restroom plaques, signs for the hotel bar, laundry, etc. A B&B or large lodge in the mountains, near the sea or lake, or..., may never open another location, but they might well love the CNC themed signs with logo, and want them everywhere, indoors and out.
Finding these folks isn't all that difficult. Finding agencies that do branding for such chains is pretty easy as well. There are thousands of small agencies to be approached and if you talk branding using the CNC produced items, you may well reach them. If you help the get started by helping design and then provide a sample, they can pitch their client, and you may have a client. Designers, PR agents, art directors, in house agencies are all prospective clients, and it's not hard to reach them.
If anyone wants further discussion of their CNC marketing plans, I am happy to reply.