Within this linked article, there is a fairly comprehensive list of all the requirements of a patent illustration. At first glance, the list may be overwhelming. There seems to be many requirements that a person would not think of. You may wonder, how are these even relevant to patent illustration? But, regardless, these requirements must be met.
This leads us to the importance of a patent illustrator. Without a patent illustrator who is experienced, the requirements may be somewhat met, at best. An experienced patent illustrator can be sure that the illustrations are neat, follow the rules, and meet deadlines. The illustrator can also help ensure that the illustration provides the required explanation that the patent itself needs. Always remember, if you are using illustrations, experience is a key factor in quality of work.