How long should one wait to reapply if patent is not granted?

Most new products are developed in stages. This is particularly true when only one or two inventors are involved and research is often needed. Sometimes what appears to be a minor improvement will be significant in the Patent Office, particularly, if functionality is the issue. Under U.S. law, an inventor can link a new Patent Application to a previous Patent Application, if the older one is still pending in the Patent Office. Based upon your fact pattern, it would seem that you would be well-advised to move forward immediately if you can link to your previous Patent Application. You should seek the advice of Counsel here, to make sure that that you don't lose any rights here. Good luck!

You cannot reapply for the "same invention" - if the first case was published and then abandoned. The 18 month publication acts as prior art to the same invention. Any new application must be a non-obvious improvement of the first version in order to reapply. Also - any marketing of the invention can also act as prior art against any refiling. Talk to a patent attorney and have all facts ready - date of filing, date of first sale or offer for sale, date of abandonment, etc. GOOD LUCK.