There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
urtha-
verb. to work, wreak, fashion, make, devise
urna-
verb. to blaze, burn (intr.)
The verb G. {urtha- >>} urna- “blaze, burn (intr.)” appeared in the Gnomish Lexicon of the 1910s (GL/75), probably derived from the early root ᴱ√URU which had several fire-related derivatives (QL/98).
Neo-Sindarin: For purposes of Neo-Sindarin, I think this verb can be adapted as ᴺS. orna- from the later root √UR, and it can be used for “burn” in general (both transitive and intransitive) since the other transitive Gnomish “burn” words like G. gusta- cannot be easily adapted.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A verb in the Gnomish Lexicon of the 1910s glossed “work, wreak, fashion, make, devise”, which Tolkien indicated was related to G. ûr “smith” and G. {aur >>} aurin “made, wrought, fashioned” (GL/75).