You may have already found your Frank Cupler but thought I'd give you the following information:
1920 census:Stone, Coburn Fork Pct., Pike County, KY, ED126/Sheet 1B, HN11/FN12
Ray Cupler, head, w, m, 35, md, b. PA/parents b. PA, coal miner
Lula Cupler, wife, w, f, 26, md, b. VA/parents b. VA
Alvin Cupler, son, w, m, 6, single, b. WVA, fa. PA, mo. VA
1930 census:Pct. 11, Whitman, Logan Mag. Dist., Logan Co., West Virginia, ED19/Sheet 18A, page 83, HN321/FN323
Ray B. Cupler, head, w, m, 41, md. at age 25, b. PA, parents PA, either machinist or mechanic in coal mine
Alvin Cupler, son, w, m, 17, single, b. WVA, fa. PA, mo. TN
Frank Cupler, son, w, m, 6, single, b. KY, fa. PA, mo. TN
Also a Angelina Ratts, servant, her son.
This may not be your Frank, but it is the only one shown on the 1930 census index.Hope it helps.