DAY CTLR LOST SEPARATION WHILE VECTORING 2 ACFT TO ILS FINAL BTWN 3000 FT AND 4000 FT.

Narrative

I WAS WORKING N SCOPE WITH ARRS TO DAYTON ARPT. ACFT X WAS ESTABLISHED ON THE LOC AT 3000 FT CLRED FOR THE ILS RWY 24R APCH. I HAD ACFT Y ON A TIGHT BASE BEHIND ACFT X. WHEN I TURNED ACFT Y TO A 150 DEG HDG THIS WAS POINTED AT ABOUT A 10 MI FINAL; 10 MI N OF DAYTON ARPT; ACFT X AT THE TIME WAS ON A 11 MI FINAL. WHEN ACFT Y WAS 8 MI N; I OBSERVED ACFT Y WAS TOO TIGHT SO I TURNED ACFT Y TO A 080 DEG HDG; WITH PLT ACKNOWLEDGEMENT. I THEN HAD A DEP COME OFF DAYTON ARPT; IDENTED HIM WITH INSTRUCTIONS. I THEN OBSERVED ACFT Y STILL ON A 150 DEG HDG. I INITIATED A TURN TO A HEADING OF 080 DEGS WITH A TFC CALL ON THE ACFT X ON FINAL AT 12 O'CLOCK POS; 3 MI. THE ACFT Y WAS THEN TAKING THE TURN DSNDING OUT OF 4000 FT. WITH THE TAILWIND PUSH ON ACFT Y I ESTIMATE THAT ACFT Y CAME WITHIN 2-2 1/2 MI OF ACFT X LATERALLY AND ABOUT 500-600 FT VERTLY. ACFT Y WAS POINTED ABOUT 3/4-1 MI BEHIND ACFT X ON THE APCH. MY FIRST INSTINCT WAS TO TURN ACFT Y OUT FIRST; FOR SAFETY CONCERNS; RATHER THAN ATTEMPT TO CLB BACK UP TO 4000 FT AS LATERAL SEPARATION WOULD HAVE DECREASED WITH THAT OPTION. TO RECTIFY THE WHOLE SCENARIO; I REALIZE I SHOULD HAVE ACFT Y AT 4000 FT; ENSURED VERT SEPARATION AT ALL TIMES; LEFT UNTIL LATERAL SEPARATION WAS ESTABLISHED.