We are looking for they best brand/type of tap for machining AR500 plate steel- the size is 3/4-10 and pretty much everything we have tried is just shattering taps- tried to slow down/speed up SFM, tried "peck tapping" (one rev then clean off) tried different styles of taps (i am not exactally sure which ones they tried but none have worked so far)

we have had pretty good results from Emuge on a514 which is around 250 brinell but the ar 500 has a brinell of 450-550

one of my suggestions was to pre drill just a few thous. larger to reduce the torque but it is being frowned upon so that is out....