We applied a 0.3 mJ, 1.7 ns, 46.9 nm soft-x-ray argon laser to ablate the surface of large bandgap dielectrics: $\mathrm{Ca}{\mathrm{F}}_2$ and LiF crystals. We studied the ablation versus the fluence of the soft-x-ray beam, varying the fluence in the range $0.05\text{–}3\mathrm{J}∕{\mathrm{cm}}^2$ . Ablation thresholds of 0.06 and $0.1\mathrm{J}∕{\mathrm{cm}}^2$ and ablation depths of 14 and 20 nm were found for $\mathrm{Ca}{\mathrm{F}}_2$ and LiF, respectively. These results define new ablation conditions for these large bandgap dielectrics that can be of interest for the fine processing of these materials.