May one cut his nails on Erev Shabbos Chol Hamoed, or Erev Yom Tov Achron?
If one cut his nails on Erev Yom Tov: One who cut his nails on Erev Yom Tov [or in close proximity to Erev Yom Tov to the point there was nothing to cut before Yom Tov] is permitted to cut his nails during Chol Hamoed.
If one did not cut them Erev Yom Tov: Some Poskim rule it is forbidden to cut nails on Erev Shabbos, or Erev Yom Tov of the last days, if he did not cut them on Erev Yom Tov of the first days. So is also implied to be the opinion of Admur. Others however rule it is permitted to cut nails on Erev Shabbos [or Erev Yom Tov] if one is accustomed to do so on every Erev Shabbos throughout the year. According to all it is forbidden to cut the nails on Erev Shabbos if he is not accustomed to always do so.
 M”A 532/1; Chayeh Adam 109/3; M”B 532/2; Kitzur SH”A 104/12; Chol Hamoed Kehilchasa 4/5; Kaf Hachaim 532/7
Other Opinions: The Elya Raba 532/1 rules one may only remove the nails with a knife and not with scissors.
 Aruch Hashulchan 532/2
 The reason for this allowance is because even regarding a haircut there are Poskim which allow it to be done on Chol Hamoed if one cut his hair on Erev Yom Tov. Thus regarding cutting nails which is itself disputed whether it is at all forbidden during Chol Hamoed, one may certainly be lenient if he cut his nails on Erev Yom Tov. [M”A 532/1; P”M 532 A”A 1]
 See Shaareiy Teshuvah 468/1; Kaf Hachaim 532/5
 Shvus Yaakov 1/17; Koveitz Mibeis Levi 1/47 that so is the custom; Piskeiy Teshuvos 532/1
 468/6 from the fact he forbids cutting the nails on Erev Pesach past Chatzos even though it is Erev Yom Tov. See Shvus Yaakov ibid. It is thus a wonderment that Chol Hamoed Kihilchasa 4/6 rules plainly that it is allowed despite this clear ruling of Admur.
 Nachalas Shiva 2/57; Shulchan Gavoa 532/2; Chol Hamoed Kihilchasa 4/6; Kaf Hachaim 532/5 concludes one who is lenient has upon whom to rely.
 Chol Hamoed Kihilchasa 4/6
 As it is permitted to cut nails for the sake of a Mitzvah and cutting them on Erev Shabbos in honor of Shabbos is a Mitzvah. [ibid]