Here is an article I found which discusses this issue:
http://www.vbm-torah.org/halakha/electric-razor.htmHALAKHA
"Shaving with an Electric Razor"by Rav Shabtai RappaportTranslated and adapted by Rav Eliezer Kwass INTRODUCTIONThe Torah (Vayikra 19:27) prohibits "destroying the corners" of one's beard. The word "destroying" (hashchata) is explained in the Oral Law as referring to shaving down to the skin with a razor blade. Before modern times, a Jew who wanted to follow the halakha but did not want a beard would either have to remove his facial hair with (sometimes painful) cream or try his best to get a close shave using scissors (which is permitted according to many authorities, though some forbid it - see below).
The invention of the modern electric shaver challenges the halakhist to clarify the distinction between the prohibited razor shave and the permitted scissors shave. A group of modern poskim were presented with this question and many prohibited the use of electric shavers to achieve a close shave. Others permit its use, and among some segments of the observant community shaving with an electric razor is common practice.
The following article is an attempt to clarify the distinction between shaving with a razor and shaving with scissors and to then apply it to some of the electric shavers on the market in the mid 1980s. [One would obviously have to re-examine shavers in today's market.] It does not include a summary of responsa literature on the topic.
Several years ago the first section of an article of mine about shaving with an electric razor appeared in Daf Kesher (#66, Cheshvan 5747, vol. 1, pp. 261-265). That article dealt with the difference between shaving with a razor blade ("ta'ar"), which is biblically prohibited (Vayikra 19:27), and shaving with scissors ("misparayim ke-ein ta'ar"), which many poskim, among them the Shulchan Arukh and Rama (YD 181:10), permit.
We came to two conclusions:
1. The reason for the permissibility of scissors is not that it cannot achieve the RESULTS that a razor blade can, but because the shaving PROCESS involved is different. Even if someone would invent a pair of scissors that could shave as close as a razor, it would still be permitted to shave with it. According to the poskim - (especially the Maharshal in Yam Shel Shlomo Yevamot 12:17) - the process of cutting one's beard with a scissors is by definition excluded from the prohibition.
The Talmud derives from one phrase that the biblical prohibition against shaving one's beard does not apply to plucking it out, and from another it learns that the prohibition does not apply to using scissors. If shaving the beard with scissors is permitted only because it is an abnormal method, why the need for a second derivation? Apparently, we reasoned, PLUCKING is abnormal and using SCISSORS, though a normal enough method for shaving, is a different process than that of using a razor and is permitted for that reason.
2. The prohibition of shaving the corners of one's beard differs from the prohibition of a man removing hair in a feminine way, which is one aspect of the injunction, "lo yilbash" "A man should not wear a woman's clothes" (Devarim 22:5). Scissors are excluded from both prohibitions, but for different reasons. The removal of a man's hair in a way of "lo yilbash" would be permitted with scissors, because it is irregular for a woman to remove bodily hair with scissors; for a man to use scissors to remove his beard is normal, but it is permitted because it does not involve destroying the beard ("hashchata").
Because a woman is interested in totally removing hair for beauty, she usually uses a razor. Therefore, even though there not be a recognizable difference between a razor and scissors, only a razor is biblically prohibited. But because scissors can achieve similar results it is prohibited by a rabbinic decree.
We closed that article with the following unkept promise: "What remains to be explained is what, ultimately, is the difference between shaving with a razor ("ta'ar") and shaving with scissors ("misparayim ke-ein ta'ar"). Though there is not necessarily a difference between the RESULTS achieved by the two, the PROCESS involved differs, and one who wants to remove hair completely usually uses a razor. In a subsequent article we will clarify this and its ramifications for the issue of shaving with electric razors."
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