Show of hands everyone; how many of you have – at some point – given yourself a nick or cut from a exposed blade tab on a double edged blade? I suspect most of us have done it by accident at least once which is why some safety razors covers the tabs.
Back in late January 1930 – ninety years ago pretty much on the date – Albin K Peterson was granted the earliest patent I’m aware of that covers blade tabs… literally. Mr Peterson had noticed the inherent danger of the tabs, although possible not when he was shaving his beard… to quote his patent:

The Gillette type of safety razor is highly desirable because the blades can be replaced and a sharp blade always had at a small cost. In these days of scant attire for women, they often employ a safety razor for shaving unsightly hair from the arm pits. It has been found dangerous, however, to use the average safety razor, whether the Gillette or other types, because the sharp corners of the blade protrude sufficiently to cut the skin when contacting with a cupped or depressed area, such as the arm pit.

So… body-shaming the ladies in your patent filing? Classy. Anyhow – the invention don’t seem all that non-intuitive to me in hindsight, even if the patent clerk found it novel enough to grant a patent. Mr Peterson’s big idea was just a change to the shape of the top cap, made to include an overhang that covered the blade tabs. Granted; the overhangs were a bit on the large side, curved to slide smoothly in an armpit, but still just overhangs.
Interestingly enough, Mr Peterson also wanted to modify the base plate slightly to ensure a snugger fit with his improved top cap… in his own words:

The guard member consists of a curved body portion 6 to which may be secured, by shaft 2 protruding into the handle 7 and figures 6 and 7. The prongs 9 are shortened just sufficiently to fit snugly within the shields 4 thus, together with the latter, forming a complete housing for the corner of the razor blade. The prongs 8 are preferably of such a length that when the razor is assembled the tips of the prongs will be in a line forming a tangent with the outer surface of the shields 4.

It is, of course, possible to merely reduce the length of the four end prongs of the guard member of the standard Gillette type of safety razor so that it will fit into my improved blade receiving member. Thus by providing my improved blade receiving member with the standard Gillette type of safety razor, the guard member of which has, been altered as above described, the user can alternatively employ the set for shaving ‘said to be adapted to shave any part of the human body without fear of injury thereto.

Today double edged razors with covered blade tabs is fairly common, but I’ve yet to seen any with such massive overhangs as Mr Peterson suggested.

In 1920 Mary M McCaffrey filed a patent for a safety razor for shaving armpits – the earliest such patent I’ve found that has been filed by a lady. Like the underarm razor patented by Joseph J Schermack in 1931 – and the Shermac he later manufactured – Mrs McCaffrey’s razor was round, and for a good reason:

To shave hair from the armpit or any depressed portion of the body with the ordinary straight edge safety or. other razor is more or less unsatisfactory, therefore provide a safety razor which will effectively and safely do such work, and to this end use is made of a circular blade so constructed that it may be flexed as desired.

A lot of the patent goes on to describe the special blade – that could be flexed as desired due to a number of  of elliptical openings placed around the centre – and the slot in it that had to be protected with a guard so the corners didn’t cut. Or as the rather verbose wording of the patent text tries to explain it:

Blade 3 is best illustrated in Fig. 4;, and is provided with a slot 6 to permit greater flexing and also with elliptical openings 12 placed radially in blade 3 to prevent buckling when being made and to assist in allowing appropriate flexing when pressure is placed means of screwing handle 1 on stem 5, which flexing is produced by slightly raised circular, portion 16 on head 2 (exaggerated in drawing) fitting into depressed circular portion 13 on cap 4 (also exaggerated) The center of the raised circular portion 16 on head 2 passes when in position over elliptical openings 12 slightly beyond the wide portion of said openings radially placed producing thereby an even flexing of blade 3, and thus eliminating to a great extent the tendency of circular blades to break on the outer edge thereof.

Clear as mud, as many patent texts are, but the drawing is at least easy to understand.

Judging by the apparent lack of success that McCaffrey’s razor, and the blade of the slightly more successful razor later patented and marketed by Shermack, I suspect that the blade of this razor was overly complicated – making the manufacture of the blades complicated and expensive.

For those who missed the last post i made about an old patent, axilla is the anatomical term for armpit.

Ever since society started shaming women into shaving their armpits (around 1915 or thereabouts, as mentioned in a previous post), guys have invented razors for just that use. This is one of the earliest I’ve found, applied for in December 1917 by Mr Oswald T Fleury.
As he states in the patent text:

The practice of removing hairs from the axilla is, at the present time, becoming more predominant and,.in order to accomplish this purpose, he ordinary safety razor is sometimes ’employed but has been found more or less unsatisfactory owing to the fact that access ca mot readily be obtained to the curvature o the arm pit to remove the hairs therefrom with the straight edge blades commonly used.

If you’re not steady in anatomical latin, axilla simply means armpit.
The invention itself isn’t too complicated; a semicircular single edge safety razor with a curvature shaped to fit the armpit – however it is interesting in that it has no top cap, but uses two tabs fitting in corresponding slots cut in the blade and bottom plate to hold the blade secure, and a cup or ring to hold two halves of the handle together. Hopefully that is clearer from the drawing than from the text.

…having a handle with threaded orifice, a flexible slotted circular blade provided with slot with parallel edges and a series of elliptical openings placed radially in said blade, a circular head provided with guard teeth and special guard portion integral therewith to cover slot in Blade, a slightly curved circular raised portion, and an elliptical raised portion all integral therewith, a circular clamping cap member provided with a slightly depressed circular portion and a threaded stem for screwing into threaded orifice provided with handle, substantially as described.

A quick look online finds no indication that this patent ever turned into a marketable product, but there have been a veritable flood of specialised razors for armpits since… some successful, but most not so much.