SE shimming - What is it? Why is it done? How is it done?

Simply put, ‘shimming’ is the act of putting some object underneath a blade in a razor. This changes the way the blade sits in the razor and affects how the razor shaves.

Pretty much the only SE blades available for shaving today are Personna GEM single edge blades, like these, available from Connaught Shaving. Back in the olden days the available blades were slightly different. They were meant to be stropped and had a thicker spine than modern blades. This means that the modern blades sit in the razor at a different angle than the original blades. To use the razor as intended we need to compensate for this. I have some original ‘Corrux’ blades I compared to the modern GEM blades using my digital caliper..

An original Corrux stropping blade is 1.95mm thick at the back of the spine. Here is a diagram of one. Note the thickness of the spine.

A modern GEM blade is only 0.96mm thick at the back of the spine:

The angle when using a modern GEM blade in an SE razor designed for stropping blades is clearly very different from the intended angle.
The modern GEM blade needs to be propped up (shimmed) to give the same shaving angle:

The amount needed to prop up the blade is about half the thickness of the spine below the stropping blade, or about a quarter of the thickness of the entire stropping blade spine. Look at the blue line in this detail view:

From the red line to the blue line it's about 0.5mm.
From the blue line to the green line (blades) it's about 0.5mm.
From the red line to the green line it's about 1mm.
From the red line to the top of the stropping blade (right hand blade) it's about 2mm.

This means that for a modern GEM blade to have the correct shaving angle in a razor designed for old stropping blades, the GEM blade needs to be propped up by approximately 0.5mm - something has to be in the space between the red and blue lines - the shim.

Any object that is about 0.5mm thick, as long as an SE blade (approximately 39mm) and about as wide as the spine of an SE blade (7mm) will do. The length and width of the shim are not too important as long as the shim fits in the razor - it's the thickness that is important here. As long as you know that your material is about 0.5mm thick, you can cut anything to size. You could use cardboard, but the shim wouldn't last for several shaves.

There are two ‘objects’ that are commonly used for shimming. First, let's have a look at this picture again:

On the left is the modern GEM blade. It's 0.5mm from the blue line to the green line. Half the thickness of the spine of a modern GEM blade is the thickness we're after. So you can remove the spine from a GEM blade, break it in half and use that as a shim. Have a look at this post on TSR to see detailed instructions with images on how this is done.

The second type of objects used for shimming are (used) Schick injector blades. They are 38mm long and about as wide as the spine of an SE blade. They are 0.25mm thick, so you need to use two of them to achieve the desired thickness. Before you use them as a shim, I recommend that you dull the blades - don't blame me if you cut yourself if you don't. I run the edge across a knife sharpener several times, but you could use a brick, a coarse hone or sandpaper instead. You could use superglue to stick the two injector blades together for easier handling.

If you have some Twin injector blades, you can just use one of them. They are twice as thick as normal injector blades, pretty much exactly 0.5mm. Both vintage NOS Schick Twin blades and modern Schick Twin blades from Japan (easily found on eBay, but quite expensive) will do the trick. If you have injector razors that can take Twin blades, you should get some anyway - they are fantastic blades.

Another way of shimming modern GEM blades is to use a small rubber band. The rubber band in the following pictures is 1 inch long (when laid flat) and ¼ inch wide (rubber bands seem to be measured in inches). The blade with the rubber band is 2.19mm thick, which is slightly more than required, but it works. The rubber has the added advantage that it properly removes any blade chatter. One thing to keep in mind when using the rubber band shim is that the rubber band stops the blade from sliding around in the head, so you shouldn't rely on the spring in the head moving the blade towards the blade stops. Just make sure the blade is seated properly when closing the head.

One disadvantage of the rubber band shim is the availability of suitable rubber bands. I have one rubber band of the correct size and no idea where it came from. If you know of a good source of 1 inch long, ¼ inch wide rubber bands, please let me know.

A few years ago rubber bands called “Loom bands” where popular with teenagers and they used them to — do things with them. You can still get thousands of them for a few pounds on ebay and they can be used for shimming a GEM blade as well. They are a bit narrow, so you need more than one to shim the blade:

Another great material for rubber shims are bicycle inner tubes. I got hold of some 27×1¼″ tube. A 5mm strip cut from this works really well as a shim on a GEM blade.
Bicycle inner tubes are in fact my preferred way of shimming SE blades.

I notice two main changes from a shimmed Ever-Ready 1912. First of all the shave becomes much quieter, less like ‘buttering toast’. Secondly the shave angle changes. I find that with a shimmed 1912 I shave with the top of the razor's head pretty much flat on my face. Give it a go - I wouldn't want to use a GEM blade in a 1912 without a shim.