This is intended as a guide for beginners wishing to construct armour components using compression articulation.  I make no claim that this is the "correct" method.  The techniques described here were formulated using resources such as TOMAR by Brian Price, study of museum pieces and photos as well as a whole lot of trial and error.

Some people may not yet know what compression articulation is.  I guess the basic description would be; articulation that allows movement by compressing when the limb or joint is bent and expanding when the joint is extended or straightened.  It is essentially the opposite of shell articulation, which is fully extended when the joint is in it's bent position.  Below are examples of compression articulation.

Below is a typical example of shell articulation

The factors that determine success with compression articulation are the curve of the lames and the placement of the rivets.  If the lames used have too sharp of a curve, the end result will have gaps when compressed.  If the curve is too weak, the articulation will not compress fully therefore limiting compression.  It is up to the armour to determine, through trial and error the proper curvature for the particular piece being created.  There may be mathematical formulas for calculating such curves but I have not discovered them.

Below is a photo of me cutting out the lames for inside elbow compression articulation.

Compression articulation lames are not typically domed and curled as with shell articulation.  They are simply curled.  This should be done by hammering from the inside as shown below.  This technique significantly strengthens the lame and allows for better overall control of shape.

Below is a view from the inside, the hammer marks are clearly visible.

From the exterior you can see the facets from the surface of the anvil.  This anvil could use a smother surface but that roughness will get ground off anyway.  After hammering the lame, it should be nice and springy letting you know that it is hammer hardened.

Now it's time to hit the grinder.  In this case a belt grinder but any grinder will do.  Remove the facets from the exterior of the lame and put a clean edge on the inside edge of the lame's curve.

When working the edge, grind away from the inside as shown below.  This will help reduce burrs on the interior which will cause unsightly scratches on the underlying lame and can even cause troublesome locking when the joint is fully extended.

Don't forget to put a nice 45 degree bevel on the outside corner of the edge to make it look nice.  Remember what Mr. Price said and don't create a knife edge!

Take the lame through the rest of the standard surface finishing procedures.

Another little trick is to polish the inside lip, again to prevent scratching and locking of the underlying lame.

Rivet placement is very important for clean looking and proper functioning compression articulation.  Unfortunately I cannot provide a rule that will always work.  The only way to get good at placement is try it and re-try it.  Using clamps to hold two lames together while marking them is a useful technique.  It is sometimes necessary to move holes or completely discard the lame and re-make it just to get it correct.  Mistakes become less frequent as one's experience increases.  Below are some shots of the process.

Once you have a few lames joined it should look something like the example below.

In the case of inside elbow compression articulation, a center piece is needed as well as a full set of lames facing in the opposite direction.  Also keep in mind that in some cases, and underlying leather strap or two may be needed to keep the lames from compressing too much or splitting apart when fully extended. The strap would be riveted to each lame on the edge that is covered by the following lame.  This type of leather is common on the compression articulation of a sabaton and sometimes a gauntlet.

Once the piece is complete it is usually necessary to do some follow up finishing.

To secure this group into the arm harness, rivets are used in the locations illustrated by red arrows below.