Wednesday, December 11, 2019

Heat treating armour - A modern way

Many amourers and knife makers heat treat their own stuff, and while I have heat treated my own things before, I'm going to a professional company for this project. Having grown up around aerospace manufacturing, I learned years ago that there is more to heat treating than just making it hot and quenching it, and making it hot again. Modern heat treating has come a long way, and because of the complexity of this project, and the other advantages I'll address here in a bit,  I am using Certified Steel Treating (CST) Corporation in Los Angeles Ca.

Without going into too many technical details of what heat treating is, let me outline the process for those unfamiliar with what's involved in heat treating steel. However, first off, I am not an expert in heat treating, so forgive me if I get some technical bits wrong here.

The basics of Heat Treating steel.

 First: Heat the metal to the correct temperature, this varies with the type and alloy of metal being hardened, but with steel you are in 1500-1650 f / 815-870 c temp range. In addition; The amount of time at that specific temperature is important.
 Second: Rapidly cooling the piece, by quickly submersing it in a "quench" of water or oil or molten salt (see below)
 Third: Reheating the piece to a much lower temperature, in this case 500-750f / 260 - 400c to "temper" it so it is not brittle like a piece of glass.  This is where you can control how hard or flexible the piece can be. Either hard like a file, or flexible like a spring. The choice of metal alloy you use is a big factor of these properties.

For my Greenwich armour one of the factors in deciding to use a commercial heat treating company was I'm using a "modern" steel, in this case 1050, and they will know exactly how to process it to the desired hardness. If it's too hard, it will crack when struck, too soft and it will dent easily. 1050 is a close modern equivalent to what the medieval or renaissance armorer was using. This alloy of steel has just enough carbon (.50%) so it can be hardened, but is not an exotic modern alloy with lots of other types metals mixed in.

The big advantage to a commercial company, is the use of modern vacuum or atmospherically controlled furnaces, which eliminates oxygen around the heated part. This keeps the surface from oxidizing or "burning" while it's glowing orange, resulting in a "scale" on the surface.
This way, your piece can be surface finished to bright or polished, and the surface will be undamaged by the heat treating process. It will turn blue, but bringing it back to "white" is pretty easy.
Another advantage, is salt quenching. The advantage here is lowering the thermal shock to the piece being hardened. Going from 1500f to 80f  of your oil or water quench tank, is a severe drop and can cause a lot of distortion in the work. In order to harden the steel however, you do not need to drop the temperature by 1400 degrees, you only need a drop of  800 or so. One way to do this, is to heat salt to 600 degrees and quench the piece in that. The only down side to a salt quench is you can't have any plates riveted together or other places the salt can get trapped. Because after quenching, they will thoroughly clean the parts, and any place they can't get to, that traps the salt, will corrode.

Since this process is done on a lot of material in a commercial heat treating facility, it's pretty reasonable cost wise. A batch of around 20 ponds of material will cost in the neighborhood of $200 (This is a bit of a guess from memory, but when I get this next batch back, I'll update the cost)

I-Beam clamp from McMaster-Carr (PN-29915T81)
In order to keep the pieces from warping or distorting, you want to brace the parts with a fixture that is more rigid than the part, so it will hold the part in place. There are a number of ways to do this, but I like to clamp or pin the pieces, then weld a frame to these clamp points.
On the most recent pieces, in this case the pauldrons, fauld, and arms, I found some "beam clamps" which are used for securing things to metal I-beams. These can be bought on Amazon for around $1 each, but the only ones I found are galvanized, which would have to be stripped off before using them. Another source is the company McMaster-Carr, they have unplated ones for $2.30, so I used those.  These clamps come with a 3/8"-16 bolt and nut, so once clamped the nut can be used as a jam nut to lock the bolt in place. These are threaded on both sides, so another bolt can be threaded in from the other side giving you the option to pinch the part between the bolts.

The resulting clamp arrangement means you can now just "Connect the dots" with some steel bar, or in this case square tubing. The clamps can be pivoted to facilitate using a straight piece of tubing to connect multiple clamps like seen above on the fauld lames. Here is the finished bracing.

I try to leave a flat stable surface on one or more sides so the parts can sit nicely in the furnace. Anywhere there are rivet holes between plates, #5 screws are used to secure the plates to each other. While a #5 is an odd size, it is almost exactly an 1/8 inch in diameter, which fits perfectly in the rivet holes. Once the pieces come back from the heat treater, I'll cut the clamps off the frames, so I can reuse them. This also is a great way to use up the short scraps of steel tube our shop seems to generate.
The arms and pauldrons are braced in a similar manner.

For the cuirass, I used a technique I used before, where I make tabs from 1/8" strap stock with holes, that secure to the armour through rivet holes with the #5 screws, and then I connect these tabs with steel tube. In addition, I drill holes in the steel tube and weld nuts over the holes and thread a bolt through and pin the armour. In the case of the cuirass, this requires a frame on the outside as well. I try to design it so I don't have to cut any of the tubes to remove the armour.
 In addition, I have added tabs on the front and back of the bottom skirt to trap it against the inner steel frame.
Once these come back, I'll clean the surface back to white (shiny silver) and start the etching.

Sunday, September 29, 2019

Greenwich Armour: The work to get to this point.

As I stated in an earlier post, this armour was started by Robert MacPherson (Talents I have seen) and after an injury, Mac was unable to continue with the armour. Mainly because the work left to be done was all of the "heavy" work, the thicker jousting pieces and sinking all of the surfaces than needed etching & gilding.
Jeffery Wasson took up the challenge of completing this massive project. Massive, in that, not only was this a complex, advanced late period armour, but it was also a complete garniture. That being an armour with multiple separate components to allow the armour to be configured in multiple ways for different specific uses. In particularly, jousting.
For jousting, the Greenwich armours had additional heavy reinforcing plates that mounted over the main armour in order to improve the safety of  riding head to head with another jouster, who was trying to hit you with a metal tipped heavy wooden lance.
Imagine riding on the freeway in the back of a pickup truck and leaping out into a street sign and hitting the sign post. The impact is tremendous. So to help keep the guys from getting injured (or killed) heavy plates were affixed over the base armour, which helped tie loose appendages together to keep your arm from being dislocated or your neck broken.
Just like modern sports, jousting evolved over time with changes in rules and improvements to safety, usually motivated by serious injury or death. So by the late 16th century, jousting armour was pretty sophisticated and substantial. To the best of my knowledge, this is the first  replica of a complete Greenwich garniture built in at least the last 100 years (I'm not sure if any replicas were built during the Victorian period) So there is a lot to learn by trial and error in recreating these parts and making sure they interact with each other in the correct manner.
Here are some images of this process (work by Jeff Wasson):

Examining the original arm armour at the
Wallace Collection. The burgonet and
falling buff are in the foreground
(Thanks to Dr. Tobias Capwell)
The fitting of the close helm visor. (one of two)
The garniture has two helmets and 4 visor options. The burgonet has a bar grill and a falling buff and the close helm has a tilting visor and a field visor. The close helm locks onto the gorget, via a rolled top edge on the gorget and the ridge you can see on the bottom of the close helm. When properly made, the rotation is effortless.

The burgonet with it's falling buff. The bar grill
fits beneath this. The black pen lines, show
where the decoration areas need to be sunk.
The close helm with the tilting visor.
 Again, the lines indicate areas to be sunk.
The close helm being fit the gorget or "collar"

The burgonet with it's sunken boarders.

The rough ground breast with its sunken boarders.
 Sinking the boarder moves the whole piece
often requiring the piece to be reworked
in order to refit it to its mating pieces.

The breastplate being heated in order to sink
the decoration areas. Heat is required
because the breast is about 2 mm thick

If all this isn't difficult enough, an optional  second
"reinforcing" breastplate is also fit over the main one.
The reinforcing BP is 3 to 4mm thick and is intended
to be proof against heavy rifle rounds.

The reinforcing BP also needs sunken boarders.
Once the decoration areas are sunk,
the reinforcing BP needs to be refit to
the main breastplate. Areas that should not
touch are marked with soapstone and corrected.

In addition to sunken areas, the more traditional
rolled edges need to be added to many
of the plates.

The backplate is considerably thinner, but still needs
sunken areas for decoration. The rolled edges also
get grooves hammered in, called "roping".

An earlier test fit of all these pieces.

Pauldrons (Shoulder defences) are particularly tricky.
Not only do these need to fit perfectly, they also need to be
the correct proportion for the period of armour.

Roping being added to the rolled edge
of the couter (elbow)

Here we have the gorget, burgonet, falling buff, spurs
arms and tassets all ready for heat treat and decoration.

In addition to all that, the jousting plate known a
grandguard is patterned over the breastplate
and pauldrons.

Here is the formed grandguard, now, continuing
up over the left side of the helmet, again with the
to be sunken areas indicated with soapstone lines.
All of the specialized tilting pieces.
All the pieces for the torso defense.