Yet another articulation thread

This forum is designed to help us spread the knowledge of armouring.
Post Reply
User avatar
Hew
Archive Member
Posts: 2871
Joined: Tue May 04, 2004 5:02 pm
Location: Sackville, New Brunswick, Canada
Contact:

Yet another articulation thread

Post by Hew »

Background:
I started to make some elbows, using "Constructing Articulated Joint Armor" from http://www.armourarchive.org/essays/gun ... ed_armour/ . I figured "Oh boy - patterns based on body measurements."
Measured my elbow as instructed, did the calculations (B=45% of A, etc.) drew the template, cut the steel into a nice little flat fish, filed corners and edges, and started dishing. It came out nicely, except that it was way too big for my elbow. Hey, guess what, it fit my knees perfectly, which I needed anyway.

I drilled the holes in the cop as recommended, such-and-such distance from ends and sides. I cut and shaped the lames, with just a hint of dishing, did a test fit with plastic spring clamps (similar to Sasha's G-clamp method - http://www.armourarchive.org/essays/sasha_articulation/ ) drilled the lames, and installed temporary nuts and bolts.

With a bit of tapping and bending, I had a cop and two lames that articulated wonderfully, from 180 to 315 defgrees with very little gapping or sticking. I was impressed with my first such effort.

Then things went horribly wrong. I put them on my knee, and discovered that when fully bent (as if I was kneeling and sitting on my heels) the top edge of the upper lame was about three inches off my leg. Not good. So I made some narrower lames out of cardboard, two on top and two below, and tried them in place of the steel lames. Better, but still not good. I taped on bits of cardboard to the inside of the wing and the inner end of the cop, so as to provide an expendible surface to punch "rivet" holes into, and moved the holes closer together (ie bottom holes at either side went up a bit, top holes at either side went down a bit. A tad better, but still a huge gap between the upper edge of the upper lame and my leg when bent.

So, after a much thought, I figured out that the human knee does not hinge around a line on the back of the knee (which about where the holes are now), but around some line running transversely near the middle of the knee. Therefore I reasoned that it would be necessary to move the articulation holes farther from the ends of the cop, so that the lames rotate through a much smaller radius.

So, I guess what I'm asking is if there is an easy way to find the correct radius by, say, wrapping your knee in two pieces of cardboard and marking up something as you bend your knee, so as to find the two spots on each piece that do not shift or move around relative to each other? Maybe taping two hinged sticks to you upper and lower leg to see which placement results in the smoothest flex? Is there a rule of thumb (better than Gundo's) to find the optimum radius (eg. some percentage of some tape measurement)?

The only thing I can think of is to make a mockup in cardboard and punch holes until you find ones that work, but that seem ... unscientific.

As I said before - the articulation was smooth, it was just in the wrong place.
"It is a primitive form of thought that things exist or do not exist." - Sir Arthur Eddington
Signo
Archive Member
Posts: 4963
Joined: Thu Jul 25, 2002 1:01 am
Location: Italy
Contact:

Post by Signo »

I usually think to limbs like they are cylindrical, i measure the wide of the articulation and this is my diameter, then i think the shell and lames to cover only a half of the circumference. In this way pivots are very near to knee or elbow real pivot point. And the armour look more like a real armour were the articulation is often not on the diameter, but toward the outer edge.
User avatar
Sean Powell
Archive Member
Posts: 9908
Joined: Sat Jul 13, 2002 1:01 am
Location: Holden MA

Post by Sean Powell »

The knee pivots by the condyles at the end of the femur rolling and sliding across the top of the tibia plateau. Picture a pair of balls sitting in a shallow depression that is greased with cartilage. When the balls roll they don't actually move but the contact point slides.

What I am trying to say is: if you put a finger on either side of your knee and feel two bony bumps and then connect the points of these bumps, you will have the axis that the knee rotates on... and it will roughly pass through the center of the leg and not behind the knee.

Patterning from formula is difficult as each armored has a different technique for shaping or shapes to a different degree. Some stretch the steel more than others. Some barely put in a curve. Some plan on uber-sized pads and others plan for almost none. It takes practice and a willingness to repattern and adjust after your own mistakes to make consistently good armor. (Not speaking from experience here. I make merely passable armor)

I would suggest putting on whatever pads you expect to wear, look at some good pictures of period armor, approximate the location of the rivets and measure that distance on your arm. Then transfer the measurement to a cardboard pattern to see if the pattern makes sense. Remember that for joints like elbows the armor doesn't contact the bones of the joint but stands slightly off the skin and distributes the impact the cuisse and greave or vam/rear-braces. This minimizes bulky padding which allows a good period shape. If you can fit your head inside your knee or knee inside your elbow then it should probably be shaped differently.

I was always taught to pattern multiple times in cardboard before cutting steel. It is cheaper and faster.

Additionally you can cut a simple cardboard caliper to measure the width and depth of a joint. Draw a half ellipse the right width and half the depth on cardboard. Measure the arc-length of this and add some for the pattern then shape until the ellipse fits.

I'm not sure if this will help but good luck. If you can post pics we might be able to help more.

Happy hammering,
Sean
lorenzo2
Archive Member
Posts: 1573
Joined: Thu Sep 26, 2002 1:01 am

Post by lorenzo2 »

You need to show some pics in the open and closed positions. With those there are folks here who can quickly offer help. Without pics, it would be dumb luck if anything said can be of much help.
User avatar
Agnarr
Archive Member
Posts: 8198
Joined: Wed Apr 02, 2003 2:01 am
Location: Indianapolis
Contact:

Post by Agnarr »

Yes, pics please.
User avatar
Hew
Archive Member
Posts: 2871
Joined: Tue May 04, 2004 5:02 pm
Location: Sackville, New Brunswick, Canada
Contact:

Post by Hew »

We got photos...

Knee cop and two lames in fully bent position.
The lower lame (on the right) is temporarily bolted in place, but the upper one is merely taped in position with the rivet hole in the cop lined up with marks on the lame.
No gap between the lames and the cop. this is good
Image

Knee cop and two lames in fully extended position.
Again, the lower lame is bolted in place while the upper is taped in position with the rivet hole in the cop still lined up with marks on the lame.
Still no gap between the lames and the cop. This is good too.
Image

Now notice the gap between the upper edge of the top lame and my lower thigh. The radius of the bent assembly is far too large. Not so good. the upper lame is taped into position, like in the first photo, with the hypothetical rivet holes lined up.
Image
Even sticking in one layer of blue camping foam under the top and bottom lame doesn't close it up much.

I still haven't decided whether to have four lames on a side plus demi-greave and cuisse, or just two lames plus demi-greaves and cuisse.

If I start over and make a new pair from scratch, I think I will make the centre of the cop more deeply dished than the piece above, with less dishing along the upper and lower edge.

BTW - these pieces are a lot smoother than they look in the photos. The apparent bumps are just highlight patterns created by sandpaper.
"It is a primitive form of thought that things exist or do not exist." - Sir Arthur Eddington
belmtho
Archive Member
Posts: 356
Joined: Wed Mar 10, 2004 5:13 am

Post by belmtho »

rember that you will be able to articulate the demi greave and cuisse plates, which will give you a greater range of movement.
tom
whhhhhhhhhhhhhhhhhhhhaaaaaaaaaaaaaaaaa
Signo
Archive Member
Posts: 4963
Joined: Thu Jul 25, 2002 1:01 am
Location: Italy
Contact:

Post by Signo »

Yes but first of all your knee cop is too flat, the deeper is the wider is the angle you can reach.
Dish it more, at least dobule it's depth.
I think you are on the right way.
lorenzo2
Archive Member
Posts: 1573
Joined: Thu Sep 26, 2002 1:01 am

Post by lorenzo2 »

Signo has got it. If you dish it deeper the angle the cop edge makes with the leg will come closer to the perpendicular with your leg. This in turn will permit the finished assembly toopen more. If the cop is resisting deeper dishing/raising you may need to anneal part way throughthe shaping process.
User avatar
Hew
Archive Member
Posts: 2871
Joined: Tue May 04, 2004 5:02 pm
Location: Sackville, New Brunswick, Canada
Contact:

Post by Hew »

A friend of mine said she would let me borrow her legs for a while (which sounds a lot creepier than it is :wink: ) because they fit me quite well. They also bend nearly 330 degrees, without any sticking and very little (maybe 1/8" or so) gapping (ie. between the surfaces of the lames, not the edges).

Two things I noted:
1. The knee cop is much more deeply dished than mine, so a couple of you have nailed that one.
2. The articulation rivets are [i]much[/] closer to the front, as I suspected they needed to be.
3. The first pair of lames (one above and one below the cop) actually overlap by about 1/2" behind the cop when the leg is fully extended. I wasn't sure about that, because mine met edge to edge.

So, it looks like I'm gonna be building a clone of her legs, except her cuisses and greaves are waxed leather, and I'm going all steel. Don't like her wings, either. Still, it'll save a lot of time and grief.
"It is a primitive form of thought that things exist or do not exist." - Sir Arthur Eddington
Signo
Archive Member
Posts: 4963
Joined: Thu Jul 25, 2002 1:01 am
Location: Italy
Contact:

Post by Signo »

Avoid like hell that inner lames overlap creating that scissor effect that wounded many people while wearing that kind of articulation!
Inner lames must remain separated.
Post Reply