Make a Hinge!

Like many things in blacksmithing, hinges look difficult until you've made one -- and then they are easy. Hinges look as if they require precision. But in fact a hinge is fairly easy to make, and the precision comes almost automatically.

When you need to make a set of identical hinges, it's a good idea to make one hinge to use as a model, writing down your steps as you go. Then make all of the hinges in a set together. If you do that, they will all look like they belong to the same set, and you'll find that the work goes a lot faster.

Start out by sketching out the hinge design. Decide the length of your hinge barrel (the width of the hinge at the barrel). If you plan to use a pre-made rivet as the hinge pin, the rivet will determine the maximum usable width of the hinge. Remember that 2.5 times the diameter of a rivet is needed for peening, so if you have a headed 0.25" diameter rivet with a 1.5" shank length, the longest hinge barrel it can accommodate is 7/8" (1.5" - (2.5 x (0.25"))). If you make your own hinge pin from a rod, the hinge barrel can be any length you want -- but your hinge pin should start out the length of the hinge barrel plus five times the rod diameter because you'll need to peen both ends of the rod..

Here is the hinge design we'll use as an example:

Figure 1: Hinge Design

And here is the strap layout (same for both parts of this hinge):

Figure 2: Barrel and strap dimensions

Note that the extra strap length needed to form the barrel is slightly more than the diameter of the barrel, where the barrel diameter is measured from the middles of the barrel walls. Also note that the end of the strap is beveled so that it can fit snugly against the hinge plate after the barrel is formed. The decorative "hooks" on the ends of this hinge are basically bent triangles, made by splitting the end of the strap to a depth of 7/8" inch, then drawing out and tapering, and finally bending over the anvil horn. A triangle drawn out from a rectangle, keeping the height of the triangle the same as the height of the original rectangle, ends up twice as long as the rectangle. So, the length of the "hook" along its curve ends up at about 1-5/8".

A rectangle of dimensions A x B draws out to a triangle of dimensions A x 2B.

Figure 3: Barrel cross-section

So much for the planning. Let's make a hinge!

On this hinge I began with a scrap piece of 1/8" steel sheet. Using a talc stick, I laid out the outlines of three rectangles, each 9.5" long, twice the length of a single half-hinge strap. These I cut out using a plasma cutter. A hot cut chisel or hack saw would work just as well, but would be slower. Then I cut the rectangles each in half, to end up with six straps 4.75" long and 1.5" wide, so I can make three hinges.

Figure 4: Preparing to cut the hinge straps

Figure 5: The straps -- cut and marked

These are four of the straps. Note that I've put a center punch mark 7/8" in from on end of each strap. These mark the end of the slit for forming the two hooks on each piece.

Figure 6: Cutting the slit

With a hot cut chisel (or a hack saw), cut the slits starting from the center punch marks. I use a 1/2" aluminum plate on the face of my anvil to cut against, to protect my anvil and the cutting chisel. A piece of mild steel works as well.

Figure 7: Slits, done

Here are the four straps with their slits done.

Use a thin fuller to spread the slits and give the bottom of the slit a slight radius. Don't use a sharp chisel because it can start a crack.

Figure 7: Spread the slit using a thin fuller

Figure 8: Shape the hooks on the anvil horn

On the anvil horn, shape the hooks. You will alternate between the horn and the anvil face, bending and drawing out the hook on the horn, then flattening it on the face.

After the hooks are formed and flattened, gently hammer everywhere on the hinge surface to give it that dented, hammered look. Chamfer the edges. Then, grind or file the back side of the end of the strap at 45 degrees. This bevel at the end will help the barrel close on itself in a much nicer way than if you leave the end square.

Figure 9: Begin rolling the barrel

Now start rolling the barrel by hanging the end of your strap slightly over the radiused edge of your anvil face, tapping, moving it out a little more, tapping again, and so on. Give the barrel cylinder a somewhat bigger radius than you want it to end up having, because you will shrink it in a later step.

Figure 11: Continue rolling the barrel

Oh the face of the anvil, continue rolling the barrel. In this photo you can see the 45 degree bevel at the end of the strap. Roll until it forms a little more than half a cylinder. Your hammer blows will be at an angle slightly above horizontal, not down against the face, so you are only rolling the steel toward you, not squashing it down.

Figure 12: Finish rolling the barrel

Finish rolling the barrel by inserting a 3/8" rod into the partly-formed cylinder, then again hammering back toward yourself. (The rod is the same diameter as the hinge pin you'll use.) When you have gained enough experience in the barrel rolling process, you'll be able to close the cylinder without using the rod. It doesn't have to be perfect at this stage,

because it will become nearly perfect at a later stage. Just make it fairly round and fairly tight around the rod.

You can use the non-radiused edge of your anvil face to help close the cylinder. Glancing blows on the lower side of the cylinder will help roll it evenly. Make sure the cylinder axis is square to the hinge plate.

Figure 13: Using the anvil edge to help close the cylinder

Figure 14: Tuck the beveled edge in

If the beveled end is not neatly against the flat part of the hinge, clamp the barrel (with the rod still in it) into your vise as shown, and use a dull chisel to tuck the beveled end in. Now is the time to drill screw holes. If you want the hole pattern on both ends of a hinge to match, and if you want the hole patterns on a bunch of hinges to be exactly the same,

you need to make a jig or template to locate the holes. For this, I made a simple steel template:

Figure 15: Hole template and unfinished hinge partsThis template just presses up against the closed cylinder. I use a small diameter center punch to mark the hinge plate through the holes in the template, then drill and countersink at the marks.

Figure 16: Countersink the holes

Figure 17: Ready to cut the barrels

Here are two hinge sets with holes drilled and countersunk. Next step: finish the barrels.

The real key to making a good hinge is to cut the barrel parts so that they fit together closely without binding when the hinge is opened and closed. It's easy to make a sloppy hinge with loose-fitting barrel parts, but it takes just a bit of care to make the parts fit together almost perfectly.

Figure 2 shows where the barrel cuts are to be made. Precise location of the cuts is important.

If you use a hacksaw and simply cut each part on the lines shown, there will be a gap the width of your hacksaw blade between the parts and your hinge will be loose. So when I cut barrels, I first mark them as shown, and then offset the hacksaw cut so that the edge of the hacksaw blade lines up with the mark. For the part that forms the middle portion of the barrel, the hacksaw blade is offset outward toward the ends of the barrel; and for the part the forms the end portions of the barrel, the hacksaw blade is offset inward towards the middle of the barrel.

Make sure your hacksaw is sharp. If it is dull, it is likely to make an angled or curved cut. Hold the part in your vise and make each cut through the barrel cylinder to a point on the strap a bit beyond the tangent point of the cylinder with the back of the hinge plate, as indicated in Figure 3. Cut all the way through the curled-under beveled edge, without scarring the hinge plate. Your cut needs to be perpendicular to the cylinder axis. If you're not sure you can make the cut just right, offset your cut a bit more to leave a bit of extra material, so you can file it down to fit.

Heat the hinge parts, clamp them in your vise, and use a pair of scrolling tongs to open the portions of the cylinder that you will need to remove on each part.

Figure 18: Bend the end portions out on one part of the hinge for removal

Figure 19: Open the middle portion on the other part for removal

The easiest way to make the cross-cuts to remove these portions is to use a cold-cut chisel as wide as the length of the middle section of the hinge barrel.

In case you haven't ever made a chisel, here's how to make one that will serve the purpose:

1. At red heat, cut and straighten a piece of heavy coil spring to make a rod about 6" long.2. Heat one end of the rod to orange, and forge it to a wedge slightly wider than the final width

you'll want.3. Allow to cool slowly in the air.4. Grind it to its final width and shape, with a bevel of about 45 to 50 degrees. Don't overheat it

while grinding.5. Heat the whole tool to orange, then quench the last inch of the forged end in oil until it stops

smoking. This will take about ten seconds.6. Quickly scrape the scale off the quenched end, deeply enough that you can see the shiny raw

steel. Heat conducts from the still red portion of the tool into the quenched portion. As the temperature of the quenched portion rises, its color will change, starting with a light straw color, then a dark straw color, and gradually becoming reddish and then blueish. As soon as the color at the beveled edge reaches a straw color, quench the forged end in oil again and keep it there until the rest of the tool is dark red or black, then quench the whole tool until it is cool enough to handle with your bare hands.

This heat treatment leaves the cutting edge hard, but tough enough to survive the impact it receives when it's used.

If you need to make a drift, you can do it using a 3/8" steel rod. Heat it to yellow, cool the ends in oil or water, hold it vertically on the anvil face (using tongs, of course!), and give it a good whack straight down with a 3- or 4-pound hammer to upset the middle. Straighten it on a block of wood with a wood or lead mallet, then grind a slight taper from the ends to the middle without reducing the diameter of the middle. If you use mild steel, heat to orange and quench in water. If you use tool or spring steel, heat to orange, quench in oil, then bake it in your kitchen oven for an hour at 425 degrees F.

Clean up the edges of your cuts with a file, holding the part in a vise. The cross cuts should be beveled as indicated in Figure 3. Fine-tune the facing edges of the barrel parts by filing and fitting the parts together. When you've got it right, the parts will fit neatly together without binding, at all angles the hinge will swing through.

Finish the barrel by heating the parts, putting the parts together, inserting a drift that is very slightly larger than 3/8" diameter, and driving the drift through.

Figure 20: File the edges of the barrel parts

Wire brush or tumble the parts to remove scale. Apply wax or other surface finish.

Finally, assemble the hinge, insert the hinge pin, and peen the pin to lock it in place forever. Your hinge is done!

Figure 21: The finished hinge!

Steve McGrewIncandescent Ironworks, Ltd., Spokane, WA

www.incandescent-iron.com<stevem@incandescent-iron.com>