Making sewn / laced hinges.

The modern alternatives (mylar, plastic pin types etc) seem to have replaced sewn hinges, whilst I can't get enough of them!

I find them a lot easier than the plastic ones, as there is no need for slots to be cut, cutting a 1mm wide slot in a 3mm rudder is bound to end in tears!

They're brilliant for all sheet surfaces, and really look the part on vintage models. 

I use them on control line and radio control models. As long as the holes are drilled with reasonable accuracy, it's very difficult to end up with a messy and unsightly hinge, unlike bandage!

It seems like many people have virtually forgotten about this method, or do not know where to start - so here's a quick guide on how I hinge control surfaces.

 

Introduction

For this example, I'll be hinging a tailplane/elevator for my latest experimental model - a small, electric pylon racer/ sports model. I hope to add plans later, if it flies! (Update, it didn't fly)

The tailplane and elevator are both cut from medium 3/32" (2.4mm) balsa, with a span of roughly 270mm (to give you an idea of the scale).

 

Drilling Holes

This example uses a spacing of 7mm between holes, about 5mm from the hinging edge. 

For your model, I'm afraid you'll have to stick with trial and error, and what looks "about right". Avoid using too many holes, as this will put un-necessary load on the servo and could end up splitting the wood.

Offset the holes away from the hinging edge depending on the material. Move the holes further in for soft balsa, whilst plywood is strong enough for the holes to be a few mm from the edge

Look at the item to be hinged, with the hinge line horizontal. Assume 0º is facing straight ahead (ie up the fuselage for my example)- the holes should be drilled such that the string points ±20-30° from 0. All of this will become clear in my example. 

There is no science in what's written above, it's just worked for me. I'm sure there's some fancy formula to calculate the optimum angle, spacing and offset from the edge, but I'd much rather be flying than number crunching. 

I find it easiest to mark out a line with a ruler 7mm (in this example) from the hinge line, then mark the hole positions along this line. Alternatively, make a jig from brass angle section (email me for more details). 

Use a different number of holes on the stationary surface than on the moving one (see example). Using the same number of holes will move the surface left or right, once the string has been tightened. It's difficult to explain in words, so here's a diagram.

Diagram A shows the bottom holes will move to the right, whilst B will move in the opposite direction.  The movement in C cancels itself out, meaning the surfaces will not move left or right. Either use A and B combined, or use C.  

 

Thread and Tools.

 You'll see in the example I use a fairly thick thread - this is Cox control line wires. The name of the material is Dacron. I assume it's polyester based, all I know is that it's very strong. If you dont have any Dacron, use thick polyester thread or thin, braided fishing line.  

As a guide, the example below used 12" of thread, with 3" left and 1" excess on the needle. So 8" for a hinge with only 9 holes and a length of just over and inch! 

 

Tip: 
Threading a needle with thick thread is a pain, so I push a loop of copper wire (one strand from normal electrical cabling) through the eye, thread the string through the eye and pull out the wire. The copper loop pulls the thread through.
 
 

 

Step by step instructions

Hopefully, this will explain how to make sewn hinges. If you're still stuck and need help, email me at ollie(at)  topcocameley1(d0t)com

 

Step 1

Thread the needle and pull thread through the first hole.

 

Step 2

Knot the end of the string with a double knot.

 

Step 3

Pull the string around to the top of the tailplane, so that it double-backs on itself.

 

Step 4

Thread the string through the first hole of the elevator. Unless you've missed something, you will always thread through holes in the same direction, in this case, top downwards. Pull the string tight to reduce the hinge gap.

 

Step 5

Pull the string through the hinge gap... 

 

Step 6

...then thread the string though the 2nd hole of the tailplane 

 

Step 7

Keep pulling the string tight to reduce slack. Repeat the previous steps until you reach the final hole, then push the string through the gap. 

 

Step 8

Thread the string through the last hole of the elevator, as shown. You will still be threading through holes from the same side as you started, if not, you've missed out a step. 

 

Step 9

Continue to thread through the holes and gap until you reach the first knot. Make sure all the sting is tight, whilst moving the surface up and down and side to side to take up any slack.  Thread the string through the gap once more and again through the first hole, locking the hinge

 

Step 10

Use glue to lock the string in place. I use aliphatic resin in a small squeeze bottle, to "inject" glue into the holes. Wipe off any excess, and it may be necessary  to apply glue a couple of times to partially fill the holes. 

 

 

So there you have it, an easy way of hinging surfaces, whilst giving the model a "vintage" look!


All text & images : © Ollie Harris September 2014