Nylon line adjuster

[Jmk89]

When installing dethermaliser lines and similar hooks and endings, I find it rather tricky to ensure that the line length is exactly right, and even when I do manage that, it's often the case that at some time or other, I want to change the length of the line by a relatively small amount.

Traditionally, this requires a turnbuckle or similar. However, the turnbuckles made for model boat rigging are often decorative only or, if functional,  can be quite bulky and heavy for lightweight rubber models and gliders.   
There was an item on making turnbuckles for A/2 gliders etc by Martin Dilley  in Free Flight Scene in AeroModeller sometime in the 1970's). Although, Martin's turnbuckles used very fine screws, it did involve some quite tricky soldering and I thought maybe I could come up with something a bit lighter and simpler.

Here is my recently developed adjuster as installed in "Tyra".  The installation is to adjust the hook position for the spring that provides the "go" to the damper timer.  Getting that right is pretty important for making the timer operate for suitable times.


The first photo shows a hook bent out of a pin which has been heated using a small butane torch and, while still warm,  gently pressed into the edge of a M2 nylon nut. To do this, I hold the nut in a pair of always closed tweezers with the tweezer nose covering the entire through hole and I hold the pin in a pair of small surgical forceps and gently press the pin into the nylon nut. So long as you hold the pin still while the melted nylon re-sets, the joint is pretty strong and this technique avoids the need for using CA to attach the pin hook (somehow, it is inevitable that the CA gets into the threaded part of the screw if I try that!).


Here are the three parts of the adjuster . On the left is the nut with hook after the "tail" has been clipped. In the middle is a miniature eye screw. I. I find these very helpful not only in this application, but also instead of pieces of tubing or wire hoops as line guides between the timer/tow hook and the tail plane/rudder. Finally, on the right is a nylon M2 screw with a Phillips head.


The next photo shows the assembled adjuster  - my scales say it weighs 0.19g, so that's pretty good.


Finally, here is a photo of the installation in Tyra, which enables about a 1 cm adjustment of the hook position for the spring that turns the damper timer. That a 10 mm range can, in effect, adjust the timer run from about 20 seconds to about 120 seconds. Having that adjustment range makes those timers much easier to use, particularly as, even using a fairly long spring, the pull does vary quite significantly over the range of the amount of fishing line wound around the rotor part of the damper.

To install the adjuster, first do a test to ensure that the nut fits on the screw after you have melted the hook into the nut (sometimes I get a bit enthusiastic and melt into the threads - it is to try to stop this that the tweezer nose covers the hole, but sometimes I push through that barrier!). If that is okay, take those pieces apart, and about 4 mm "behind" where you think you want your hook, make a pinhole, screw the eye screw into the pinhole and security with a drop of CA. Then push the nylon screw through the eye of the screw and put on the nut (I find that it is easier to hold the nut (either fingers or forceps will do) and turn the screw with a Phillips head screwdriver (smallest possible size is best - mine comes from a spectacles repair kit).

Obviously, if you want more adjustment length, use a longer screw

[Jmk89]

Here's the page from AM October 1978 with Martin Dilly's turnbuckles