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Home made plastic strut


John Aero

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I was playing about with an idea this morning, so I thought that I'd pass it on. Sometimes you need a small amount of a particular thickness and width of strut. Thin plastic is very difficult to sand down as it has little rigidity. 

 

This is easily solved by using a Fret or Jewelers saw to hold it in tension. The second part of this idea is to bolt together two of the light Stanley blades so they form a V.  Use the widest screw head and nut you can find as this will give more holding friction.  I use this little device to sharpen trailing edges on vac forms.

 

The V knife is simply drawn along the edge of the tension-ed  plastic strip so that it shaves off the plastic.  By varying the angle of the Vee you can graduate the section by faceting. There's no need to remove the strip to repeat the shaving on the other side as this can be reached within the hoop of the saw. Finish off with suitable abrasive paper into a smooth ellipse.  The whole thing only takes minutes. If you need multiples, then simply count the strokes on one setting, replace the strip with another and do the same number of strokes. Adjust the Vee and repeat the exercise, again counting the strokes. Do the same with the abrasive paper.

 

John

 

IMG_3006_zpsrxid0a1i.jpg

 

 

 

I used the light Stanley blades because they had a hole in the fitting, suitable for a  reasonable screw size. I'm now thinking of modifying a pair of sharp scissors but the temptation is tempered by the marital stare if I approach the sewing box, (well I'm not using mine).

 

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The original stock in this experiment was Evergreen .040 x .080 thou.

 

I managed to photograph a section. This is the section through the centre few inches about 3" or 75 mm. A larger adjustable frame Piercing Saw would be better

 

John

 

 

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I tried another experiment today. Some years ago Ray Rimmell (Windsock and former Scale Models Editor) gave me two huge coils (probably a couple of hundred metres) of fine Piano wire. He had wanted to use the wire for rigging but he could never straighten it. At the time neither could I, so it's lain in a drawer ever since. I had tried to tension and heat it before but it never worked. However today I sprung a length of .0008" in the same saw and I ran a lighted candle along the length. It worked, I achieved 6" straight lengths. So I will try it on my next Moth rig.

 

John

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11 hours ago, John Aero said:

. . . The second part of this idea is to bolt together two of the light Stanley blades so they form a V.  Use the widest screw head and nut you can find as this will give more holding friction.  I use this little device to sharpen trailing edges on vac forms.

. . .

Thanks.

I always knew there was a reason why I have some of those blades in my 'blades' box but no handle to take them

All good things come to those who wait

I have several 1/48 biplanes to restore/rebuild for which I need to make struts and your technique is both most useful and most timely

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Bravo! I like this!

 

As for straightening coiled wire, I cut a length of wire, clamp one end in a vise, grab the other end with vise grips, and then pull until it slightly stretches (i.e., the wire yields). This plastic deformation results in a straight length of wire. To be sure, solid steel wire will have a higher yield strength than brass, copper, or other soft materials, but the process works regardless.

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10 hours ago, dnl42 said:

Bravo! I like this!

 

As for straightening coiled wire, I cut a length of wire, clamp one end in a vise, grab the other end with vise grips, and then pull until it slightly stretches (i.e., the wire yields). This plastic deformation results in a straight length of wire. To be sure, solid steel wire will have a higher yield strength than brass, copper, or other soft materials, but the process works regardless.

I do similar with an old spool of armature wire, about 0.3mm, except it being more malleable and me more impatient I just grip each end with some ancient flat ended tweezers  It has weathered to a nice steel grey colour, so is suitable for some rigging. It will kink if knocked about but is much more resilient than if simply rolled.

 

Paul.

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Thank you chaps for the thoughts on the wire. I did make a rig using a 5 ft carpenters cramp to stretch the wire but it always curved when relaxed. The wire is so fine that it will glow and 'ping' even if the candle dwells too long, let alone a soldering torch.

 

John.

All metallurgical thoughts welcome 🤓

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7 minutes ago, John Aero said:

All metallurgical thoughts welcome 

Piano wire is heat treated which gives it that springyness and is why coiled wire will return to it's pretension shape when tension is removed.

All you're doing with the candle is annealing it to remove the original heat treatment.

It will now hold any shape you bend it to, and simple stretching will return it to a straight wire as others have suggested above.

For the piano wire to retain it's springyness once it's been annealed it needs to be hardened and then tempered again whilst still under tension.

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5 hours ago, John Aero said:

Thanks Dave,,  I will play further. So, if I heat the coil (or a few Metres of it) and then stretch it, it will then straighten?

 

John

If the bit you've already done holds it's shape after bending, yes it should. You might want to check with a smaller length before committing the whole coil though!

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What a great idea for the strut scraper, John, assisted greatly by the photos. I've been wondering how to scratch a Townend ring, so this process might work well there for profiling a piece of strip prior to curving it. Thanks for posting.

Jon

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Just another comment on the saw frame types. Coping and Hack saw frames and blades normally use  small pegs to secure the blades. These frames are no good for the above process, 

 

Piercing saws and Fret saws use a screw clamp at each end of the frame to hold the blade and these will also hold other items such as the plastic strip and wire,  Fret saws have a much bigger/taller frame than Piercing saws. Both have their uses in model work and are relatively cheap. High quality piercing saws often have an adjustable width frame.  The latter saws are fitted with blades by pressing the saw outer clamp against a bench to spring the frame whilst the blade is clamped at the outer end and then at the handle end. When the pressure on the frame is relaxed the blade is now under tension. 

 

As Melvyn said the blade s of all these saws must never be used loose.

 

John

 

 

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imho, the piercing saw is the better. My fret saw frame is non-adjustable and can literally pull a too short a blade apart. A good piercing saw (aka a jewellers saw) frame is adjustable for the length of blade it has to hold.

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I agree, I have a Swiss Jewelers saw which is adjustable for blade length so if you break the blade you can still use the longest piece. It also has the screw tension-er as well. The Fretsaw simply allows you to cut further into sheet material, for which I tend to use one of my mechanical Fret saws.

 

John

 

Top Left a Swiss Jewelers/Piercing saw, Right a junior hack saw, Bottom left a standard Piercing saw and bottom right is a Coping saw, (with the blade in backwards).

A fret saw is just the same as the Piercing saw but the frame is about three times the height.

 

IMG_3015_zpszmp8yxcg.jpg

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I think I need to I point out that I am such a child I am having real problems trying not to get the Tommy Cooper ‘I’ve got a saw head’ line in here, luckily I came download it!

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