My take on a stretch jig

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Over the month you could check the pressure in the tube every day and pump up as necessary, digital tyre pressure gauges are cheap

Stuart
to much hassle im afraid
well its even hard to pump a given amount into the tire, let alone a really tiny amount.

only thing that could be tested is glue it to a stator and see what happens. to the resonance (could drop few hz because of the glue or cutout of my jig is 1mm smaller whatever, but at least it is repeatable), and then see what happens to it over time.
 
Well here a 3d version(without base etc and details :)) , i am not sure yet if i should make the small circle that's on the metal tube a little larger, this would increase the maximum length of Mylar it can pull sideways(it pulls 1/4 of the circumference). but it will lose some of the arm so a little more weight might be needed to pull to correct resonance.

in previous post i showed one of these arms, and the weight alone when you hold it at the hole in the small circle has already some force.

i also did a test with some glue on the clamps to see if it can hold Mylar. this is hit and miss. although tolerances are pretty ok there is still a tiny bit of room in the clamping so mylar slips. witch is not weird since my machine wont mill to 3 um precision :) that would be fun :)

i might try single sided foam tape, i once used that to hold Mylar between 2 mdf piece of wood, and it never slipped before it broke(and that was 6um)


I did not draw the rubber bands that come between the outer hole in the clamp arm and the top hole in the 1/4 circle. i also only draw one weight(the black circle) just to hope clear how this would work.


Further, there is an option to automate all this, for now i will drill an extra hole in the 1/4 circular piece so i can lock the clamp in the open position. later on i would like it to be automated. when i could get a ram of some sort it can push the 1/4 circles into the beginning position, and at the same time push the clamps against a bar so it will go in the open position. so 4 rams needed in total. or another solution :)
any suggestions or stuff i miss please let me know. don't want to make soooooo many pieces and come to the conclusion its is a dumb idea :) haha
 

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So far i gained knowledge that my clamps are holding and my tire is not leaking any air. (not even a tiny bit) at least the panel would be glued by now. since glue dries in 40 to 60 minutes.

last be not least. you can see that just mechanical stretching a membrane then glue it to a stator is not gone give you a steady result. it will drop. be it 2.5 hz over 17 hours, who knows where it will end up

ESL63 wanted to know measurement over a time span of a month. and i am curious to. be it i cant miss my jigg for a month. or i have to buy new clamps.

Interesting and looking forward to your future results. BTW, what glue are you using to attach the Mylar to the frames?
 
yeah i got side tracked again :( still need to come up with a good and solid way for stretching. i did buy 22 kilo's of scrap lead for weights :) but i have to melt them down to small compact size. never melted lead so must buy some protective gear first i guess.

i use some sort of polyurethane. 1 component kit . its really fast drying. i delute it with allot of acetone. you then spread it on the foil NOT on the stator, and be sure to apoly a little wider then the stator spacer is wide so there will be glue every where on the edge of the stator. (else it will make anoying sound when playing low frequency) i got a foam strip underneath the the mylar where the stator comes on top so the glue will follow every nook and cranny of the stator, it will be hardened in 45 minutes.

glue brand is bison TIX top speed
 
i use 2 component epoxy, but its used for mouldings, so its really thin. i mix it with a tiny bit of cotton fibres, thismakes it a bit thicker and it will release epoxy when presured. then use a roller to aplly it on the stator frame. put pcb on top then a trash bag since its PE plastic witch dont stick to the epoxy verry well, then a piece of wood the size of the stator pcbs with the holes at the right place and repeat stack them all, and at the end a heavy weight 60 kilos of crap like sandbags and other stuff :) the glue need to dry at least a night so better do 8 in one go :)
 
Well since i am not able to get any wood :( i don't have a car, neither a license to drive :)

i tried the tube stretcher once more. i got a new roll of 40 meters 3 micron foil again so this would be the 3'rd roll i spends on this project... nice another 70 euro... hobby aint cheap. well at least i come closer and closer to a original panel. and well it means allot to me to be able to repair these baby's as close as i possible can and preferred closer then anyone else in the Netherlands :) since quite a few people repair these panels and since i got so many minor problems i ask myself sometimes if people really got rid of them or deliver a lesser/ or at least not equal to original product.

so well i used the stretch jig again. but the resonance needed by quad is pretty close to bursting range, at least at some critical points. so this time i apply the mylar as before with the clamps. but then i line the whole tube part with 2 pieces of tape. this ensures me that the mylar wont stretch in these parts(since its hard to heat these sections), and wont rip either. i then stretch to 70 hz, heat , restretch to 70hz heat, restretch to 70 etc. the drop it makes from the heating will get smaller and smaller. the last drop before restretch was only 3 hz. so verry close to best possible. i now let it rest and measure the resonance every 30 minutes. i so hope this works since my head spins from making a new jigg at the moment and i really would like to be done with these so i got some money to invest in a proper jig (and some one that has a car to get some wood :) )

so far after 90 minutes it dropped 1.5hz, i wonder if it will settle on the 3 hz it dropped from heating it. this would be anoying but at the same time gives me a guide line to how to do it proper , do the same thing over and over until after heating it settles at 70 :)
 
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70hz seems a bit low. And that is before coating whis is adding mass and lower the resonance further.

here you might have a point!. Thx. i will take a look what happens when glue dried and circles are melted. it kinda of depends indeed on the weight of the coating. i know licron is pretty thin, lets see what it does. i got measurements although the process now, so i could change things accordingly to get a desired result in the end.
 
Ok , with a heat gun you can stabilize the mylar but, the tire stretch jigg is a no go for this method. first my jigg

- wastes to much mylar.
- is not consequent, mylar rips every now and then and its very very frustrating.
- stretching while heated cant be done its either heating then stretch then reheat etc..... annoying as well
- apply mylar to jigg takes long and is potential another step where you can rip it.

so i kind of have to build the other jigg, or at least a spin off.

the drawing shows how the thing would work. i left the clamping part of the mylar out since this picture is about dimensions.

it actually works like a pulley system.

The front ring where the mylar gets attached to is 50mmin diameter and the bigger 1/4 circle is 320mm in diameter at this point. so its ratio is 1 : 6,25 . so hanging a weight on it of 1 Kg it pulls on the mylar with 6.25Kg , that is way to much.

as i recollect the 57 stretch jigg used 45 Kg for the 6 micron foil. you can imagine for the 3uM we wont want to come anything near that value or it rips :)

so i actually thought of making weights of around 1 kg from molten lead in water drain pipe of a 40mmm diameter. inner diameter is around 34mm

so surface area is 9,07 cm2 if i make them 10 cm high i got 90 cubic cm. 90 cubic cm filled with lead is +-1Kg.

if i hang this one kg on the current drawing i end up with 6.25kgz of pulling force... times how many clamps i can fit on the table. my guess is around 40 or so. that would result in a total amount of force acting on the foil or 40x6.25 kg :) haha 250 Kg well thats only about 5 times the amount needed for a 6 um foil :)

So i can reduce the ratio, by either making everything smaller, or using less weight. or a combination of both to still be able to accurately add small weights to get the desired tension.

Last option is not making the large wheel smaller but the smaller bigger. this reduces the ratio torque wise. but gives the clamp a greater length it can pull while being complete linear. with this setup it can only pull 4cm, but on the opposite side of the clamp there is exactly the same clamp pulling in the reverse direction so in the end it can pull a maximum of 8cm. i hope this is enough. accordingly to the data sheets mylar only stretches for 3% normal width of 3Um mylar is 680mm so it will only stretch as much as 20mm in total over its length. thats leaves me 60mm for positional errors when putting the film into the clamps... think that would be doable
 

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I haven't read everything, but an interesting idea I saw elsewhere for tensioning was to hang empty jugs around for weights and add water to them incrementally (like torquing head bolts), so weight is never excessive at any given point. Ignore if non-applicable.

it is usefull, i want to make the small tests with water botles. since adding a bit more water or sand is more easy then forging a new weight of lead :) the lead is only for the end result when you know what weight to be used.

the normal jig with clamps and weights relies on having the same amount of pulleys (pricey) , and you have to open all clamps by hand. also the first few clamps are fidling work because the mylar gets pulled by one weight and you have to clamp the opposite clamp so it wont all just fall down the table
 
well bought a pull scale. nice stuff for only 10 euro it measures from 4 grams to 35 Kg :) awesome .

well i rigged it between the prototype pulling thingy and clamped the scale.

Thig prototype was even larger the 1/4 circle diameter was +-400mm instead of 320, wich in theory makes the ratio to the small circle that holds the mylar 1:8

The weight of the wooden contraption alone pulls at 2.3 Kg as seen on the scale.

no lets see what it does when added mass

i added 300 grams the way i would attack the weights in the final rig.. so 2.3Kg is the default. lets see how much increase i get from the 300 gramms.


well it readout was +-4.5 Kg minus the 2.3 Kg that leaves us 2.2kg increase from 300 gramms added. 2.2/0.3Kg = 7.33 ratio. well thats pretty close to the calculated 1:8 ratio. considering the measurement og the weight was not extreme accurate and does gets amplified by 8 to small fault becomes a bigger one.


so successful experiment. ratio theory is correct, and clamp could work so we can move on :)


here is a small video, i try to let you see how it could work in the end.

https://youtu.be/GDOrKXgQ2ww

don't mind me not finding right words in English :) i have this when recording myself allot :) hehe oooh and dont mind the mess.... i go ballistic when trying stuff so it gets messy quick :(
 

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Some machining later. i milled my clamps and rings that will go on the 1/4 circles.

just a few ofc not all of them at once. i try to get one side complete to see how all works.

still there will be 12-14 clamps on the longs side of the jigg so 14 times 2 for every piece you see. this is just 1/2 of the longs side items i need. its not the machining thats anoying its screwing every piece to the table inhaling large amounts of dust ;) , and getting the wood by bike..... on a windy day i cant get 2 plates of wood 120 by 60 cm by bike :) sop yesterday i did not get any. today i got some 12mm for the clams and rings :)
 

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so added the rest of the components to the clamp. and coated the circles with 30nf from 3M . this wil leave a pretty sticky surface so the mylar wont slip. on the clamp itself i added double sided 0.5mm foam tape. also sticky against any creep or just sliding between the clamps.

in small test i could not pull 6um mylar out of the clamps without tearing it. i recon i wont need that much force in normal conditions, so the point where the rubber band is might change according to hom much force i need to clamp mylar, if less is enough i change the spot so they open more easy

hope it all works out, its quite the undertake to make, an after all not so simple jigg :)
 

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