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Old 4th November 2015, 05:29 PM   #1
WrineX is offline WrineX  Netherlands
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Default My take on a stretch jig

First of all why ?

well i ran into some problems with the following jigs.

1. Tape..... well just plain random.
2. Tire Jig, nice but somehow loses tension, either tape is or the tire is. also when heat treated membrane the jig wont pull it straight to the required tension but the mylar just slacks.
3. weights clamps and pulleys. this is the one i am after but!, i want it to be easy in use. and the option of automation the opening of the clamps. there is no fun in opening 40 clamps and putting the mylar in one by one. further to much pulleys that are expensive, and to much weight needed. lead is still not insane cheap so i would love to not spend 100 euro on weight.(ofc this depends on your application, if you need to make allot and money is no issue hell yeah !)


Dont mind my shitty modeling skills but i hope i can explain what happens.

This is my first iteration.

First of all the green circle will fit on a metal shaft 22mm thick, the blue part has a circle as wel atached to the blue structure, so its green circle blue circle and green circle.

The red part will be the clamp holding the mylar on the green circle. you can slide it downwards with a leaver(red). there will be 2 of these clamps one on both ends of the blue piece.

the black line between represents some rubber bands..... the pivot point of the clamp is all the way to the left. the middle pin is just to keep both clamps (on both sides of the blue thing) together and to lock it in the open place . as seen at the bottom, since the rubber bands pull up but as well to the left. so when you force the leaver downwards(the red thing) at the end (to the right)
it will engage in the lock position. also it has a leaver of around 2 to the pivot point so any rubber bands force wil almost equal 2 times that, the leaver on the right (red has almost 4 times the ratioj so it will be pretty easy to pull the clamps open)



now for the blue part. why is this 1/4 of a circle?? think of it as a pulley, but only 1/4 of it. just like a pulley or a wrench, a wrench increases torque on the bolt. but when forces are not at a 90 degree angle(on the end of the wrench) torque is lost. and allot of it.

Click the image to open in full size.

If i hang a weight from the top of the 1/4 circle with a rope down, and use the 1/4 circle as a pulley, the force it puts on the green donuts to turn backwards will be equal over the entire 1/4 of the green circle. but amplified. by the arm length. in this manner i could use lower weights, and save money on pulleys as well. wood is dirt cheap

See the blue part as the wrench, when you have a wire with a weight on it lying on it as if it is a belt, the angle will always be 90 degrees


if you would build a ramp to put the 1/4 circle back to this position you could automate the the opening of the clamps as well with the same upwards motion. (like a ramp or something)

any good ideas please tell me, im breaking my head for like 3 weeks to find a solution that does not cost 100000 euros to make, and could be automated and could give same results time after time.
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Last edited by WrineX; 4th November 2015 at 05:54 PM.
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Old 4th November 2015, 05:39 PM   #2
WrineX is offline WrineX  Netherlands
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Oh in this case linear motion is only as far as 1/4 of the circumference of the green circle. that is 47 mm for a 60 diameter mm circle. you can increase the circle but lose torque.
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Old 5th November 2015, 04:12 PM   #3
WrineX is offline WrineX  Netherlands
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Oke i woke up this morning got to work and sat in the train...reread some of my posts,,, and this might be the best post of a contraption drawn in a 2d picture with text to explain what i try to do and. THERE IS NO WAY anyone going to understand it haha i had to be drunk when i wrote this (well i know i was) so i will mill some prototype maybe that explains a bit more. still sober(kind of) so There we go to the cold shed

here is the tool path of the contraption
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Old 5th November 2015, 11:22 PM   #4
WrineX is offline WrineX  Netherlands
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Well i finished the milling before i left home, and now took some pictures. hopefully this explains more


still managed to **** up making the tool path. first of all somehow the circles inner dimensions is not 22.3 mm but 21.7 so it wont fit on the metal pipe. further, one drill hole that is used as pivot for the clamp got misplaced in the tool path program (cambam) so it wont fit but both are easy to correct and should not be a problem in the future.

the clamping force with 1 rubber band on each side is pretty high thats good news i will add foam or rubber glue on the clams to increase friction so stuff wont creep.
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Old 7th November 2015, 10:59 AM   #5
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I'm intrigued by your jig but still a bit confused on it's operation. Perhaps if you could show it in the larger context of actually stretching a diaphragm, I might then see the light and say "wow, that's cool!"
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Old 7th November 2015, 03:57 PM   #6
WrineX is offline WrineX  Netherlands
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yeah i might make a 3d drawing because, i need to make 30 more of these to see if it actually works. that kinda sucks haha
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Old 10th November 2015, 08:38 AM   #7
WrineX is offline WrineX  Netherlands
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Ok i gave the tire contraption one more go..

But i had a nother problem, which it thought i fixed.... i tape the mylar with double sided tape on the bottom of the jigg. i noticed creep of the tape and even complete failure. now i added adhesive on the wood, so the tape wont slip as much. but in my latest test this was the result the next morning. so complete failure at some parts and minor on others.

It only takes a very very small creep or loosening of the tape to screw up my test results.

I tested on this same jigg with the same tape a :

1. Normal stretched Mylar.
2. Heated Mylar then stretched.

It gave some nice results. BUT since this morning i discovered this tape being as it is..... both tests are compromised. the lowering of the resonance could well be the tape sliding ever so slightly.

before i make this weird looking jigg i want to give this more simple method one more change.

Whats next! i will make a piece of wood that fits the bottom of this jigg, butis slightly wider. then the wood that holds the tape now. i will add the glue again to give it some more friction and then i will be using 32 clamps to hold the mylar stuck to the wood. i used these clamps once the same way as the original stretch jigg from quad they will hold on to the mylar no mater what, it will break before the clamp will let go.

If this still drops res frequency, its either the tire losing air, or the mylar overstretching.

i got high hopes. its a cheap and simple method of seeing whose to blame! for now its the tape and maybe something else. lets rule one out !
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Old 10th November 2015, 01:09 PM   #8
WrineX is offline WrineX  Netherlands
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So , altered the frame to accept the clamps on the inner rim.

picture 1 i put Mylar on the floor and put the jig on top of it, wrap the mylar around at all sides, and use clamps to hold it in place. i might need a few more, if i can find some. another 12 or so will be more then enough.


picture 2 is the Mylar stretched with the measure mic on top of a stator. i look for the desired resonance in this case just a random high value and get my timer going to remeasure after 10,20,30 minutes then 1 hour etc. to see how much it drops.
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Last edited by WrineX; 10th November 2015 at 01:17 PM.
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Old 10th November 2015, 04:42 PM   #9
405man is offline 405man  Scotland
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How are you measuring the resonant frequency

Stuart
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Old 10th November 2015, 04:46 PM   #10
WrineX is offline WrineX  Netherlands
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there on the translucent box, there is a wooden baffle with a woofer in it. i play a sweep from 20 to 120 hz, when swept there will be a peak of the resonance of the foil. the mc is really close to this foil so it will detect it easy as a big hump. in the frequency measurement

i like this method more then pulling on tape and such. since in this case it does not matter witch material you use(3 um 6 um 12 um), you measure what the resonance is of that particular membrane


almost forgot to mention the hole in the jig has the size of an quad panels foil area(without spacers), otherwise this would not be accurate.

Last edited by WrineX; 10th November 2015 at 04:51 PM.
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