# My DIY Pneumatic String Stretcher



## shanedut (Sep 28, 2009)

Here is my Pneumatic string tensioner that i have made. It is made out of a 63mm x 100 mm cylinder with a 16mm rod. Or 2.5" x 4" by 5/8" rod and its rated for up to 130 psi. The cylinder is mounted on a piece of 1/4" thick 3.5" square tubing. I have not had an easy time finding springs or thrust washers easily here in Canada and have not felt like having to machine parts and pieces. So this was my way around that and with a little thought you could do this with no welding at all. I thought of this idea after seeing the Specialty Archery server and stretchers. It will tension up to 450lbs at 100psi, 400 at 95psi, 350 at 85psi and 300 at 70. The Cylinder at 125 psi should be capable of 500 lbs but i see no need to go any higher than 350. I designed this system to work easily off of any air compressor that will produce 100psi. The nice thing with it is no matter how long the string is on there it always has the same tension because the air pressure is always constant.

Here are some pics


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## shanedut (Sep 28, 2009)

Here are a couple more pics


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## Flame-Tamer (Mar 1, 2009)

How bot a list of parts


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## Guardian Shoote (Jan 11, 2007)

Neet


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## shanedut (Sep 28, 2009)

The parts needed for the Cylinder are a 1/4" silencer for the one end mostly used just to keep dust out of that end of the cylinder, 1/4" regulator i took mine off an old air compressor, 1/4" valve (ball valve would work), 1\4" tee, 1\4" drain valve or pressure release valve either will work. My cylinder had 3/8" ports so i had to have reducer bushings. to adapt it. The regulator is not needed you could regulate it off the compressor. I use it because i have a serving machine like SDLAW posted on here except it has this same cylinder set up. This way i can have 2 different cylinders hooked up and they can each be independant. I used simple plug and play air hose but its not needed. Then for the cylinder i used the mounts made for it, and for the post hooked to the rod i used the normal rod tang,just cut they eye off of it and drilled and pressed a 1/4" bolt in it and then ground the head off. The other end is pretty straight forward just like any other stretcher.

I used a 4 inch stroke cylinder but it does not need to be that long it only needs to be 3" at max 2" would probably work but, i like to have a little room to play and cost wise its only a few dollars more. I have around a $120 dollars in this one and thats without really shopping around. I bought all my stuff for it at princess auto in Canada. Its not the cheapest but they had everything. I'm sure if you shopped around at Fastenal and a few other places you would find it cheaper. 

I also forgot to mention but you can spin the post on the cylinder while it is loaded to about a 100lbs so you can twist your strings if you wanted with this set up also.

Shane


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## ruttnwapati (Sep 22, 2008)

I like it. Nice job


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## BowBaker1640 (Aug 6, 2010)

thank you i just have a few questions. can you show where you attach you air supply and do you happen to have a part number for the cylinder?


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## BowBaker1640 (Aug 6, 2010)

can you also tell me what they mean by the bore? i see it has a 5/8" shaft but i'm just not sure where they are getting the measurement for the bore or if that really even matters. thank you


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## BowBaker1640 (Aug 6, 2010)

the reason i'm so interested in this is i'm in the middle of rebuilding my string jig and i could set it up like this very easily once i figure out the details that i'm asking about. thank you


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## shanedut (Sep 28, 2009)

If you look in post #2 you will see a green hose thats where the air comes in. The air comes in to the left of the regulator in the pictures. I used simple plug in hose because i know it will be plumbed in there and stay at that end of the uni-strut. You really do have to have the Tee and the Valve to be able to release the pressure off the cylinder just in case you were wondering why it was there. The bore size of the cylinder is just the inside size of the cylinder that the piston rides up and down. The bore also determins how much tension is applied. 

The part numer on the cylinder is E-MC TBC63X100 its a cheap chinese cylinder i'm sure, there are no other markings on it.


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## Randy McRae (Dec 25, 2008)

Am I understanding it, that you are putting 100 lbs. of pressure on the string then being able to twist it up by turning the shaft? If so do you think it will have any affect on the seals?


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## BowBaker1640 (Aug 6, 2010)

ok so basically the bigger the bore the more air it takes to operate? i just want to make sure i have all this info right so i don't buy the wrong air cylinder. thank you


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## shanedut (Sep 28, 2009)

No not nessicarily more air it will take less pressure to produce more tension. So a 2.5" bore will produce more tenison than a 1" one and use less air pressure.


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## HOYTINIT (Aug 28, 2012)

BowBaker1640 said:


> ok so basically the bigger the bore the more air it takes to operate? i just want to make sure i have all this info right so i don't buy the wrong air cylinder. thank you



You won't even notice the difference...


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## BowBaker1640 (Aug 6, 2010)

ok see this is where i will need the help so that i can find the right cylinder on ebay or someplace like that. thank you


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## Gunner7800 (Jul 11, 2007)

Pretty cool setup. I think I would find a way to lock the air cylinder and put the twister on the other end. That way you could use some sort of crank handle, would be easier than turning the cylinder by hand.


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## HOYTINIT (Aug 28, 2012)

BowBaker1640 said:


> ok see this is where i will need the help so that i can find the right cylinder on ebay or someplace like that. thank you


just look for a 2 or 2 1/2 x 6" cylinder ..ebay is probably the cheapest way to go


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## Cheese1 (Sep 6, 2009)

Very nice, well done.


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## BowBaker1640 (Aug 6, 2010)

Gunner7800 said:


> Pretty cool setup. I think I would find a way to lock the air cylinder and put the twister on the other end. That way you could use some sort of crank handle, would be easier than turning the cylinder by hand.


i was thinking along that idea myself


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## shanedut (Sep 28, 2009)

HOYTINIT said:


> just look for a 2 or 2 1/2 x 6" cylinder ..ebay is probably the cheapest way to go


Actually i just switch it over to my SDlaw server and turn by motor power but a very good idea for ones using this as their only stretcher.


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## dogrunner (Jul 14, 2010)

when you twist with air preasure do it build tension like with a spring or does the air keep the tension equal


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## BowBaker1640 (Aug 6, 2010)

dogrunner said:


> when you twist with air preasure do it build tension like with a spring or does the air keep the tension equal


check out the thread in arrows and strings " specialty archery serving machine " and watch the video on page 3 i think that will answer your question


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## flag (Oct 4, 2009)

dogrunner said:


> when you twist with air preasure do it build tension like with a spring or does the air keep the tension equal


as long as you use a regulator it will not build tension while twisting the regulator will let air off as it builds up so it keeps constant tension while it twist.


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## HOYTINIT (Aug 28, 2012)

if you don't use a regulator air pressure will stay constant.provided you are not using compressor for anything else or have leaks...you will not notice a thing..

it will be what ever the pressure is in your air tank


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## dsal (Dec 24, 2008)

Used shanedut idea and works like a charm, thanks shanedut.


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## BE2000 (Jul 13, 2011)

Very cool idea!


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## smokn_speed_bow (Oct 25, 2010)

Where your air inlet holes actually 3/8 npt or were they in mm and 3/8 fit?


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## shanedut (Sep 28, 2009)

smokn_speed_bow said:


> Where your air inlet holes actually 3/8 npt or were they in mm and 3/8 fit?


They were 3/8npt fittings actually.


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