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Airsoft Tension/Compression Mortar

I've been looking for a way to make an airsoft mortar which uses either tension (by way of wrist rocket or similar bands) or compression (by way of a spring). I'm thinking it'd be similar to the trip mine here:https://www.instructables.com/id/Build-an-Airsoft-Trip-Mine/If anybody could give me ideas or post an instructable, that would be great. I don't want to use air compressors or light anything on fire, because it's just not practical mid game (that would also be just a manipulation of a potato gun). I also think compression or tension could be a lot safer if done properly. Any ideas on making shells to hold airsoft bb's and properly disperse them when fired would be great too.P.S. I'm totally willing to offer my input on the situation if somebody else wants to collaborate on such an 'ible.

Topic by spectral08    |  last reply


3d Printed Concrete Forms for Architectural Post Tensioned Concrete Sculptures

I am looking at the feasibility of 3D printing concrete forms to make a staircase that goes up a 4' retaining wall. The forms would be cylindrical, split in half, and during the pour would be supported using a wood support system. Ideally I would have one main highly curved support "column" (think more of a snake or spaghetti noodle) with then stairs that slide in via a mortise and tenon type connection. The stairs would be poured individually in a separate production process than the main support. I plan on using a combination of a wire mesh, rebar and tension cables for the concrete reinforcement. The tension cables would run the length of the main support beam and would be hydraulically tensioned just before the formwork was removed. I have ample concrete experience as a civil engineer and a construction manager but this idea seems like I need some outside input.Does anyone have any experience 3d printing concrete forms. What is the best material that will hold up to the moisture and high alkalinity of concrete?At this point I have no real conceptual drawings but I'm looking to see if any similar projects have been attempted and hopefully learn and improve on them!

Topic by cjh83  


K'Nex sniper rifle contest!!!

K'Nex sniper rifle contest!!!the first contest for this group. this contest is not intended to give people time to make a sniper rifle now, but already have a sniper rifle made AND posted. all you have to do to enter is to put your instructable in the group. this saturday i will make another forum with a list of the entrants. then the voting will begin. so to enter you1. have to have a sniper rifle2. have a insructable for it.thats it.3. it has to be made out of knex only, they can be modified as broken but not melted down to make a barrel or anything like that.4. it can only use compression(string) torsion(string twisted) and tension(rubberbands), no air compression allowed.so good luck to everyone!for inspiration, i will put a picture of my newest creation, MY SNIPER RIFLE! it is finished and i will post a instructable soon.(i won't enter it into the contest though)

Topic by dsman195276    |  last reply


polyester rope as bow sring? Answered

I will soon post an instructable on how to make a reverse compound crossbow. but i've been stuck into something which is quite basic, the string that needs to be used,  the crossbow will have a draw weight of about 150-175lbs. i have came across a rope  which has a diameter of 4mm, and claims to withstand a tension of 1500N(150KG) I just want to know if it would be ok to use the rope,  i  know that it is very important to use a string specially made for bows and crossbows but we all like it dangerous(especially if you're broke) thanks in advance

Question by ARJOON    |  last reply


Is there a pure knex gun i.e pistol, rifle, crossbow? Answered

I'm looking for a pure, yes pure knex weapon. 100%. I heard that someone made one but I didnt understand the mech so I need pictures. If you show me how to make it and it is good I would be grateful, spread the word of giving it 5* winning a contest and so on. Just post images or instructables. THE RACE IS ON! If you can make one faster than me I will give full credit.I made one but its very weak, it works as if the tension from pulling a connector back shoots forward. Ty for the knex catapaults but i need guns like pistols instead of those catapaults and such.

Question by knex_mepalm    |  last reply


Freestanding LEGO Brick Tower Build Challenge

Not sure where this would fit - so square pegs it is!I'm interested in starting up a competition to build the tallest freestanding LEGO brick structure and I think Instructables could be a great place to play it out. As you've all probably seen, recently students in Vienna built the tallest LEGO tower at an amazing 29.48m. Photo at SF GateThe catch with that tower however, as pointed out by many in the blogosphere, is that it is 'supported' by wires, which keep it from falling in the wind. While they may just be a safety feature and not part of the structure, I agree with many who have said this is not really a freestranding structure - for that it would be LEGO brick and nothing else.So now, the challenge: Post an instructable showing how you built your tallest LEGO brick freestanding structure. This way, in the spirit of the DIY community, the next person can build off your design and improve it to create a bigger tower. Instructables should clearly show your method of construction, however there is no need for a brick by brick play. If you use a special technique to build the major components of your tower - such as a feature that allowed you to reach your desired height - highlight that for sure. For a baseline, I've found it very difficult to find any postings online of the tallest LEGO freestanding structure out there. Most publicity has been on these mega towers supported by tension cables. I was however to find one student's project here which topped out at a very modest 11 feet. 11ft TowerI hope to post my own attempt to beat this tower shortly - however if you've got the bricks - start building!! Then please link your instructable here.If you have any verified information on previous FREESTANDING builds out there, please post them too!Thanks!Daniel

Topic by bodgetastic    |  last reply


Black & Decker Bandsaw, Model DN330-H2 Manual.

Hi Folks. I have posted this in questions but that was two days ago & it still has not appeared so I figured it wouldn't hurt to try in the forums as well. The following appeared on the Cafe pages of my local FreeGle group this morning & I wondered if anyone in the wonderful world of Instructables could help. Ladies & Gentlemen I've acquired a Black & Decker Bandsaw, Model DN330-H2. It would be very helpful to have a copy of the instruction manual and I should be most grateful if anybody who has the manual for a similar model would allow me to have a copy. I've used bandsaws in the past but it would be really useful to know how the manufacturer suggests that blades are fitted and tensioned. I've tried the B&D; website and all I can find is an "exploded" diagram and a parts list. If anyone has a copy of the manual for this or any other bandsaw in the Black & Decker DN330 range in a format they could email me or perhaps a link to a web site it would be truly appreciated. All the best. N.G.

Topic by Nostalgic Guy  


The Kinetic Rifle V.1

Here it is: the bullpup, tube mag, bolt-action, pump-action, sling semi-repeater.  This is by far my most favorite gun I have ever built.   The reason I call it a "semi-repeater" is because while it has a magazine, loading it involves a two-step process of pulling back the rubber band and then pulling the pump.  Therefore you don't have to load each individual bullet into the barrel by hand, the pump does that for you, but the band still has to be pulled back manually.  The gun was originally intended to have the pump bull back the band as well, but to do so the pullback distance would have to be greater, requiring a larger barrel to house a longer pullback, requiring pieces I just don't have.  When I get the pieces I am going to make the pump pull the band back, and I will post that as the V.2. What I love about this gun is that it takes many concepts and combines them to work in sync with one another.  I also like the fact that there is almost no limit to how powerful you can make this gun, since the ratchet can hold an incredible amount of tension.  Overall it is an incredible gun, averaging ~60ft with the 1 band used in the video.  Though it isn't the most reasonable choice for a war (it only holds 4 shots in the mag and is huge), it is well on its way to becoming the most efficient knex repeater out there. -Kinetic iMovie wrecks.

Topic by Kinetic    |  last reply


Help with some engineering issues on a folding tail gate ramp?

I'm building a folding ramp to replace my tailgate on my truck. It's going to be used to load/unload a ztr lawn mower. (It's been built primarily from discarded bed frames, with the addition of some expanded steel grating.) Because these mowers are back heavy, and low to the ground, a longer ramp is needed than you need to load a conventional mower. My solution is a spring loaded 8' ramp that is comprised of two 4' sections that fold down and out. It functions, it fits, the mower goes up and down it ok. The problem is that it is so heavy, that after it comes down about 2/3 of the travel, it is very difficult to control. When it comes down hard, it puts tremendous stress on the center - where the two sections of ramp meet. It can be hard enough to break it. I know my welding isn't the best, but that's really not the issue here. This is a design problem. I'm going to post a few pictures, to better illustrate my situation, and to show some of the things I've tried to soften the blow. The picture of the partially folded ramp was taken at the point where it begins to get difficult to lower without losing control. So, to clarify, I need a way to lower and raise the ramp with more control, and or soften the blow towards the middle.  The springs I'm using are 140lb garage door extension springs, the largest springs available at any big box home center. I need to get this finished yesterday, so I'm going to try some things while I'm waiting for a response, like move the springs back further in the bed to put more tension on the whole thing. I'll also post this to the welding web forum, but I started here because I've got a lot of faith in the ingenuity of the instructables community. If we get the bugs out of this thing and anyone wants it in instructable form, I'll do my best. Thanks for reading the War and Peace of ramp questions. -Amir

Question by Amir    |  last reply


I Have My K'nex Back!

Well, I've got some explaining to do.  It turns out my K'nex was never actually sold.  My parents hid my K'nex from me, telling me they sold it, only to give it back to me extremely recently under one stipulation: I can't build guns anymore, unfortunately.  Trust me, I'm not complaining; I'm just ecstatic that I can build with them again.  I'm sorry for the huge lack of activity lately, but I haven't had that many ideas before I got my K'nex back.  My first K'nex creation in a while is this really cool compact lock.  Being K'nex, of course, I wouldn't advise that you lock anything with it, but it is nigh on impossible to open with force unless the button is pushed, or you deconstruct the lock itself.  It is powered completely by tension, and doesn't need any rubber bands or power source other than the K'nex from which it is made.  It is also extremely fun to mess around with, and I could spend about an hour just fiddling with the mechanism; such is my attention span.  I'm thinking about working on instructions, but I wanted to see what you guys thought of it first. The second thing I'd like to share with you all is this 3D Owl I printed over at Fab Lab in Chicago at the Museum of Science and Industry.  I would like to sincerely thank Matt Chalker, the head executive of the Museum of Science and Industry's Fab Lab, the museum itself, and all that make Fab Labs possible for such a wonderful experience.  Along with this owl, we made many things out of wood via the wood laser engraver, and finger puppets for each member of my family, depicting our faces, of course. (I have more pictures of both the owl and the lock.  If anyone is interested, I could post them in the comments.  They're pretty much the items on different backgrounds, though.) Enjoy! -DarkOwl

Topic by DarkOwlProductions    |  last reply


Can a cracked guitar neck be fixed?

Hi, I finally signed to Instructables. :) My colleague is a big DIY guy and that's how I came across Instructables. Today, while searching for something I came across homemade recipes for musical instruments and that really hooked me on. Especially the one on turning an 6-string acoustic to bass acc. :) I had tried learning the guitar but didn't want to spend too much on the instrument, so I bought a second hand one from a garage sale (proceeds were for the city's stray dogs - so for me it was a bit of a win-win...almost :) ) What I realised much later is that: 1) The wood under two of the tuners (on the under/ventral side of the guitar) has splinters 2) One of these tuners has lost a fastening screw because the hole in the wood has widened and splintered a bit 3) the base of neck, just before the curve block that connects to the box, has a 1-2mm crack running across it (horizontally) Question is, can these issues be fixed so that a beginner like myself or someone who really doesnt have the money to own a guitar but wants to learn can still use it for some time? I never found the time to go to a music shop to have it checked. I also feel they will probably turn me away because they are more interested in selling guitars than fixing them. I really dont want to just throw it away. Second hand it may be, it just doesn't feel right... Your inputs would be greatly appreciated. Thanks! P.S.: Am at work right now but I will try and post images of the guitar as soon as I can. I had taken photographs of it a looong time ago. As a result, tuning goes off every now and again. On a colder day, tension increases and the crack widens. Update: Terribly sorry for the delay in uploading the pictures. I had a set that I had taken a year or so ago but I seem to have deleted them. Just got some time off work, here are the pictures. The crack, which I had earlier described as horizontal, is in fact, vertical. So much for my memory...

Topic by aristarkhos    |  last reply


"Knex War?" (The Math Bit)

Hey guy! Sharir1701 here and I just want to start off by saying that I'm not back into Knex warfare, but I have something to show you. About a year and a half ago, I posted this forum topic. There I explained why, in my opinion, just adding more rubber bands to a gun will not actually produce an overall better gun (past a certain, low point). I'm not getting back into that discussion, but I simply wanted to share something regarding that. Don't ask me how or why (I don't know, myself), but a few days ago I suddenly remembered that old assumption I made. Being a perfectionist, I hate leaving things unfinished or unexplained (particularly math and physics related inquiries). Back when I posted that topic, I had little to no formal Physics knowledge, and the beginnings of an understanding in mathematics. Now, I have a much broader understanding, much more knowledge, and an ability to explain and evaluate what I once couldn't. Anyway, what I'm trying to say is, back then, I didn't have the tools to prove my claims. I firmly believed in them, but I couldn't confirm them. It's nothing complicated, but, like I said, just something I'd like to share. I also want to point out that, although I personally don't enjoy spending days upon days perfecting a little plastic mechanism for firing (mostly) non-aerodynamic plastic projectiles, anymore, there still is a warm spot in my heart for the craft I once loved. More to the point - this is a small article just showing something I did in a few minutes the other day, that helps me to better understand how a Knex gun works. I hope that in writing this, more people that are still building guns, will think about more accurately calculating certain things about their guns to help improve their performance and hopefully produce more efficient guns. The final note I have is that I'm about to show you equations, all of which can be plugged with real, measurable numbers, to calculate to a high degree of accuracy, the forces at play. This means you can actually calculate the most efficient layout for a gun, and also that in designing your next, you will be able to use these equations, and many others, to find optimal solutions to your problems. So, what's all this fuss about? Well, basically, I just proved with a few, painfully easy equations that my conjecture about the forces in a gun, working on the pin, is true. I'll just get to it: First, Hooke's Law states that the force necessary to change the length of a spring or a (tense) rubber band is F=K*dX, where F is the force, dX is the distance you want to change, and K is a constant number, that each rubber band (or spring) has. You can quite easily measure both of these. For rubber bands connected parallel to each other (assuming they are the same type of rubber band, which ever is your chosen standard), this equation becomes F=K*dX*N, where N is the number of rubber bands used. dX and K are both constant in the regards of the pull of a pin on a standard Knex pin gun. Therefor, the amount of force required to cock a pin (pull it back to it's full length) is linearly correlated to the number of bands you put on your gun. Next, if we examine Newton's equation of work and energy, W=dE=F*dX, where W is the work, dE is the change in energy in your system (input from an external force, i.e. your hand), F is the force applied along a length of movement, and dX is that length. Let us define the base position of the pin (not cocked, minimum tension on the rubber bands, fully in the barrel, etc.) as having 0 energy. This then means that the work applied to the pin by cocking it is equal to all the potential energy it has. From this, plugging in the force, we get Ep=K*(dX)^2*N. Let us assume a perfect world, where we neglect the effects of friction and air resistance, and assume all the momentum of the pin is transferred into the bullet as it fires (I will briefly mention in the end, why everything we're neglecting here just strengthens my claim in reality, but let's continue for now). After being released (in other words, shot), the maximum velocity the pin reaches right before the end of it's journey can be found using the equation for kinetic energy Ek=1/2*M*(Vmax)^2, using the fact that (again, neglecting energy wasted as heat due to friction) the energy is conserved, as no external force is working on the system, which then means that Ep,start=Ek,end => K*(dX)^2*N=1/2*M*(Vmax)^2 => Vmax = sqrt(2*K*(dX)^2/M) * sqrt(N). The first sqrt term in the final equation is all one big constant (again, K is the ratio associated with the rubber band, dX is the distance the pin travels, and M is the mass of the pin), meaning we can conclude that (C for constant) Vmax=C*sqrt(N). Finally, force applied by a moving, massive object can be calculated using Newton's second law, F=dP/dT (P is the pin's momentum, T is the time it takes for the pin to go from velocity Vmax to 0, transferring all it's energy into the gun and the bullet, but as I said, let us assume all of it goes into the bullet), or F=M*dV/dT (M, mass of the pin, dV is the difference in velocity, Vmax-0, which is simply Vmax. This is because P=M*V, which means dP=M*dV, ignoring relativity). So, F=M*C/dT*sqrt(N). The time varies slightly, but insignificantly, so let us assume it is a constant. So that's it. The force exerted by the pin on the bullet is some constant (calculatable, as mentioned and as shown), times the sqrt of N, the number of rubber bands on the gun. So there you go. Just a little something I did out of the blue the other day and thought I would share a proof of my conjecture from what feels like eons ago. I hope you enjoyed. Finally, I would like to tell you guys, perhaps as a little tease, since I'm not sure if I will ever upload it, but I have made 1 more gun after I stopped posting. I have already slightly teased about it in my user info. I guess I'll tell you guys what it is if I'm already posting something here again :) Possibly my most enjoyable, most well received, and quite innovative gun of all time? The REMPAR-2. I built the REMPAR-3 (I was also going to call it S5 when I thought about posting it). In a brief summary, it's a pump action, chambering (or bolt action as I and many others falsely used to call it), magazine fed rifle, that's only 5 layers thick all over, except one tiny area where it's 8 layers thick (1.5 extra on either side), as a reinforcement, not necessary if you use less rubber bands. Oh, actually, there's another small necessary area where it's 7 layers thick, but it's tiny and doesn't make the gun look bulky at all, and who cares. Plus, the one is around the pump, which looks quite natural, and the other is "disguised" as a detachable sight (not really detachable) that also looks fine. It also looked fairly good for a gun that I made, it used (if I remember correctly) a grand total of 0 broken pieces, which is a big accomplishment for me (the mag has some broken white rods, but fuck off), and it worked flawlessly, reaching ranges over 80ft and being able to go at 2-4 rounds per second, depending on your skill level with it. In other words, I could shoot 4rps; My girlfriend, with no experience or practice, could do 2rps, which says something about the gun's comfortability and ease of use in my opinion. It shot blue rods up to an accuracy of about 5x5cm (2x2in) over 30ft, which is amazing for a Knex gun, and it was truly super comfortable. It wasn't even long at all, which is saying a lot, looking at some other people's attempts at 5-wide pump actions (I may also be guilty of an attempt several years ago). Being quite short and only 5 wide, it is also quite light. I'm sorry, I just really liked this gun, I think it was truly my best creation ever (of course, the S3 is by far the most innovative gun I've made, but it's mostly a concept gun, not meant for real effectiveness). I may post it in the future, but I'll make no promises. I suppose I won't leave you guys completely hanging and take a picture of it. Oh yes, there's also a neat, fun little thing I did, originally because I saw no other option, but then I actually really loved it. I'm talking about the mag-lock. It locks automatically (there's a band on it, but it ripped a long time ago, so...) and the mag cannot fall out. Then you pull on it with your middle finger, similar to a trigger, and the mag just drops right out. Love it :)

Topic by Sharir1701    |  last reply


Oodassault 3.7

Yeah, I've done this too much. 3 different models, 7 revisions for this model alone, 2 already posted. The 3.6 was satisfactory but I noticed there were still some problems for some people and it required some tweaking to make sure it worked right even though it was pretty reliable when it was set up right. This one is a lot more user friendly. I changed up some things so it's guaranteed to work without all the tweaking. It was just a few minor mods really. You won't probably catch any changes from the image alone at first so I'm obviously going to list them. -The simplest but probably most effective is adding another light grey in the middle above the magazine. At first I had a gap there to make stripper clip loading easier. However, it made the ammo shoot up a little higher and sometimes would cause it to spin out faster. I also suspect this may have been the reason a second round would be dragged out if the magazine wasn't set up right. -There's a green rod and spacer wedged in between the bottom of the magazine where the tilt bands are placed so that it doesn't squish the mag pusher. This allows for a weaker rubber band on the pusher so there's less chance of it exploding. -I changed how the the magazine rests against the rest of the gun by using mini knex adapters. I'm not sure if this is required as far as reliability goes but I suspect that it may have been why some people's guide rods were shot off. The magazine tilted in ever so slightly but just enough for the ammo to catch the rod. The mini K'nex also have a larger gap so it's a little easier to slide ammo in. Not too much of a difference but hey, whatever works. -The one you guys probably will like best. I changed the tilter just a little. It requires a rubber band to stay up but I didn't think it was a big deal. It allows the magazine to tilt out farther and the red connector can grip around an orange connector on the trigger guard in such a way that it takes some of the stress off your finger. This means you can use more tension on the magazine to make sure it stays shut without wearing out your finger. -Finally, I knew this for a bit but decided I'd finally show you that you can use green rods instead of white rods on the top middle three holes (the bottom pairs and the front and back pairs would be required to keep the gun sturdy). You can use green rods then instead of black Ys to block the green rods in the holes. I used this method for a simple rail like thingy and added a custom sight. It's more for looks than function but it actually works quite well. So yeah that's it. Between all the mods, it's guaranteed to work perfectly now as far as I know. Nothing has gone wrong since building the gun with everything changed. No magazine explosions, double shots, or anything that would otherwise be undesirable. Also, it's a little more accurate and gets a bit more range I'm guessing thanks to slightly more stable ammo. I'm not trying to make this sound super hyped. You should just know that I come from a long line of descendants whose ancestors built the Great Wall of China.

Topic by TheDunkis    |  last reply