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Different end-to-end magnetic calf closure system


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I had this as part of my full build last fall, but after wearing it a few times, and trooping for over 5 hours yesterday, I can now call it a successful method with confidence:

 

Magnetic calf-closure system:

Okay, I decided to try something new for my shin closures. This first set of photos is from my initial test, followed by the successful implementation of it. 

Many people have used Cricket's magnet closure system. Having trooped with some Velcro on my clone, I know that Velcro is not the most trustworthy. While I wanted to use magnets, I came up with a different approach. The good part with this method is that if it is a terrible failure, it is more removable than the disk magnets with holes method. 

My primary reason for trying a new approach is that we all know that magnets are strongest pole to pole, and have their most strength in that direction. If you have a stack of disk magnets, you slide them to detach them because it is way easier than pulling straight up. The issue with Cricket's design is that we are trying to resist the calf armor from opening side to side, and yet that is how the magnets are weakest. Update: @Scimitar points out in the comments below, that Cricket's system actually has the magnets recessed, so that the cover strip magnets lock in before connecting, which would mean they only open by pulling away against their strongest pull. So my method's only advantage is that it is all internal, and could be more removable (no drilled holes), but is not necessarily a better use of magnets. Thanks!

I had some strong cylinder magnets, 1/4" N-52 that are magnetically aligned along the length. I would put them on either side of the opening on the inside, so that they have their strong pull directed at each other. They are nearly 5 lbs of strength each, so I needed to cut that down a little, and I also didn't want them snapping directly together which would chip them over time (some of mine are already chipped). So I needed to create a sort of case around them that I could glue down. Because there will be plastic on the face, they will be a little easier to separate with that material, and protected. Here are the magnets from K&J Magnetics, and I believe I will use 24 total for the two calves:

TPkh2zH.png

 

To make the magnet pockets, I made a slot in a scrap piece of thicker aluminum by drilling two holes and filing it out. This could be made of wood as well, just something that you can press hard on, and doesn't mind some heat or pressure. For these magnets, the hole needed to be larger on all sides to accommodate the plastic, and I ended up with a 9mm x 16mm opening. It helps to have one edge bent up, so you can press it flush, sort of like a spatula. For the plastic, the cover-strip sheet that came with the kit was too thick, about 2mm, so I found some scraps I trimmed off my clone arms, and my thigh scraps from this suit will have plenty as well. That trimmed plastic is between 1mm and 1.5mm, and the thicker 1.5mm was more difficult to stretch, so the thinner is better in this case. 

I put a piece of sheet mild steel down on a scrap of plywood. This was both a non-stick surface, a heat sink, and the magnet holds itself in place on the steel. First I heated the plastic on low, until it just started to go floppy. Pressed down my aluminum guide, and got it halfway down. Then I hit it, while on the magnet, with the high heat until it just starts really shriveling (this is about 5 seconds of high heat, and rapidly gets too hot, so act fast), and pressed the guide slot down over it until totally flush with the metal base. Sometimes it took a few re-heatings to get it flush, and it needs to be so that when mounted, it glues flat to the inside of the armor, with the magnet contained.

JavqV8L.jpg

 

Then I clipped it to have side tabs for gluing (though a few will need a different shape, at the top and bottom channel shapes in the shin), and then trim one edge really close. The magnet needs to be as close to the edge as possible, so I sanded it more flush on a sanding belt (and rounded the corners). Now for my initial test. I clamped them onto the edges of some strips, and they seem to work well enough. So I made then more pockets, so I could test it on the shin halves.

p5ylXR8.jpg

 

I was most worried that they might be too strong, so I did five on each side, taped in place, right up to the edge of the plastic. I marked my stack of magnets that were all stuck end to end with two colored sharpies, red on one and blue on the other, so I could make sure one whole side was mounted with red ends at the edge and the other side all blue ends at the edge (When I do this on the armor, I will glue the magnets into the ABS pockets and mark them on the underside). I taped them all in, and tried it out, and it works really well. In fact, I think I will do six pairs on each calf instead of five, because it was not too difficult to open, but it really wanted to stay in place. If this doesn't work, I can still remove the pockets, and go with a different closure, because the armor will be un-affected.

FaWv1VT.jpg

 

 

Installing the system:

 

After my initial test of my butted-magnet system, I finally got to completing the shin armor so I could try it out. A note about magnets: they are only really at full strength when exactly touching. Even 1mm apart, and they are at about half strength. So for this to work, the pairs of magnets need to be as close to each other as possible. Because of that, I tried one method on one, and through that process came up with a better method for the second that ensured optimal placement. 

To begin with, I created a bunch more of my heat-formed "pockets", including a different type for the top and bottom edges (longer rather than wider shape because of how close to the top and bottom edges it would be). I have my 25mm cover strips all ready to use, but because of the nature of mounting these, save the cover strips for after the closure is complete. Even though my armor was pretty close to butted, it needed to be a lot closer for this to work. I started by fine sanding the edges, and a little mild heating to get the edges to meet more flush. The tops will get the mobility cuts, but I waited until after the closures were complete to know what the true edge would look like. Once I had it flush, I taped it closed matched up, and drew my marks. These marks would be on-center for each magnet pair. I started with the top and bottom, and then divided the distance between by 5 (giving me four marks between, for a total of six magnetic closures, 12 magnets in all, per shin). My number was about 63mm between each line.

zEeIDMB.jpg

 

Once marked, I removed the tape. I used some coarse 60-grit sandpaper to roughen the back side behind each mark, where the pockets would be glued.  In the right photo, you can see what my pockets would look like. I paired them up to ensure they were similar. 

GClzD7F.jpg

 

A note on glue. I know the Stormtrooper lives and breathes E6000, and for most of the armor, that glue is a great choice. For this process, you will really need speed, and quick results, so CA glue with an accelerator spray is ideal. Because I once was unsure, CA glues (Cyanoacrylate adhesives) are often called "Super Glue" and it's a clear glue that sticks really well to things like plastic, fabric, and... skin. Many people call this "Gorilla Glue" but the problem with that (or any brand) is that Gorilla glue makes about ten products, including wood glue, and an expanding glue, all called "Gorilla Glue". CA glue is the preferred name to ensure people know what to use. Now, for the accelerator spray. Zap-A-Gap makes one, but there are many types. What it is is a spray that you can spritz on a wet bond, and it sets the glue (at least on the edges) in about 3 seconds. No kidding. Like you could take a quarter, glue it to the side of your work bench, spritz the edges, and then let go. In my experience, if you quickly pried it up, the CA glue would be wet underneath for some time, but it would be "clamped" by the already cured edges while the remainder dries. This closure method relies a lot on that rapid dry time.

 

Gluing magnets into the pockets. It is fairly important to keep track of polarity for the magnets, so put them ALL in a line, and use two different colored sharpies to mark each end, so that you have (for example) a blue and red end on each, and every red wants to stick to a blue. On the pockets, mark the "center line" that is where the center of the magnet would be on the seam edge, so you can line it up from the outside. Sand the bottom of each pocket to prep for gluing. Then set out your pockets bottom-side-up (if possible, on a piece of sheet steel like I have, or some other magnetic surface to keep them from sliding or trying to attach each other. Mark them red and blue as well to keep track of what goes where. Drop some CA glue in the bottom of each, and set a magnet in each pocket, aligned toward each other by color, so you have a red side and a blue side (or whatever colors you use). If you have accelerator, you can spritz these and be ready to move to the next step:

ZXzzr8o.jpg

 

Note: the following process was what I tried on one calf, and then improved on it, so be sure and read ahead for a much better process for gluing. Start on one side and in order down one "color" set, take each pocket, and add CA glue to the bottom edge, filling in more around the magnet. Mount it in place lined up with the edge line on-center for each magnet, and as perfectly close to flush with the seam edge as you can. This works best when the magnets are just touching. As each is set in place, spritz with CA glue accelerator, and then add a line of glue around the back edge and sides of the pocket, and spritz again. Move up one side, and then down the other, taking care to keep it from shutting before everything is truly cured (I would give it at least 30 minutes to an hour). These magnets are quite powerful, and could likely pop free from un-cured glue. Here is where I found a problem, and a new solution: Once I finally put the sides together, they clicked nicely with a satisfying click. The trouble was, you can see in the first photo, is there were gaps where various pockets were too close together, which then kept the better positioned ones from touching. So I had to go to each joint, and with a small piece of sandpaper wrapped on a bit of plastic, sand them until they met flush. 

mDwaKfI.jpg

 

I eventually got it much closer, but it took a lot of fine sanding and trouble to get them to match:

5IeJ2Z4.jpg

 

My solution for a more precise alignment of the magnets: I realized that the magnets want to be close and perfectly aligned. That's their purpose. So I should use that. So I did as before, and glued one side (like the "red" side), again, as close to the edge as possible. Full CA glue on each, and spritzed with accelerator to lock them in, and then I let that side sit for an hour to fully cure. First, I taped the calf closed as perfectly as I could, with the edges tight together. Then I took the other set of pockets with the magnets glued in, the "blue" side, and put glue on just the back half, away from the seam edge. I didn't want to risk getting any glue on the seam or opposing magnets, and it does spread out a bit. So for now, just glue the back side (pictured). Then I carefully, in order, set the magnets down the side across from their "mates" and the magnets themselves snapped into the perfect spot, touching exactly. If the other side was a little over the line, they would lock in back a little. It aligned them perfectly. As I went, I would place a pocket, then do some CA glue along the back and back corners, a little on the edges (remember, nowhere close to the seam edge), and then spritz with the CA accelerator, locking them in. Once that side was done, I set it aside for a half hour to more fully cure before removing the tape, popping it open, and then gluing the remaining spots, including around the edges up to the seam edge.

B5ItxRF.jpg

 

That one went together much more quickly, and it was nearly perfect. One of the pockets had pried up a little, so had to be clamped and re-glued, but otherwise a much easier method. I then taped the top edge, and now that it was in the final alignment, ground my mobility cuts.

 

And now the moment: Does it work? I tried them on, and they snap right shut around my calves. In the little I have worn them this morning, they seem to work really well. I will say that I expected them to be a little harder to open. I walked around, up and down stairs, and they stay closed, but when I do something extreme with the top edge, like crouching in a kneeling position, the top can spring open. I tried them on before the mobility cuts, and they sprung open more often when bending my knees past 90 degrees. Because of this, I am adding a "fail-safe snap" (popper for the UK folks) on a 1" black nylon strap inside that crosses the top of the seam on either side of the top magnet snapping on one side. The strap will be connected by reaching in from the top after the armor magnetically closes around my calf, that should ensure it never opens without me doing it. I will add pics of that in my next post, but for now it is on E-6000 time. Also I will finally add my rear cover strips, which should help finish these out!

Edited by OddViking327
Corrected an assumption
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Posted (edited)

I mounted my fail-safe snap at the top, and it works. I just made a single snap mount and strap, roughened the spots next to the pockets to prep them and glued them in with E6000. First the bottom mount, and let dry for 24 hours, and then snapped the strap on, and glued and clamped the end down taught. Once the second part was cured the next day, I tried it out, and it can be easily reached to snap shut, and extreme bending my leg never opens the top. To pop it open is even easier, just slide a finger down under the strap and it pops off. 

 

K92jT1g.jpg

 

Finally to finish them off, I added the 25mm  cover strips once it was all finished. Because the seam needs to click flush, the excess E-6000 glue needs to be removed from the inside along the cover strip (by lightly cutting with a blade, and then scraping and sometimes pulling it off in long, glorious strips when it works). So far, especially with my snap failsafe, they seem very secure. I had to pad the front of the inside to try and push that sniper plate further out from my knee, and so that top magnet is more strained and needs the snap on that side to maintain closure:

frSTJZH.jpg

 

Update after a few months: The top "failsafe strap" feels like a vital piece, I never worry about them with that on. So I would highly recommend it. Second, someone, I can't recall who, was planning to make a 3D printed "magnet pocket" instead of heat forming ABS. I don't have a printer, but I totally think that approach would be easier. If someone does create that file, hopefully they can share it so others can make a superior version of this. The key is, it needs a fairly thin wall on the side that meets the opposing magnet for optimal magnetic strength.

Edited by OddViking327
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WOW... this is AWESOME!!  It never ceases to amaze me how creative our folks can be!  :salute:  (Where were you with this idea 7 years ago)? :laugh1:

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I'm glad to see you pulled this out into a dedicated thread Colin, as I've now added it to the all-in-one resource compilation I have going. It was super cool following you as you pioneered this new style while you were building, and seeing it again is reigniting my consideration of going this route. Great job!

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I’m trying to play with some 3D printed closure “housings” to help mount, align and protect the magnets. One design idea:

a7b81dbe8b0c3f1175682f20e674d281.jpg

a6b82d1640783dce271e328361555640.jpg
8201108c51456f1cff6d3d9096325653.jpg

I suck at CAD design and might need one of you as a CAD jockey volunteer to try some other design ideas...


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I’m trying to play with some 3D printed closure “housings” to help mount, align and protect the magnets.

Now that’s a clean method! My guess is that the walls at the contact point would need to be even thinner, but it’s hard to gauge the scale just from looking at the photo. Are you printing in ABS?


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Now that’s a clean method! My guess is that the walls at the contact point would need to be even thinner, but it’s hard to gauge the scale just from looking at the photo. Are you printing in ABS?


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No, these are just PLA. I’m a beginner and it’s all I’ve played with so far. I suppose ABS would offer better strength and material compatibility. I envision just gluing these on with E6000.

I’d propose we get a team together and get this idea developed, tested and perfected. Offer the .STL files on forum here for anyone to use for free.


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No, these are just PLA. I’m a beginner and it’s all I’ve played with so far. I suppose ABS would offer better strength and material compatibility. I envision just gluing these on with E6000.

I’d propose we get a team together and get this idea developed, tested and perfected. Offer the .STL files on forum here for anyone to use for free.


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Seems like an excellent idea to me, and I certainly don’t mean this as a derailment of Colin’s FANTASTIC implementation of this technique. Honestly I don’t even think walls are necessary where the magnets meet, as they’ve always been absent on Christine’s design. Just thoroughly encase the magnets in glue within their cradle/tube/base and I don’t think they’re going anywhere. GREAT work by all of you furthering the opportunities afforded by magnets!!


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This design looks great! I agree with thinner walls at the contact point, but having some thin walls at the contact point is important. These snap together, and are magnets often chip when that happens to harshly. But also, the closer the can get, the better, as magnet strength diminishes greatly over distance, so even a minimum print thickness will work. Finally, they should probably be encased on top, but then, I suppose they can get glued in before mounting.

for glue, I know E6000 is preferred for the rest of the build, but in this case, you need the speed of CA (with accelerator) to lock them in place one by one, as you can’t afford drift on the first row, or squeezing out on the second set that meets it.

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Very nice design and execution! Always love seeing new techniques to deal with the shins.

 

On 5/5/2021 at 4:06 PM, OddViking327 said:

The issue with Cricket's design is that we are trying to resist the calf armor from opening side to side, and yet that is how the magnets are weakest.

 

I hope this doesn't come across as trying to detract from your method, but I feel it's worthwhile to note that in Cricket's method the magnets attached to the outer cover strip snap down into a matched recess inside the leg armor/inner cover strip, so any side to side movement of the magnets isn't possible which maintains their pole/pole strength.

 

Image for clarity:

 

51162564316_6ff093dc3b_c.jpg

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@Scimitar Ah, that is good to know. I had thought they were also inset into the strip. So that would help maintain that strength. Good to know, so mine is just an alternate version. I will correct that assumption above.

 

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  • 2 weeks later...

I love idea and execution of this! Definitely gonna have to try this method out on my build now. Ordering magnets now. Thanks Colin!

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