Spiral spring - Hidden blade

I've seen many designs for Assassin's Creed hidden blade design, and I think they are all great, but my one peeve was that none of them were truly retractable. They only extended by a coil spring or force, and were pushed back in. I've come up with a design I wanted to test out but have no idea where to find or how to make, a spiral spring, AKA clockwork spring.

The spring is the key to the design and only needs winding once in a while to operate.

It's not the best looking picture I know and it's definitely not to scale but I hope you can make sense of it. The string pulls the bell crank, which allows the snail cam to spin out half a turn to extend, and then again to retract. For safety reasons I didn't make it definitively locking on the opposite side of the cam but another bell crank like mechanism could make it so.

The spiral spring will be attached to the underside of the cam and will keep the force on the cam, which can be wound with the key.

I know it's rough but I wanted to know any improvements on my design that anyone may have and if anyone knows how to make a spiral spring. What thickness of metal and type of metal do I use? Do I just wind it around something or do I have to heat it so when it cools it will keep it's shape? Can I just take apart a tape measure?

I don't honestly think It will only need two scissor mechanisms to extend properly but this is just a representation.

Any questions, comments, concerns, and feedback is greatly welcome.
Thank you all very much.

Hey there,

I'm also working on a retractable hidden blade that wrist flicks out - for me the problem has always been getting it back in and not out, so I'm not too worried if it doesn't shoot out.

I think your best best for clockwork springs are watchmakers, but the kind who assemble grandfather clocks and so on. Check the pic below for the spring that I have!

I'm farmiliar with the system you're going to use to build yours, but I must confess that I don't like the scissor jack system myself - I'm interested to see your progress on this though

Thanks for the advice on where to find the spring.
Yeah I had thoughts of the scissor jack too, not sure how far I can extend it and keep everything at the length it should be at. Any recommendation of what I should use? I'm not a fan of the drawer slider though, only seems to lend it self to sliding things out not back in, but I'll work on that when I have time tonight.

I like how yours is looking, may I ask how you are building yours?

personally I'd have gone with a 'centrifugal' style of deployment (just throw it out like a gravity knife) you'd need some way to lock them when out and a loose spring to pull the blades back in when you unlock, but it would stop your problems with overly complex mechanisms.
cheerio

youngpaddy1 said:

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personally I'd have gone with a 'centrifugal' style of deployment (just throw it out like a gravity knife) you'd need some way to lock them when out and a loose spring to pull the blades back in when you unlock, but it would stop your problems with overly complex mechanisms.
cheerio

Well my only complexity for me (at the moment anyway) is the spring, if it's strong enough and etc.
But that's not too bad of an Idea, I could think up a few ways to do that. The problem I think would be that it could come out if I were to run or is someone bumped into me, It wouldn't be sharpened but it does still have a point. And if I did make a locking mechanism to keep it in, I would need the ring or something similar to allow it to open so it wouldn't be too bad. I'll look into it, Thanks for the thought.

Idle,

Very interesting idea! For the spring, why not disassemble a wind-up alarm clock or kitchen timer? There are some smallish ones that should have a useable spring along with other parts that might come in handy...

Mark in Okinawa

FlyingDachshund said:

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Idle,

Very interesting idea! For the spring, why not disassemble a wind-up alarm clock or kitchen timer? There are some smallish ones that should have a useable spring along with other parts that might come in handy...

Mark in Okinawa

THAT.... is an excellent Idea! wow that would save me a lot of searching online and around town. Thanks a lot for that Idea

Now I just need to hit up the flea market and downtown this weekend.









In the mean time does anyone have a better suggestion to scissor jacks while staying true to my design? I was thinking something LIKE a drawer slide but I'd rather make it from scratch or mod an extending tai chi practice sword so it isn't as bulky. The only thing I could come up with is a pulley system

Idle,

To replace the scissor jack you might consider a rack-and-pinion gear setup like this. The cam spins the pinion, and the rack is affixed to the part that holds the blade. You can play aound with gear ratios to get the amount of extension you want.

Mark in Okinawa

Ruskin: I like that sound of what your doing, hope I get to see it.


FlyingDachshund: That sounded really good.. till I started drawing it out. to get the blade to extend the full amount the back end of the rack would stick out when closed... Unless I got a plastic one that curves around the inside... like one used in those toy tops! .... I'll have to work on this. Thanks for another idea!.. I hope it's strong enough, this may end up making things more complicated.



EDIT: wait... the cam spins in the same direction. If I pull it twice it will just push the blade out farther. unless I use the ring pull system to pull the blade out and the spring to push it back in. In which case I could just use a regular spring instead of a coil spring but uhh... I dont think I can pull or twist my hand/wrist far enough to extend the blade all the way out.

Good point, I hadn't considered that...

Mark in Okinawa

Yeah it kinda hit me too






Does anyone know if there is any real reason not to use scissor jacks? What's bad about them?

This is the problem with the 3 part blade, getting it all the way out. I've seen plenty of stock and blade designs ( 2 part ) which are fine, but don't extend very far unless the housing goes back past your elbow to fit the blade in!

My design will have a decent closed length and the blade will extend just past my outstreched fingers - whether the mechanism will work properly still remains to be seen!

Yeah... the scissor jack thing... to me it seems like alot of work. Remember that in the closed state, the width of the pieces can't be wider than the blade itself. This in turn means that you have to have thin pieces and that you will need much more of them to get the blade out to where you want it. All this will need to be handled by the coil spring and it may come out a little slower than you'de like. That being said, you'de also have to have exact timing to release the bell crank section, because if the second stopper on the crank misses it, it will simply go back in again, which could be a bit anti-climatic!

yeah those are the same problems I figured :\ if at the very least it could be a spring assisted modle. If it doesn't come out fully, a little jerk and it will. A flick of my finger or lifting my arm up could help get it back in, but it will lose a lot of it's "pizazz."

I think my best bet is to wind it up tightly or make sure I get a good strong spring.

Idle,

Giving the rack and pinion further thought, you could still use it if you attached the rack to the cam and used it to drive a small gear. I'm envisioning a system where you use a double gear and you drive it with the rack attached to the cam, with the larger diameter gear driving another rack attached to your blade. This would allow you to amplify the movement of the cam using the gears, getting you more extension than you would get if you just pushed the blade out with a piston attached to the cam...

Mark in Okinawa

took me like 3 reads to understand it but I like it! getting full extension is a big deal but.. there's still the problem of retracting. I might make this as a second hidden blade anyway just because of the extension.

Actually, retracting is allowed for - I wish I could do a quick diagram but imagine one end of one rack attached to a point on the cam so it oscilates back and forth when the cam turns like this. This advances and retracts the rack, making the gear travel in either direction and thus extending or retracting the blade attached to the second rack.

Mark in Okinawa

This could be handy for a zip gun for a gun prop so it slides into your palm

Wes,

That was my thought as well, and the clockwork askpect of it gives it a cool steampunk vibe. I'd been looking for a way to do this but Idle's clock-spring approach hadn't occured to me, so I'm glad he posted about it!

Mark in Okinawa

I would be worried about the legality of a spring loaded wrist blade myself!

Flying,

I thought about what you were trying to explain for 10 minutes but I finally got it hahah. I was stuck on there being only one rack and the cam being the gear. now I see that the cam has a piston that is actually a rack, turning a small pinion that has a larger pinion on top of it pushing the rack that has the blade attached to it. And you're right that would definitely work!

Now I need to hit up the flea-market and dollar stores for parts.

Oh, since your interested in the steampunk aspect of it. you could probably make this so the spring is on the outside part of the device, not against your forearm, with a plexiglass window to see the spring operating. definitely would give it some flair.

and I dont know if this will help you or anyone else but I found this on deviantart by a man named Kudrik.
Hidden Blade by ~Kudrik on deviantART

It is a housing for the hidden blade and he includes a tutorial for how he made it here
hidden blade blueprint by ~Kudrik on deviantART
and here
hidden blade blueprint part 2 by ~Kudrik on deviantART

I don't know if you know how to work with metal but I'm not that great. So I thought this was good help for starting out.

You can find the video for Kudrik's blade here -
YouTube - Hidden blade