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Paul Alciatore
03-19-2012, 12:23 AM
As I detailed in an earlier thread, I am making some small spring latches for a baby crib. I have revised the design according to some earlier comments and I am now making the parts. But the design is based on a standard, coil spring and although the spring will be fully enclosed, I now want to replace that with something safer.

So I would like some recommendations for a springy material that I can form a "spring" from. The design calls for a compression spring that is about 3/8" in diameter and about 3/4" long. Both of those dimensions can be adjusted, but not by a lot. The stroke length is about 1/4". My first thought is to use some kind of rubber foam material and make a cylinder from it. I need a positive latching action, but not too much as it will be operated by the side of one finger, probably a thumb. I want something inexpensive and easy to get in small quantities. And easy to work with: my shop is still in storage and I am using hand tools.

Ron of Va
03-19-2012, 05:36 AM
Short piece of a cable tie bent into a half U secured at one end, can be pretty springy. That's all I've got this early:)

Paul Alciatore
03-23-2012, 04:56 PM
Short piece of a cable tie bent into a half U secured at one end, can be pretty springy. That's all I've got this early:)

But the fastener would be just as dangerous in small hands as a spring.

Humm, perhaps I could heat form a cable tie into a helix for a spring. But I would prefer some kind of foam. But what kind?

Black_Moons
03-23-2012, 05:05 PM
How about don't use a spring, Use a cable and pulley and weight? Or a weighted lever? Can adjust the arm lengths and weight to get just the right force you want. If you make the latch vertical, it will fall into place.

Only downside I see is an issue of momentum if body parts can get caught in the locking mechanism if you go for a strong force.

Actually, maybe you don't need a spring at all, maybe you just need friction?

UHMW gib + a small recessed screw to set the friction (to account for wear), just make it strong enough that an adult can move it with mild discomfort and kids will be unable to. No stored energy in friction to worry about.

Tony
03-23-2012, 05:10 PM
popular option for compression springs is urethane rubber. available in
all sorts of durometers and diameters. I haven't quite followed along with
what you're doing, but maybe that could be an option since you're talking
foam.

keep in mind urethane will give you a lot of bang for your buck (force wise)
but if left in a compressed state for a long time it will take a set.

Tony

rohart
03-23-2012, 05:42 PM
So how will a rubber solution be safer ? Sure, if you leave some tools lying around, then the baby could be more dangerous with a spring than with rubber, but if the baby has to eat the components whole ? At least the spring will show up on the x-ray.

I was going to suggest a stack of thin belleville washers, but again I guess they would be more dangerous than a spring. A spring won't constrict an airway, it won't constrict the digestive system, if the edges are smooth it won't scratch. The worst that could happen if the mite could stick a finger up the middle, and then it would serve it right.

I think that a different kind of latch may be called for. A hasp with a long heavy U-shaped hoop as the locking device. A baby's got to be really going it to harm itself with two feet of smooth 1/4" stainless rod. And nobody would forget to latch it. Second thoughts, I suppose it could wrap the darned thing round its neck, and...

Mr Fixit
03-24-2012, 12:23 AM
Haven't followed the project, but what about using gravity and weight as your force to work the latch? It would need to work in the vertical plain but if heavy enough maybe it would lock but be hard to lift for someone so small in a crib.
Just me thinking out side of the box.

Mr fixit for the family :)
Chris

Paul Alciatore
03-24-2012, 02:16 AM
OK, gravity will not work because the latch is horizontal. No room for pulleys or levers. Really. K.I.S.S.

My present design is a plastic bolt that slides inside a square aluminum tube. The spring will be fully enclosed but I would like something that does not have sharp edges like metal springs in case it ever gets liberated. Foam of some type would be a lot nicer on the intestinal track than a metal spring. Probably overly cautious, but better safe than sorry.

Oh, the difficulty in opening it is that there are two latches that are about four feet apart so no baby can operate both at one time. If they spring back then it would be difficult for her to get both open at one time. But an adult can easily reach both and open them quickly and easily.

fredf
03-24-2012, 04:36 AM
Oh, the difficulty in opening it is that there are two latches that are about four feet apart so no baby can operate both at one time. If they spring back then it would be difficult for her to get both open at one time. But an adult can easily reach both and open them quickly and easily.


This sounds like a drop side crib?? Weren't they banned for safety problems?? Not trying to be critical, but just another thought

flylo
03-24-2012, 05:05 AM
What about a friction ball catch like used on doors that swing both ways. It's an encased steel ball where about 1/3 yo 1/2 is exposed & behind it an enclosed spring pushing the ball. The exposed ball normally rest in a recessed plate the matches the ball. Or use a magnetic catch.

nitsuj
03-24-2012, 10:59 AM
If its going to be enclosed, the metal spring would be the cheapest, easiest safest solution. I've seen plastic springs, but they seem easily breakable and no idea where to get them. Perhaps a solid rubber cylinder, add some springiness by drilling a few holes along its length at a 90 degree angle to each other?