Plastic Spring Clip

Polycarbonate.

Polypropylene is used to mold cases with "living" hinges. The molding incorporates a thin section that joins the top and bottom parts and acts as a hinge.

Now, is it stiff enough for this application: heat is an enemy, too: plastic creep. etc.etc.

Tell us about the environment and stresses it wil see.

Polycarbonate could work as PWSlack suggests. It is stiffer, that could be good, or not.

http://www.leespring.com/int_learn_LeeP.asp
http://www.eng-tips.com/viewthread.cfm?qid=307256

Ooooh, don't get me started on plastic springs.
The biggest mistake I see (endlessly) with plastic springs is that they are not tapered.
Idiots people design a straight finger type spring and wonder why it snaps off at the root.
Please, please please taper it, if you wonder why, just look at a tree or a longbow.
Del

To me, "plastic spring" is an oxymoron.

Unless the spring is unstressed most of the time, it will loose its springlike qualities over time. (Cold flow)

Heat? that'll definitely take the spring out, too. But, if it can rest un-stressed, it can work.

I'm not current anymore, but acetal might work too.

A clever designer will be an asset here, to distribute the stress along the entire length of the device and help with material selection.

Here is what I am talking about, only one end is fixed and the hook end is movable. Very simple, less than 1/16 inch travel for the hook end to possibly a max 1/8 inch. nothing complicated. I have tried metal and it is just too clunky and think plastic would be more streamlined.

Thanks all

3M Scotchply is worth a look:

http://www.scribd.com/doc/53197568/SPRING-3M

Mark Bingham
Relativity PL

By the way folksI have read your replies thus far and they have been helpful. Usually I would just play around with different plastics but time is getting down to the wire here and I have tried many options and this seems to be the best and most practical. the temperatures I am sure will be some issue as it is for an outdoor adventure tool which might be subject to very cold temperatures and possibly up to 100 or more degrees depending on the location. I would say as a general rule -40 to 120 degrees F. Again this is very simple and I could probably come up with some good onese to try but thought my friends on CR4 would know. Polycarbonate and ABS are two I considered, but think I will take your advice and contact plastic manufacturers(only problem there is getting response back, I sent a request before and took them weeks to get back to me. I have some ABS in my shop, just might give it a try to see how it works.

Thanks all again and for future suggestions.

"I have some ABS in my shop,"

The properties of a part machined from extruded stock will not be the same as a molded part.

Thanks Lyn, I do understand that but perhaps trying it to see if it holds up might work to narrow down a list of materials. This is for a simple prototype to prove functionality, I would rather it be molded if possible but right now need to show concept, after which I can fine tune it as needed. Any suggestions on this are appreciated.

I wouldn't leave messages at a plastics manufacturer... that's hit or miss. There are several manufacturers you can talk to. Do some googling and some GlobalSpec'ing and use the phone to track down and talk to an Application Engineer directly. Just ask for that. If you get sent to voicemail, get back to the front desk and tell them and ask to speak to another one. If you get through, normally they are more than happy to share their knowledge immediately. Browse through company websites, particularly the "meet us" type of pages on some company websites... they often list direct phone numbers to various Dept heads, and sometimes even to all the engineers themselves.

Personally, I think polycarb isn't going to hold up very long, particularly in the colder environments. It's not famous for holding up under any kind of stress. By the way, there are two types of polycarb; one is a thermoplastic (Lexan), the other is a thermoset. Its properties are different, but I'm not too familiar with them. ABS could be a better choice. Although at the warmer temperatures, it also may tend to lose some spring. And as was mentioned, beware of molded vs machined ABS.

Contact a resin supplier and give them full requirements and they will make a recommendation. Best of all it probably is a free service.

Just a thought: What if you went back to metal and had it teflon coated. The coating will stop the clunking you are experiencing.

by clunky I meant that the metal just isnt too neat looking for my desires, not that it makes a clunking sound. I think plastic would be a much better fit here though I am looking at all possibilities right now. thanks.

A plastic piece that performs the same as a comparable metal piece, would of course need to be more massive than the metal piece.

True, but remember this will also have a small tab to be able to move with the thumb, I am afraid metal might pose more problems though I havent ruled it out completely. I think a simple plastic tab should do the trick, As this needs to hold up but the forces on it are not that great, basically it is a fold out brush for a piece of climbing equipment. Due to the nature of the design the pressure of the brush will be against this clip, but I am not anticipating a great deal of stress on it. I think acetal might do the trick, I just did some research on it and glass filled acetal might even be better.

I took a second look at the profile in the photo and you may want to consider an aluminum extrusion for the job. just cut to proper length and you can anodize or heat treat to spec.

Thanks Roy, I was just in my shop and looking at a piece of aluminum and wondering if I couldnt use it for this. One problem is the confines I have to work in are very small, the option I have for aluminum is if I can mount it to the other side and have a bend in it so that the hook will be on top of the plane that the main piece is in. I will try aluminum and see if it works.

Thanks

glass filled acetal

Delrin would take care of the heat issues. If it has to be made from plastics that is as close as you're gonna get if you want it off the shelf.

Good luck.

... or... a variation of plastic coating, you have the option of cutting a slot in your plastic and inserting a strip of spring steel. But the slot would need be properly designed so it causes no stressed areas prone to cracking.

But overall, I'd lean toward acetal, for the wear characteristics and the stiffness. And do remember the taper.

I have ordered some delrin and hope it will fit the bill. here is a picture(blurry) of one I did using a small piece of stainless welded to the main section and offset to catch. this works very well but would prefer to stay away from the metal as I think it has too much tendency to catch on things and possilby bend inadvertently, where plastic would likely not bend as easily(though the metal could be thicker but then you wouldnt be able to move it with your thumb or finger. I think if Imake a piece out of plastic with the same characteristic and screw it or rivet it on it would work very well.

Hey guys, just wanted to update the delrin worked miraculously. I was able to machine a piece just right and all I need now is to make a prettier version for the final piece as the one I made is quite rough. It works very well for the purpose. Thanks all for your help.

Best regards,

Shawn

You're very welcome Shawn. It's satisfying to know that once in a while all our brainstorming actually ends up in some positive results. Bottom line... that's why we're all here; to help each other. Good luck with your gizmo!