Wire broke on several frames

[Gwickstrom]

Hi all
I wondered if anyone has run into this problem. We are framing 32x44 pictures with glass it weighs 18lbs
We have had 3 customers complain the wire snapped at the same location. The wire is rated for 44lbs
We can only think the wire is defective.?

[silvercleave]

angle for hanging.jpg (95.25 KiB) Viewed 11537 times

Breaking strain is in a straight line, perhaps this might explain it for you

[David McCormack]

If your wire is hanging on one wall hook and is fairly taught between your D-rings then for an 18lbs frame the force on each D-ring will be 103lbs assuming it makes an angle of 5 degrees. Even for 10 degrees it will be 51lbs which is still over the breaking strain of your wire.

As soon as you make an angle of 30 degrees or more on two wall hooks the force drops to 18lbs or less.

Either hang on two wall hooks or consider no wire and use strap hangers etc.

Welcome to the forum

[Uncle Sumo]

Where did all this "science" come from? Force equals mass x acceleration. The picture is not increasing in mass and gravity is constant in most people`s living rooms. The picture is stationary so there is no kinetic energy or impact strain. In short...

Yer whaa?

[Roboframer]

Put a five gallon jerry can of water by your feet, bend knees, lift - no problem. Now stand an arm's length away from it bend knees and now try and lift it, you'll need more force (and if you can keep your arm parallel to the ground sign up for the Olympic weightlifting team)!

The wire snapped anyway so if two wall hooks were used and there was an angle of 40-60 degrees (or whatever) between hooks and hangers what else caused it?

BTW, for a frame that weight I'd be using more than a single hole 'D' ring.

[IFGL]

that is not what is happening Roboframer, a fair comparison is splitting the can in half putting each half on the end of a poll then lift the poll from the middle, their is equal weight on either side canceling each other out.

I have also long wondered where this has come from it just doesn't seem correct, that said it's been a long time since I was in collage,

regardless of the maths the cord is still better loose especially on thinner frames.

[Roboframer]

I never covered any of this stuff anyway I just rely on those that have providing diagrams like above, which makes sense to me, as did my jerry can experiment, but anyway, scroll down to 'thinking conceptually' in this link

"The principle is that as the angle with the horizontal increases, the amount of tensional force required to hold the sign at equilibrium decreases"

Which is what the above diagram shows.

[JohnMcafee]

The forces needed to support a picture in the above diagram are computed using the The triangle of forces law.

Interesting fact: If the string is perfectly straight, at 0 degrees to the horizontal, then the force on that string would be infinite - regardless of the weight of the frame.

[Roboframer]

Moral of story, don't break the law!

[JohnMcafee]

Regarding the original post:

About 12 years ago I compared the stated breaking strengths of picture wire and cord - haven't used wire since.

[David McCormack]

The frame hanging diagram is correct.

A little experiment can show very nicely just how correct it is.

You will need:

1. Picture cord
2. Pair of scissors
3. Fletcher Multimaster point driver
4. Pair of thumbs & forefingers

Best explained with a couple of photos...... be back later

[prospero]

Going by that diagram (not saying it's not correct), if you hang from two hooks the wire between the hooks will be at 0º . So given that the force increases exponentially on the shallow angles the tension on the middle part should be astronomical.

[Roboframer]

I never used to like the idea of wire, I'd never tried it but I didn't like the look of the stuff I got in for re-framing or the bleeding fingers when I had to remove it without cutting. I don't think I'd ever seen coated stainless steel wire.

Then Euro mouldings went bust and I could not find the same low stretch polyester cord anywhere but while looking I discovered super softstrand wire and liked it, a lot. It's sexy.

I never liked the bulk that a knot in cord each side of a frame caused..... or even one side come to that, so my preferred method was to double it up and connect it with a reef not, slide that reef knot close to one side and then tidy up/fasten the two together with magic tape. Looked OK.

I use S Strand No3, 5 & 6. No 3 has a breaking strain of 22kgs but a recommended maximum picture weight of 10kgs and that 10 kgs is pushing the limit of when I move away from wire and on to stuff like strap hangers, Z bars, etc anyway. So, whichever I use, it's overkill. It's not much more expensive than the best cords, won't stretch, looks a million times better, I'm using half the quantity that I was using of cord and less magic tape!

Anyway - how was the frame in the OP hung in relation to the diagram - hmmmmm?

[Roboframer]

We mark the points where the wall hooks should placed ... with a lickle panda at the moment. If customers want to ignore the instructions (which are given verbally as well) it's up to them but on a frame this size if they did use just one hook the wire angle would still be not bad and the hook would not show above the frame.

hooks Wire 001.JPG (140.04 KiB) Viewed 11344 times

hooks Wire 002.JPG (150.03 KiB) Viewed 11344 times

[prospero]

Any fishing fiends among our company?

Got one of those springy weighing scales?

If you were to put one in the middle of the wire the vector diagram could be proved empirically.

Theoretically, if you stretched the wire really tight and picked it up by the wire the scale should read just what is what.

[Roboframer]

Mr Newton sorted all this out for us donkeys ago - those that want to argue the toss go and make a nice diagram on a blackboard and submit it to the ministry of complicated diagrams.

[JFeig]

Take a look at any cantilever crane, the closer the weight is to the pivot point the heavier the load sustained.

[David McCormack]

OK then, for a bit of fun, cut a length of cord about a metre long and tie a loop at each end big enough for your thumb and forefinger to fit through. Pass the cord through a Multimaster or something like and support it with your thumbs and forefingers in the loops as in the first photo. There’s not much force from the 490g weight of the Multimaster.

Now pull your hands apart so the cord is as straight as you can get it and hold it there as long as you can. Keep your hands still and stop pulling. The force pulling the cord through your thumb and forefinger is now around 2kg or more at each end.

While you’re at it, try and pull the cord so it is completely straight and let me know how you get on?

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[JohnMcafee]

Nice practical demonstration of the triangle of forces, David.

POF.jpg (139.76 KiB) Viewed 11275 times

A = Force applied by David to hold the his hands apart
B= Half the weight of the point gun
C= String tension

Decreasing the angle between A and C results in the triangle becoming wider thus increasing forces A and C

[David McCormack]

Force applied by David to hold his hands apart

That's me Mrs