Technical help please

[Cognisant]

Can anyone help me figure this out?

http://www.stocksprings.com.au/index.php?main_page=page_2

Where the line 4.5 intersects with the column of wire dia. of .048" we get a figure of ±10.1%.

This is the load tolerance of the above example.

Convert 10.1% to 3.5 lb. which gives a tolerance of 5.6 oz. at .900" deflection.

Where did 10.1 come from?
And if I'm supposed to divide the free length (whatever that is) by the wire diameter to figure out how many coils there are why am I ending up with a ridiculous number like 84?

Why couldn't they have a nice little bit of algebra that incorporates all the relevant factors so I can easily figure out exactly what kind of spring I want? Jeez

 

[Melllvar]

And if I'm supposed to divide the free length (whatever that is) by the wire diameter to figure out how many coils there are why am I ending up with a ridiculous number like 84?

Free length
The overall length of a spring in the unloaded position.

http://www.engineersedge.com/spring_terms.htm

Seems like free length / diameter should give the number of coils, or alternatively total spring length / circumference of coil. Hence some number must be wrong.

Where did 10.1 come from?

It seems they looked it up from a table based on the two other ratios calculated. I didn't see the table anywhere on the page you linked to though.

Spoiler

Free Length 4.050"; Mean Dia. .390"; Wire Dia. .048" to give a load of 3.5lb when extended .900". First we calculate the index or...

Ok the equations got all screwed up in the copy n' paste, but it's there in the link, right above the originally quoted text.

 

[Cognisant]

http://www.stocksprings.com.au/index.php?main_page=index&cPath=2

There are three different types of spring here an each type does have its own table, of sorts, but it's hard to figure out which type has the best load tolerance / length when they're all different lengths, diameters and it appears the load tolerance per mm changes (decreases) as the length increases.

Edit: Maybe I should just give up on having custom springs made and try to find premade ones that suit my purposes.