Handle Length Calculations?

[BESON]

I've just been making one-of type projects as I've been learning about leather working. Whenever I've made handles for something like a tote bag, I just guess and check how long the piece of leather needs to be to get the drop length I want when factoring how far apart it's attached. I'm not much for math sorts of things, but is there any sort of calculations that one can do to get a handle "drop" length?

 

For instance, if I'm wanting an 8 inch drop (from handle extended to top of bag) and the two sides would be X inches apart on the bag, how long would the piece need to be (not including the extra that it hangs below to attach it to the side of the bag)? It seems like doubling the desired drop length gets me close, but I wondered if there was a better way of calculating things. 

[JLSleather]

Well, there's the "theory" of it all --- but I wouldnt think that TOO critical, since a detailed (gnats backside) calculation would need to involve leather thickness and stretch, which would vary all over the place.  if a guy was good with a "pretty close' length, then 

divide distance between attachment points (span) in half

this span x itself (squared), plus the drop distance x itself (squared), would equal 1/2 the needed length x itself (squared), OR

(span)^2 + (drop)^2 = L^2

eg; 

if your handles are sewn 10" apart, and you want it to "drop" 24" to the top of the bend, then

(10)^2 + (24)^2 = L^2, OR

100 + 576 = L^2, 

676 = L^2

L=(676)^-1

L= 26"

This is ONE SIDE, so the strap would be 52"

 

 

 

Edited October 3, 2016 by JLSleather

[JLSleather]

Or, to use your 8" drop.. guessing your handles are 10" apart, then 

1/2 of 10" is 5", SO

5^2 + 8^2 = L^2

25 + 64 = L^2

L= (89)^-1

L= 9 7/16"

So the strap would be 18 7/8" long.

 

[TonyRV2]

This doesn't have to be rocket surgery....its leather work for petes sake and something like the length of your straps if done to an accuracy of +/- a couple of inches is not going to ruin the project.  I would just do this.  Approximate the loop of the strap as an easier shape to deal with, like half of a rectangle.  Then the calculation for length becomes simple.  Twice the drop plus the distance between the attachment points.  Naturally, this is going to give you a length a bit longer than the length of an arc shape, but it should accommodate the extra length needed for attachment as well.  After doing it this way a few times you'll get a feel for how much you might vary from this simple calculation. 

[TinkerTailor]

Get 2 hunks of rope and hold them up to bag. Mark right spot and measure.

[JLSleather]

A $2 conway buckle makes the whole thing adjustable, for that matter.

 

[TonyRV2]

3 hours ago, TinkerTailor said:

Get 2 hunks of rope and hold them up to bag. Mark right spot and measure.

Thats the best suggestion yet!! 

[bikermutt07]

I just measured over the wife's shoulder and asked her how low she wanted it. Then added for lap onto bag. Worked like a charm.

[JLSleather]

39 minutes ago, bikermutt07 said:

I just measured over the wife's shoulder and asked her how low she wanted it. Then added for lap onto bag. Worked like a charm.

Yeah, that would work.  But some of us would have to travel considerably to come measure yer wife

On shoulder straps, I just usually 2-piece the thing and add a buckle --- she can adjust it from there.

 

[bikermutt07]

Well, the door's always open and I'll leave the light on for ya.