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# parallel or is this called opposing series either way i need some math help

## parallel or is this called opposing series either way i need some math help

(OP)
I've got a 450mm long spring with a rate of .50kg/mm (call this one the main spring)
and I have a 70mm long spring with a rate of .60kg/mm (call this one shorty)

1)main spring has a 12mm rod that goes thru the center of spring,

2) at North and south end of rod are flat fixed plates for springs to seat against,
(imagine in a workout gym the flat bench bar(would be the 12mm rod)
with the 45lb plates being the fixed ends, this is shape I'm trying to describe)

3)at north end of main spring there is a large washer that main spring seats against but
with a hole n it that allows rod to go through it with shorty on the other side.
(somebody tell my how to upload a photo and this would be a lot simpler)

4)(these are made up numbers so I can see how to do the math,)
lets preload the 450mm main spring to 400mm, and assume the 70mm shorty goes to 20mm long
(im aware that this probably wouldn't happen, here again, im looking for a formula)

5)what would the rate of main spring be until it came of shorty(by pushing on south end)?
are these indeed in a "opposing series" configuration as one is pushing on the other in opposite directions making the rate go down,
if "no" how can the be called parallel when in line with each other and how would the rate go up?

5) with large washer at north end fixed or in a vice, I push on south end of rod compressing main spring while extending shorty spring.
so main spring would be doing all the work shorty is there as a top out or bumper spring, still I would love to know what the rate is of the main spring until it comes off of shorty?

6)here is how I have been trying to do it, k1 x k2 / k1 + k2 = rate
.5x.6/.5+.6=.27
I thought I had it right,i was like .50 becomes a .27 sounds good, all in a days work.......
but then I used a .7kg/mm for a shorty spring
and I got .29kg/mm
.5x.7/.5+.7=.29
in my way of thinking if the higher rate of shorty spring should make the main spring softer when in a opposing series configuration.
but the math Im using is as if you were sticking springs on top of each other, which I'm not doing.
So do I subtract the final number form the main spring rate,
.5-.27=.23
.5-.29=.21
is this correct?
I've got the numbers now moving in the direction I believe to be correct, but that's a really a lower rate than I was expecting??
or do I subtract it form the stiffer spring?
.6-.27=.33
.7-.29=.41
here again in my understanding of springs in series the rate isn't moving in the right direction??
Any imput would be awesome, thankyou
Daivah

### RE: parallel or is this called opposing series either way i need some math help

do us all a favour and post a drawing

### RE: parallel or is this called opposing series either way i need some math help

(OP)
I wanted to upload a pic, but ran into issues.
not quite a solid works drawing, but should get the job done.
what does the Desert Fox say? (ding ding ding gading a ding, sorry I couldn't resist)
f
i
x
e
e d e
n w n
d a d
p mainspring-rod s shortyspring-rod p rod,mainspring and both endplates dynamically move together >>>>> and <<<<<
l (400mmto150) h (20mmto70) l
a compresses e extends a
t r t
e w e
I
t
h
t
h
r
u
h
o
l
e

<south end
north end>
main spring compresses this direction>>>> while shorty spring extends this direction
with the main spring at 400mm and the shorty at 20mm what would that make the rate?
can the rate (shorty and main) be calculated at 30,40,50,60mm ?
im only concerned with the rate when both springs are interacting.
is this parallel or is this opposing series configuration?
thanks DF!
Daivah

### RE: parallel or is this called opposing series either way i need some math help

(OP)
well Desert Fox,that didn't work
D@mn! that took a lot of time to draw with letters!
@\$@%%#^#*#*)*&^!

### RE: parallel or is this called opposing series either way i need some math help

(OP)
http://web.mail.comcast.net/service/home/~/?auth=c...

Alright guys,
I just signed up last nite and I did have a lot of pumpkin pie and whip cream,
try that DF,
I previewed it and clicked on it and it showed pic of springs in the "opposing series"
configuration, I just slapped some springs together, they are not the actual rates
in math equation.
thanks again
Daivah

### RE: parallel or is this called opposing series either way i need some math help

Look at the bottom to where you type your post, it says how to add an attachtment.
The attachment needs to be in PDF format so that the members can open and read it.
All I can see is something about infinity and corn cast email.

Regards

Desertfox

### RE: parallel or is this called opposing series either way i need some math help

Hi

Okay you have two springs connected in series so you need to find the equivalent stiffness of the combined springs, this is similar to resistors in an electrical circuit connected in parallel.
See this site

http://en.wikipedia.org/wiki/Series_and_parallel_s...

### RE: parallel or is this called opposing series either way i need some math help

Also, bear in mind that the combined rate will only be in effect until one of the springs gets compressed down to solid height; at this point the rate of the other spring will take over.

### RE: parallel or is this called opposing series either way i need some math help

(OP)
hey guys thanks for the response's.
still not quite sure how to work the math,
every example I have found on net says
"as long as the spring rates are the same..."

Cowski
were you able to open pic?
the reason I ask is I totally get what your saying when spings are in series and one goes to solid and then the other
spring is on its rate, that is straight fwd makes total since.

in pic the way this set up is,
you are in a "opposing series" in initial travel,
big spring compresses little spring extends, and in the real world its over a very short distance of 20-40mm.
in the pic I preloaded the main spring (bigger spring) 10mm and the shorty spring compressed 13mm
the actual rates are .41kg/mm for the longer spring and .52kg/mm for the shorty.

my definitive goal here is to have the shorty close to or even at SH with main spring at 5-15 preload.
and for it to give the longest push possible on main spring.
what ive been running into is that the shorty is over powering the big spring (its a regular David and Goliath battle)
or it ends up being to soft and it doesn't do what im wanting the initial spring rate to do, which is to be softer.
I deal with rates from .25 to 1.1kg/mm and it would be more efficient to do some math to get me close with each main spring
rather than guessing and testing like I have been doing.
thanks for all of y'alls imput.
Daivah

### RE: parallel or is this called opposing series either way i need some math help

I opened the pic, but the details were too small for me to make out what was going on. All I could make out for sure was that you have 2 compression springs. Reading through your first post I see in #4 that it appears both springs are getting shorter (loaded in compression)

#### Quote:

4)(these are made up numbers so I can see how to do the math,)
lets preload the 450mm main spring to 400mm, and assume the 70mm shorty goes to 20mm long

but in the second #5 (5b?) it states that the large spring is compressing and the small is extending.

#### Quote:

5) with large washer at north end fixed or in a vice, I push on south end of rod compressing main spring while extending shorty spring.

I assumed #4 was the correct description, but apparently this is not the case?

### RE: parallel or is this called opposing series either way i need some math help

(OP)
he fellas,
Iwas able to get a hold of a spring tester and now matter how hard you try to make a series formula work for springs
in parallel it just wont work,
so that was my problem the whole time,

my set up had a actual .45 main and a .545kg/mm shorty,
I started testing in mm increments and by the 3rd millimeter I could see what was going on when I was
thanks for all the input,
Daivah

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