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Seat Spring Construction (Coil Springs)


MikeC5
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Posted (edited)

This may be a bit esoteric but maybe someone has run into this before.  I'm remaking the seat base spring assemblies for my '25 DB (they were rusted beyond redemption) and have just realized that I cannot find replacement coils with near the top/bottom diameter of the original coils (~ 3.5").  I've looked and looked but everything I find at places that sell these springs are 4 1/4 to 4.5" diameter.  What's the big deal?  None, I hope.  What it means is that I will have to reduce the number of coils to fit in the same frame (45 vs. 31).   The diagrams show what I mean.  My question is will the reduced number of larger diameter springs make for an unsupportive/uncomfortable seat?   Does anyone know of a source that sells coils closer to the 3.5" diameter?

Bottom spring detail.jpg

large coils.jpg

image (3).jpg

Edited by MikeC5 (see edit history)
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Posted (edited)

Hi Bob,

I did the best I could with a protractor and (eye balled) tangent points between end of radius and straight section.  The accuracy was not better than a degree despite my extra significant digits.  This is what was left of the original spring...

P3210382.JPG

Edited by MikeC5 (see edit history)
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I know Snyder's does this and I did use them to recreate the seat backs which were more complex due to the 3D shape of the frame.  I wanted to do the bases myself since they are relatively simple (having them made ain't cheap either).  

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This is a timely post. I have been considering the replacement of the sinuous or zig zag springs in a modern (only 50 ish) car with coil springs to try for a real luxury feel seat.

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While you are measuring springs, breakout your calipers and see if the springs around the edge of the seat are bigger diameter wire. This was commonly done to provide different support for different parts of one’s butt….

 

Many times on seat cushions, they were either different spring rates or doubled up on ends.

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Thanks for the tip David.  I will double check this.  One thing I also recently found out; there is more than one standard that define the diameter of wire to 'gage'.  It appears the most common one is the AWG (American Wire Gage) which seems to be used only for conductors (as in electrical wiring).  Then there is U.S. Standard Gage, which is significantly different.  I need to contact some of these suppliers and ask for the actual wire diameter to avoid confusion....  https://www.pyromation.com/Catalog/w03.pdf

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Posted (edited)

An old mattress or two might give you some of the springs but not all.  The springs vary in height, front to back.  On the front cushion, they go from 4" to 8" (4, 5, 6, 7, 8).  This is what gives the seat a wedge shape which, I believe, is to provide thigh support.  The rear seat cushion goes 5, 6, 7, 8, 9" springs.  Because of the hourglass shape of them, I don't think trying to cut down longer ones to makes shorter ones would work very well (you would end up with different diameters on the large end depending on how much is trimmed off).

P3210379.JPG

Edited by MikeC5 (see edit history)
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My first job out of the service was working for an engineering company that custom made machines for assembly lines and my first lesson on the job was that if you are going to work with a spring you need to be smarter than the spring.

 

Older flippable mattresses have large loops on both ends, don't clip the loops on the top side and don't worry about the bottom side, springs can be bent to fit.

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Posted (edited)

Thanks Digger.  One other thing that I can't seem to nail down is what gauge definition is used for these types of springs?  Retail suppliers advertise 8 or 9 gauge springs but none of them can tell me what diameter wire they're made from (calipers are in short supply, it seems).  There are a few different gauge definitions; AWG, SWG, Birmingham, Music wire, etc..  All of these have a different diameter (in inches) for a 9 gauge wire.  I'd like to be sure I'm getting springs with the same (or close) wire diameter.  Anyone have any insight on this?  

Edited by MikeC5 (see edit history)
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On 5/17/2022 at 10:40 AM, MikeC5 said:

Anyone have any insight on this?

Wire gage and material type are manufacturing specs, retailer's sell from product sheets that list size shape and strength. Two visually identical springs can have two tremendously different compression tensions depending on manufacturing process and material composition. 

 

Metallurgy has advanced a bit over the last hundred years and you might not find the same gage shape and strength as the springs that were made in 1925, but you should be able to find new springs that will work. Companies like Sealy and The Original Mattress Factory are still making coil spring mattresses the old fashion way and would probably be your best source for information and supplies.   

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On 5/13/2022 at 7:12 PM, Digger914 said:

Looks like an old bed mattress would give you everything you need from springs to cotton batting and because they cost money to get rid of they are usually free.

I was going that direction for my 1920 Dodge, but the springs were designed for the weight to be spread out over them, not all in one place so do not support the weight directly on them very well. The wire used is not real heavy like what would be used for car seats. 

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1 hour ago, Mark Gregush said:

I was going that direction for my 1920 Dodge, but the springs were designed for the weight to be spread out over them, not all in one place so do not support the weight directly on them very well. The wire used is not real heavy like what would be used for car seats. 

Not all mattresses have the same springs, or are all spring mattress made the same way and individual coils support weight differently than interconnected coils.

Mattresses come in soft, medium, firm and if you special order, extra firm. I'm 6'3' 230lbs  have a fist full of bad disks in my back so I sleep on an extra firm mattress with a board underneath and have no problem with the mattress squishing own when I sit on the edge. Got my new mattress from The Original Mattress Factory and because their factory is also a showroom, I got to see how mattresses are made.

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I realize that I won't find exact duplicates of the original springs (unless maybe I have them custom made) but at least in outward appearance, these hourglass upholstery springs look pretty much the same.   I suspect there aren't that many manufacturers of them and retail supplies come from the same few factories.  Short of designing a spring to match the originals (including estimating the spring constant from the old springs) and having them made, the best I can do is try to match the shape, number of turns and wire diameter.  I certainly won't hurt to try asking one of the mattress manufacturers too.

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Posted (edited)

As I mentioned in an earlier post, the vendors do not know if AWG is the measurement system used.  Unfortunately, AWG isn't the only measurement system to call wire diameter 'gauge'.  I posted this link earlier which shows that a given gauge wire diameter can differ considerably depending on which measurement system is used.....

https://www.pyromation.com/Catalog/w03.pdf  If I could get them to put a caliper on a spring, I could deduce which system is used....  

Edited by MikeC5 (see edit history)
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