COIL SPRINGS:

Following on many of Nick Haskell's (Stickframe's) great vehicle builds, I have been trying to come up with my own way of making better looking coil springs for the many Oshkosh TAK-4 suspension units being offered these days in model form for modern US vehicles. (Assorted MRAP's, Mk23's and hopefully one day a HEMTT A3)

Fortunately, I just recently lucked into a new product at my LHS; offered by Plastruct:


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Modification of Panda's M-ATV MRAP 4x4 shown above which is currently on my work bench.






First I selected a drill bit that would give me the desired inside diameter of the spring and clamped the bit in my small bench vice. Then I took two pieces of the plastic coated wire and holding them tightly by their ends with a pair of pliers, I began to wrap the wire around the drill bit. (I tried using just a single strand of wire with hopes to expand the spring lengthwise after bending but this proved inconsistent.)

In the end, bending two pieces of the wire at the same time, I get the correct "coils per inch" spacing in the bend. The Plastruct wire has the perfect hardness to permanently hold this bend when complete. Afterwards, it is a very easy task to "unscrew" the two coils from each other when done.

p.s. The plastic coating that Plastruct uses on this wire does not react to our model solvents so Superglue will be necessary to attach the springs to the model.

Sorry I know I have posted this "trick" before within another build thread but I don't think I have ever posted it as a separate item. Please excuse if I am repeating myself.

Experimental Oshkosh MRAP with upgraded coil springs:

That's a pretty neat trick indeed!

Your route does achieve that desired consistent pitch and spacing, but may yield an over-spaced spring for some applications - an alternative I frequently use is to wind my wire onto a long machine-screw or bolt of the right thread pitch - this gives an equally-consistent spring and may get the desired spacing when you want something more packed together.

I'm less sure about using wire with some insulation on it... bare copper wire of many gauges is available, and the copper will take any primer and CA glue. Of course it, too, won't react with our usual solvent cements...!

Thanks for posting this here - that's a good-looking spring!

Bob

Admittedly I am getting seven turns per spring whereas the actual Oshkosh TAK-4 suspension has eight turns per coil.

. . . . . . . . . . . Oshkosh catalog drawing

In hindsight I should have cut my springs at eight turns and compressed them slightly upon install. This would probably make them even more realistic looking.

I assume different Oshkosh vehicles will have different spring configurations based on gross weight and axle loading. (I got my hands on a big Oshkosh airport fire truck this past weekend. The entire TAK-4 suspension assembly there was a scaled up, much heavier version of the smaller MRAP and Mk23 suspensions. Sorry no photos.)

My primary goal here is/was to make a much better looking, more realistic spring than the solid cast plastic item that comes with the model.

p.s. The plastic covered wire comes is several gauges. I happened to think this gauge came closest to duplicating the look of the Oshkosh original.

Michael:

Turns out that I actually have the same Panda M-ATV kit in my "soon" pile! And I, too, plan on replacing the molded springs with some wire item... I think that your specific effort looks very good (albeit, as you noted, your spring, at 7 turns, is a tad over-spaced). I wouldn't have known for sure had you not mentioned that the real thing is generally 8 turns per coil! It LOOKS GREAT.

I'm actually speaking to the larger, more - general business of making wire replacements for those often-cruddy molded springs in kits. Your route worked out very nicely for your specific Oshkosh spring. More generally, springs come in many pitches, with many thicknesses of wire, and the problem of getting both "correct wire thickness" AND consistent spacing is "legion" when making wire springs. Using a screw of the correct diameter and pitch helps get the spring right in almost any instance. The choice of wire / wire product of course addresses matching up to whatever wire thickness you seek to depict.

I'll be likely using your approach (paired wires on a drill-bit) for my M-ATV springs, as you did get a nice spacing. I'll likely use a gauged copper wire - because I have tons of the stuff on hand!

Cheers! Bob

Thanks Bob

I feel my real "discovery' here is the use of the double wires to achieve almost exact coil spacing.

I had a lot of unacceptable failed attempts as I tried to roll a single wire into a spring and then expand (stretch) it to the desired length. The coil spacing always ended up extremely uneven.

Personally I think the idea of rolling the wire on a screw thread would only work for smaller diameter springs with a high coil count. Unless you could get your hands on some "double lead" screws * * . These screws actually have two cut screw channels at a much higher pitch angle and are perfect for rolling two springs at once.

* * Square D Company used to offer their load center (fuse box) panel covers with double lead screws. Once started these screws with two thread channels at twice the pitch angle could be run in very quickly saving the contractor time and labor.

Hi Mike,

I have been doing this for years, and even posted the result on this site in one of the group builds - you should join some !


(duck, weave, dodge....)

I use copper gauge wire but to thin the spacings, I do not roll two same gauge lengths. You can do the same thing with a smaller gauge of wire for the spacings. Just need a little care (nothing you can't handle at all) to stop the larger gauge riding over the smaller.

If needs be the smaller gauge can be rolled lengthwise with Tamiya tape to get the right diameter.

Michael: Your double wire wrap worked well for your specific spacing and gauge. And as it does apparently work for that specific spring, I plan on going your route for those. I need not reinvent any wheels, here!

FWIW: The diversity of screws and bolts is, well, "legion". Just today, in continued execution of my house-rebuild project, I probably, between carriage bolts (2 sizes), lag screws of 2 sizes, wood and sheet-metal screws of 5 sizes, drywall screws (3 different pitches all in #6!), fan screws, and electric (Double D!) fitting screws, used maybe 20 or so different screw diameters and thread pitch combos. My hardware pile probably includes well over 250 different... I have the utmost confidence that I could find in that pile just about any combo of size, thread-depth, coarseness and pitch, and any wire gauge needed to make about any spring to be seen as such in a 1/35th scale vehicle! I am also supremely confident that a double-wire wrap, while seemingly near-ideal for the spacing in those Oshkosh springs you did up, would be far from equally useful for many other springs, both that large and smaller.

As for stretching and compressing DIY wire springs... Generally, it is very hard to stretch or compress such and MAINTAIN the desired equal spacing... unless using spring steel, you are much better off, IMHO, building in from the first your desired spacing, given that the wire we usually use is not actually spring steel.

Bob

Peter - Excellent extension of the concept! - To use a smaller diameter wire as the spacer to attain a tighter coil spacing - I never thought of that.

Bob - I will most definitely be using a wrapped screw thread in the very near future to manufacture some smaller springs. - I am looking forward to it.

Great ideas both!

Thanks, great information. I wanted to update the HB ERB as it has a large coil and a smaller coil inside of it as I recall and couldn’t figure what to do.

WOW, multiple concentric coil springs, one inside the other. Now that's a whole new challenge! But I think the various techniques offered above can handle it. I have only had one model with that feature and the model company did a wonderful job replicating it.

And the twist is in opposite directions from bison126's collection
EBR FL11/75

Bronco handles the concentric coil springs on their Kfz.12 like this:

.

VERY IMPRESSIVE MOLDING!

I agree that is impressive.

Here is what HB gives you.
https://www.super-hobby.com/products/French-Panhard-EBR-11-Wheeled-Reconnaissance-Vehicle.html?partner_id=9

I my opinion the Bronco solution is impressive but overkill, given that the finished springs are extremely hard to see when fully assembled and the inner springs even harder to inspect.

Rye Field's AML 90 comes with a separate packet that includes metal springs.

I like the Mirror Models Caterpillar D7 Bulldozer better than the MiniArt offering because they use REAL coil springs rather than molded plastic ones in the suspension.

A minor detail but important to me.

[/quote]

Rye Field's AML 90 comes with a separate packet that includes metal springs. [/quote]

I think that you are referring to the Tiger Model AML-90 kit - which is pretty spectacular in many ways (full interior, etc.). FAIK, RFM does not make an AML-90 kit... But I can always be educated and corrected!

Vulcan Model's British Mk.VI light tank kits also have these spring-in-spring (real springs, mounted on an operating rod, no less...) in their suspension.

IMHO, when you meet this in styrene, you should "always" replace those bits - even those pretty well done Bronco bits on their Kfz. 12 kit - with metal coils. And yes, when you do so, they are actually pretty clear and visible if one looks at all closely. My experience has been that once you start doing these springs, it becomes an easy task and thus an easy "upgrade" to most any build where such springs are visible. And adding "operating rods" where needed is also an easy step with about anything one wants to use as a rod - sprue, styrene rods, wire, etc.

Cheers! Bob

Why not submit this for a how too feature?

When you say "pulled apart" that is more or less the real issue here.

When I started trying to make the spring coils for the Oshkosh TAK-4 suspension I at first wound just a single wire and then tried to pull it out to make an open coil spring. The problem was the "coils" did not expand uniformly. That is why I came up with the idea of rolling two wires at the same time: one is the spring and the other is the uniform spacer.

Of course in my case I ended up with two equal matching springs.

I am sure your product is very usable but I suspect it will still suffer all the same problems we encountered in making a good looking coil uniform coil spring, just as we did.

Not trying to debate here . . . .

All I can say is that when I wound a single wire and then tried to "pull it out" to expand it, the coil spacing never came out uniform. But when I started wrapping two wires at the same time all I had to do was "unscrew" the two coils and the spacing was near perfect as shown in the photo.

Bob's idea of wrapping a single wire around a properly sized threaded machine screw sounds like it too would produce the desired affect.

Based on this discussion I will probably re-do the coils on my MRAP to now have the proper eight turns instead of seven to the spring.

______________________


Thanks everyone for all the contributions.

Keep 'em coming!

Rye Field's AML 90 comes with a separate packet that includes metal springs. [/quote]

I think that you are referring to the Tiger Model AML-90 kit - which is pretty spectacular in many ways (full interior, etc.). FAIK, RFM does not make an AML-90 kit... But I can always be educated and corrected!

Vulcan Model's British Mk.VI light tank kits also have these spring-in-spring (real springs, mounted on an operating rod, no less...) in their suspension.

IMHO, when you meet this in styrene, you should "always" replace those bits - even those pretty well done Bronco bits on their Kfz. 12 kit - with metal coils. And yes, when you do so, they are actually pretty clear and visible if one looks at all closely. My experience has been that once you start doing these springs, it becomes an easy task and thus an easy "upgrade" to most any build where such springs are visible. And adding "operating rods" where needed is also an easy step with about anything one wants to use as a rod - sprue, styrene rods, wire, etc.

Cheers! Bob [/quote]

I stand corrected...Tiger Model it is...caused by a brain fart a few minutes before when looking at Tiger Model kits. I have the Tiger kit in the stash too!

That's a good idea Michael but limiting yourself to the Plastruct wire will really restrict what you can do. You can use Evergreen or Plastruct rod (round and square cross-section) by super gluing it to the shaft, wrapping a section of helix, then super gluing the other end. Dip this in boiling water for a few seconds and the plastic will be set to shape.

As mentioned previously there are a world of steel bars, plastic stock, and wire diameters so one ought to be able to find just about any combination needed.

KL