Wound Steel String for Acoustic Guitar

[Anonymous]

Hi everybody,

I've been searching on the Autodesk forums, but I haven't been able to find much information about how to create wounded steel strings on Inventor.

Here is the deal. Usually, the first two strings are just flat and not wounded, for that, you probably just draw a circle and make a sweep through a 3D path.

The other strings are another beast. Let me explain: The other four strings are usually wounded, this means they have a core, and an external wound of another material, which in steel strings is normally bronze or phosphor-bronze alloy. Let me show you how:

This image shows the usual two types of cores, round and hexagonal.

Moreover, there are several winding methods:

Is it possible to create a round wound around a string (swept circle or hexagon) with a coil, or other feature that I'm not aware of, that can keep both items linked but at the same time allows to assign different materials to them?

Thanks a lot!

[SharkDesign]

You can only assign different materials if you make them as two parts and assemble them. 

Having them as a multibody will allow two different colours/appearances, but not physical materials.

[Anonymous]

Thanks for the reply. So how would you make just the round wound part?

[SharkDesign]

Try using a coil. 

If that doesn't work you might need a spiral in 3d sketch and do a sweep. 

[JDMather]

This is pretty basic geometry in Inventor.

What version of Inventor are you using? 2012? 2021? 2022?

Once the version is known an example can be provided.

[Anonymous]

Hi there. I'm using Inventor 2020 Professional. Any help or guidance is welcome, even if it's a basic geometry. Cheers!

[johnsonshiue]

Hi! Please google the following terms. You will see quite a few instructive videos and pages.

autodesk inventor coil, helical path sweep

Many thanks!

[3D4Play · Accepted solution]

You can do this in a couple of ways, depending upon what you want your end result to be. Regardless if it's a single (multibody) part or an assembly (with two separate parts), you will use the coil feature. Here are two screenshots showing how to do it as a single part, but with two distinct bodies, so you can assign different visual treatments to the resulting features. Note, you're not assigning materials, per se, you are merely telling Inventor how to display the surfaces.

First screenshot shows how to setup the sketches - it's actually two sketches. The first sketch is the inner string - I chose a .010" extruded circle - then extruded it 1". The second sketch is the winding string. I set the outer finished dimension of the wound string at .036", which happens to be the A-string on my custom light gauge 10-46 set. Note that the .013" diameter of the winding string is a reference dimension; you need that value when you set the pitch pitch of the coil, and it is parameter d4. So, the coil is formed by the circle profile, coiling about the string axis, at a pitch = d4, and to a coil height of 1". I circled the key selection to make the coil a separate body, instead of combining it with the original extrusion.

Now, when you follow these instructions exactly, the coil will fail, and you'll get an error that the coil is self-intersecting. Technically, it shouldn't fail, because the coils are wrapping dead-on next to each other. But, it will probably fail, and the way to get it to work is to make the coil pitch ever-so-slightly larger than the winding string's diameter, so (what you don't see in the final result, second screen shot) I made the pitch height d4 + 0001. The successful result is two bodies that you can change properties on. I made the inner wire display as polished steel, and the outer wire display as brass. I did this in 2022, but your workflow will be similar in 2020. IFF you really need to make the material accurate, in terms of physical properties, then you do need to make two separate parts, and assign material in the physical properties.

Along with the links already posted, this should help you.

[3D4Play]

BTW, I forgot to mention: helical coils eat up performance like pacman eating dots. If you try to build an entire set of six strings, four of them wound, at full scale length of your guitar, you should expect to take a performance hit - that's something on the order of maybe 10k wraps in the helical...so, Inventor might look at that for a minute. 😉

[Anonymous]

This explanation is simply fantastic, very detailed. Thank you very much! I'll explore this way of doing the string, and create two separate parts, to assign different materials :]

[JDMather]

Your circular profile does not appear to be perpendicular to the path which will result in a "squashed" wire.

Setting the profile perpendicular to the path generally results is a more computationally efficient solve.  (Although all helix-based geometry is computationally expensive.)

@Anonymous 

See Attached example file.

[Anonymous]

Hi there. Thank you for the .ipt file and your help of course. I'll explore the solution you attached to see in detail what you refer to 🙂