Spiral has no smooth surface but steps

[Dennis.Stucke]

Hi everyone,

I'm trying to design a piece that includes a spiral structure. I managed to create the spiral with the "coils" tool (Fig. 2) as well as with the "sweeping" tool (Fig. 1). But with both I have the issue that the surface of the spiral is not smooth but has a stairs-like surface. The height of these stairs depends on the dimensions of the spiral. Also when I export the parts to stl-format the stairs-like surface remains. 

I am sure that this effect is not just optical as I can select the edges as it can be seen in figure 1. This works at least in the stl-file. In the ipt-file I cannot select the edges.

Is there any option to generate a smooth surface? Or is there a limit on how small the details in an inventor part can be? It would surprise me if this is the case as the middle pole has a diameter of 0.8 mm and therefore the steps have a height of around 0.2 mm which is not exessively small.

In case this is a normal behaviour and there is no setting to get a smooth surface is there a workaround to circumvent that problem?

Fig. 1: spiral generated with sweep function.

Fig. 2: Spiral generated with coil function.  

Thank you in advance for your help.

Kind regards,

Dennis

[blandb]

Can you share the part?

[Gabriel_Watson]

What are your settings here?

At the "Hardware" tab, try "Quality".

[Dennis.Stucke]

@Gabriel_Watson I have the same setting for display quality as you have in the display tab. I changed the setting in the Hardware tab but I didn't solve the issue. It's just that the steps are now smaller but not gone.

I also added the ipt. and the respective stl file in case you want to have a look at it. @blandb 

Thank you a lot for your effort.

[JDMather]

@Dennis.Stucke 

These two dimensions (one aligned and the other vertical) do not make logical sense to me?

Notice the gap.

Also, your profiles are not perpendicular to the start of the Helix.

[Dennis.Stucke]

Thanks for the hint. 

The vertical dimension is actually a mistake. I want the thickness of the spiral to be 0.8 mm. But changing this doesn't solve the problem.

@JDMather What exactly do you mean with "not perpendicular to the start of the helix"?

If you mean that the profile is at an angle to the horizontal then this is intentional. If this is causing the issue than I have to search for another way to design the part.

[JDMather]

Not sure when I will get time to post example, but you need to create a Helix (I generally use surface body Coil rather than 3D Sketch Helix as it is easier to edit).

Then create a Workplane at the start of the Helix perpendicular to the Helix.

Then create your sketch on the new Workplane. 
Sweep.

[JDMather · Accepted solution]

@Dennis.Stucke 

Examine the Attached.

[Dennis.Stucke]

It works. Thank you very much @JDMather and all others who tried to help.

I just have one additional question. I'm trying to understand what exactly is different in this approach that makes it work compared to my approach that didn't work. 

This is important to me as I always want to understand what I'm doing in order to improve my skills and to be able to apply it in the future.

[JDMather]

@Dennis.Stucke 
Make sure you understand that last extrusion I did - I suspect that you really need to reduce the height of the helix by the thickness of the material.

To understand the geometry let’s assume winding a simple cylinder into a helical spring.

Modeling as a circular profile that is not perpendicular to helical path would result in a flattened “elliptical” cross-section profile. In most cases this doesn’t matter as the coil spring is merely for cosmetic purposes - the actual spring will be purchased off-the-shelf item. But if we are designing real geometry that won’t simply be standard vendor item we have to take the logical steps to replicate the real world geometry. No Easy Button solution.

I’ll try to post an illustrative example latter today.