GSA1 - Generic Studio Arm Mounting Grommet

I was looking for a way to attach a budget-friendly, generic microphone boom to my desk. Taking inspiration from the Rode PSA-1, I designed this model. It includes a two-part hub that is secured in a 25 mm hole (which can be drilled using a Forstner drill bit) with a nut. And a top-cap adds a neat look and makes the arm move smoothly.

With it's niche application I guess this model is mostly a learning platform. Look at the Fusion 360 file to find my approaches to:

• Workflow for printable thread geometry

• Customizing with parameters

• Designing for printable overhangs

Printability

When tightening the nut on installation, forces are applied along the threaded section. To account for that, the hub part of this model comes in two variances: An upright printing version tailored for using PETG with it's magnificent layer bonding; And a version to be printed laying on its side for other materials utilizing print orientation for strength. Orienting the parts sideways did require modification to the geometry.

Printable curvature 

To make an overhanging round section printable, a tangential extension is used limiting the overhang to a specific value: 50 deg in this case.  The flat top section will be identified as bridging by the slicer. This is still not optimal in regards of surface finish, but grants better results than simply printing the rounded shape.

Minimal Feature Size

The sideways orientation leads to some sub-Millimeter features, that are relatively hard to print smoothly and generate unnecessary retraction moves. Artifacts in the print may lead to problems in the thread engagement. Additionally to that, the spirals load bearing capability decreases further up the rounded shape; At the base of the hub-half, all strength comes from the materials ductility. At the top, all strength comes from layer bonding. 

Remark:  Minimal Feature Size can be set in the slicer as well.

Printable Threads

The section of the threaded profile that faces downwards is angled at 50 degrees, making it easy to print. Additionally, a 0.3 mm clearance ensures the nut can be threaded onto the hub smoothly, while still achieving a secure fit.

Note: Refer to the Fusion 360 file for a detailed view of how this feature is implemented.

Technical Details

Customization

The provided Fusion 360 file is parameterized. Dimensions like the hubs length, outer- and inner-diameter can be changed with ease, thread geometry will be more of a challenge. The features for increased printability can be selected and disabled via the timeline.

Remarks

My microphone arm features a sheet-metal base that can be bent open. I ran the cable through this. At least the product pictures of the unit sold by ‘Neewer’ looks as if the shaft is welded. Maybe someone can verify this in the comments. If you plan to utilize the full potential of this model keep that in mind. 

Note: The sharp edges of the stem can cut cable sheathing easily; use plastic as protective layer when pulling the cable through. 

Print Instructions

I suggest printing the hub in a different material than top-cap and nut. In my experience PETG on PETG tends to bind more easily than for example PLA and PETG.

If you choose to print the hub with a material that yields high layer adhesion, print the hub top-side facing down (files named with PETG suffix). For materials with relatively low layer adhesion, like PLA, print sideways. Or just be careful when tightening.

I suggest hub in PETG, nut and top-cap in PLA.

The STL files are already oriented in their intended print orientation. 

Related Models

• Neewer 6mm Cable Retainer Clip by Francesco Di Cosmo

• Neewer Cable Retainer Clip by JDBull

Similar Solutions

• Microphone Stand Desktop Adapter - Grommet & Nut by queenMaev