Magnet Design Guidance

Develop a standard method and fixtures to characterize magnetic force of small neodymium magnets for application in 3D printed designs.

Description

I have dabbled a bit using magnets as print-in-place components in 3D printing projects. They work well for latches and to retain small steel bits and such, but for me the process is trial-and-error primarily. Most recently I built 5 pairs of magnets into a lunchbox design to latch it firmly closed. I wasn't sure if it would be too strong or not strong enough before trying it. It's easy enough with 3D printing to try a few things quickly, but I would like to have a better understanding from the start to predict performance and build it into the design. There are lots of variables that I think could affect the performance. I want a standard, repeatable way to test and quantify the effects of the variables.

Project objectives are to develop:

1) Design guidelines on how to apply magnets in future designs with predictable results.
2) Characterization of the typical magnets I use in my designs.
3) A process and fixture to repeat the characterization of other magnets reli

Details

Components to develop

Fixtures compatible with a standard kitchen digital scale as the force measurement instrument

Test fixture to measure tensile force to separate magnets and magnet+steel target

Test fixture to measure shear force to separate magnets and magnet+steel target

Test fixture to measure peel force to separate magnets and magnet+steel target

Test method for each force measurement - tensile, shear and peel

Spacing shims in increments of typical 3D printing layer thicknesses

Requirements

Test fixtures shall be operable using one hand (to allow for picture or note-taking).

Shall measure force up to 5kgf.

Shall accommodate up to 7 magnets or targets per side.

Shall allow for testing any number of magnets or targets up to the maximum of 7.

Shall control the face-to-face gap between mating magnets.

Shall identify the tolerance of magnet position for a given set of fixtures.

Shall accommodate magnets in any orientation (all N up, alternating N and S up)

Desirements

Could accommodate more than one size magnet or target in a single printed fixture. Only a single size would be tested simultaneously.

Files

Video Aug 23, 10 31 18 PM.mov

Latch concept using alternating orientation magnets and a translating slide.

quicktime - 5.18 MB - 08/24/2022 at 02:35

Download

Video Aug 23, 10 34 10 PM.mov

Simple 5 magnet pair latch on lunchbox design.

quicktime - 4.16 MB - 08/24/2022 at 02:35

Download

Components

1 × 6mm dia x 3mm thick magnet

1 × 10mm dia x 1.7mm thick magnet

1 × 4.8mm [0.188in] steel ball bearing

1 × 5.6mm [.219in] steel ball bearing

1 × Ozeri model ZK14-S - 5kg digital kitchen scale

Project Logs

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Fixture Design Guidance Prototype

Matt • 10/02/2022 at 02:23 • 0 comments

Developed a simple magnet mounting fixture that allows the 6mm dia x 3mm t magnets to press in.

Arrangement of the magnet holes allow for 6 or 7 in a circular pattern (middle filled or not). Also includes a straight line for up to 5 magnets. This arrangement will allow for several different arrangements in symmetric patterns from 1 to 7.

Magnet interface holes are designed to contact the cylindrical surface on 3 sides with small flexures built in.

Printed 2 copies in ABS for fit check.

Magnets press in well and are retained tightly.

Placing the fixture face-down on a flat surface you can press the fixture flush with the surface and press the magnets one-by-one with a small screwdriver or pin to align them all with the same surface on the fixture.

Next step is to add features to connect one to the digital scale connect one to a small pull handle or fixture.

Discussions

Magnet Design Guidance

Description

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