Tuesday 18 December 2018

Enclosure for line driver - Fusion 360 and Cetus 3D printer

Design enclosure in Fusion 360:

Now that I have bodged the driver board together, it would seem rude not to make an enclosure to house it in.

Flash up quick sketch from the PCB dimensions and extrude to create the PCB, then import the 2D view (JPG) from EasyEDA into Fusion 360 and use it as a "decal" to give a visual to the surface of the board. It didn't work out too well, due to the holes in the PCB which resulted in a sort of black hole vortex effect near them.

Import 3D CAD models of almost identical spring terminal 5.08mm connectors from Traceparts like this for the 5-way part. The best format to choose is Autodesk Inventor. Probably not surprising really, given that they own Fusion.

Assemble connectors onto PCB to form a virtual PCBA. 

Then project the outline to create another sketch offset from the bottom of the board by the desired (3mm) clearance. This will form the basis for the main housing. Offset the projected geometry to give some finite clearance (0.5mm all round) and define the positions of the mounting holes etc.

Extrude the profile to form walls and standoffs, then cut extrude at each end to clear the connectors (by 0.5mm or so).

Provide tab feature on side wall to hold PCB down on one side.

They fit together like this:

Project top face geometry onto another sketch plane located on the top surface of the main housing. Then extrude to form a cover and locating tabs, taking care to clear the connector bodies.

Extrude 2 pillars from the cover to hold the PCBA down when the cover is fitted.

Make countersunk holes on either side of main housing to align with holes in the tabs on the cover. This will allow 2 self tappers to secure the cover. I couldn't be arsed to design a spring clip just for this, as I'm only making a few of them.

Goes together like this:

It would look like this if I made the lid transparent:

Just need to make them now.

3D printing the enclosure:

Here we go. Ran the first set over night. The rafts and supports came away easily enough and I managed to only slightly nip one feature with the cutters (the PCB hold down tab). Looks good overall. I used the "fast" setting rather than wait forever for the normal or fine settings. The surface finish is fine for this application:

The PCBA fits very nicely indeed:

And the cover snaps into place:

I'll probably get away without needing to fit the self tappers, as the cover is a snap fit due to the close fit of the rails and pillars with the main housing features. Besides, it will spend its life sitting in a cabinet. 

I'm printing off another enclosure even as we speak. I need one for each of the 2 servo motors.

Bargain buckets.

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