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safety – CNC Maker Zone

3D printing door pullers to fight Covid-19

Door handles, and anything you need to pull, are important transmission points for viruses and bacteria. So, with all the concerns about Coronavirus and COVID-19, I obviously wanted to make some handle pullers I could use outside my apartment and to give to relatives and friends to help keep them safe. I didn’t find exactly what I wanted online so this is the result of me designing my own model using LibreCAD and OpenSCAD. Here’s what the finished design looks like:

A 3D printed door puller photo

Most of all, I wanted the puller not to look sterile and medical: there’s enough anxiety around viruses already, so why add to that. For that reason I designed it to have a chunky and colourful look, with rounded corners and extra parts to fit around holes to increase the number of filament colours I could use. Also, I designed the opener to close into a case with a latching action to make sure it didn’t come open when not wanted, so as not to cause unwanted contamination.

A few door pullers printed in different colours

To construct the opener from the STL files you need the opener itself, the case, the hinge inner and outer rings, and two surround rings. There’s two versions of each of the rings (round and cog-like) to give a bit more variety to the look, which can be mixed and matched. The opener simply needs placing inside the case, then insert the outer ring. With a bit of glue inside that you can then insert the inner ring.

If you’re careful with the gluing the rings will then still rotate letting you use the opener as a fidget ring too. The surround rings can then be glued into the smaller finger holes, which are positioned not to conflict with the opener when closing it up. If the latching is a bit stiff, a little light filing at the end of the opener will help. Adding a keyring loop and/or carabiner finishes the job and makes it easy to carry on a bag or belt loop. If you have big hands, making the finger holes too tight, you can just increase the X and Y scales in your slicer (keep them both the same so the holes stay circular).

Two door pullers, one partly open and the other fully open.

To download all the STL files to make your own door puller, just click the link below to MyMiniFactory: don’t worry, the project is completely free to download and use. Also, if you want to customise the models in some other way, the LibreCAD DXF file, and the OpenSCAD file, are included there too. The OpenSCAD file includes variables for opener and case thicknesses as well, making it easy to build a thicker or thinner version with little effort. But, however you build it, take care and avoid the viruses 🙂

View this project on MyMiniFactory.com
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Adding a spindle motor switch

I tend to prefer to minimise safety risks when I’m using my CNC, and that includes making sure I don’t injure myself touching fast-rotating cutting bits. Obviously it’s unlikely that the motor will start up when I’m removing or attaching a bit, although it’s a little more possible when the G-Code file includes pauses for tool changing. But, to be completely sure nothing can go wrong, I made the 3D printed switch box below to allow me to isolate the spindle motor from its electrical supply. It prints as two parts which need to be glued together to fit the top of a 20mm extrusion, like in the photo above. The hole in the front is made to house a standard 18x11mm rocker switch. Click here to go to Thingiverse to get the STL files for your 3D printer.

3D model of the spindle switch box

Once the two parts of the box are stuck together, with the switch inserted, the positive wire from the spindle motor controller to the motor itself, which should be red, needs to be cut. The position where you do that needs to be planned so that the wires can be run to the box and the full movement of the motor along the CNC’s x-axis isn’t compromised. Personally I found the best place is near the controller board as on my CNC the red wire ran straight past the box position. You can use standard spade connectors crimped onto the ends of the wire, after stripping some insulation from the end. Below is a photo of the back of my switch box so you can see what I mean.

The back of the switch box showing wiring

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