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December 26, 2018 – CNC Maker Zone

Routing a fish with 1.5mm Mahogany sheet

Mahogany is a wonderful wood with fine, beautiful looking, grain. It’s ideal for any CNC routing project where you want to give your work a professional, and high-quality, look. So I thought it a good idea to write a short article about my experience of working with it on my cheap Chinese 1610 CNC machine. I decided I’d use a small (c. 50mm or 2″ long) fish design because it includes some shallow work for inlay, as well as a full-depth cut around the outside. The sheet was cut from a 1.5mm thick sustainably sourced plank and, according to my meter, had a water content around 9%. Below is a photo of the wood on the CNC during cutting.

A mahogany fish being cut on a CNC router

As this was a small piece I chose to use a 1mm end-milling bit, so that the shallow details would look tidy. Bits/tools of that size are easily broken through overly deep or fast cutting. For that reason I cut in two passes for the shallow details and three for the outside cut-through, which equates to between 0.5mm and 0.6mm depth per pass. Also, I kept the feed rate down at 50 mm/min which, although a little slow to watch, usually keeps my small diameter bits in one piece. The spindle speed was the maximum of 1000 rpm which, together with the low feed rate, provides a nice clean cut in my experience.

As you can see in the photo below, after just a light sanding, including using a folded piece of sandpaper to run along the shallow grooves, the fish looked quite nice. The only issue I’ve found, if it can be called an ‘issue’, is that the cutting tolerance around the bit is a little more than I’d like: with a 1mm diameter bit I ended up with 1.5mm wide grooves. That’s a 50% overcut which, given the simplicity of the spindle system, and the amount of vibration, is probably technically not bad for a small tool, although it does cause some difficulties cutting thin grooves for things like hammered wire inlaying. Overall though, my experience is that Mahogany can give inspiring and impressive results.

The completed Mahogany fish with the 1mm cutting bit

If you want to have a go at routing your own fish too, below is the SVG file for you to download and use in your favourite software. If you need a DXF file for your CNC router software don’t forget Inkscake will let you save one from the SVG file. And, click here if you’d like to see how this project turned out after some Danish Oil finishing.

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CNC hold-downs using a 3D printer

One of the downsides of buying a cheap CNC router is that you’re left to your own devices when it comes to the best ways to hold down thin sheet materials like wood and plastic. Lucky then that there are plenty of designs online for hold-downs to secure your workpiece when cutting or engraving. On this page I thought I’d introduce you to two of my designs: one for edges and one for corners, both of which can be customised, if you have the need and knowledge, using OpenSCAD. Of course, making them means you’ll need your own 3D printer, an amenable Maker acauaintance, or a willingness to pay for 3D printing online.

Firstly, here’s a photo of my edge hold-downs. They have a small step-out at the bottom to hold the sheet above the CNC bed, so cuts can fall downwards and valuable cutting tools can be kept away from the underlying metal surface. They also have a sloped vertical face to help ensure the sheet doesn’t get pulled upwards. They also have holes and slots so they can be fixed to the bed using standard bed-bolts or some suitably sized bolts and wing-nuts. Click here to visit the Thingiverse page to download STL files for 3D printing and the OpenSCAD file.

3D printed CNC edge hold downs on the bed of the CNC machine

While the edge versions are very useful, sometimes we’d rather hold down corners, either instead or as well. So below is my design for corner hold-downs. They’re very similar to the above design, but have a right-angle end to restrain the sheet on both the X and Y axes simultaneously. As for the edges, there’s a version for fixed corner positions (with a bolt hole) as well as one for adjustable corner positions (with a bolt slot) so they work with a wide range of sheet dimensions. To get the STL and OpenSCAD files for these you can click here.

3D printed CNC corner hold downs on the bed of the CNC machine

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