Introduction: Milling Lighting Gobos
Lighting gobos are used in high-intensity spotlights to give shape to light. A gobo is a fun tool that’s great for everything from pro theater to kindergarten birthday parties.
Basic gobos are made by cutting a shape or image out of thin metal to make designs on walls or screens. “Gobo” is a lighting term that comes from “goes between optics.” We thought a gobo would be a fun and simple way to show off what the Othermill can do.
We made our gobo specifically for an old Ikea Isbrytare spot lamp we had lying around, but you can make these for any gobo holder up to 5"x4". We designed ours in EAGLE for ease of use with Otherplan, our custom motion-control software.
Step 1: Tools and Materials
- Computer with Otherplan installed
- Calipers for measuring
- Utility scissors or tin snips
- Hot glue gun and glue
- Beverage cans, stiff-sided (1 or 2)
- Machining waxas a sacrificial layer, or substitute something like soft wood or rubber
- Steel wool or fine-grit sandpaper
- Double-sided tape
NOTE: This works best if you have a specific light for which you're making the gobo, so the gobo can be sized appropriately.
Step 2: Prep Your Material
For a proof of concept, and because aluminum is expensive, we used an empty beverage can as our material. (Asian drink brands tend to work better for this, as the aluminum is more rigid. Seek out your favorite ethnic grocery and give them a try.)
If you need this to be a bit less punk rock and slightly more precise, go ahead and spring for brand-new flat aluminum stock. You can find it at most craft stores or hobby websites. The aluminum we used was about .0125" (about .3mm) thick.
If you're using a can, cut the top and bottom off with the utility scissors. Cut down the side, unroll the aluminum, and flatten the can as much as possible. The can will also naturally flatten out as you continue through the steps, so there's no need to get it absolutely perfect here.
Step 3: Trim, Measure, and Scrub
Tidy up the edges of your can with the utility shears. By now you've realized the edges are sharp. Be careful!
Measure out the size of the gobo you want to make. It's a good idea to start with material slightly bigger than your final product. In this case, our lamp had a holder that fit a 2"x2" circle, so we cut a 3" x 3" square for a workpiece.
With the steel wool or sandpaper, scrub off the lining and paint on the can. This will ensure that when the gobo is exposed to the hot lamp in the lighting element, nothing will burn off or cause fumes.
Step 4: Load Your Materials
A sacrificial layer is the term used in machining to describe something that goes between the workpiece (the part you're making) and the bed of the machine. In this case, because we're cutting such thin material, we're using machining wax underneath our aluminum so that the tool in the mill doesn't chew up the machine bed when it cuts all the way through. If you don't have machining wax, you can use a piece of fine-grained softer wood.
Secure the aluminum to the sacrificial layer using double-sided tape. Press down firmly to make it as flat as possible. Alternately, you can use a few beads of hot glue and press firmly. Take care not to use too much adhesive, as it could gum up the tool in the mill.
If this is your first time setting up the Othermill, check out our Getting Started guide for details.
In Otherplan, choose Machine > Load/Unload Material. The machine bed will come forward so you can set your material on it. Secure the bottom of the sacrificial layer to the bed of the machine with a drop or two of hot glue along each edge.
Step 5: Import the File Into Otherplan
Download this file for a gobo of the OMC logo.
In Otherplan, import the file by clicking "Import Files" in the Plans panel.
You can also make your own file in any shape you like. EAGLE worked well for us, although it has its artistic limitations.
If you're already familiar with other CAM software, you could convert a custom image to an Otherplan-supported file. Otherplan supports EAGLE .brd files, Gerber files, vector graphics (.svg), and G-code, with more to come.
NOTE: If you do create your own file (and we hope you do!), the image has to be a certain ratio to the material in order for it to show up properly in the lighting element. For example, in our 2"x2" circular gobo, the cut-out size that worked was roughly .75". Any larger and it won’t project properly.
Step 6: Set Your File Origins in Otherplan
Once you've imported the file, it should appear in a panel in Otherplan. In that panel, edit the origin so that the x-axis is 10mm, y is 10mm, and z is the thickness of your sacrificial layer. Press return. The plan should update and move onscreen so it’s rendered in the middle of the material on the bed.
Setting the z-axis to the thickness of the sacrificial layer will make the file look like it's floating in space in the Otherplan window, but it means that the machine will only cut through the gobo aluminum, not the whole sacrificial layer.
Step 7: Set Your Material Origins
In the Setup Material panel, select Single Sided FR-1 as the material, select “Custom Size,” and set the dimensions to match the size of the material you're using (in our case, 3"x3"x0.013").
Step 8: Select Your Tool and Set Up Your Tooling
In the Tool window, select the 1/32" flat end mill, and run through the tool insertion, setup, and locate wizard.
In the Plans window, select the 1/32" flat end mill as both the Trace tool and Outline tool.
Set the Trace Clearance to 0".
Step 9: Cut Your Traces
Have a look at the material in your machine and the material as rendered in Otherplan, and double check your settings.
In the Plans panel, click Cut Traces.
Otherplan will give you one more chance to make sure everything looks really right. Once you start cutting, there's no going back!
If everything looks good, click Cut Traces again.
The machine will start up with a jolly whirr and start cutting your material.
(Now would be a good time to familiarize yourself with the Othermill's Emergency Stop button, the big red one on the side of the machine, in case anything goes oddly.)
Step 10: Cut Your Outline
Once your traces are done cutting, the machine will stop cutting and return to home.
Make sure your workpiece looks the way you expect. If everything looks good so far, click Cut Outline to drill the holes and cut the finished gobo out of the material.
Step 11: Finish Up and Enjoy Your Gobo
If everything has gone smoothly, the machine will re-home when its finished, and you'll have a gobo!
Remove it from the machine by choosing Machine > Unload Material. Remove any cruft or uneven edges with a craft file or a bit of sandpaper. Be careful, though, as small metal flanges can be sharp and delicate.
Now all that's left is to put your new gobo in your lighting element and shine it somewhere!
As always, feel free to send your questions or comment to us at firstname.lastname@example.org. And if you make your own custom gobo, be sure to share it with us!