Hacking and Casting a Universal Air Marker

In this Intractable I show you how I use my design process to retrofit and hack a vintage LetraJet AirMarker for use with Copic, Prismacolor, Tria, windsor Newton or most any current day marker. Watch the video here

I start with a vintage Tria LetraJet AirMarker because it has a nice trigger action and I found it cheap on ebay for under $20 with shipping.

If you have ever used an AirMarker or own one of these follow along and check out the process I used to modify it.

I Used the following:

1. Tria letrajet air marker

2. Pen and paper to sketch, digital sketching app

3. 3D printer, Ultimaker2

4. Band saw, but a hand saw will work too

5. Primer and sandpaper and sanding block

6. Silicone molding supplies, mold box and Silicone to make molds

7. Urethane resin and syringe

8. Misc. supplies, x-acto, clay, wood and mold release agent

Step 1: Design the Look of the Retrofit

I begin by sketching the look of the snap-on-body. I start by sketching a side view on top of a photo I took of the original unit on paper and then scan that in and finish the sketch in Photoshop on my Cintiq.

It's down and dirty, rough, but it lets me work out the proportion of the add on, so that it looks good when I am finished.

This is a crucial step that most people omit. It's also part of what differentiates Designers from makers.

Step 2: Prototype and Test Fitting

Next: I needed to test the fit of the adapter on the existing body and see how well it holds the markers in place.

I built a basic form in Fusion 360 based on the existing AirMarker's profile that I measured with some calipers and then did some educated guessing along with a bunch of trial and error.

You can see how many prototypes I made to test things out to get the fit that I was after.

I printed them on an Ultimaker2

They snapped on to the existing air marker, then I could test the markers to see how they were held in place. Sometimes they were two tight and sometimes they were too loose or the connection needed to be more universal. Eventually I found the right fit.

Step 3: CAD to Make the Final Body

Now it is time to build the final body in CAD.

I used the successful profile shape from the last step and extruded into a longer form to get the look and feel I designed when I started the project from my initial design concept.

Check out the video to see more detail of this process.

Next: print out the part and check to see how well it works.

Step 4: Machining the Rapid Prototype Part and Cutting the AirMarker

With a good print in hand I need to make a few adjustments.

The part snapped on to the markers pretty good now I needed to make it fit the existing AirMarker a bit better.

I needed to cut and hack the attachment snap of the AirMarker to get the new adapter to fit.

I cut this off with my band saw.

It fit pretty good but I need to open up the air Lever are a bit more so that I could depress the lever all the way to the body.

It was not efficient to make the changes in CAD and reprint a new adapter so I machined the 3D printed part on my drill with my cross slide (poor mans Bridgeport)

I wrapped a piece of leather around the part and slid it on a mandrel so as not to damage the part when I machined it. This worked like a charm and I was able to open up the space for the lever to have the action that it needs to function.

Next: priming and prep the part.

Step 5: Sanding and Finishing the Rapid Prototype

The part needs to finished with primer so that it has a nice uniform surface suitable for casting.

To do this it needs several coats of primer and a bunch of sanding. I needed to eliminate the build lines from the prototype part on the outside. I used Duplicolor primer to build up the surface. Next I sand with a 220 grit wet dry sandpaper and successive coats of primer and eded up with a 400 grit wet sand finish on the part.

Step 6: Making a Two Part Silicone Mold of the Master Part

Now it's time for the the real fun: Silicone Molding.

I made a two part silicone mold from the master part.

I won't go into to much detail here since I have other instructables about the process. You can watch my previous video here and check out the Intractable here

I have premade mold boxes that I use for making silicone tooling, so I grab one of them and section it off to insert the clayed up part and get it ready to pour part "A" of the silicone.

Once the "A" side has cured I remove the bottom from the form and apply mold release (vasoline thinned with naphtha) to the exposed silicone and then pour the B-side. I add the runner/gate but forget to add the vents, they need to be cut into he silicone by hand.

See the video details here

Almost finished. Next up: injection cast the part in resin!

Step 7: Casting the Final Resin Part

I mix up some of my favorite resin and add a hind of black and blue colorant to leave the resin with a bit of translucency.

I de-gas the resin and suck it up into a syringe and then inject it into the opening in the silicone.

I also have another Intsructable about this process you can see that video here and the Instructable here

Next it all goes into a heated pressure tank to ensure a strong bubble free part.

Once it has cured I remove it from the tank and check out my part. Success! I have made my a good part. I can now snap it on the original modified AirMarker and use it to render some new design concepts.

Hope you enjoyed this instructable. Make sure to like and follow me here and look for more in the future.

Eric Strebel, is an Industrial Designer living in Southfield MI. He has a home-based Industrial design studio “Botzen Design”and has been designing consumer products for 25+ years ranging from sunglasses for Bauch & Lomb, Traps eyewear, entry level luxury vehicles for Ford, wireless charging PowerMat for Homedics, to magnetic toys for Guidecraft. He specializes in tabletop and handheld products, ranging from routers to cosmetic products to Bluetooth devices and everything in between, he also teaches Industrial Design at Wayne State University and CCS (College for Creative Studies)

Follow Eric on Twitter @botzendesign and Subscribe to his Youtube channel. You can check out my previous Instructable here about how to make your own Home made silent shop compressor from a refrigerator motor