Making a Conoco Gas Truck, Part II

I continued working on the core for the tank supports and side troughs. In my previous post, I showed the inserts I was planning on using for the hollow part of the troughs. Here you can see me milling out the pockets for the two inserts.


Once finished, I flipped this mold over and milled recessed holes for screws to hold the inserts in place. Then I used a 4-40 tap to tap the holes in the inserts. Or at least, that was the idea—I broke the tap. Darn. So instead I put the inserts into the pocket and then banged on them with a mallet to firmly seat them, hoping I wouldn’t need the screws to hold the inserts in place.

The next photo shows me starting the process of milling away the unwanted, extra material from the inserts. This will take about two hours, and then I have to make several other passes with smaller cutters.


Quite a few hours later, I finally had the core finished. For this I used both flat and bull-nose cutters, varying from 1/8” down to .015” in diameter. Here is what it looks like when all finished:


Now for the moment of truth. Will I be able to fill this completely with styrene, or will I have to adjust the gates and runners so I can fill the cavity? And the answer is:


There’s a little bit of flash in some places that I think I can probably eliminate or at least reduce with some changes to the gating, but the answer is most certainly yes! So being the person I am who likes instant gratification, I threw together the parts I’ve made so far (without doing a very good job of cleaning up the flash). Here’s what they look like mounted on a PBL truck:


Not bad, eh? I like it. But I just realized I forgot to make cavities for the tank lids. Woops. At this point I need to create the mold for the end of the truck and the tank lids, and then it will be ready to go.


  1. Very instructive. I really like your work. Have a sherline CNC and eyeing a desktop injection molding machine. I'm inspired.

    Shannon Haworth


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