This was a fun weekend experiment, and a fairly Rube Goldberg way of designing the skateboard: I used Google Tilt Brush on my Vive to sketch out the board in VR (allowing me to experiment with many life-sized designs quickly), which I exported & brought into Fusion360 for CAD tracing, then CAM output. I knew that the 1/2" HDPE sheet wouldn’t support the weight of an adult, but I figured I may as well test my cut settings for this material anyway 
Whole cut took less than an hour out of a 12x30" sheet. Used a 1/8" 1-flute upcut endmill, DeWalt on 1, 120"/min did just fine. I had started at 60"/min, but got some melting around the cut, the more I sped it up the better it got. It looks rougher than it really is, the endmill makes interesting patterns in the plastic that reflect in the light.
I may try a 3/4" thick sheet next, see if that will hold an adult’s weight, but not weigh too much itself.
It is great attempt.
1 Hour… That tells what’s wrong with those pockets.
I would rather to use large area clean with 1/4" bit, then you can do second stage with 1/8" bit.
Also check the step-over rate on your tool database. the rule is 1/3rd of the bit size for better pocket surface.
Don’t rush it. Go several passes with shallower DOC. Job like this could take over 3 Hours. You’ll see the difference.
What I do if this one is my project is;
(I have Aspire and Vcarve pro) I generate Vcarve tool-path with 90 degree Vbit and give .05" flat depth, use 1/4" bit for large area cleaning on first stage.
That way you have nice 45 degree clean edges on those motifs.
Just my idea, if it make sense.
Looks pretty cool. I think the tool paths make it look cool. you could probably laminate it to plywood to get the strength you need.
Thanks for the feedback @AlanDavis : First time I’ve used this material so I’ll take all the help I can get While there is no doubt the pockets could be better, I intentionally caught the reflection in the sun (which makes them look ‘worse’), since that black is so hard to shoot otherwise.
I completely agree though, normally I’d use a 1/4" but for the rough. Issue is, I don’t have any 1-flute bits of that size, so I just used what I had (1/8"). Just fyi, my stepover was .5 bit width. I had planned to use my v-bit as well, but the next issue is, that my v-bit is on a .5" shaft, while my 1/8" bit is on a 1/8" shaft, and the chucks really don’t like to come loose without a bunch of tugging, and I was afraid I’d loose registration during that process.
But again, appreciate your thoughts, I’ll reference them next time I do a cut like this