But THEN there is a DAD's division! The rules for the Dad's division are as follows:
1) Weighs less than 5 ounces
2) Fits within 1-3/4" by 6-15/16"
3) Uses the wheels in the kit
4) Bring it!
Now, I am a member at TechShop (the one in RDU) - http://techshoprdu.com
I decided that I would use the opportunity to learn some new skills, and I would use the Shopbot!
Follow along for an adventure to learn what to do (and what not to do....)
Step 1: Computer Work
It turns out that Sketchup was NOT designed for this type of work. I wasn't going to pay $495 for the pro version (which had solid tools.) I should have just gone to Techshop and used Autodesk Inventor there. (But I didn't know how to use that either, and I decided that I would just go ahead.)
Anyway, I browsed the Google 3D Warehouse and downloaded a model of a Camaro. Then I scaled it from the full size down to the width I needed my wheelbase. (1.5") I deleted side view mirrors and other details (like the inside of the car).
I downloaded a free plugin that let me export STL from Sketchup. Then I pulled it into Partworks3D (on the Techshop computers) which let me do the CAM work. (That is the photo above.)
Step 2: Preparing the wood
Step 3: Run shopbot
Obviously not enough hot glue to hold it. I then cover the bottom in hot glue. I put everything back, tell the shopbot to go home and the bit comes flying across and breaks in half when it hits the block. I hadn't recalibrated the Z azis after my escapade.
I go buy another bit from the Techshop retail store, and continue.
The bottom is cutting fine. Then I put in the ballnose bit, and because the outer part hadn't been fully removed yet the collet runs into the wood and causes some burning. (from the friction.)
I hit the e-stop again. And decide that I have found enough problems with the cutting from the bottom, that I'll cut from the top and find the OTHER problems in my CAD/CAM work.
I go to remove the hot glue, and it won't come up. In the process of getting it to come up, I slice my hand with a chisel. Luckily it was a sharp chisel so the cut was small. (sorry, no picture of the blood....)
Finally I get it to come up, and then glue it to the otherside of the board.
Step 4: Pass 1 - top
Unfortunately, I look and the fenders aren't even close to the size they need to be. I am puzzling over this when a friend mentions to me, "Of course you realize that the wheels in pinewood derby aren't scale to a real car." As soon as he says this it is obvious he is right.
I try to increase the size in Sketchup, but am failing miserably. (Have I mentioned how much Sketchup is not made for this task yet?)
I realize that I only have time for 1 more Shopbot session before the race, so I need to get it right. So I decide to remove as much error from the process as possible.
1) Make it so I can do it with only a single cutting pass from the top. This means reducing some detail.
2) Make it with no fenders, out of just a single pinewood derby block. This will make it more the dimensions of a "normal" pinewood derby car.
I finally find a Sketchup extension where you can select multiple vertices and set their Z to the minimum of all of them. This lets me drop the sides of the car so there won't be wheelwells.
Step 5: Pass 2
I realized looking at it with just the rough cut, that the car wasn't centered on my wood. Turns out the table wasn't perfectly zeroed. Luckily I had one more piece of wood and some time left in my shopbot slot.