I'm an advocate for having a door to access the oil dipstick. I don't find it easy or convenient to remove the top cowl just to check the oil level. So here's my approach for making the access door.
Step 1 -- Locate where the put the door
With the top cowl off the airplane, I removed the dipstick and covered the dipstick tube with a ziplock baggie and some tape. I found a tube that was a close fit to the dipstick tube. I slid this tube over the dipstick tube and re-installed the top cowl. Reaching up from under the cowl, I slid the tube upward to the cowl. I marked the outline of the tube where it contacted the cowl. I had to fudge a bit because the tube didn't touch the cowl all the way around. I removed the cowl, removed the tube, removed the tape and baggie, and re-inserted the dipstick.
Step 2 -- Decide what diameter hole to use
Don't cut a hole in the cowl just yet!! I took a small sheet of plywood and started drilling holes of various diameters in it. I found that a 4-inch hole was a comfortable fit for my hand to go through. My dipstick is within 2 inches of the top cowl. It is easy to reach. Therefore, my hole did not need to be any bigger.
Step 3 -- Cut out the door
I marked out a 4-inch diameter circle centered on the marks I made from the slip pipe. I marked an X over the door and onto the surrounding cowl surface. These marks would help me to realign the door with the cowl later. I carefully cut out the cover.
Step 4 -- Make the flanges for the door to sit on
I applied box sealant tape over the inside surface of the door. I prep-sanded the inside of the cowl around the door opening. I mixed up some 5-minute glue. (Bondo will work, too.) I glued little rectangles of foam on the outside of the cowl spaced around the hole. Turning the cowl over, I next glued the door to the foam rectangles, being careful to rotate and align the door to the existing marks. To make the flanges, I made a 3-BID layup in the form of a circle and applied it on the inside the cowl, centered over the door and its box sealant tape and overlapping an inch onto the inside surface of the cowl. When cured, I removed the foam rectangles and popped the door off. I cut away most of the 3-BID layup to create the flanges. My flanges are a little less than 3/16th inch wide all the way around the opening. I installed the top cowl and did a trial run with the dipstick. The first picture shows the 3-BID layup covering the hole. The second picture is after cutting and shaping the flanges. The third picture shows that the hole is centered over the dipstick. So far so good.
Step 5 -- Make the J-Hinges, Flox the J-Hinges into Place
The first picture shows the J-hinges that I made for the oil dipstick door. It took me a while to figure out the geometry. Note that the brackets are drilled to accept flox pads. The second picture shows the J-hinges being floxed to the inside of the top cowl and to the inside of the dipstick door. I made several trial runs with bracket locations before settling on the exact placement. When I thought I had it, I bondoed the door onto the cowl. I mixed up some flox and floxed the J-hinges onto the cowl and door. After cure, I opened the door for the first time. Not sure what happened, but I found that the door didn't open far enough. Plus the edge of the door would touch the cowl. I fixed it by slicing off a small portion of the door and floxing it back onto the cowl opening. Now, the door opens wide enough to get my hand into the hole and remove the dipstick without the edge of the door hitting the cowl.
The next step will be to install the door lock. I don't like the one supplied with the plans. I have ordered another type. When it comes in, I'll glue it to the door and I'll be done.