Introduction: Wooden Aperture
Step 1: Choosing Materials
I just used what was available in my shop. Spare lumber, some screws and bolts. The most important part is the arm. If the aperture is closed the arms need to bend. Thickness and flexibility is important. The 3mm plywood I used is maybe a little too rigid but it will work.
8x Arms, 1 holding ring, 1 hinging ring: 3mm plywood
2x Outside ring: 18mm particle board (I used an old tabletop)
8x Hinge: screw and bold, M2x10mm. Plastic washer M2 (can be metal as well)
8x Pushpin: screw and bold, M2x25mm
16x Copper wire: 3mm x 6cm
Small materials like 16mm woodscrew, 8mm plywood pushrod, glue, scrap wood
Step 2: Holding and Hinging Rings
Use a pair of compasses to draw two rings directly on the 3mm plywood sheet. The outside diameter is 21cm. The inner diameter is 12cm. Divide the 2 rings in 8 parts. Saw and sand.
Step 3: Slot for Pushpin
Make in the holding ring slots. The slots should be 1 mm wider than the diameter of the pushpins. I used M2 screws, so the slots have a width of 3mm. The length is 35mm. The length of the slot will determine how far the aperture can be closed. But longer slots with weaken the holding ring. And even if that is not a problem, the thickness of the arms will also limit the closing. By changing the shape of the arm, you can influence the closing limits. Using 3mm plywood, the shape and slot length are ok. Changing them will not close the aperture any further. You need to decrease the thickness of the plywood or use other materials to improve. An easy way to get a nice slot is to clamp the holding ring in a bench vice and a shape with a thin flat file.
Step 4: Arms
To make eight equal arms, I used a technique I learned from making wings for model airplanes. On some spare lumber I drew the shape of the arm twice. I roughly cut (to big) out 8 pieces of plywood and drilled the two 3mm holes with care. Everything is sandwiched together with two 3mm screws and bolts and shaped.
Step 5: Connect Arm to Hinging Ring
Drill holes in the hinging ring. Use an arm to find the proper spot by positioning the arm as close as possible to the inner side. The hinge hole in the arms should be countersinked on one side and the pushpin hole of the arms should be countersinked on the other side. I have put plastic washers between the arm, the hinging ring and the bolt for improved hinging. Probably it will work without or with metal washers. Connect the arms with the hinging ring. You can now try to close the aperture. I you are satisfied, use the M2 (25mm) screws and bolts, to construct the pushpins.
Step 6: Enclosure: Front Side
Saw two ring of any wood you like (diameter outside 23cm and inner side 18.5cm ). I used an old tabletop (particle board: wood pattern one side and dark brown the other). Cut the 3mm rods at 6cm length. Drill all 16 holes (about 10mm depth) in both rings. Put 14 rods in one ring. Leave out two rods for the handle. This is your front view. Screw the hinging ring to the enclosure ring. Put the holding ring in place, with the pushrods in the slots. Try moving and operating the aperture. Remove the holding ring.
Step 7: Enclosure: Back Side and Handle
Saw, use a router or file to make a slot in spare lumber (1st picture). Saw 4 pieces wood and use a screw to keep the holding ring in place (2nd picture). The holding ring should move easily. Put the construction together. Try to open and close and decide where to connect an operating handle. Take a part the construction and glue or screw the handle in place. Your Aperture is ready.
YouTube clip Wooden Aperture
Jan Willem Kooi