A Mechanical Iris Window With Porthole

In this Instructable I will describe the process of building a mechanical iris diaphragm window with a porthole into an existing wall opening. I've always appreciated old fashioned ingenuity where the mechanics were as much art as function and a mechanical iris is a great example of this. Irises have a unique balance and symmetry and the steampunk world has taken the device to a new level of appreciation.

Several months back began creating a studio in the attic above my garage. Little by little I've been filling the space with tools, decor and computer equipment. The room had one small window on the one framed in wall. This wall is something of a focal point in the room and I've been want to do something creative with the window and a big round iris seemed perfect.

The space originally was completely unfinished with open rafters, roof and wall framing with a simple screened window built into the framing. On the exterior of the house this window is covered with louvers so even with the lights on at night it doesn't draw much attention. I began insulating and laying the sub-flooring and covering the walls and ceiling with OSB sheeting. The window was only finished on the outside so I covered the void with OSB and marked the opening. I found some inexpensive laminate flooring and used it on the floor and for a different look I covered the windowed wall with it as well.

Thanks everyone for taking a look see - please vote for me in the Full Spectrum Laser Contest!https://www.instructables.com/contest/fullspectrum2014/

Step 1: The Design

I began by drawing up the project in AutoCad. I knew I'd be using my Carvewright CNC to mill out as much of the project as I could so I planned most of the parts to fit in the machine. The early design, shown in the shop drawings throughout this Instructable, used the leftover flooring as the iris framework and mechanics. The material seemed to machine well and I thought the color contrasts would make it *pop*. That was the idea anyway.

The existing window opening is 24" wide. That's a little large for a window like this. It would take a considerable amount of material for the leaves not to mention weight concerns. An 18" aperture seems a bit more practical. Plus, with louvers on the outside of the house, it's not like I have some grand view outside anyway.

I played with a few designs of different numbers of leaves. Irises can be built around an unlimited number of leaves from one (think guillotine) on up. I chose to use 12 leaves because it gave a nice round opening and the 30 degree increments work well around a circle.

The main cover shell contains the leaves and the cam. The cam ring holds the travel pins on the leaves and rotates to operate the aperture. To open and close the iris I added a partial spur gear to the cam to mate with the pinion gear mounted to the side. This way the cam plate will be enclosed under the housing cover and the small gear allows the aperture to function without having to open the porthole. The porthole cover has a clear polycarbonite Lexan window to assist in keeping out the elements.

As with most projects, things change and after much trial and error I determined the laminate had to go. There's a learning curve in using this laminate in the Carvewright. The biggest problem is it's so slick it's hard to hold in place which leads to tracking and misalignment problems. The grain patterned surface is also very brittle and chips out easily. Plus it quickly dulls the bits and will burn them up over time. Factor in various software issues, machine issues and user issues and I started running out of patience ( and laminate ). After much frustration, new software and a lot of cursing, I decided to switch to tried and true Carvewright friendly plywood for the bulk of the project. I used good grade of Baltic Birch 1/2" ply with few inner voids. This stuff stains well and looks good. Overall I'm pleased with the results. I still think it *pops*.

I'm posting the dxf CAD file here, as well as pdf files of the drawings. The pdf's should print to scale on a common letter sized sheet. Although my design changed, the CAD files should work fine if someone was of a mind to pull out the part patterns for their own uses. Everything is drawn to scale and I can only assume you could drop them straight into a laser cutter or even a waterjet and assemble them with no problem. Carvewright owners - use at your own risk!

Step 2: The Leaves

The leaves are the focal point of the entire project and need to be sturdy and flat. I contemplated using either fiberglass or carbon fiber, but quickly decided on sheet metal. I have access to aluminum, carbon steel and stainless steel sheet. For appearance and exposure to the weather, stainless seems like the best choice.

The leaves are sandwiched between the cam plate and the wall and each leaf has a pin on the cam side and the back side. They measure 4" wide with an inside radius of 9" and an outside radius of 13". The stainless is 18 gauge 304 grade with a #4 polish and was cut on a CNC plasma table.

For pins I chose 1/4" weld nuts or "tee nuts" with a slab base. The flat base welds easily to the leaf and the collar extension sits about 1/4" tall to fit in the wall and cam. During assembly to the wall I ran 1/4-20 x 1/2" bolts from behind into the pivot side tee nuts just enough to keep them from falling out. The travel pins are held in the cam in a similar fashion with more 1/2" long bolts. I had a coworker tig weld the pins in place and then he buffed a radial pattern to the polished surface.

I tweaked the pin locations a bit for this design instead of placing them in the center of the rounded ends of each leaf. The pivot pins going to the wall are offset towards the rounded end allowing a bit more swing away from the housing shell. Likewise, the travel pins are offset towards the outer edge which keeps the travel path further away from the aperture opening.

Step 3: The Cam Ring

The cam plate is a flat ring with slots for the leaf pins to travel through as the cam is rotated. The ring width matches the leaf radii, inside 9" and outside 13", so that the leaves disappear behind it when fully open. The pin paths are simply radial grooves extended out from the center point. As the cam rotates it pulls the leaf pins in or out to open or close the aperture.

To fit in the Carvewright I broke the ring into 4 quarters with a key to join the pieces together. In the original design, shown in the drawings, the key is a butterfly style similar to woodworking keys but with a radial design to it. The key was a separate piece, like in the early housing and porthole patterns, to give contrast between the darker and lighter laminates. After giving up on the flooring and the contrast, I opted to just use half keys, male and female, to simplify matters. I switched the cam material to the same .220" polycarbonite I used in the porthole. The poly is plenty durable for the teeth to mesh without fear of cracking. The 4 quarters glued up well with cyanoacrylate glue and weights to keep it flat while setting up.

One of the quarters has the gear teeth along the perimeter. The teeth started as #6 diametral pitched teeth on a 26" pitch diameter. After tweaking diameters and clearances a bit I changed the diameter to 25-1/2" and just scaled the teeth down proportionally. Technically it's no longer #6 as anyone familiar with spur gears will notice, but they mesh fine and there's no significant backlash.

The drawing shows just 60 degrees of teeth but after the design changes I opted to spread them out further. According to my layout, the iris needs 54 degrees of rotation between fully open and fully closed. My concern was the orientation of the teeth after everything was assembled. The pivot holes and the pinion gear hole are in a fixed location. The cam rotation, and especially the gear teeth, are going to end up where they end up. I didn't want to put it together and find out it should have three degrees to the left. As it turns out, everything fit well.

Step 4: The Pinion Gear

The pinion gear assembly is made up of three layers - the bottom hub, the toothed gear body and the top. The bottom hub is a spacer to bring the gear layer out to mesh with the cam teeth. The gear layer and bottom hub have a hole a wee larger than 1/2" diameter to allow a 1/2" O.D. nylon bushing to loosely ride inside. The top has a hole large enough for a 1/4" hanger bolt to hold the gear and bushing to the wall with an acorn nut on top.

Since this is a sandwich of layers and the 3 parts are meant to be oriented together I added holes to line up with alignment pins. These pins are toymaker's wooden axle pegs from the hobby store. Size wise they're 7/32" diameter which is a good fit with glue inside a 1/4" hole and they leave a nice little wooden dome on the top. Lengthwise they're longer than the sandwich is thick but are trimmed to length easily enough.

Like the cam, the gear teeth started as #6 diametral pitch, but were scaled down to match the cam teeth. As a result, the pitch diameter has changed and would actually be considered 4-1/6" if one were to do the math.

Step 5: The Cover Housing

The cover housing is a 12 sided polygon shell that mounts against the wall and encapsulates the internal mechanism. Inside the bottom cover ring is a set of 12 nylon bushings positioned for the cam ring to rotate around. The bushings also act as a stop for the leaves when the aperture is fully open. The bushings ride on 12 bolts coming from the wall. A rounded cutout is positioned on the right side at 30 degrees up from horizontal for the pinion gear to tuck inside and engage the spur gears along the cam. On the face of the cover are two mounting plates on either side for the hinge and sash lock from the porthole.

The upper and lower cover rings were cut from plywood on the Carvewright. The rings were cut in quarters to fit the width of the machine with male and female half butterfly keys like the cam plate. The two porthole mounting plates with alignment holes were also cut on the Carvewright. Like the pinion gear I used the wooden toy axle pegs as alignment pins to position the pieces. Not only do these pegs align the parts but the domes left on the face stain nicely and add some cool detail to the outer rim next to the porthole. Some more sanding, wood glue, clamping and staining and the cover was complete.

The last detail I added here is a layer of polyethylene tape along the inside edge where the cam ring rides. This stuff is slicker than... teflon. It's cut in strips to fit between the bushings on the inner circumference. Hopefully it'll eliminate any friction problems that may occur between the nylon bushings.

Step 6: The Porthole

The porthole is a combination of plywood and clear polycarbonate with a little hardware to fasten it down. In the original design, as shown in the drawings, I had planned to use several small pieces of contrasting colored flooring. Sure looked great in my head. But, after several attempts and headaches, I took it back to the drawing board. Ultimately I ended up with two symmetrical pieces of plywood in the same shape as the jigsaw puzzle I had drawn. Again, the plywood halves are fastened with half butterfly keys, like the cam and cover. The "glass" fits inside a recessed area in the framing and the entire assembly fits between the mounting plates from the housing face with a pair of hinges on the left and a window sash lock on the right.

The porthole window was kind of an afterthought once I started designing the rest of the iris. I have enough trouble keeping a constant temperature in the attic space as it is and certainly didn't want to create any additional drafts. My first thought for the porthole was just a big circle of poly, like a ship's porthole. The Carvewright, however, can only fit material widths of 14-1/2" and the opening was over 18" so I had to break it down into smaller chunks. I did some Googling of "round windows" and decided on this design. The style has a good appearance, almost like a cathedral window. Maybe even a Gothic look.

Once out of the Carvewright I cleaned, sanded and stained the porthole halves. I used wood glue to join the plywood halves and Gorilla glued the clear plastic in place. I again used some weight to keep the assembly nice and flat while the glue set. After sanding and staining, I laid the porthole in place on the housing positioned the hinges and window sash in place. I drilled a few tiny pilot holes for the tiny brass screws in the cover and went ahead and secured the hardware to the porthole.

The last detail added to the porthole backside was a thin layer of flat closed cell foam for added weatherproofing. This material was originally sold as a drawer liner for toolboxes and is maybe 1/16" thick. I've had a roll of this stuff for years, using it now and then for cushioning or insulation for various projects. I used a strong spray adhesive to stick it down.

Step 7: The Wall Openings

After all the components were assembled, glued, cleaned and stained, came the time to start tearing into the wall. The wall penetrations consist of the 18" diameter window cutout and smaller drill holes for the leaf pivot pins, the cover mounting bolts and the pinion gear mount. The wall is a layer of 1/4" OSB behind a 7mm layer of laminate flooring, so it's just a hair over 1/2" thick. Behind the wall is the 2x4 framing that measures 24" wide by 30" high. A few of the mounting bolts will hit this framing. The large circle will be the last hole to cut in order to keep the center point intact and keep the elements out until the whole assembly is ready to install.

The first holes located are from the pivot hole template. You could layout everything out on the wall with a big compass and protractor set, however, life is easier with templates. I drew the pivot hole template in AutoCad and taped it to the wall. I have the luxury of using a wide format printer from my office at work which is nice but an array of letter sized templates taped together would work just as well. I taped it in place and drilled the 5/16" drill holes.

Next I transferred the cover mounting hole pattern to the wall. The assembled cover face was used as a template to locate the mounting holes in the wall. To use this as a template I had to temporarily mount the cover in place face down. I did this by running a couple of screws through the alignment pin holes. I used a 1/4" bit to match drill each hole into the wall.

I've got 2 conditions behind the wall with the cover holes - 8 holes drill straight through the layers and 5 holes hit the 2x4 framing. For the 8 thru holes I can reach a 1/4-20 x 2-1/2" long bolt in from behind. I want to keep these bolts fitting fairly tight for the cam and housing installation so I used a 1/4" drill bit. The other 5 are going into the 2x4's and require 1/4" hanger bolts, the double ended screws with a lag on one end and bolt threads on the other. These spots need a pilot hole to be drilled through the wall and into the 2x4 with a 3/16" pilot drill. Then the hole is chased with a 5/16" bit just through the wall layers to widen it for the bolt end. The fifth hole for the pinion is made later after the main assembly is complete in order to ensure the gear teeth mesh correctly.

The center point for the 18" diameter cutout is marked and I used a small trim router with a shop made circle jig. The jig is simply a big flat compass with a pin on one end and a mount for the router, 9" center to bit edge. The center pin is a screw through the wall for a strong mount allowing the whole jig to rotate about the center point. To build the jig I used a leftover plank of the flooring laminate. I drilled a few holes to bolt the trim router down and a larger hole for the bit to extend through. A strong sheet metal screw is fastened through the other end and into the center of the opening. I drilled a pilot hole along the perimeter of the wall opening for the bit to drop in, flipped the switch and routed the circle.

Step 8: Putting It All Together

So the pieces are built and the wall is prepped. Now the real fun begins. The leaf pins are inserted one by one and a 1/4-20 x 1/2" bolt is threaded into each of the tee nut pins from behind the wall. With the leaves in place the cam ring is installed, orienting the geared section along the upper right side. The only trick to positioning the cam is to make sure the leaves stay overlapped correctly. One by one the travel pins are slid into the slots and more 1/2" bolts are threaded in from the cam side. Once the pins are all in and the cam is under tension from the leaves it pretty well holds itself in place. I have to say it looks pretty cool with the transparent cam showing the inner workings.

Starting with the cover mounting holes, I installed a couple of the 1/4-20 x 2-1/2" bolts from behind the wall. These are a little long, 2-1/4" would have worked better but weren't available when I needed them. So I shimmed them up a bit with more nylon bushings cut down to 1/4" long. This leaves approximately 1-3/4" of stud sticking through the wall - just enough for the shell thickness and a shiny brass acorn nut on top.

The housing shell is lifted in place over the two studs and oriented with the pinion cutout on the upper right side, and then the other bolts are installed from behind. The 1/4-20 x 3" hanger bolts are next run through the housing holes into the predrilled holes in the 2x4 framing. To simplify this I stuck an acorn nut on the end and used a hex socket bit in my drill. After all were in place I cinched the rest of the cap nuts down tight.

Installing the porthole is now a simple matter of driving the screws in the pilot holes to secure the hinges and the sash lock to the housing. The trickiest part of the porthole install was peeling away the protective plastic on the Lexan.

The pinion gear found its home almost as easily. I had left off marking the mount hole for it until the bulk of the assembly was in place. The housing cover cutout for it has about 1/16" clearance around the gear top. I centered it as best I could with the gear teeth meshed and marked the hole. Another 3/16" drill into the 2x4 behind the wall, a 5/16" diameter chaser through the wall layer and the last hanger bolt and acorn nut can be installed through the gear assembly.

The last missing detail I didn't think about until everything was assembled was a crank for the gear to operate the iris! This was a quick fix from my junk drawer - a brass cabinet knob from a past kitchen makeover. I had to drill out one of the alignment pins in the pinion to get the knob screw in but it went in easily enough and cranks just fine.

Step 9: Aftermath and Further Ideas

So its finally done. This was definitely a learning experience for me, which is usually the best part of a project like this. There's several things I'd do differently if I was to start this project over - and I just might. Not that I don't like it, I just see lots of room for improvement. Many times I consider my first builds to be prototypes and thus I have dubbed this project Iris Mark One.

The most obvious revision to me is the choice of material and finish. I switched from the flooring laminate to plywood because I wasn't getting good results. The plywood improved the results and the look was... okay. Even with quality ply. Now that I've proved to myself the design works I want to go with real wood, like a nice grained cherry.

I will also go back to a more traditional stain. This go around I used a dark hickory gel stain. I had never used gel stain before and, surprise again, there's a learning curve there too. This stuff is more like paint than stain. The first coat went on and wiped off fine. The second touch up coat didn't absorb as well and dried in a few minutes resulting in a thick mess. I smoothed it down as much as I could and started thinking about Mark Two.

I've gotten to know my Carvewright much better. I'm more familiar with its limitations and capabilities. In the process of trying to get accurate cuts I've had to purchase and learn new software in an effort to make it better able to accurately "machine" parts. Where the Carvewright really shines is producing relief carvings. While this window was aimed a t being utilitarian, I'm thinking the next cover will feature some intricate design carved into it.

The last change would have to be the leaf design. The cardboard model I made early on worked fine and rotated smoothly. The larger, and hence heavier, steel pieces are a little stiff to turn. They also "pucker out" when spiraled in to a smaller point which adds resistance. They function alright but not as smooth as I'd like. I'm thinking I want to try, for lack of a better description, "half leaves". Rather than a banana shape, the style I'm thinking of is wedge shaped with the pivot and travel pins on the outer end and the other end extends just past the center of the aperture. This would lighten things up considerably and wouldn't have the same overlapped stacking effect.

So hopefully the Mark Two will be a great improvement and give me further ideas for the subsequent Mark Three!