Monday, September 02, 2013

Iris Slots

The doors are now stuck on my Eden iris. The hard part was lining them up so that the exact curve on the front edge of one door matched the curve on the rear of the next one. The way I did that was to lay the outer doors out on top of the inner doors, carefully moving and shifting each bit, bit by bit, weighing down the correct ones to stop them moving. Here's two outer doors in place, showing the inner doors.

It took half a day of placing, shifting, staring, thinking, before I thought I'd done enough. It wasn't perfect, two doors were up to 2mm out, but I decided not to muse forever like Leonardo would have. That was probably as good as it would get so I lifted one door at a time, marked the area to be glued in pencil with a paper template, sanded a little to create tooth then carefully applied aliphatic resin glue to each surface, brushed it even then weighed it down as it stuck. After an hour or so I moved onto the next door. At the end of the day all seven were stuck. Here it is at that stage...

Then I opened the doors, and after a tense moment or two where one door had glued to its neighbour, they slid open...

Now each has to be opened by hand so there is a crucial job left, well, two and one is critical in that it needs to be millimetre perfect. Each door will have a metal pin coming from the top which must be in exactly the right place. It has to be pretty vertical but if it's not perfectly vertical it'll still work, but they must be on the same radius. To open the iris those pins move outwards in unison, that's basically all they need to do. The pins fit in a special slotted ring (the bezel) such that rotating it makes the pins move outwards. It's important that the pins are in the right place or they won't fit the bezel.

Here's the prototype:

I deliberately made it badly so that I knew the tolerances. Basically they were worst at this bit. The prototype struggled with opening and the result wasn't that pretty. The wobble, the difference between the size of the pins and the width of the slots needed to be minimal. If it's too large it will not only hang loose and look ugly, it will also distort the shape of the doors as they open and instead of nice seven-fold symmetry, it will sort of sag.

So those slots need to be just a tiny bit bigger than the pins. Here are the slots on the full size version...

I drew them with a beam compass and cut them with a jigsaw, with a plan to sand them to size. The problem is that sanding inside a long thin curvy slot like that is a nightmare. My first thought was to use a spindle with sandpaper on, but it would have to be on a pedestal so that the slots remain vertical (a Dremel tool would be a no-no). The spikey giant bezel made doing anything on the pedestal drill awkward and dangerous, and I had to make the sanding spindle thing because they don't make them that thin. It barely worked, and naturally produced a lumpy result, sanding a long thing slot with a tiny cylinder...

Ideally I'd have a gently curving sander, perhaps a belt that bent at the perfect angle (well I say ideally, ideally I'd use a computer controlled machine to cut the thing in the first place, but I'll ignore that option for now, but keep it in mind, just in case). Anyway I thought that the jigsaw worked quite well... so what if I attached a sander to the jigsaw... so my plan is to take a metal plate and bend it to the correct curve...

Then glue sandpaper to it, then glue it to a jigsaw blade to make an electric sander that works at just the right curve and at a right angle to the surface. I'd have to make a second concave blade for the inner curve.

When that's done I can check the measurements with a paper template, then check the position of the pins on the doors. Once they're in there's no going back, no adjusting the doors, no shifting and sanding. Any gaps will remain gaps. Putting the pins in will be a make or break moment...

If in doubt though I'll stick the pins based on the correct measure. It's easier to make a new bezel than make everything else again. I hope to have all of the engineering bits done within two weeks, then the painting can begin, and the decoration.

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