Wax mold resin casting

Many years ago I had a dream of building a machine unlike anything that was around at the time (and as far as I can determine still doesn't exist in quite the way I envisioned it). Every so often I'd get fired up and attempt to make it, but basically I lacked the skills and the equipment to build a complex machine from scratch.

Then people started building their own CNC mills, and 3D printers came on the market. I was weighing up my options - laser cutter, 3D printer, milling machine - when the ShapeOko came on Kickstarter. I'd already come across Michal Zalewski's guerrilla guide to CNC manufacturing, so I jumped at it and got serial number 877 - it's currently running with a few mods under LinuxCNC with a serial stepper driver, and I've just ordered the parts to add a second motor to what most people call the Y-axis (but which is set up as the X-axis on my machine). Yeah, I've wired my Z-axis in reverse to the standard configuration, too - it's what works for the way I use it.

At first I thought I'd be able to make the parts I wanted out of wood, aluminium, or acrylic. I started with wood, but the results weren't really suitable, I didn't have an adequate method of holding the workpiece in place, and I made my first tool blunt in a couple of weeks. I'd already discovered the limitations of having only a single motor per axis so I didn't even try aluminium. And acrylic was a no-go from the supply point of view. I could only find suppliers that would sell huge sheets (we're talking several square meters), and only up to 5mm thick. They would get something thicker in on special order, but the price was ridiculous. So then I looked at lost-wax casting. I made several prototype parts in wax, but there is only one foundry in the country - it's on the other side of the island (4 hour drive each way) - and my contact with them via email and phone wasn't looking very promising for what I needed to make.

Here in Fiji there are no hobby shops and basically nothing to cater to the maker market except for general hardware stores (with way less variety of stock than developed countries) and engineering suppliers (who are outfitted primarily for commercial and industrial transport and construction). That means any materials like Renshape, cool resins, silicon molding materials, etc. need to be purchased from overseas, attracting costs for shipping, as well as charges for customs & duty, and VAT on arrival. I started experimenting with silicone caulk and Oogoo, along with car body filler, plaster, and wood filler.

I was able to find exactly two resins in the country - a 1:4 epoxy resin (around $100 per litre) and fibre-glass resin (at about $20 per litre). But I needed to invent a way to mold it reliably. and that's when it hit me - instead of making a wax part, then making a crappy mold around it, and then pouring resin into that mold, why not carve the mold shape directly into the wax and pour the resin into it? So, that's what I now do. I buy candles from the supermarket and melt them down into blocks of wax using aluminium baking trays in my oven. Then I draw up the parts I want and hand-write the gcode that will carve the inside of the shape from the bottom up to make a mold. Then mix up the fibre-glass resin and if all goes well I get my part.

Resin curing is an exothermic reaction, and it melts the wax that is used to mold it. That means each mold can only be used once. But cutting wax is much faster than cutting heavier materials - I regularly rough out at feeds of 2000 mm/min and large details can be done accurately enough at 500 mm/min. My parts are a far cry from what Michal Zalewski makes. Sometimes there are flaws in the wax blocks (remember they are just Diwali candles, not specially formulated engineering wax) and large areas of wax tend to create bubbles in the contact surface of the resin, but it's a small price to pay for being able to make things using only materials I can source locally at a reasonable cost.

Ravoravo

On Thurday the Ravoravo stood intact watching over the shoreline as the Pacific Dawn sailed into harbour. By Saturday she had broken apart and lay in ruins.

"Ravoravo" has a couple of meanings in Fijian - one suggests the unbroken cycle of the tides coming in and going out. We expect many things in life to remain constant like the tides or rising and setting of the sun, yet so many things have an end, and we can never be sure when it will come. On Thursday I was in two minds about whether to stop and take the first photo here, thinking that there would be another chance later. But it was my last chance. Perhaps it is even the last photo ever taken of that boat in one piece. I certainly didn't expect to find her broken up and being used for firewood just a few days later.

Yesterday I was watching an episode of "The Glee Club" at a friend's house. I wasn't really expecting anything philosophical to come out of that, but there was a poignant moment that stuck in my mind - a conversation between a father and his son who was about to move away. The father said something along these lines: " The older you get, the more you realise how short the time is. When you leave, things will change, and they will never go back to being the same. We will still love each other and we will be there for each other, but it will be different. Change is good and beautiful but there will be times I'll wish for the old days... "

Death can come at any age. People move away. Relationships change or end. Cherish what you have while you have it, before the day comes when you discover it is no longer there and you can't go back.

How to impress your photography friends

So Shrishti and I were out exploring one weekend and ended up at The Pearl, where she's practising shooting on manual. Take a shot... Way too dark. Adjust... Take another shot... Still much too dark...

So I ask, "What ISO are you on?"
"400", she replies.
I look up at the sky, look around where we are sitting, then look at what she's taking a photo of and say, "Try 1/200th of a second at f/8".

Oh snap! It's out by less than half a stop...

"How did you do that?"

"Oh, just experience..."

Yeah, I lied. It's actually experience plus a handy little rule commonly referred to as "the sunny 16 rule".

The sunny 16 rule says that around noon on a nice sunny day, the correct exposure is the reciprocal of the ISO at f/16. So with ISO 400 I would have said shutter of 1/400s and aperture of f/16 if she was shooting something in bright sun. But it wasn't bright sun - it was overcast, so I subtracted a stop for that (1/200s at f/16) - and it was about 4pm so I took off another half a stop - and the subject of the photo was a little dark and in the shade, so I subtracted another half-stop from that to arrive at 1/200s at f/8.

So I took the rule and adjusted it to fit the situation. The rule is the starting point, and knowing how much to shift it is experience.

Next time you're shooting outdoors, give the rule a try. f/16, and shutter of 1/ISO. Take the photo and see how far you have to adjust it to get a good exposure. Do it enough times and it will become second nature.

Now artificial light is a story that will have to wait for another day...

About DivePeak

This is a personal website - DivePeak isn't a company, and I don't do paid work. There are other professional photographers in Fiji who would love to shoot your advertisement, capture the special moments of your wedding, or record your function. I take portraits for fun - mostly for friends, but sometimes for others. Most of the weddings and engagements I attend are for friends. If you want me to take photos for you, please bear in mind that my work (market research) takes priority over my hobby (photography) - I can only shoot in my spare time, and I can never give you a guarantee that I can be anywhere at a particular time.

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