Casting for lasts

Instep side

One of the most difficult roadblocks I’ve run into for making my own shoes is good lasts. The better the last matches the foot, the better the fit of the shoe. The better the footbed matches the stabilized foot (vertical support system, forefoot flat on the floor, heel not weight bearing), the less stress put on the leg/ankle.

Because I have both fit issues (3┬ŻEEEEEE and 4EEEEE) and support issues (high arch and instep and wrecked left ankle), having a superior fitting last is essential.

Looking down into the heel bed

In the past when I cast my foot I had problems. Part of this is simply learning curve, part of it is technique requiring modification or improvement. When casting your foot in plaster, any movement of the foot changes the final shape of the mold, pushing the mold material and making a loose fitting cast. I’ve wracked my brain on this one and I have the answer to that, finally.  An elastic bandage.

The day before yesterday I cast part of my foot with the intent to build a mold for creating a modified foot bed press for my left foot (bad ankle leg). I bought an Art Minds Plaster Wrap from the craft store and cut half of it into lengths ranging from just over 1′ to just under 1┬Ż’.  After collecting all my bits and pieces (plastic to set my foot on while casting, pan of warm water, serrated butter knife, plastic bag, elastic wrap, small bowl with a few tablespoons of olive oil and a 2″ paint brush) together in a convenient spot and protecting the floor, I painted the area of the foot I was casting with olive oil.

I had a reason for not wrapping my foot in plastic before adding the plaster wrap.  No matter what you do, the plastic changes the shape of the foot.  Where there’s only one tiny thin layer it doesn’t make much difference, but every fold and wrinkle adds up to a sloppy fit.  The sloppier the fit the more you have to do to the mold to make it work.  It’s much easier just to paint the foot with olive oil.  Using a paint brush kept it off my hands and gave me a nice thick coat of oil on my foot.

I dipped the pieces of plaster wrap in warm water, squeegeeing off as much of the extra water as I could and proceeded to wrap my foot.

When I finished adding the plaster wrap I covered my foot with a plastic bag and wrapped it with an elastic bandage.  This final bit is the true trick.  It provides tension and keeps the plaster wrap tight against the foot so the end result is a snug fit while the plaster sets.  Before, when casting my foot, I would invariably end up with loose spots in the casting that made the casting less than useful.

With my foot all en-swathed, I sat with a small amount of weight pressing down through my leg into my forefoot with my heel slightly off the ground until the plaster set enough to hold its shape.  I paid particular attention to having my leg properly aligned vertically above my ankle and my ankle flexed to a create a right angle between my foot and my leg.

When the plaster had cured to leather hard, I unwrapped the elastic bandage, removed the plastic wrap and, using a butter knife with a serrated edge, carefully sawed down the front of the casting to almost the edge above the toes.  I pried the edges apart and slid my foot out, wrapping a piece of plastic bag around the casting to close up the front edges before setting it aside to finish curing/drying.

Next time I do this I will be casting the whole foot.  I will fold/roll a piece of plaster wrap lengthwise to create a thicker top edge.  This will help strengthen the casting.  I’ll also get Wadly to help.  This is a much easier job with two people, one to own the foot and hand over the tools and materials, the other to do the wrapping.

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