Researching Smooth-On Resins for Shoe Lasts
samples, specifications, and costs
I’ve begun researching how to cast shoe lasts in resin at home. The Smooth-On company’s customer service team wasn’t able to say straight out which product would work best, but sent me some coin-shaped, cured samples of a few of their products.
With those samples in hand, and a little research on their website, my top candidates are their 300 and 380 resins. I gather 380 is more or less 300 with filler for more strength.
They cost roughly the same, at a little over $100 for a gallon direct from Smooth-On. 380 is harder and shrinks less, but is also more viscous, and therefore potentially harder to cast without bubbles. 380 also takes more time to cure: 60 minutes as opposed to 10 minutes to cure, and 6-minute versus 3-minute pot life.
I suspect viscosity matters relatively little for lasts, since they’re smooth, bulbous shapes without tiny details. The detail 300 seems designed to reproduce is far finer than even, say, the round-head nails sometimes driven onto master lasts to mark measurement points. On the other hand, the added strength of 380 may not really matter, given the thickness of all parts of a last overall. Even at the tips of the toes, there will be a substantial thickness of material.
The sample bag I received had a number of other products that I disqualified for various reasons:
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KX Flex 90 is flexible, not hard.
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EpoxaCast 690 is trickier to mix, and also substantially more expensive.
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TASK 2 and 3 are meant only for much thinner models.
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320 would likely work, but seems to be just a variant of 300 designed to be easier to color. If it’s important to have your last a particular color, this might suit.
For now, I am not running out to buy resin and try this, largely due to cost. A gallon would likely suffice for a pair of lasts, but HDPE lasts imported from Mexico can be had through resellers like Sorrell Notions and Finding for well less than the costs of a gallon of these resins. While I haven’t reached out to any yet, I suspect several Mexican last makers—perhaps Horma, SA de CV, Hormas Cortés, or Hormas El Árbol—might be willing to print and ship HDPE lasts from 3D models at lesser cost.
There may also be cheaper resin alternatives.