A Means of Making Shoe Lasts

Shoe lasts are quite useful when making shoes though not always strictly neccisary. As feet are not all quite exactly alike and a good fit seems to matter for shoes, one wants a set of lasts that are well matched to the person for whom a pair of shoes are being made. This article describes a way I've made a couple of sets of lasts based on existing shoes.

Polycaprolactone is a plastic frequently sold under the name polymorph, for about fourty dollars a kilo. Its quite solid and sturdy enough to hammer nails into at room temperature, and not particularly prone to shattering. But when raised to about the boiling point of water it melts into a thick and maleable goo. It can be melted and reshaped quite a few times without apparent trouble.

My first attempt at making a last with it I tried pouring the PCL directly into a shoe (with a plastic bag as liner), but the material is too viscous and I was left with a significant void in the toe (also it sticks a lot to the bag). The way that seems to work better is to build in layers, and outside of the shoe but with the shoe as a guide.

Many shoes have removeable insoles and these make this job much easier, with a sheet of plastic over the insole (and if neccisary something to support it in as close to possible the shape it would be in the shoe) I lay a thin layer of PCL into the sole and allow it to harden. After this is cool and strong enough to hold its shape additional layers can be added until the shape is approximately what it needs to be, periodically letting the last cool and harden and checking it against the example shoe. Its much easier to add material than remove it of course, but both are possible, as is a certain amount of careful bending even when its quite thick.

To make the last easier to remove from shoes later, I leave a cavity in the heel/anke area where a lever can be inserted. And when finished with a set its relatively easy to melt them down and use for some other purpose.

While this is a handy and nice way to make a last there's certainly some care which must be taken to ensure that both lasts match eachother in width and height, as well as making the last smooth and such.

Laying PCL into the insole over a plastic bag.

Bottom view of an insole after its been cooled and removed from the bag liner.

Adding layers to the lasts, the cavity in the ankle saves some plastic and makes for easier removal from shoes later.

Finished lasts in the example shoes.