Replacing a Broken Ski Boot Part

A guy came to Nova Labs last week looking for help replacing  a broken part on his antique ski boots.  The boots were matched with his antique ski collection, so he couldn’t just buy new boots.

The part was thin and saddle-shaped.  I decided a squish mold would get the job done.

A squish mold is a type of two part mold.  It is optimized for casting thin parts exactly like this one. A squish mold also lets you make castings of a part with holes through it, without the part locking in the mold.

Like other two part molds, a squish mold starts with a clay bed.

But instead of partially burying your positive in the clay bed, you fill the hollow side with clay. Then you attach the clay filled positive to the clay bed.

Build a mold box around the clay bed. It doesn’t matter if the clay doesn’t completely cover the bottom of the box. In fact, leaving a border free of clay makes the mold easier to use.

For this I used Smooth-on’s Sorta-Clear 37 mold rubber. It took several trial kits. I didn’t order enough, so I had to top the mold off with some left-over Dragon Skin 10.  The orange dot is a bit of Rebound 25.  I used it for the second half of the mold.  I did a little test pour to make sure it would cure properly.

The next day, I flipped the mold over…

and pulled the clay out.  This is now the bottom half of the mold.

I sprayed the bottom half with two coats of Mann Ease Release 200  and let it dry for 30 minutes.  Then I poured the cavity full of the Rebound 25. The Ease Release prevents the newly poured rubber from bounding to the bottom half of the mold.  Even with the Ease Release though, it took some serious pulling to get the two halves apart.  The positive popped right out.

The orange Rebound is the top half of the mold.

To cast in a squish mold, mix your resin and pour it into the lower half of the mold. Then “squish” the top half down into the the lower half.  The top half will displace the liquid resin, causing it to fill the cavity.  I put a heavy block of wood I had lying around to press the top half of the mold firmly into the bottom half.

Here’s a copy using Smooth-Cast 57D ready for demolding. Notice the thin flashing where the resin was squeezed up and out of the mold. That was easy to clean up. I could tear most of it off by hand. There were a couple of places I cut off with a razor knife.

Here’s the finished part next to the original.  I’m going to try a couple of other resins I have on hand to try to get a closer match on the color.

Here’s the new piece mounted in the boots.  My “client” says the fit is perfect.

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About fzinger

I read and I write. I read a lot and I write when I can.
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