Hopefully all of the electrons I’m expending documenting all of the ways I can think of to cast tires will help someone else along the way. After the success of the “fixed width” mold, I decided to try a similar approach to make “tubes of tires” that I could cut to whatever width I needed.
I simplified the inner mandrel to just have printed cylinders of different sizes that slip fit over 4mm brass tubing. In order to cast different wheel sizes (tire ID’s) I just need to print different sizes of cylinders. I settled on 1mm undersize for the tire to get some “stretch” over the wheel at installation.
I made outer molds that correspond to a 22″ rolling diameter, a 24″ rolling diameter, and a 28″ rolling diameter. I oversized the cast parts by about 1mm on the OD to give room to true them.
The mandrels and outer molds are interchangeable.
I experimented with cutting them to width freehand but the results weren’t good. I needed a fixture to assist.
By swapping out the indexing block, I can cut different widths. I made blocks for 4mm to 7mm wide tires.
The mandrel just slips into place, and is retained by the plunger on the left.
The mandrel is rotated by hand, and the pressure on the blade is also applied by hand. It is a bit tedious, but the results are good.
I stopped cutting midway and pulled off the tires to show the process.
Overall, this process is pretty effective. Pouring the tires is relatively quick, as you are pouring around 10 at a time. It takes a few runs to get used to eyeballing how much Urethane to pour into the outer mold before putting in the mandrel. Inserting the end of the mandrel into the guide in the bottom of the mold is blind operation and can take a few attempts to land.
Cutting the tires to width, even with the fixture I designed is slow and difficult. The Shore 20 compound is so soft, it wants to stretch and bend instead of cut. Still, with a little time on the truer, they all come out very good in the end.
The files needed to print your own molds and mandrels may be found HERE.
The files needed to print your own tire cutter may be found HERE.