The crusher room is now entered down steps but originally the floor was level with the canal wharf. Mining subsidence has lowered the whole area by about 6 feet (2 metres) and the canal wharf has had to be raised to maintain the water level. The blocked up lower part of the windows in the Gear Room can be seen. The crusher was installed in this position, probably from another location on the site, in the 1930s after the calcining kiln was decommissioned. The two kiln draw holes can be seen behind.
In the middle of the floor is a circular iron turntable plate sitting on rollers. Carts wheeled in from outside were turned to be pushed into the gear room.
Oversized flints, bone and Cornish stone often had to be reduced in size before grinding. There would probably have been a number of crushers of this type on the site. It is of the oscillating jaw type where the distance between the jaws reduces as the materials falls from the top feed hopper to discharge at the bottom. It would have been fed from the wharf side (see bricked up wall). The crusher is belt driven by a small horizontal steam engine made around the 1880s. Steam is fed from the Cornish boiler down the length of the gear room.