How Lapidary Sphere Machines Work: Cups, Grit and Setup

Understand the job before the machine

A polished sphere begins with material selected and prepared for that form. The rough’s size, fractures, cavities and features affect what can be retained. A spherical finish cannot recover material removed during preparation or make an unsuitable specimen sound.

Describe the intended diameter and material to the manufacturer or an experienced instructor. Ask what preparation is required before the sphere machine stage. A machine’s stated size range does not prove that an irregular rock of the same largest dimension is ready to load.

A current product page can differ from an old catalog

Covington’s current three-headed 383TSM page lists a sphere range from 2.5 to ten inches. An older catalog retrieved during research gives a different upper range. Use that discrepancy as a reason to confirm the actual revision and instructions instead of silently combining the most attractive figures.

The current listing also identifies a selected set of cups and thread options. Those choices belong in the order. If buying secondhand, the original machine label, cup mount and supplied manual are more useful than a seller’s general statement that it is a Covington sphere machine.

Cups and heads are not interchangeable labels

Record cup diameter, mounting thread and the intended stage. The same outside size does not establish that a cup belongs on the same shaft or uses the same abrasive process. Ask the maker to identify the full proposed set for the target sphere size.

A three-headed machine should not be evaluated as merely three ordinary grinders. The support, movement and cup arrangement belong to the machine design. Do not substitute an unapproved cup or change a mount because a different abrasive appears cheaper.

Distinguish loose grit from diamond tooling

Sphere-making systems can differ in how the abrasive is supplied and how later stages are performed. Determine whether the selected equipment and cups use an approved loose-grit arrangement, diamond tooling or other documented finishing components. A generic shopping list can otherwise mix incompatible stages.

Ask which items are included with the base machine and which must be purchased separately. Keep any polishing medium and its carrier identifiable. The compound guide is useful for terminology, but the sphere-machine maker must approve the actual process.

Plan a substantial installation where required

The Covington current listing describes a substantial machine with a posted weight and freight delivery. Confirm whether published weight and dimensions refer to the installed machine or shipment before choosing support and delivery access. Obtain the actual freight and handling quote rather than assuming ordinary parcel delivery.

Include water or grit feed, catch arrangements and access for cleaning under the instructions. Do not interpret a product description of continuous feed as permission to leave the machine unattended. Read its operation and supervision requirements for the exact installation.

Production claims need a defined starting condition

A timed demonstration may start with a carefully prepared preform, a particular cup and an experienced operator. It should not be read as the time required to turn any rough specimen into a finished sphere. Preparation, repeated stages and polishing must be accounted for separately.

We have not measured roundness, material-removal rate or finished gloss. A credible comparison would identify starting material, preform dimensions, tooling, stages and the method used to assess the final sphere. This article explains the purchase record rather than inventing such results.

Build the complete tooling budget

Ask for the machine, selected cup set, required preparation equipment, later-stage tooling, approved consumables, delivery and support. List optional expansion separately. A low base price is incomplete if the necessary cup and polishing system have not been identified.

For a first project, compare access to a suitable club workshop or instruction with owning the complete installation. Confirm the electrical variant and keep the manufacturer’s response. A supported process for an identified preform is more valuable than a broad promise of turning every attractive rock into a sphere.

Sources and verification

Sources checked October 22, 2026. Manufacturer specifications and manuals describe the equipment; our selection and planning advice is editorial analysis. We have not physically tested these products. Confirm the exact revision and current instructions before ordering or operating.

• Covington current 383TSM configuration
• Covington 383 instructions
• Covington current sphere equipment