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How a Clamshell Pipe Cutter Works


 A clamshell pipe cutter, also known as the clamshell lathe, is a type of portable machine tool used during construction or maintenance of pipelines, mostly in the oil and gas and petrochemicals industries. As Mirage is a clamshell pipe cutter manufacturer, it goes without saying that our engineers know these machines inside out.

So let’s find out why they’re such a common and how do they work.

Although mostly used in the oil & gas and petrochemical sectors, any industry needing large diameter metal pipes cutting or preparing for welding can benefit from a clamshell pipe cutter.


How is the main body constructed?

The body of the machine is split into two sections, allowing the machine to be offered around the piping section. Machines are normally stored assembled, so the clamshell halves need to be separated before installation. To enable this, the design uses locking pins which are placed into holes through the gear and housing. This prevents gear rotation when the Clamshell is split.

When positioned around the pipe, the two halves are re-joined and locked together using the swing bolt and clamps. Next, the locator pads are adjusted by turning the set screws, tightening them onto the pipe. The modular design of this assembly allows for extensions to bolted to the locator pads, allowing the machine to be used on smaller pipe diameters.

How are clamshell pipe cutters powered?

The power is transferred from the motor via a pinion gear on a shaft which drives the ring within the housing. An internal bearing race allows the cutting head to rotate about the housing. The slide assembly mounted onto this housing has a tool block, which is designed to hold the cutting tool (tool bit).

Depending upon the range chosen, clamshell pipe cutters can be powered by motors that include hydraulic, pneumatic and electric. These motors are available with different mounting configurations for use when obstructions are present.

How does the feed work?

Feed is applied by a ‘tripper’ mechanism. A tripper wheel on the feed assembly is moved each time it passes the tripper pin fixed to the static part of the housing. The star wheel rotates the feed screw which ‘feeds’ the tool bit into the work piece.

How do clamshells sever and bevel?

The type of tool bit chosen determines what operation is carried out. The commonest operations include; sever, bevel, or sever and bevel with the same tool bit.

The tool block slide assembly

The slide assembly includes a tool block, with some machines capable of accepting a ‘Quick Slide’ which makes for a fast setup and adjustment. These are bolted to the face of the clamshell assembly and can be adjusted in ½” increments. You will notice there are two tool block slide assemblies. This is to enable a ‘lead and trail’ cutting operation, for example the first tool makes the leading cut with a tool bit thickness of 6mm and the second relieves the cut using a thickness of 8mm.

Can clamshell pipe cutters do more than just cut and bevel?

Yes, not only can different types of cut and weld prep be made using a standard clamshell pipe cutter, there’s many other operations, such as counter boring, journal turning, facing, RTJ grooves, angle boring, weld crown removal and shaft repairs. These can be carried out using clamshell cutter accessories. Find out more about these in our previous article Clamshell Lathe: Accessories Available.


The engineering behind a clamshell cutter is pretty simple, so there’s plenty of cheap low quality clamshells out there in the market. On the surface, most machines look very similar, but good results can only be sustained time after time using robust and well-engineered machines.

As the saying goes Quality is remembered long after the price is forgotten”.

(Leon M Cautillo).

For more information,  see the range of DL Ricci Clamshell Pipe Cutters on the Mirage website
or if you need assistance,  get in touch with your regional contact below.

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