Answers to common questions about the clamping shells, tool holders, cutting tools and fixings used with a compact tube squaring machine for small-bore tube.
What accessories does a tube squaring machine use and what does each one do?
A tube squaring (facing) machine holds a tube end in clamping shells and cuts the end face square with a rotating cutting tool. The clamping shells grip the tube, the tool holder positions the cutting tool, and the cutting tool, usually an insert with more than one cutting edge, removes the material. Small screws fix the tool and holder in place.
The machine is designed to prepare tube ends and welded small fittings for welding. The shells, holders and tools are matched to the machine series, so check your machine's manual and parts list before choosing any accessory.
How do I choose the right clamping shells for my tube?
The inner diameter of the clamping shells must match the outer diameter of the tube. The size is marked on the shells, so measure the tube's outside diameter first and pick the shell with the same marking. Always measure the tube rather than relying on the nominal size, as tube standards differ.
Shells are fitted in an upper and lower pair, and stainless steel types are made for gripping the tube without deforming it. The machine's working range limits the tube sizes you can use, and an adapter shell may extend that range on some machines, so check the manual for what your model accepts.
Why do tube ends need to be squared before orbital welding?
Many small-bore orbital welds are made without filler metal, so the quality of the joint comes mainly from how well the ends are prepared. A guide to orbital welding says the ends should be square, clean and well matched, and that a gap, burr or contamination can cause a defective weld that no change of welding settings can cure.
A facing machine produces a square, burr-free end with a good surface finish, which is why it is often used after cutting. Your welding procedure will state the preparation needed for the joint.
When should I replace the cutting insert?
Replace the cutting tool when it is blunt, worn, chipped or damaged. The maker's manual lists a blunt tool as a cause of a jagged tube end or a burr that is too large, and says worn tools must be replaced straight away and damaged ones never used. It also says that working with sharp tools helps to reduce vibration.
Many inserts have two cutting edges, so you can often turn a worn insert to use the second edge before discarding it. After fitting or turning an insert, check that the screw is tight and clean the seat first so the tool sits firmly.
What is a tool holder and how do I choose one?
The tool holder carries the cutting tool and sets its position on the machine. Different holders suit different jobs, such as squaring only, squaring and bevelling, or working on small welded fittings. Each holder has a range of tube sizes it is intended for, and a holder for small fittings is meant to be used only with the matching shells.
Choose the holder by the job you are doing, the tube outside diameter and the wall thickness, and confirm it is listed for your machine in the manual. Fit it firmly, as a loose tool or holder is a known cause of vibration.
Why does the tool vibrate or leave a step or burr on the tube end?
The maker's troubleshooting table lists the usual causes. Vibration comes from the speed being too high, from a loose tool or holder, from play in the machine, or from a blunt tool. A step in the face can come from too much feed or from a battery that is nearly flat on a cordless machine. A jagged end or large burr usually means a blunt tool.
The remedies are to reduce the speed, tighten the tool and holder, replace a blunt tool, and feed in gently. Check the machine for play too.