How to Make Quality Mandrel Bends


Quality mandrel bends can be difficult to obtain because when a tube is bent, the outside wall collapses and thins out and the inside compresses. When bending thin wall tube to a tight radius, it is necessary to use a mandrel and wiper die. The mandrel allows material to be bent into smooth curves minimizing the amount of ovality, undesirable creasing, kinking, or collapsing which can occur during the bending process.

When ordering mandrel tooling you must include the following information: profile shape, interior and exterior dimensions, wall thickness, material type, minimum distance between bends and the number of bends per day required. It is also highly recommended that you supply dimensional drawings of the finished product.



The center former, pressure die, clamp die, wiper die and flexible mandrel are specific to material type and dimension.

Component for Quality Mandrel Bends

Center Former/Bend Die: The primary tool which determines bend radius. Manufactured from tool steel or alloy steel and heat treated depending on requirements. Clamp face is serrated to assist grip strength.

Clamp Die

Clamp Die: Matches center former clamp surface. The clamp die’s primary function is to hold tube securely to the center former.


Pressure Die: Maintains constant pressure on tube at tangent where the bend occurs, providing reactionary force to make the bend. Length of the pressure die depends on the degree of bend (DOB) of part being bent and the machine design.


Wiper Die: Manufactured to match center former radius. Mounts into the groove of the center former with tip positioned near tangent point of bend.  Primary function is to prevent wrinkling on the inside radius of the tube. Wiper dies are typically manufactured from AMPCO® bronze.


Sample Quality Mandrel Bends

2″ Stainless Steel
.065 wall – 3″ CLR
Cutaway to show mandrel

Mandrels: Generally made from the same material as the wiper die. Primary function of the mandrel is to prevent inside diameter of the tube from collapsing to create quality mandrel bends. Choosing the correct mandrel is very important in determining the quality of bend. Three basic styles of mandrels are:
1. Plug mandrel used for heavier walled tube or large CLR bending.

2.  Standard open pitch mandrel is most widely used because it covers the widest range of bending applications. Standard mandrels are made with one to three balls. Open pitch mandrel is the most durable of the three flexible mandrel configurations because it uses the largest size links possible.

3. Thin wall mandrel (close pitch mandrel) used mostly for thin wall tubing. Thin wall style mandrels use the same style linkage as standard mandrels except the link size is the next size smaller than it would be on a standard mandrel. For example, where a standard style mandrel would use a #10 size link, a thin wall style mandrel would use a #9 size link. The ball segments are now closer together and provide more support needed for thin walled tube bending. Strength is sacrificed for more support.


Well, maybe two more. These items are just as important as the components listed above to create and maintain quality, repeatable mandrel bends on your Ercolina tube bender.


Collet: The collet is mounted in the tailstock of machine and holds material securely in carriage. Collets are size-specific and must match the tooling mounted on machine.

Lubrication: Comes in several different forms such as oil, grease, and paste. The kind of lubrication used will depend on material to be bent. A generous amount of lubrication may be applied to mandrel and inside of tube, however precautions should be taken to avoid getting lubrication on center former and clamp die. Proper lubrication is important to making good quality mandrel bends.


Ercolina’s line of CNC and NC mandrel benders are an investment in your business that will provide years of high-quality tubing, profile, and pipe bending.

Durable construction, innovative bending head design, and accurate NC control give our semi-automatic line of mandrel benders the ability to eliminate welds, elbows, and seams with quality bends. Sturdy steel construction and precise computer controls give our CNC bending machines the ability to create quality mandrel bends every time, even when your bending application requires complex or tight-radius bends.




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