How to Choose a Tube Bender From the Part Drawing

Most buyers who ask how to choose a tube bender start by looking at machine lists, and the same goes for anyone asking how to choose a pipe bending machine. That is the wrong end to start from. A list shows what a machine can do, and it says nothing about what your part needs. The reliable way to choose is to read the numbers off the part drawing first, then match them to machine specifications, because every number on the drawing rules some machines out and keeps others in.

This article gives the sequence for tube bending machine selection. It uses Telhoo’s published ranges as the worked examples, since the data is public, but the method applies to any bender. The sequence is also what a supplier will ask you for, so having the answers ready speeds up any quotation. The comparison of the two control levels has its own article, CNC vs NC pipe bender and how to choose.

How to Choose a Tube Bender, Step One, Tube Size and Wall

Every bender is rated for a tube diameter and a wall thickness together, because the bending torque depends on both. Write down the largest outside diameter and the heaviest wall you will run, and also the smallest size, since a machine sized for the largest tube is not always good at the smallest. The first pass is simple. Discard every machine whose rating is below your largest tube.

Read the rating against the material. Published capacity is usually quoted in mild steel, and stainless is rated lower in the same machine. Telhoo’s 168NC, for example, is rated Φ168 × 14 mm in mild steel and Φ135 × 10 mm in stainless, and the 130NC takes Φ130 × 8 mm mild steel or Φ102 × 3 mm stainless. If your work is stainless, use the stainless figure. The reasons are in bending stainless steel tubing and what changes.

That table is the first filter and nothing more. A machine that passes it can still be wrong on radius, material or control, and the next steps test those. Where a part falls between two sizes, the larger machine is not automatically safer, since a large machine on a small tube can be harder to set and slower to change over.

Step Two, Radius and Wall Factor Set the Tooling

The tightest centerline radius on the part, and the ratio of diameter to wall, decide the tooling and whether a mandrel is needed. UK and Australian drawings call the radius the centreline radius, and it is the radius to the axis of the tube, as defined in centerline radius explained for tube bending.

Work out two numbers. The D of bend is the centerline radius divided by the outside diameter. The wall factor is the outside diameter divided by the wall. As starting points, above 3D with a wall factor under 20 the bend can run without a mandrel, between 2D and 3D a plug or single ball mandrel is likely, and below 2D or above a wall factor of 30 a multi-ball mandrel and wiper die are needed. The method is set out in types of mandrels for tube bending and how to select one.

The radius also has to fit the machine. Every bender has a maximum radius it can swing, because the bend die has to sit on the head. Telhoo publishes a maximum bend radius for its larger models, with the 63CNC at 250 mm, the 89CNC at 300 mm, the 115CNC and 130CNC at 500 mm, the 168CNC at 800 mm and the 219CNC at 900 mm. A large radius on a small tube may still need a bigger machine, as covered in tube bend radius standards and how to choose a radius.

If the part carries more than one radius, count them. Each radius is a separate die set, so two radii mean a tooling change in the middle of the job or a machine with stacked tooling. That counts toward the choice between machines, and it is better learned before the order than after.

Step Three, Bends and Plane Changes Set NC or CNC

The control level follows how much of the part the machine has to remember. Telhoo’s NC range is semi-automatic, with hydraulic bending, manual feeding and rotating, and optional electric rotation. The CNC range is fully automatic, with servo bend, feed and rotation under a stored program. The NC machines control the bend angle digitally, and the CNC machines control the whole sequence.

The full comparison, including what each control costs in setup time and repeatability, is in CNC vs NC pipe bender and how to choose. The short rule is that the number of bends and plane changes per part matters more than the industry the part goes into.

Step Four, Material Sets the Force and the Rating

The same geometry bends differently in different metals. Stainless needs more force and springs back more, aluminum springs back further and cracks in hard tempers, copper marks and ovalizes, and carbon steel is the steady baseline. The machine rating drops for the harder metals, as the 168NC pair shows, and the tooling surface has to be chosen for the metal. The comparison is in aluminum tube bending and how tube metals compare.

Telhoo’s pages list mild steel, stainless steel, copper and aluminum among the materials its benders handle. The exact capacity, radius and tooling for a given alloy and temper should be confirmed against your drawing before an order, and a trial bend on real tube is the quickest way to settle a borderline case. If you bend several metals on one machine, plan separate tool sets and keep them segregated.

Step Five, Batch Size and Variants Set How Much Automation Pays

Batch size and the number of part numbers decide how much automation is worth. A few part numbers at high volume repay a CNC bender and possibly a loader, because handling is repeated many times and setup is rare. Many part numbers with frequent changes need stored programs and quick tooling, otherwise changeover erases the gain. Low volume and mixed batches are often better served by an NC machine with good tooling.

Heavy parts change the arithmetic. At large sizes the cycle is dominated by loading and not by bending, so a loader or crane handling matters more than bend speed. Telhoo’s 168CNC page notes that at Φ168 × 15 mm the bend is slow and deliberate and loading is a crane job. The effect of automation on cycle time is covered in automated tube bending cell and where the time goes.

Step Six, Mandrel Length Has to Reach the Furthest Bend

The last test is the one buyers most often skip. The mandrel length is the reach of the mandrel rod into the tube, and it limits how far from the clamped end a supported bend can be placed. A part whose last bend sits beyond the mandrel length is formed unsupported and will ovalize. Check the length against the part and not against the tube.

Telhoo’s published mandrel lengths run from 1,850 mm on the 38NC to 4,700 mm on the 168NC, and from 3,000 mm on the 63CNC to 6,000 mm on the 168CNC. If a long part needs more reach than the machine offers, ask whether it can be bent from both ends, and whether the geometry allows it.

What Else to Check Before You Decide

Beyond the six steps, a few practical checks prevent surprises. First, the tooling. Ask what dies are included, how they are made, and who builds new sets for new radii, since tooling is per diameter and radius and is a recurring need. Second, the stations around the bender. Tube has to be cut to a repeatable length before it is bent, and the ends may need chamfering or end forming afterwards. Telhoo’s automatic pipe cutting machine, pipe chamfering machine and tube end forming machine ranges cover those.

Third, the supplier. Look for installation, training and spare parts support, a record of similar work, and the willingness to run a sample on your tube before you buy. Telhoo’s published cases show the pattern, with a 63CNC copper coil line and a 115NC steel structure line in Thailand, both with overseas installation and operator training described on the case pages. Fourth, the standards and documents you need for your market, such as CE, and the paperwork for export. These belong in the specification and not in the aftermath.

What Drives the Cost of a Tube Bender, Without Prices

Prices belong in a quotation and not in an article, but the factors that move them are worth knowing, because they explain why two machines that look alike can cost very different amounts. The capacity class is the largest factor, since a frame that bends Φ168 mm pipe is far heavier and more expensive than one for Φ38 mm tube. The control level comes next, and a CNC bender with servo axes costs more than an NC machine with manual feed and rotation. Options add to it, such as electric rotation on an NC machine, stacked tooling, an automatic loader and a longer mandrel.

Tooling is a recurring cost that the purchase price does not show. Each diameter and radius needs its own die set, and each mandrel is specific to a bore, so a shop running many sizes spends more on tooling than one running a few. Then there are the costs around the machine, such as cutting, end forming and handling equipment, and the costs of installation, training and spare parts. A fair budget counts all of these, and a fair comparison puts each machine’s quotation on the same list of inclusions.

Choosing for the Parts You Will Make Next

A machine is bought for years, and the parts will change. It is worth asking what range of tube sizes and radii you expect to run in the next few years and whether the machine can grow with them. A model with headroom on wall thickness, a mandrel length longer than today’s longest part, and an option for electric rotation or automatic loading can be extended. A model sized exactly to today’s part cannot.

The same applies to materials. If stainless or aluminum work may be added, check the rating and the tooling options for those metals now, and not after the first stainless order. And if volume may rise, check whether an NC machine can be upgraded or whether the step to CNC is a separate purchase. Telhoo’s NC range, for example, lists electric rotation as an option, which is a way to add some automation to a semi-automatic machine without going to full CNC.

Comparing Quotations Side by Side

When quotations arrive, compare them on a common list. Check that each one states the rated tube in your material and not only in mild steel. Check the maximum bend radius, the mandrel length and the bend angle the machine can reach. Check what tooling is included and for which diameters and radii. Check the control, including whether programs can be stored and exported. And check the support, including installation, training, spare parts and the warranty terms.

Then compare the lead time and what the supplier will do before shipment. Pre-shipment testing on the machine, ideally on your tube, is a strong signal. Ask if you can send a sample and receive bent parts back with measurements. A supplier that will do this is confident in the specification, and the result tells you more than any data sheet. If a quotation is much lower than the others, find out which item has been left out before treating it as a bargain.

Running a Trial Before You Buy

The safest way to settle a borderline choice is a trial bend on your own tube. Send a short length of the real tube, the drawing and the acceptance limits, and ask for bent samples with ovality, wall thinning and angle measured. The trial shows whether the radius works at that wall and in that material, which mandrel and wiper are needed, and how much springback to expect. It also shows how the supplier works, including how fast they respond and how clearly they report.

Keep the sample and the report. They become the reference for the first article on your own machine and for any later disagreement about what the machine should do. A good trial costs little compared with a machine that does not fit the part, and it is the clearest answer to the question of how to choose a tube bender when the numbers leave doubt.

After the Choice, Installation and Training

Choosing the machine is not the end of the process. The machine has to be installed, commissioned and run by people who know it. Ask what installation and training the supplier provides and where, and whether operators can be trained on your own parts. Telhoo’s published cases describe overseas installation, commissioning and operator training at the customer’s site, with documents and manuals in the customer’s language, and that kind of support is part of what the price buys.

Plan the first weeks too. A new bender needs trial pieces, a first article for every part number, stored programs and springback corrections, and a spare parts list. Setting these up carefully pays back in the first batch, and it builds the record that later helps with troubleshooting.

A Worked Example of Choosing a Tube Bender

This example is illustrative and is not a customer drawing. A maker of stainless handrail wants to bend Φ42.4 × 2 mm tube on a 3D radius, about 120 parts a day, each with two bends in one plane, and an occasional Φ50.8 × 2 mm part.

Step one gives a largest tube of Φ50.8 × 2 mm in stainless, so the 50NC class is the first match, with the stainless rating to be confirmed. Step two gives a wall factor of about 21 for the smaller tube and 25 for the larger, with a 3D radius, which suggests no mandrel or a plug at most. Step three finds two bends in one plane, which favors NC. Step four notes stainless, so the tooling needs a dissimilar surface and a chlorine-free lubricant. Step five finds modest variety and moderate volume, so NC with good tooling pays. Step six checks the mandrel length against a part a meter or so long, which is within any of the machines considered.

The result is a short list of one or two NC models, with a trial bend on the real tube to confirm the stainless rating and the radius. The same sequence applied to a six-bend exhaust section in thin-wall stainless would point to CNC with a mandrel and a wiper, as covered in mandrel exhaust tube bending and what the part demands.

One more habit separates good purchases from poor ones, and it is writing the specification down before talking to suppliers. A one-page sheet listing the tube sizes and walls, the materials, the radii, the bend counts, the volumes and the tolerances gives every supplier the same starting point. It also makes the answers comparable, because each supplier is responding to the same question. Buyers who skip this step often find that quotations differ because the suppliers assumed different parts, and not because the machines differ. Writing the sheet also forces the buyer to notice gaps in their own knowledge, such as a radius nobody has measured or a wall tolerance nobody has agreed, while there is still time to fix them.

Common Mistakes When Choosing a Tube Bender

The same mistakes recur, and each is easy to avoid once named. The first is choosing from the maximum diameter alone, which ignores wall, radius and material. The second is buying more control than the part needs, since CNC earns its cost on bend count and volume and not on prestige. The third is ignoring the radius count, so that a part with three radii arrives at a machine with one tooling stack. The fourth is skipping the mandrel length check, and the fifth is leaving tooling and cutting out of the budget.

The sixth is buying on price alone. The purchase price is only part of the cost of owning a bender. Tooling, setup time, scrap, training and support all add to it, and a cheaper machine that scraps more tube or takes longer to change over can cost more over its life. Compare machines on what the part needs and on the supplier’s support, and compare prices only after the specification matches.

What to Send for Tube Bending Machine Selection

• Tube outside diameter and wall for every size you run, including the smallest.
• Material and grade or temper, and whether the tube is welded or drawn.
• Every centerline radius, and whether the design can standardize on fewer.
• Bends per part and plane changes, ideally as a drawing or 3D file.
• The furthest bend from the tube end, to test the mandrel length.
• Batch size, variants and any automation target, including whether cutting or end forming should be in the line.

Send those and the reply can name the capacity class, the control level and the tooling. Send us the part drawing, and for the wider process view see our tube bending solutions page. The two machine ranges are on the CNC automatic pipe bending machine and NC semi-automatic tube bender pages.