facebook

Bend Quality

If you are using any tubing bender and having issues with bend quality and deformation, you have come to the right place. We will help you learn how to measure and calculate your bend quality, and also how you can improve the bend quality you are getting on your M600 Tubing Bender (standard or Mandrel). You will need calipers to perform these measurements.

 

Bend Quality Defects: 

Wrinkles/Kinks

What are they- Repeated waves or ripples on the inside of the bend.

What causes them- D ratio too low, wall ratio too high, clamp block slipping, machine set up wrong.

Excessive Deformation

What is it- Tubing is flat on the outside of the bend (depends on the application what is expected). Also known as ovality, flattening, etc.

What causes it- D ratio too low, wall ratio too high, clamp block slipping, machine set up wrong.

Bump at Bend Start

What is it- This is just like a wrinkle, but only occurs once at the start of a bend.

What causes it- D ratio too low, wall ratio too high.

Material Cracks

What is it- As the tubing bends and the outside is in tension, the stress exceeds the ultimate strength of the material and fractures (cracks).

What causes it- D ratio too low, wall ratio too high, or mandrel too far forward on mandrel applications. This is much more common on aluminum.

Solutions: 

D Ratio Too Low

Since the D ratio is the bend radius (CLR) divided by the diameter of the tubing, increasing that ratio would require using a larger bend radius die or using smaller tubing. An alternative to changing bend radii or tube diameter is to use a mandrel to improve bend quality. Non-mandrel applications that produce bends in the 9-11.5% deformation range are EASY to get down to 2% or less deformation with a mandrel. 

Wall Ratio Too High

Since the wall ratio of tubing is the diameter of the tubing divided by it’s wall thickness, decreasing that ratio would require using a higher wall thickness or using smaller tubing. An alternative to changing material (especially if you’re building a chassis from NHRA or SFI or other safety manual specifications) is to use a mandrel to improve bend quality. Non-mandrel applications that produce bends in the 9-11.5% deformation range are EASY to get down to 2% or less deformation with a mandrel.

Machine Set Up Wrong

Including full operation instructions here is not practical, but we will tell you the most common set up mistake made that affects bend quality is using a pressure die in the back of the machine (this hole is labeled “HD, never use on .120 wall or thinner”). If you are mandrel bending, the most common set up problem is mandrel position. Getting the perfect mandrel position will be the result of running several test bends with recordings of achieved bend quality and mandrel position used. 

Clamp Block Slipping

The clamp block usually slides when it is clamped on dirty/oily material, or If your material kinks/wrinkles. Kinks can cause the clamp block to slide when the material binds up in the machine. The clamp block slipping can also cause wrinkles, so it can be either a cause or a symptom. The solution is simple. If your clamp block has grooves/scratches from sliding, they must be removed. Recondition the surface with 220 grit sandpaper or emery cloth, rubbing the same way twisting the tube would rub the surface. Only a few light passes until the offending slip lines are gone (no more). Now clean it with laquer thinner or acetone and a clean rag. Do not use any other cleaner. Clean your tubing at the clamp location the same way. We know this is extra work. Doing things right usually is. Now follow the clamping instructions, keeping bolt torque even. Remember that sliding oily tubing through your clamp blocks not only scratches them, but fills in those scratches with oil. Clamp blocks are extremely affordable, so keep that in mind for spares and/or replacements. We have not yet seen an application (even with the added drag from a mandrel) where one clean clamp was not enough clamping force.