How to Maneuver a Race Track When the Conditions are Tight

The Race Track 
Every once in a while you may take on a job that presents unforeseen challenges. I’m sure the flash backs are whizzing through your mind’s eye now. When they first happen they can be painful at first. However, when you figure out the puzzle, a great sense of accomplishment is realized. That is the good part. It is getting to that part that we all strive for. Tube bending, as you very well know, can present such challenges. A race track is no exception. 

The race track is an oval configuration that is often employed in a heat transfer application. The geometry of the bent tube has been known to lock onto a bend die after making just a few bends. The race track configuration is a series of 180° bends (a.k.a., return bends), all in the same direction with a slight plane rotation between each bend; see lead photo. 

To make progressive return bends in a single work piece as shown in Figure 1, it often comes down to the tooling working in a timely fashion with the machine’s software. Without one or the other, the process of elegantly forming a race track on a cnc tube bender may become a real concern. 

Approach #1: A Little Ramp + A Delayed Bend Head Return 
This approach involves pushing the race track past the bend die, then a slight plane rotation, and then the return of the bend head. With this approach the back of the bend die need a ramp ground on it to help guide the previous bend past the bend die. I suggest going to http://youtu.be/eYK1VDizKXQ to see the process in action. This approach allows for a grip section in the bend die for which is often needed when making tight radius bends. 


 

This approach works well when the length L of the race track allows for a little flexing when moving from bend to bend; see Figure 2 below. A shorter leg would yield a stiffer race track and thus may prevent the carriage on a cnc tube bender from pushing the bent configuration past the bend die. 

Approach #2: A Notch In A Round Bend Die + An Intermediate Returning Swing Arm 
This approach is a little more elegant then the first. It makes use of a round bend die with a notch: see Figure 3. 



With this approach that race track never has to push past the previous bend. This is a big advantage. With this approach the machine makes a 180° bend, then the swing arm has to return to 90° (a wait position), then the L axis move forward to the next bend while the plane rotation is made. Once the plane rotation is made the swing arm can then return to its home position; see Figures 4. 

On the down side, this approach requires no grip section in the bend die so employing this method for a tight radius configuration can become more of a challenge. 
These are just two of several ways to form a race track. Choosing the right approach is often determined by the means available. 




 


About the Author

George Winton, P.E. designs and builds CNC tube fabrication equipment for Winton Machine in Suwanee, GA. He can be reached at gwinton@wintonmachine.com or 888.321.1499

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