Category Archives: Tube Bending

Building the Frame: Roll Hoop to Tail

Posted by jjludemann on

Building the Chassis Nose

Posted by jjludemann on
Starting Nose

Starting the nose tubes.

More Tubes

Test fitting the A, C, & D bulkhead side and bottom tubes.

Adjusting Jigs

Adjusting the jigs to fit as I go. Have to make sure they can be removed after welding.

Top Tubes

Test fitting the C to D bulkhead top tubes

Tube Rippling

Top tube: seam on inside of bend. Bottom tube: seam 45 degrees from inside of bend. Note slight rippling on upper tube. This is why seams must not be located on a major axis of bends.

Front Roll Hoop

Front roll hoop ready for welding.

Front Roll Hoop Done

Front roll hoop fully welded.

Better Weld

Welds are getting better. Now as long as I don't have to stand on my head I can make a pretty good weld.

Front Roll Hoop in Place

Front roll hoop in place. This required cutting the top tube frames. Not a problem as each piece will retain the correct shape.

Starting to Weld

A to C bulkheads welded. There is no B bulkhead (:-).

A, C, & D Bulkheads Welded

A to C to D bulkheads welded

Front Roll Hoop Welded

Front roll hoop welded, top diagonals added.

D-E Sides

D to E side diagonals added.

Nose Finished

The basic frame of the nose from the tip to the front roll hoop, finished.

By the Pricking of My Thumbs, Something Wicked This Way Comes

Posted by jjludemann on
Bwahahahah!

A mysterious form begins to take shape on the slab

Now it’s time to test one of the big unknowns of this project: can the top rails be formed in the shape of a complex 3D spline, and can the left and right sides be made to match? The CAD software won’t even allow a structural member in the shape of a spline, requiring them to be composed of straight sections and arc sections. Other exoskeleton cars have been built, but as far as I know always with a single curve in the main frame members. And of course a tubing bender is designed with the assumption that it will be used to form constant-radius segments. I believe this is the first car to be done this way, so I’ve put a lot of effort into the chassis jigs to get it right. The top rail spline is a key to the beauty of this design. To make a long story short, it is in fact possible to bend a 3D spline on a tubing bender. It just takes a lot of trial and error, patience, and about a day of work per rail. And luckily, overbending can be corrected by running the tube back through the bender, clocked 180 degrees.

“The pricking of my thumbs” is not entirely rhetorical. In fact I almost cut off my left thumb while building the top rails, so a word about safety. A tubing bender is a SERIOUS PIECE OF EQUIPMENT. It won’t even notice bones and flesh being fed into its’ rollers. I had already turned off the bender and reached to grab the tube as it was twisting on the way into the bender. The bender caught my glove and started pulling my thumb in, stopping at the last possible millisecond before inflicting permanent damage. It hurt and left a mark, but I was insanely lucky. So, 1.) Never wear gloves while using a tube bender. They protect you about as much as Saran Wrap, and it’s better to have your fleshy appendages dangling about unprotected to remind you of the danger. 2.) NEVER, NEVER touch the tube on the side being fed into the bender. Always handle the side being fed out. and 3.) Before pushing the “on” switch, stop, think, and say to yourself  “I’m not going to become an amputee on this bend.”

Straight tube

So here's the problem: how do we make this straight tube fit all those notches located in 3D?

Half Done

Left top frame rail about half done

Left rail done

Top left frame tube fitted to chassis jigs

2 Top Tubes

Both top frame tubes bent to shape and matched to each other, in place on the chassis jigs. Now it's possible to get a feel for the size and shape of the car. It's really going to be beautiful!

Really Light

The main frame rail, running from the front to the back of the car, is so light I can lift it with a single finger.

Vroom, Vroom

Sitting inside the chassis for the first time. Time to make vroom vroom noises.

 

Building the Front Keel

Posted by jjludemann on

To get optimal suspension geometry and aerodynamics I’ve designed the car with a front keel under a raised nose. This gives the longest possible lower front A-arms, minimizing the angle changes of the front suspension as it goes through bump and jounce motions. The raised nose clear airflow around the front wing. My computational fluid dynamics (CFD) studies show airflow around the front wing is extremely important as the wing operates in ground effect and generates downforce all out of proportion to its size. I spent a considerable amount of time trying to increase the downforce generated by the underbody and rear wing to match that of the front wing, even though those elements are far larger.

The front keel will use a stressed skin of aluminum formed to shape and riveted to tabs welded onto the frame tubes. This is the highest-stress area of the entire chassis, as under braking something like 2800 pounds of force will be transmitted through these members. You can visualize the car supported vertically on the front keel, with two more cars stacked on top of it, so this needs to be really strong.

Front Keel Tube

Front keel tube is drilled on the milling machine for front lower A-arm attachment points. This will give perfect mounting locations.

A-arm Attachments

Lower front A-arm attachment points were cut and drilled on the lathe, then tapped.

Welding Setup

Chassis table comes in handy again for welding the lower front A-arm attachment points into the front keel tube.

Finished keel tube

Completed front keel tube assembly. Front lower A-arm attachment points welded in place, ends of keel tube capped for strength.

Keel Tube in Place

Front keel tube assembly rigidly located in place on chassis table.

Tube Bender Scrap

The 3-roller tube bender generates about 65 cm of scrap at each end on small-radius bends before it starts generating the correct constant -radius bend.

Keel down-tube

First front keel down-tube in place. The surface of the keel will be concave to let air flow better across the upper surface of the front wing, necessitating curved tubes to hold the keel.

More down-tubes

More front keel down-tubes. The two rear tubes are a recent addition to the design as this area needs to be phenomenally strong and the tubes weigh almost nothing.

Finished Front Keel

Finished front keel and front subframe

The Build Begins– The Front Subframe

Posted by jjludemann on

After more than a year and a half of design and several months of tool preparation, that long-awaited day has finally arrived: the day I touch saw to metal on an actual car part. The first step is to build the front subframe that sell sit horizontally at the bottom of the nose of the car. The chassis table already has holes drilled and tapped for 3/8″ bolts locating the subframe members precisely. Here’s the first tube in place among the pins on the chassis table.

First Tube

First tube in place on the chassis table, bent to fit pins

First Weld

Lower front frame member cut to fit and tack welded in place

Finished Subframe

Finished front subframe, fully welded. Since it's laterally symmetrical, it's flipped over to weld the bottom.

Subframe on jigs

Front subframe raised to final position, supported by chassis jigs. Note Natural-Polymer Swing Press at right. A useful tool.