Steering column

[alga]

What's the big deal, Sylvain? Are you not confident enough of your welding, or do you expect expert inspection problems? Safety in case of head on collision?

If it's the first case, I think any reasonable weld will hold fine. You can do a test, weld a tube to a rod and try to break the weld by torque (with a large lever). I'm pretty sure the breaking torque will be way beyond what an average man could exert on a steering wheel.

A neat idea for reducing the riskyness of the extension weld is to cut the extension tube at an angle. This way the seam will be elliptical, longer and stronger than a square cut circular weld.

If it's about collision safety, the ~70 cm solid extended part of the column will be about ~120 cm away from your torso, with the two Sierra collapsible mechanisms on the upper part of the column. I haven't seen many sevenesque chassis damage photos, but the ones I've seen had the engine cage largely intact, even if the wheels have been torn off.
(Here are some: http://www.locost-racing.com/lydden15-09-01.htm)

[alga]

Also, argument by authority: extending the steering column by welding in an extension was suggested in a publication by a reputable tech publishing house (Haynes), no doubt reviewed by competent engineers.

[K4KEV]

Sylvain ....it is not that you have to find a splined shaft you are taking two bits of splined shaft and welding those into each end of a piece of steel tubing the two splined bits being slid into the tube a short way say....50mm and then welded up....it is by far the most simple solution to achieving a reliable steering mechanism.