How do you locate a steering shaft hole in a blank firewall?

In today's episode of "i have no odea what im doing", i have to run a race car steering column. 

I have the u joint for the steering box, a column that came with the naskart, and various shafts, firewall support bearings, u joints, and mid run support bearings. Should have everything on hand. 

I know i have to have all the u joints in phase with one another. I need a hard point support between each pair of u joints to prevent flopping around. 

After that im lost. Especially on how to figure out just where to cut the hole in my flat steel firewall. 

Ill take whatever you can give me!

How many shaft segments will you have? 2, 3?

I'd start with getting the steering wheel positioned how you want, then lay out the shafts in an arrangement that clears whatever obstacles are in the way. Avoid big angle changes at any single joint - there's probably a rule of thumb out there. For simplicity, can you run a straight shaft from the steering wheel thru the dash, and take care of the other stuff in the engine bay?

If you have 2 shaft segments, it's pretty easy - 2 bearings on the steering shaft, none on the other. So, schematically from the driver it'd be: steering wheel, shaft, bearing, bearing, joint, shaft, joint, steering box.

3+ gets tricky. I don't know if you need one or two bearings in the intermediate shaft.

Btw, my stupid autocorrect has changed every "shaft" to "shart".. I don't know why.

Run "steering column" aka a broomstick roughly where you want inside.

Tape a good strong magnet on the point where it meets the firewall on the inside.

On the engine side, use iron filings or whatever other locating tool you want to find where the magnet is.

Best I got this early.

Don't know much on this topic, but maybe this will give some insight.  Start around 13:45 for the meat and potatoes.

https://www.youtube.com/watch?v=sVvlGm1EmuE

If your seat and pedals are positioned where you want them and you have sat in the car and made enough racecar noises with a steering wheel in your hand to gauge where you want the wheel as well I'd do something like what Mr Asa suggested.  Have you suited up to make sure that the seating position is still where you want with helmet and firesuit?

Another thought, tape a laser pointer into the quick release of the steering wheel to help determine the position of the firewall pass through.  You won't have the weight of the column or broomstick cantelevering the wheel then.

Thanks everyone!

Gave me stuff to think about that I didn't know I needed to think about. 

And the magnet/lazer pointer ideas are EXACTLY what i couldn't think of!

Thanks!

I'd model it up on paper in both X and Y to find the pass through point.

In reply to kb58 :

Can you dumb that down a bit for me? Im not following what you mean.

Draw a scale model on paper, carefully placing the rack and desired hub position, both from the side and above, then connect the two with a straight line. As mentioned, a laser level is invaluable for determining elevation and offsets.

Another way is to just eyeball it, cutting a larger hole, accepting up front that you'll want a rubber bellows at the pass-through point, which will need a big hole regardless how accurate the initial hole is. Think of a "CV boot" sort of bellows.

Can't you just cut a large square hole about where the shaft will pass through, hook everything up, then measure from the edges of the square hole to pinpoint the exact shaft location on the cut-out square, cut the correct hole, and weld the metal back into the firewall?

In reply to VolvoHeretic :

Or cut the big hole, then cut a piece of cardboard larger than the hole with a hole in the middle for the steering shaft to go in. You can even cut a slit from the side of the board to the hole so you can slip it on from the side. 
 

then hook up the steering shafts as you want so it's all connected and working.   Then slide the cardboard down to the hole and trace the hole onto the cardboard and you'll end up with a perfect template. 
 

but you have to start with the big hole.  I like the magnet idea to only drill one smaller hole. 

IMO there are two ways to do it:

Either 1) you know the endpoints, i.e. where the steering rack will be, or more likely where it will be held by a bearing before making a turn to miss part of the engine and then go to the steering rack, and also about where the steering wheel will be centered.  The exact angle of the steering wheel will be determined by the axis to the bearing/rack.  Then you need to make something that is kind of G shaped, where the top of the G goes in the engine compartment where the bearing/rack end of the column will be, and the inside end (the bottom of the G) where part of the steering column or something else coming thru the center of the steering wheel goes thru that G right leg and points to the top of the G.  Does that make some kind of weird sense?  Shaped kind of like this... 

engine compartment end here > |_____T < steering shaft (or dowel?) from steering wheel goes thru top of "T" here.  

You could make it out of, I dunno, 1-1/2" sch 80 PVC or something?  As long as the long side isn't too flexible and the dowel fits reasonably well in whatever it goes thru, it will point where you need to drill the hole.  OR...

2) You know one endpoint and the vector.  You know exactly where you want the steering wheel, and what angle you want it at, and then it will point exactly where you need to drill.  I really like that laser pointer idea above.  Of course with this method you won't know exactly where the steering shaft ends up in the engine compartment until you cut the hole.  I guess you could measure the alt/az of the steering shaft from the steering wheel where you want it, use a center punch to make a dimple on the firewall and then continue that alt/az into the engine compartment to see where it goes before drilling so you can adjust it some.  

Just my wild ramblings.  Please ignore if this sounds stupid.