Technical Narrowing a '40 Ford hood - simple right?

After a year of various health, family and business 'challenges', I'm finally easing back into working on my 30's racer basement build. After getting some great advice from fellow HAMBer about the best way to tackle fabricating a basic steel body with minimal sheet metal skills, I procured a '40 Ford hood to use for the boat tail style rear of the car.
The fat end is about 50" wide and I need it to be approx. 38". My plan was to cut out a "V" and then weld it together in the center. It's a 2 pc. design and there's a seam running the length of it - perfect for a reference point. I attached a carriage bolt to the nose to get a good idea for the center up there since the seam kind of disappears under metal to allow the trim to be attached. Back at the fat end, I marked 6" out from the center seam. Then with an 8' length of extruded aluminum channel (I checked it in several places against a 4' dryway t-square) I marked my cut lines eyeballing it to the carriage bolt at the center. But after marking it was clear that the sides were not equal as they approached the front. I tried this method several timea, then shifted to others including using a laser level, a then a protractor - but nothing gave me lines that were what I considered to be even close "enough". I did notice that as you approach the nose, the profile changes from basically flat, to a compund slope. I suspect this is what's messing with me. I thought the laser would show me the true line, but apparently not.
I've considered that the halves just may not be symmetrical, or they were mis-aligned when originally spot welded.
So I'm looking for any advice on how to best mark this thing for cutting.
Thanks

 

I think you need to cut the 'pie' out of it all the way to bottom edge of the front to get the taper you want, and the taper profile will vary as you go 'around the curve/nose. There are a lot of very talented sheet metal pounders/finessers on here that know better than I, hope they chime in. But... I would probably look at something other than a '40 hood to do this with (unless you have an undisclosed, deep seated reason to use it) rather than cut up a desirable part like that. JMHO, YMMV

 

Thanks. While it may look OK in my pic, a large portion of the sides are like like swiss cheese. I picked it up from a guy who bought it, then realized it would take way too much work to get it acceptable as a '40 hood. He was very clear of the condition when before I wen to get it.
Thankfully, the vast majority of the rot areas are what I plan on removing anyway.

 

Good answer! and.... good luck!

 

Cut one side, then swing it over the middle, overlapping. Make a scratch mark where your second line needs to be. If it's not perfectly straight, it doesn't matter. As long as you cut precisely to that scribed line.

Then, butt them together, clamp them up, and start welding.

 

@alchemy Great idea. My only concern was how I would flip the nose of the hood to trace the inital cut. I ended up using a vriation on your 'flip' idea by making a tempate. Before I started this thread I searched for various techniques to chop/cut panels and making a template was a commong theme.
Luckily I had a piece of poster board laying around. After marking the main cut over the flat portion, I clamped a piece of thin 1-1/2" angle iron with the vertical side to the outside of the line. Then using a piece of thin flat metal clamped it against the vertical of the angle in several places to 'project' the line where it would end on the nose.

The cutout template needed to be weighted down a bit to make an accurate tracing to the hood surface.


The end result was 100% better than trying to measure and mark each side separately.


On a roll !!
So I cut one side. But before I did the other, I wanted to see what sort of flange my "new" flange punch could put in this 1940's steel - since I'd have to subtract the actual width of the flange from the second cut.
But the tool was DOA!
Oh well, still made mucho progresso.
Once I get the tool issue worked out, I'll add some updates.
Thanks!

 

No, you've got it wrong. You have the two cut lines laid out, but you should only cut one. Probably use a cut off wheel, or maybe cut it a little long and sneak up on that line with some really nice sharp snips.

Then lay the loose side over the top of the rest of the uncut side, lining up close to the second line. Now scribe it exactly. Cut that line exactly, like your life depends on it (because your welds will). You should not ever use a flanger. Those are for amateurs, and will promote a place for moisture to sit and rust your hood.

Butt the two edges of the hood together and do any fine tuning and grinding so you have zero gap the whole distance. Clamp the sides so they won't wiggle or come apart. Now place tacks a few feet apart, then in between those tacks til they are about six inches, then start welding solid. If TIG, you can go end to end (as told to me by an expert body fabricator). If MIG, skip around and let the spots cool before welding near again.

 

I'll second that.

 

Ok. Well I guess I should thank HF for making such a crappy tool - otherwise I would have already cut both sides already. Thankfully I didnt have time to mess it up last night.

So I think I may be getting it now. By scribing the line on the uncut side with the edge of the cut side - I'm getting the 'benefit' of tranferring any variations on that edge. And if I were to perfectly follow that scribed line with my second cut, it should meet exactly - like a puzzled piece! Makes perfect sense now.

For the welding. Should I only butt weld it? I have access to a high quality spot welder so was thinking about spot welding a piece underneath the welded seam for added support. On the vehicle, the wider part hood will be supported it's full width by the wall behind the seats - and I plan to fab supports in the middle. so is adding a seam support worthwhile?

Thanks for sticking with me on this.

And FWIW I tried the replacement flange/punch tool last night on some scrap. As a clean fast hole punch it's fine, but worthless in making a flange - even on some aluminum.

 

I only butt weld body panels. By spot welding (needs an overlap), especially with a backer underneath, you are making it even worse than the flange. Inviting all kinds of moisture to wick into there.

Now we will get a dozen guys saying they do it all the time and just use seam sealer on places like this.

 

Please Butt weld it only!

 

Well, since you said please...

 

I think that a wooden buck designed and fab to the form of the finish product, would be a good start. You will know were you are at the start (a stock 40 hood) and you can see where you want to end up (a narrow 40 hood). You might see something different from what you were first thinking.

 

A buddy in NH. does these, he uses a hood that comes straight down on the sides,
easier to mate the lower half...
the lower 3" reveal of the '40 deluxe makes that a lot harder... my $0.02 ...

 

I think you're doing it the correct way. Make a template mark it well and slowly cut both sides. I wouldnt do the flop it over and cut it, just unnecessary work. I also agree don't use a flanger. Butt weld will be a lot better.

 

Have you thought about maybe hinging the centre like a 36 hood to allow you access into the rear (trunk area). Just another idea

 

Damn good idea

 

try a truck hood hinge, they use round tube/rod, the '32-'36 cars used the flat style hinge and funky bends on the hood edges...

 

So this hood being used for a boat-tail style back of the car, I wanted to get an idea of the proportions and such so I suspended the un-cut hood over the frame in it's approximate final location. At that time, I thought I'd use the full length of the sides and carve out some of the V so it sort of wraps around the top of the seats. After I made the intial cut, I suspended it over the frame again clamping it at the width I'd determined. At that point, it looked much longer than before. Too long for my taste.
Moving the pointed end forward to where I wanted body to end, I ended up having to basically cut off the V at the front. I can live with that. But then setting the width where I needed it - the cut angle was now different. Bad news is - wider. This meant that I'd taken too much out on my first cut.
In restrospect, I should have made my initial cut close to the centerline - where the 2 halves join, clamped it where I wanted it. I would then have seen the length was too long but could have adjust things before cutting.
Anyway, I went ahead and matched the wrong angle cut to the other side so at least it would be even on both sides.
As it stands, it looks like I'll now have 2 seams to butt weld.
Another option I considered was to solid rivet a piece over top. That would be in line with the period and look I'm going for and add some lines to break up the flatness of the top of the hood. I understand this would mean 2 seams susceptible to rust, but this will always be stored inside and be a fair weather car.
But I'm open to other ideas.
Also, any commnt relating to this are appreciated and also may help other metalwork noobs avoid this sort of thing.

@mrquickwhip I do like the hinge idea, but the gas (petrol) tank is underneath and takes up 80% of the space...

 

Plane (Plain?) geometry. Not so plain, it would seem. (seam??)

 

A 40 hood is pretty long, do you really need that long of a tail. Could you just make a straight cut across the back, an make it a little shorter. Just a thought