"Mechanix Menace": An LS7-motivated, chopped and heavily modified 1973 Datsun 240Z

[chevyz240]

I don't use FB so I appreciate the updates you take the time to make here.

Great to see the progress on this. I'm sure there are many like me who can learn from your skills.

Thanks anguilla1980!

The Facebook posts are exactly the same, except for the number of pictures. If I added all the pictures I post on FB, I would reach the limit here long before the project is finished!

[chevyz240]

Wow, thanks so much for sharing this build! I absolutely love the classic Z cars. Sure wish I had the mind to juggle so many elements of a project as you. I would be completely lost.

Thanks bkbkbk!

Yeah, I get pretty lost a lot of times myself! One thing that really can make me stressed out is thinking about how to solve problems that I will not have to deal with during the next couple of years, but I still really want to have a solution in my mind, right now! I have to practice concentrating at the subject at hand instead!

[chevyz240]

This week I have welded the rear crossmember brackets in place on the B-pillars and tacked the rear crossmember to them.

It was then time to make the front part of the jig for the trans tunnel upper tubes. This was a bit trickier to align due to the inclination of it. I also had to make a pretty extreme angle cut of the back end using a foxtail saw. As usual, a lot of measuring and alignment using my laser tools, spirit level, steel scales, cardboard shims and other tools ensued. After many hours, the result came out pretty OK.

One night when I couldn't sleep, I came up with (as I think at least) a pretty nifty little tube notching template for the rear end of the trans tunnel tubes. Naturally this was 3D printed. I am really happy that I bought my 3D printers!

The last thing I did today was to mark out alignment lines for the tubes. Due to these tubes being bent both horizontally and vertically, I can't use the jig as a template when bending the tubes. First when the tubes are correctly bent and notched, they will fit the jig. I have used the CAD model to see what angle the bends should have. I will then mark that out on another piece of particle board. The "wings" on the notching template will then be used to align it to the board, getting the notch at the correct angle. I am pretty anxious to see how this works out. Hopefully, I will find that out next week.

Over and out for this time!









As always; more pictures at https://www.facebook.com/MechanixMenace

[chevyz240]

My idea making 3D printed tube notching templates that are oriented with tabs or "wings" against the particle board bending template worked out pretty sweet! I will use that method a lot in the future.

When I clean off the rust protection oil from the tubing, I use acetone. I could clean the inside before I bend them, but I also like to clean out all the cutting debris after notching the ends, so I do that right before tacking them in place. To be able to push the wad of kitchen paper through, I had to make a jointed push tool!

I also realized that I couldn't use my regular steel square when checking the alignment of the front sloping part of the upper trans tunnel tubes, since I drew the alignment lines out from a vertical projection. That meant that the square had to be aligned vertically too. Again, the 3D printer came to the rescue. I made an alignment template with slots cut at the correct angle (12.9 degrees) for a piece of 1 mm sheet metal. That worked out well too.

After the top trans tunnel tubes were tacked in place, I had to cut the front part of the fixture away, too make room for the inner firewall tubes. I hade to cut it away from below using a foxtail saw.

Then it took me a while to come up with a fixture for those tubes, but I finally came up with a good solution. In order to get around the front vertical 2x4 of the main jig, it had to be a bit more complicated than just one piece of particle board.

I am pretty satisfied with the outcome of this week's work.

More to come next week, I hope!









As always; more pictures at https://www.facebook.com/MechanixMenace

[chevyz240]

This week, I haven't done that much, since I had a friend visting me over the weekend. I did manage to get one of the rear trans tunnel verticals tacked in place. My 3D printed notching templates helped even more than for previous tubes, since here there were two tubes at different angles involved at both tube ends.







As always; more pictures at https://www.facebook.com/MechanixMenace

[chevyz240]

The second rear trans tunnel vertical got tacked in place this week and the right hand top inner firewall tube (long name… ) as well.

Today, I also thought I should explain in detail all (well, almost all) the steps that are involved in getting a tube in place, taking this last tube as an example. See the captions for the whole story!


In this case, I first create a fixture or jig that will position the tube so it will line up with the sandwich panel that will make up the front right hand trans tunnel wall. As you can see in the CAD model, this panel is flush with the inside of the bottom tube and the outside of the top tub. (There are several reasons for this, which will be easier to understand later on.) This makes it a bit harder to make the fixture, as it can’t just be supported on the tubes themselves.







This fixture is made from the now famous 22 mm thick particle board. In this case, I had to make it in two pieces to clear a 2x4. On the bottom, it rests against the tube itself…





…but at the top it needs to be positioned 15 mm further out. This is accomplished by attaching two 3D printed spacers to the board.





I then need to mark out where the new tube should be positioned. Using the CAD model, I project the tube perpendicularly against the inner plane of the trans tunnel wall (which is the outside of the fixture). This gives me the height and length coordinates of the tube end plus the angle of the tube (this is more an extra check that the upper front tube of the trans tunnel is in the correct place) and the angle of the cut at the lower end.





In order to create a transverse line at the correct length coordinate, I first use my 3 plane laser. Since the frame jig is in the way, I have to create this line in two steps. I first mark the line on the garage floor and walls. (This picture is from a previous step, but the method is the same.)





I then use the 2 plane laser, which has thinner lines that are easier to work with, and line it up with the markings on the floor and on the wall. I then can mark out the vertical line at the correct length coordinate on the fixture.






The next step is to mark out the height coordinate. Both lasers have a reasonably accurate vertical beam, and the horizontal beam is reasonably accurate left to right, but pretty bad lengthwise. This picture shows what I mean.





If I can place the laser perpendicular against the point I want mark out and my height scale on the garage wall, I don’t need to compensate for anything, but in this case, I can’t. Therefore, I measure the ”depth difference”, which in this case is around 2100 mm. This means that the beam rises 2.3 mm. This needs to be taken into account when marking out the height coordinate.





I can now mark out the horizontal line and extend it so it can be seen from a position where the laser is perpendicular as described above. I do this to check if I have calculated correctly, which I have!





For those of you who really scrutinize this, I can add that my scale on the garage wall has the top of the car at 305 mm, which must be added to the height coordinates from the CAD model!





Using the angles from the CAD model, the edge of the tube and the bottom cut is marked on the fixture.







Now I can turn my attention to the tube itself. First I use the CAD model to design the 3D printed notching templates. As previously explained, I add “wings” that are used to rotationally orient the ends against each other.













I put the notching templates on the tube and align them to each other, making the tube a bit longer to have some margin to trim it to the perfect length.





I then scribe the cut lines.






Then I cut and grind the ends to shape.





The notch that needs to be made in the trans tunnel tubes has a tricky shape, and in this case I grind it manually, step by step, testing the fit as I go, without using a notching template. Here I actually cheated, and did it before a few of the above steps.





When the tube fits well against the dash panel diagonal tube, the trans tunnel tubes and the fixture, I can mark how much the bottom needs to be cut to make the length perfect.









Here, it is cut and put in place again and all alignments are double checked.





Now, it’s finally time to tack it in place!















When marking out the tube positions, sometimes it has to be done in many steps, creating a long tolerance chain. I was a bit worried where the lower end of the tube ended up regarding the lateral coordinate. I used the laser and found it was at 327 mm. This was easy to remember, since I had a 327 in one of my Novas (before putting a twin turbo 350 in it…) I then went up in the house and started the computer and checked the CAD model, and what did I find???





Yiiiiiiihaaaaa!!!!!!

These are the steps for getting ONE tube in place! Luckily some of them are a bit easier. Tomorrow, I think I will take a day off from the garage and learn how to fly my drone instead!

Larger pictures can be seen at https://www.facebook.com/MechanixMenace.

[andrewb70]

Is there a completion date for this?

[Motown 454]

Wow Amazing !

[Vimes]

Your thread is a real adventure. I wouldn't mind seeing you let loose in the engineering and design shop of a major OEM if this is what you're able to do in your garage in your spare time. Great work here.

[chevyz240]

Is there a completion date for this?

No Andrew, not really. Before I die, I hope!

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Wow Amazing !

Thanks Wayne!

[chevyz240]

Your thread is a real adventure. I wouldn't mind seeing you let loose in the engineering and design shop of a major OEM if this is what you're able to do in your garage in your spare time. Great work here.

Thank you very much Vimes! That feels good to hear! I am already partly doing this, but not on full cars; I design and tune shock absorbers for OEM's; Volvo, Polestar, Koenigsegg, Pagani, Lotus, Ruf and others.

[dhutton]

Wow. Such attention to detail and precision. You don’t see many folks talking about tolerance chains. Flashback to design reviews before I retired.

Don

[chevyz240]

Wow. Such attention to detail and precision. You don’t see many folks talking about tolerance chains. Flashback to design reviews before I retired.

Don

Thanks Don!

Yeah, I have always been a perfectionist and I guess my engineering background comes into play as well. Regarding precision and accuracy, when I worked with engine development for Scania, the average fuel mileage improvement of the trucks per year was 0.5%. This meant that everything you tried in the engine cells (dyno rooms) had to be measured with an accuracy on the order of 0.05% or less in order to see if it was an improvement or not.

[TANKMASTERJ]

That's totally awesome you work in R & D for Scania.
One thing I do wish I had some on my Camaro build is more time and thought it into my chassis. I'm running the Speedtech gear which is great but I wish I would have done some tube chassis weld in like you have. I do have a roll cage front to back but not at the level you are. I absolutely love your perfectionisti mindset on this build.
It's what keeps me coming back to look. That and
Well it's a Z!
Jason

[chevyz240]

That's totally awesome you work in R & D for Scania.
One thing I do wish I had some on my Camaro build is more time and thought it into my chassis. I'm running the Speedtech gear which is great but I wish I would have done some tube chassis weld in like you have. I do have a roll cage front to back but not at the level you are. I absolutely love your perfectionisti mindset on this build.
It's what keeps me coming back to look. That and
Well it's a Z!
Jason

Thanks Jason!

Well, Scania was 30 years ago almost! Now I work at Öhlins Racing designing and tuning shock absorbers. Mostly OE stuff, Polestar and Volvo for the most part the last 5-6 years, before that Koenigsegg, Pagani, Lotus, Ruf and others. And before that, racing stuff; NASCAR Cup cars, Dirt Late Model, Rally Raid, World Rally Cars, GT-cars and others. I also do a little bit of development test driving, but not so much.

Around 15 years ago I visited Detroit Speed and tried to convince them to offer Öhlins shocks as an upgrade, but unfortunately that never happened.

[wfo guy]

I liked the use of 3d for the tube markers. I have read through your thread in the past but have no memory so I don't remember much from the beginning. Please convey your thoughts on the design of the chassis. You have a lot of triangulation with smaller tubes. Is there a reason you don't use slightly larger tubes to simplify and cut down on stress risers?

[chevyz240]

I liked the use of 3d for the tube markers. I have read through your thread in the past but have no memory so I don't remember much from the beginning. Please convey your thoughts on the design of the chassis. You have a lot of triangulation with smaller tubes. Is there a reason you don't use slightly larger tubes to simplify and cut down on stress risers?

Thanks for a technical question, wfo guy!

First of all the lack of triangulation in the driver's compartment is due to the fact that I will have a sandwich design instead, consisting of 1 mm aluminum sheet on both sides of a stiff foam core. This will be glued and riveted to the tubing. This will be lighter, stronger and stiffer than triangulation plus sheet metal. It will also provide noise and heat insulation.

Regarding tubing diameter, the smallest ones are 1 3/8", which is more than enough, considering they are so short, so they will not be subjected to buckling. I don't know exactly what you mean by stress risers, do you mean that they will occur due to the smaller tubing having less material, or due to the diameter itself? If you have full triangulation, all the tubes will basically only be loaded in compression and tension.. As long as you don't have buckling, you can use small diameters. That will actually give more uniform loading in the joints. Where there is no triangulation, the tubes will also be loaded in bending and twisting, and there you will have use for larger diameters to increase the stiffness.

Since the triangulation is there more for stiffness than strength, very little material is needed to add a lot of stiffness. Using larger diameter tubing will only add weight. If I would use bigger diameter material, they would need to be very thin to have the same weight, thinner than what is easily commercially available.

Regarding simplification, it's actually easier to use smaller diameter tubing. A diagonal that goes all the way to the corners will not be able to be put in place without cutting away a tab on one side of the tube to be able to push it in place. The bigger the diameter, the bigger this tab needs to be.

I hope this answers your questions, otherwise please get back to me!

For the very front part of the chassis, I could probably get away with thinner or smaller diameter tubing, but part of the reason for choosing the dimensions of all the tubing is to be able to register the car for road use here in Sweden. It would be hard to convince the inspectors using smaller tubing.

I can also add that for crashworthiness, I will add a deformation zone at the very front, made from a thick piece of aluminum honeycomb. This will also be used in the doors.

[wfo guy]

I misjudged the size of tubing I saw. I thought maybe it was 1". What alloy and wall thickness are you using?

[chevyz240]

I misjudged the size of tubing I saw. I thought maybe it was 1". What alloy and wall thickness are you using?

The thinnest tubes are SAE 4130N, 1 3/8"x0.058".

[wfo guy]

That size tubing is over in dragster construction land where I used to be. Your comment about corner to corner for a diagonal: we used to cut those to length but not weld the top or encapsulation rail in place until all the bars were a finished size for the proper fit. The accepted clearance was less than 50 thous. I'm sure in today's world, solidworks or a companion program allows the correct dimension to be calculated and cnc cut to where this is simplified. I'm from the dinosaur days before any of that was available. In dragsters, we had flex in some areas that were advantageous for weight transfer. As I understand, the current logic in road or auto cross is to have sufficient strength to minimize chassis flex so the suspension does all of the work and is repeatable in normal conditions. Is that where your design is headed?