Creating the Lotus 72C in 1:12 scale.
Page two of the Construction/design Diary

Page one

 

 

 

 

 

 

Update 11/30/2009
It has been a few months since the last update, and a lot has happened. I decided it was time to get some prototype parts made, just to make sure I was going in the correct direction, and that parts would actually be able to be produced the way I wanted.

I went to a local company that represents and supplies Z-Corp 3D printers, they were very interested in what I was doing, and offered to run some parts for free. They wanted to see how they would turn out, because they thought some of the parts may be too thin.

The process with these printers is; they print in layers using a bonding agent (a bit like using a laser printer) in cartridges. Each layer is approx. 0.003" thick. The support table drops 0.003" every pass and the parts are supported by the same powder that the parts are made from. Once completed the parts have to be removed from the powder and then dipped in a CA glue to cure them. Because some parts were so thin, they were not able to use the vibration method in the printer to shake away the excess powder, they had to dig in carefully and find each part.

Here are some of the results:
The front and rear, right side fuel tanks that is the recesses for the torsion bar, the gear shift pocket and shaft (at the back) on the inside, From the outside the Shifter shaft recess is visible through the access hole in the tank. These parts were easy to print, but the surface finish leaves a lot to be desired, in other words, there would be an awful lot of sanding to do, to prep them for making mold masters.

The left side fuel tanks You can see the layers of how the powder was laid down during the printing process. It also showed me that I cannot have the prototype parts produced with the fuel line stubs. I will have to add them when I produce the mold masters; the same with the locating pins on the bottom.

Smaller parts were really difficult to reproduce the detail I wanted as can be see with the inlet manifold and injector mounting plate so you get an idea of size The attaching faces of the two parts were .5mm thick (0.018") which, when drawing them looks really thick, but when actually produced are way too thin and cannot be produced properly. I have to re-think those parts and possibly produce them as one piece so as not to make areas too thick.

The body skins were also at .5mm thick, unfortunately they did not survive being removed from the powder, meaning I have to thicken them, not by much, but enough to give them strength. For reference, those of you that have Model Factory Hiro kits know how excellent their resin body parts are. They are .7 to .9mm thick approx. 0.030" to 0.037". Which is almost twice as thick as I was trying to achieve. They are 1:20 so in 1:12 that thickness will be excellent.

The downside is that because I need to thicken the skins, I have to reduce the size of the fuel tanks, so they will fit in between the tub and skin.

The side pod would have been fine except for the back end which again was .5mm thick and you can see that it distorted when curing plus a corner fell off. So Back to the drawing board, well solidworks, and redo all these parts.

The parts I was most happy with, and surprised, was the air-box base and top the bottom is .5mm thick and so is the edge of the top You can really see how rough the surfaces are when produced on the Z-Corp printers. I sanded and sprayed a number of undercoats of paint, sanding between, just to get the finish you see on the the top. However, with very little sanding the parts fit together very well. I still have to redo these parts though. (I am actually working on that now. I have the new base completed and half way through the top.)

Since these parts were produced, I have been talking to another company that represents OBjet 3D printers, the finish from their printers is much better and will require less work to produce mold masters. I have also been talking to a couple of companies that use Stereo Lithography (SLA) which is another, and apparently, better system, which uses liquids and lasers to "grow" the parts. They offer a number of different quality finishes.
The finish from the Z-Corp printer is great to achieve parts with a "cast" look.

Over the last couple of months, I have been sending files of parts to a company in California, and making adjustments to them to ensure their system will produce all the detail I want to have. I will have parts produced on the OBjet printer and by SLA, then decide which to use for the mold masters. Cost wise the SLA produced parts are only a little more expensive than having them printed.

If I were to buy a 3D printer, it would be the OBjet, because of the two different finishes it can produce. That's a long way off though.

Now I am working on the final details of parts, before getting the prototype parts finally produced to make mold masters from.

The new, almost finished side skins   right and left I still need to put the fuel filler access hole in the left skin and notch the front of both, for the suspension.
The front top skin had to have the rivets appear flush with the body, so I decided it would be better to include that detail in the part, also because of the thickness problems I decided not to have overlapping joints. This makes production and assembly much easier, also gives a much better finished look.  I was considering supplying rivets for all the body parts, but decided it is not necessary, especially as they will be painted anyway. (Which is something else to consider; the amount of recess in the parts for the rivets, so when they are painted it looks right. I will go back and change that.) Some of the rivets are missing on the rear top skin     because this is where the headrest fits. The recessed circles are where the roll bar front supports get mounted. The "bosses" at the rear of the side skins is where the main roll bar mounts are. The other two holes in the top rear skin are for the seat belt anchors.  The headrest is almost finished, just some locating pins to be added and a few minor holes to be inserted, some of which have to wait until I have completed the windscreen, which incidentally, has changed from my original vacuum form prototype.

The revised left fuel tank looks like this now. I have changed the locating pin on the bottom and added a spacing "boss", which is necessary after reducing the size of the tanks (a little modeling artistic license here). I still have to remove the fuel stubs and locating pins, but that's no big deal. At the moment I use them when assembling everything in the computer.
And the right tank. They have been reduced overall by 1mm (0.039") which may not sound much, but makes a world of difference and everything has to be adjusted to suit.

The new side pods came out better this time as well with the recesses for the mesh guard and radiators. You can clearly see the four locating pins to align with the holes in the skins.
Its great! The more I have used the software, I realize how to do things more efficiently (and correctly).

I have also produced most of the parts for the front end, sub-frame and suspension, discs etc.

Update 12/1/2009
As I said I had been working on the front end,.........With the exception of some small final details, it is almost completed. I have broken down the front sub-frame into: front,  rear, and other cross member pieces to make assembly easy. The angled top cross member on each side, include the top wishbone rear support, I have taken the liberty of combining the inboard disc mounting bracket with the top cross member, which will easily be positioned with the locating pins/holes and bracket on the front sub-frame part. Also it will give strength to the assembly. The floor will be the lower cross members.

Each side of the front axle/disc brake assemblies, comprises of many parts, starting with the inboard disc carrier, universal joint housing,  The lugg inside is to locate on the notch in half shaft end part, there is obviously one at each end of the half shaft. The rear of the universal joint has the boss to mount the disc carrier.  I'm planning on this being machined in aluminum and the solid disc rotor in steel. The vented brakes were apparently only used in some practice sessions throughout 1970, so I am not including any vented discs.

At the other end of the half shaft we have the outer universal joint, again having the lugg to locate on the half shaft end part notch. Of course each UJ will have the cover plate. You have seen both these parts before when I machined them in aluminum. This UJ is inside the wheel upright, and then the axle is attached.
The upright will have top and bottom ball joints this is the sub-assembly of all those parts.

The upper wishbone is made up of three parts for ease of manufacture: top, bottom, and third piece, of rod, so assembled it will look like this. This being the left hand side. The lower wishbone is just one piece. I plan on all these pieces being white metal, but I may change to resin, to reduce weight. I have designed the ball joints and wishbone ends so they can be assembled keeping all motion for the suspension and steering to be operational.

Trying to keep true to the car and scale I have a steering box, which, I hope will work; with the steering rod, the recessed section will be inside the steering box when assembled, and with the extra notch in it lined up in the middle, should allow the drive "worm" to fit inside, and move the steering rod by friction. That is the plan anyway; I will have to see if it really works when some special parts arrive and I produce the actual prototype parts. It works in the computer. ;)

There are steering links at each end of the rod, with ball joints, at each end connecting to the wheel uprights. The "jam nuts" will be separate in the kit.

With all the parts assembled, sub-frame, discs, suspension and steering rack, this is what it will look like. I have a partial of the nose support frame shown as well.
I still have to add the brake calipers, torsion bars and brackets, plus the shocks.

It has been very difficult getting the geometry correct on the front end, because there were so many changes performed in the field, and never made it to drawings. I have to credit books, photographs, Lotus mechanics and personnel to enable me to get it this close.

 

  to be continued........................

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