1932 Cadillac V16 scale model

[Lexi]

I believe that is so because the relationship between chamber gas removal and pump efficiency is logarithmic in nature.

So you have to make a dam for the tire mould though. Does that mean something permanent OR a temporary retainer wall? If temporary, what I found works extremely well are off set printing plates. They are very light weight aluminum flexible sheets not much thicker than paper. You can easily form them into shape and cut with scissors even. Best of all, virtually nothing sticks to them. So you could make a circular pattern for your tire and tape the seam & cover with vaseline or the product you use to effect your Bell jar lid seal with. This is a great product to make temporary dams. Plasticine also helps to seal at the base.

Attached is a photo of one of these plates in an industrial setting. Also attached are 2 shots of a repair I did on a 19th century marble bracket. A piece of the marble was missing so I used the printing plate metal, plus a wooden backer board to assist in keeping its form, in order to pour an industrial plaster end piece to effect the repair. Some hand finishing work was needed. This material may prove valuable to your Cadillac model project.

You may have to buy a box of them which you would never use all in your life time. You can even reuse them so they go a long way. They are light sensitive (actinic) but that is not a factor with us. Usually a clear plastic sheet must be peeled off one side prior to use. Again, not a factor for us. I have a box of the off set plates and you are welcome to some, at no cost for you Roger. Just pay for shipping. Might be cheaper that way to get what you need. I could cut a few in half, roll up and ship in a tube. I got mine from a photo printing lab who were throwing them out as they were outdated. Clay/Lexi

[Roger Zimmermann]

Thanks for the offer, but I already have began to modify the pattern with a brass stock. I will be glued on the main body to avoid the loss of RTV if the joint is not perfect. The outside wall will be cardboard; with some way, the RTV does not stick to it.
Fortunately, the product I have has a long set time (about two hours) so there is plenty of time to have the mix without entrapped air.

[Lexi]

I did use cardboard retainer walls as well. Coated them with Vaseline to act as a release agent. Clay/Lexi

[Roger Zimmermann]

Interesting to have a conversation with somebody knowing the matter, I appreciate!

[Lexi]

Yes, but I am not in your league with the metal lathe work. I do wood turning on a lathe but I must get a small machinists lathe for metal projects. Your work is excellent Roger.  The cardboard I used for some retainer walls was that board that draftsmen use, grey on one side and white on the other. Stands up well. Plasticine coated with vaseline also works great to plug holes and seal areas. Keep up the good work buddy! Clay/Lexi

[Roger Zimmermann]

Machining on simple machines is requiring some habit, like everything. Set-back can happen, even to me! Not a big deal on a simple part but when you are in the middle of a more complex part and an error is done, well, it's the time for some choose words!

The third tentative for the white wall's mold seems to be the good one. The first picture is showing the little quantity of material was mixed with the catalyst and black paste (the used product is transparent). When some vacuum was applied to the mix, the volume expanded and expanded. I had to stop the pump to avoid an overflow. After some pump's cycling, I could let it run for a longer time. After almost one hour, I opened the vacuum chamber and purred the RTV into the mold; I used simple cardboard to create the wall. Then, back into the vacuum chamber. There was still air trapped, you can see on the third picture the elevation of the mix. After 1 1/2 hour, I saw almost no bubbles and I let the mold out of the desiccator. After 2 hours, the mix began to set.
This morning, I took the cardboard away; some plasticine was used to close the interstices between cardboard and brass mold. The crowning of the day: the black rubber is removed from the brass part. Now I have a perfect mold for the white walls, one at the time.

[Roger Zimmermann]

The first white wall is born. It's good looking but the tire's dimension is somewhat weak, depending to the lightning. Still 5 to do!

[carguyblack]

Hey Roger,
You spelled "Firestone" wrong.
(bad joke, I know!)
So cool to watch what you are able to accomplish!
Chuck

[Roger Zimmermann]

You spelled "Firestone" wrong.

Oh! All is possible! Chuck, thanks anyway!

[Lexi]

That looks better than the Cokers on my car. Good job Roger. Clay/Lexi

[Roger Zimmermann]

Well, Clay, with all I read about Cokers, this brand will never be on my shopping list!

The white wall fabrication is going well, about one each day. A fourth is to be separated from the mold soon.
On the post #480, I was pouring white silicone into the mold. As you remember, it created a mess as I used not enough catalyst. I did this job again and, today, I removed the plasticine from the back. To avoid that the plasticine in going into the tire's grove, I used some masking tape to avoid it. I noticed that the tape was not sticking to the brass but did not thought more about that. The result: the silicone went between the tape and brass and filled up the groves! After painfully removed the undesired material and using wax, I poured the silicone into the other side. To tell the truth, I'm not at all confident that I will succeed. I will see that this week-end when the new material is completely cured.

[Roger Zimmermann]

There are good days as well as bad ones, it's life. Today is the second category: yesterday, I did another white wall; thinking there was still enough wax on the mold to avoid issues. There was not, white wall destroyed, fortunately, the mold is not damaged by taking away the sticking white material.
I opened this morning the negative tire's molds. One half is so-so, the other one some tread was ripped away. The material was more or less bonded on the brass at the recess to hold the white wall. Usually RTV is not sticking to metal but this time it did. I have a possible explanation: when I cleaned the uncured RTV, some stayed on the brass and, generally, there was still a trace of that RTV on the whole brass surface. With the proper catalyst added, this uncured RTV acted as a bonding agent between brass and the fresh RTV.
The result: back to the starting line...

[Roger Zimmermann]

It's better to put things aside until better days when it was a flop! As there are enough to do, this is just a temporary set-back. Last month, I began the shock absorbers; it was the right moment to continue with them. The design was more or less performed during the assembly of many parts all silver soldered; this bad method let me do some errors later corrected. As pictured today, they are far from finished, but I'm confident I will have working shock absorbers.

[Roger Zimmermann]

With one white wall every second day, I have now seven pieces. As spares are always good, I intend to do another one. Then, I will have to begin again the tire itself...
In parallel to the white walls, I continued with the shock absorbers. I added some cosmetic details; before closing both ends with the plugs, I did the shafts on which the actuating arm will be attached. When that was done, I silver soldered the blade which should render the shock absorbers functional. By looking at the size of the blade, I doubt that the shock absorbers will be really effective. Well, it's a fun design, even as a failure! The possible movement is about 120°, which is largely enough.
There is a groove on the shaft: a very small O ring (I have some since many, many years) will be installed to prevent the loss of the Hivis. Of course, a closing plate will come at the back of the shock absorbers; some details are still to be added.

[Roger Zimmermann]

Finally, the front shock absorbers are ready. It took a long time to add the latest details; maybe no one would have notice if skipped!
Technically, those shock are ready for the viscous product I have. However, I will ad it when the actuating arm is soldered to the hub. The screw you can see will be the locking system, of course flush with the hub. I assume that the hub and arm assembly was originally pressed on the shaft. As my shafts are inserted from the back, I had to find another solution. The back is now closed by a plate and four 0.6mm screws. A short bearing is integrated to that plate; it should prevent a binding situation for the shaft.
Maybe I will have to add a paper gasket to avoid that the viscous material is oozing.
I cannot finish the rear shock absorbers because I don't know the position of the actuating shaft at nominal position from the frame. The locking screw must be more or less at 90° from the arm and the relation between the actuating arm and inner blade must be right. I will finish the rear shocks when the suspension is done.
I deducted from my pictures the the actuating lever is horizontal for the front shock absorbers; therefore I could finish them.

[Roger Zimmermann]

In parallel to the shock absorbers, I continued with the RTV product. All white walls are now done and, finally, I succeeded to have a decent pair of negative tire molds. Technically, I could directly cast the definitive tires with those molds, but it's too dangerous. If one of the negative mold is damaged, I can redo the whole scenario. At $55.00 for one kilo of the white RTV, I don't take the chance. Therefore, I will continue with my "regular" process.

[Roger Zimmermann]

There is nothing now to report about the tires because in between I began something else: the front suspension. The shop manual is stating that the V-16 models have 10 leaves in the front; I did 10 leaves for each spring. As I could not buy spring steel the exact width I wanted, I had to make the material a bit narrower; I did that work in the  room where my cars and parts are stored. After drilling the holes for the central bolt (this bold is used to assemble all the leaves and to locate the axle on the springs), I installed the springs and axle on the frame. I discovered an error (this is not the first one nor the last one!) at the clips attaching the front axle: they are too short. I can hardly install some nuts, but this error is not that bad: with all the leaves, when I put a weight of 0.7 kg over the front axle, the springs are flexing about 1 mm! In the real life, a weight over more than 2000 pound would lower the front end by 1/2". Sure, those cars were not as comfortable as recent ones, but my springs are definitively too stiff, therefore I will remove some leaves until I'm satisfied.

[The Tassie Devil(le)]

I can see the axle has been scraping the road surface by the missing paint.

But, seriously, you can leave all the spring leaves in the pack, but to allow the required flex, I would advise modifying the middle leaves to be more flexible by removing the centre of the leaves, leaving 1/8" on each side, ending the metal removal in from the ends, so that the covering leaf hides the metal removal.

Might only take 3 or 4 leaves to be modified to attain the requires springicity.

Bruce.

PS.   Maybe I am overthinking this fix.   I remember seeing the grooves in the rear leaf springs on my '55 and '57 Chevs.   Maybe the Factory did this to give the cars a softer ride, as they did ride nice.

[Roger Zimmermann]

Bruce, thanks for the suggestion! I have another solution. Right before, I removed 4 leaves; the suspension is still stiff but "volume" for the spring pack is too small. I will add flexible plastic leaves just for the look.

[Roger Zimmermann]

As the negative molds were successfully done, I could cast the material into the recess to get the half positive molds. Right now, I don't know if this further step will be OK as many factors could lead to a disaster: the material can be uncured (it can happen), stick to the mold or air bubbles. I'm waiting another 24 hours to attempt the separation.