159 replies to this topic

[Jean-Michel Piot]

Before going into the chassis domain, I would like to revisit the head light covers of the 2A model.

I now have three dies done and the third one, for the light at the right corner, shows that the new part can be more accurate than the genuine Cox part.

The Cox part does not follow the curves of the wing and the nose. This die for the cover light at the corner does. So the transparent cover is curved.

[Jean-Michel Piot]

Now the magnesium chassis...

Here are two 2Ds chassis, one with usual oxidation after 42 years, one restored.





For this kind of result the method given by Philippe de Lespinay is the best I know.

And for those who have never seen a very well-preserved chassis with that typical pinkish shade, here is a picture of a NOS kit:



So the method I use consists in disassembling the chassis, having the magnesium parts (the frame and the drop-arm) bead-blasted, and then protecting the magnesium with a varnish coating.

Here is the difference before and after bead-blasting:



After bead-blasting treatment:



The treatment was made by two friends: Guillaume Bonnefoi and "Predator", a Slotblog member as well.

Others were made in the past by another friend and real artist I've already talked about, who notably sculpted the masters of every Aston-Martin car produced by Proto Slot Kit or Ghost Models: Pierre-Yves Lebeau.

Many thanks to them all.

Once I receive the chassis, I first spray a clear coat to protect the metal.



For every spray of paint or varnish, I always use a gas protection mask.



After the coating, allow the parts to dry:



Once dry, I have time to give the pink finish.

Rather than spray a pink varnish, I prefer to apply such a pink mix with a brush. I feel this is closer to the quite heterogeneous genuine coating.







After this coat I use either flat or satin clear.

Then you can re-assemble the chassis.





All the chassis:



For the wheels I do the same, apart from the fact that I use a clear varnish. No pink there, and this only for aesthetic consideration.

Because if you look at this...



You may also find excellent Cox chassis for sale on eBay, frequently listed by Thomas Gaynor from Missouri. His name on eBay is Dezyred636.

I bought about a dozen Cox chassis from Dezyred636. The work is perfect and the man is really nice. So I highly recommend his restored chassis. Now that he protects his work with a clear coating, you simply have to add the genuine pink touch.

At this very stage, we have restored chassis, repaired bodies, and good screens.

Next time, I will show you how to copy parts with silicone moulds and resin casting, which is useful for parts in then small numbers needed...

[TSR]

For this kind of result the method given by Philippe de Lespinay is the best I know.

Thank you! Feels great to be appreciated for something!

[Mopar Rob]

I'm not up on this restoration stuff. I assume the OEM pinkish finish was some sort of Alodine treatment? If so, why not just do that again after the glass bead blasting and then coat with the satin clear finish?

BTW, very interesting thread!

[TSR]

Rob,

Indeed it was. The problem is that of lasting. The Cox Aludyne treatment was not sealing the metal, so after a while, the magnesium corrodes underneath and simply splits the outer layer.

With the method I devised years ago, the metal is sealed by the urethane clear coat, then rendered to its flat finish with a coat of Testors "flat". Not only it looks identical to the original finish but I have some parts that have been done fifteen years ago and they do not show ANY signs of corroding yet.

[Jean-Michel Piot]

Yes indeed Cox used "Aludyne"™, as used in many industries for passivation.

I used a pink varnish because I do not know how an amateur like me would get this industrial product.

But you are right, this would not be enough as we can now consider the time effects on 40 years old Cox chassis and wheels. Better spray a varnish instead or in addition.

[Michael Rigsby]

These are the kind of restoration threads that I love. You are truly a craftsman, Jean-Michel. I don't think I've seen so many Cox chassis since I was a kid, and the body work on the vintage Chaparrals is fantastic. Thank you.

Michael Rigsby

[Gus Kelley]

Hey JMP!

What attention to detail! You must have more than a couple of cohorts you're working with based on the number of cars shown. Incredible!

Gus

[Jean-Michel Piot]

Gus,

You may be right: incredible for a work done by a single man for whom all this is only a hobby...

Thanks for your comments.

[munter]

Hi Jean-Michel,

I have followed the thread so far, with great enjoyment, thank you very much.

A general question about the chassis... I could never figure out what the holes either side of the mag chassis, behind the front wheels, were for. Can you or anyone clarify this?

Again, thanks very much.

[Quickcars]

Extraordinary, sir! I cannot tell you how appreciative I am for all the effort you are taking to share your technique in restoring these old gems.

I just wish I had half your skill and 100% of your patience.

Looking forward to the next installment!

[bosmeck]

This thread needs a six-inch nail and to be hammered all the way in so it never falls from the top!

What great thread, brother J-M!

Great tips!

Looking forward to the rest.

[TSR]

Actually Chris, I have been thinking about this for a while, like making a gallery with the restorations posts regrouped in one, and all the comments grouped at the end. This would be done after the thread would have gone silent for a while, and would be locked. I might get this organized...

[Cheater]

Yeah, we can make that happen, no problem. Might be a few weeks before I'll have time to work on it, but we'll definitely do it.

No six inch nail needed... LOL!!

[Jean-Michel Piot]

As it might also take some time before all is explained in details, everything is OK then...

I'm glad to see that the thread is considered as being useful. What is time-consuming is to take pictures of everything and in such a way that one could imagine having the car in front of one's eyes and in one's hands. And I'm rewarded with your comments.

[bosmeck]

I'm glad to hear this thread will stay at the top. I understand brother J-M on the photos and I take my hat off to you for going through this in such detail. You can never get enough tips and when you see it like this it really helps so much.

Once again, JM, brilliant stuff.

[Jean-Michel Piot]

As announced, we will see now the way to make silicone molds for resin casting.

The goal is to make repro parts from genuine ones and this, in order to equip the cars that are lacking some.

For instance, here is a genuine 2D interior and a resin copy.



For the reproduction of Cox 2E parts I reached an amicable agreement with my friend Don Siegel who had a genuine and complete non build car: he accepted to let me copy every parts I wanted and in return I was pleased to build his car.




Now, let’s see the process of the creation of molds.

You need modeling paste, RTV HR (this stands for “Room Temperature Vulcanization” and “ High Resistance”) liquid silicon with its catalyst, plasticard or polystyrene foam and contact cement (you can also use Lego bricks instead), a modeler knife (X-Acto or alike), two components polyurethane resin kit (Resin + Hardener), a release agent (I use a spray), some aluminum tape, a paint brush and … a kitchen ! (where you will probably find a precise electronic balance and a microwave oven).

With all this we can create a two parts flexible mold.

The first thing to do is to cut a rectangular base in polystyrene or polystyrene foam, larger than the part to copy.



You then put modeling paste about one minute and a half in the microwave oven in order to warm it so it will be easy to partly imbed the genuine Cox part in the paste and also easy to sculpt it.

Of course the paste shall not be too hot.

Another way to warm it is put the paste in a waterproof plastic bag and use hot water.

Once warm enough you put the modeling paste on the styrene base and place the Cox part (first cleaned) on it and begin to surround the part.

There should be a rather high socle of paste.



Then, with the X-Acto, you will create neat seals surfaces with quite vertical walls on the socle. In fact the socle can have a pyramid form or have vertical walls but in no way the bottom should be narrower than the rest. For the orientation of seal plans, and the placement of the part itself, you have to imagine the way the two half molds will cooperate, so the second part of the mold and the genuine part can easily be removed.


For complex parts like the pilot body, simply observe the genuine part.. you will find traces of the separation line of the genuine 2 parts metal mold for plastic injection.



The way to “calculate “ the mold, which is something not always obvious, has already been found by Cox people. There is no need to do it again.

Once the modeling paste is sculpted you make lateral holes in the vertical or close to vertical walls. These holes are very important as they will allow a good positioning of the two halves. The other part of the mold will have corresponding dents. The flexibility of the vulcanized silicon will allow the dents to go out of the holes.



When this is done, you cement styrene vertical walls all around the base.





To make sure the whole can now be filled up with the mix of silicon and catalyst, in other terms to avoid leakage, I use aluminum tape.

Like here:




Now we are ready to pour the mix of silicon+catalyst (add catalyst in a proportion of 5% in weight) in this “box” and allow it to vulcanize.



As you can see I use a balance and simply read the quantity of silicon. I then calculate 105% of the weight and add the catalist until the balance instrument reads this exact number (this in the case where the instructions for the catalist states that you need to add 5%)



I then mix the catalyst and the silicon...



Do not let the liquid silicon with its now included catalyst go directly on the part+its modeling paste socle, but allow it to go from one side of the "box" to the other slowly. By doing this way you will avoid air bubbles.





With my little experience I strongly recommend not to use a release agent for this first part of the mould. The release agent will only be used before creating the second part, as you will see.

Another thing: make sure the catalyst bottle has not been open for more than 4 months, otherwise the mix will not vulcanize.

When the silicon is vulcanized (after half a day with good products and notably a brand new bottle of catalyst) you can remove the aluminum tape, brake-up the styrene walls, and get the modeling paste and the part out of what is now the first half of the mold.




Make sure there is no rest of paste on the Cox part and, if needed, wash in soapy water with a brush and dry.

You can now put the genuine part back in the first part of the mold.

Here, for the interior part of the 2D Chaparral, before putting the part back, I cemented few styrene rods. This will allow the air to go out of the closed mold and assure a complete fill-up of the polyurethane resin.




You can now spray some release agent in the cavity of the first part of the mold. Wait few seconds and then replace the Cox part where it was. The release agent will help to assure the part will stick to the silicon and will not move.

Do not hesitate to spray some release agent in a glass and apply some with the paintbrush on every area that was hidden to the spray cone. Indeed the release agent is used to avoid the second flow of silicon to stick to the first one. If you forget the release agent you will have big problems…

It is now time to pour another mix of RTV HR liquid silicon + its catalyst.



In fact the second part of the mould will take the place of the modeling paste. Not exactly though, because you will not totally fill-up the cavity. By the way the molds I realize often have such a defect, not to be high enough so an important reserve for resin is preserved.

Well it works nevertheless.

When the second part is vulcanized, you can separate the two parts (open the mold) and liberate the Cox part.

It is now ready for resin casting !

We will see that next time, probably tomorrow.

[Jean-Michel Piot]

Before going on with resin casting, a close-up of the main cited products...









And at last, the resin components we will now use:

[Prof. Fate]

Hi

Npt to interrupt, but I do a minor difference for my casting.

I bought a small "LEGO" set for the purpose. Easier than framing up a box, or finding a box is to just use legos to build a box of the perfect size for the mold. They are silicone proof when assembled and repeating the exact size of the box for the second part of the mold gets easier as well, as the platform is a grid of its own.

Fate

[Jean-Michel Piot]

You are right.

I cited this way to do at the beginning of this part dedicated to resin casting.

It is probably better because you can even rebuild the Lego walls around the silicon after pouring the resin if the volume for the resin reserve is important enough.

I will try one day.

[Dave Wilson]

You amaze me everytime you post Jean-Michel !
as said beofre, your hands work magic.
If only i had half of your talant

Keep upi the posts

[mcseitz]

Just had to say thanks.
mcseitz

[Jean-Michel Piot]

Some tips now: do a first casting and observe the possible areas where the resin do not go in or where an important air bubble stands.

In those areas you will have to put some drops or resin, may-be use a thin tool and make sure there is no bubble. The fact that the resin is transparent before getting hard will allow this.

This is what I do for the 2E wing:

I first put some resin in the areas where the air can be trapped.





After a quarter of an hour I fill the first part of the mold with resin, using latex gloves, and apply the second part of the mold.





Then I make sure the second part of the mold is well in place.



In order to have a resin part which will not be too thick and as faithful to the original as can be, I often gently press the sides of the mold with fingers and some times place something on the top (here other silicon molds).



Of course I do the castings on carton which is put on a dedicated part of wood, to protect what is under.

Some people put walls around and use an elastic band …

Now, some repro parts :



Just one thing: I accepted to do few resin castings for others, but please do not ask me to do more simply because the molds can only be used about 20 times. I have few cars to treat, will do few others for me in the future and I have to count all the trials or casting that did not work.

For instance, for the 2E, I cannot disassemble Don Siegel’s car and get the genuine part back to recreate another mold.

Furthermore, I refuse to create molds from a resin casted part, because of the possible little variation in thickness.

One again, its only a hobby for me. My goal is to have a little collection of vintage cars, mainly Cox, nothing less but nothing more.

Then the only way I can help is show some techniques to people who do not know them or who think it is too complicate.

I must admit that before starting resin casting few years ago I first thought it was too complicate for an amateur.

In fact it is not.

Now, at this very stage we have repaired parts, repro parts, a clean restored chassis, we are ready for the next step: decide how to enhance the model and do it.

[TSR]

Jean-Michel, can you get white resin to work, I mean truly white?

[Jean-Michel Piot]

Philippe,

You are thinking of the 2 headrests I still have to send you ? (what a shame ...)

Yes I can have white resin. The one I know has a special filler that makes it white and is a little more brittle than the standard one. But for such a part, who cares about a little less strength.

But this implies that I buy the product and I do not know if they sell in smaller quantity than 1 Kilo. I may ask.

The rest in PM ?