A 15cc sidevalve opposed twin

[Peter Twissell]

Yes, I could have bent the exhausts as the radii are not too tight.
The intake manifold has tighter bends (1D) and some of the bends are very close together.
I decided to electroform the simpler exhausts first, as a practise before embarking on the more complex intake manifold.

 

[Ken I]

Now you can let your imagination run riot in 3D and translate it into reality.

A very cool project in and of itself - thanks for the tutorial.

Regards, Ken

 

[Peter Twissell]

Indeed so, I can see applications for this process to model a variety of parts.
Cast intake and exhaust manifolds for a start, but also any part which would be pressed steel on a full size engine, such as sumps, timing covers, rocker boxes etc.
A radiator would be ideally suited to electroforming.
Essentially, any part which requires a reasonably consistent wall thickness.
As I mentioned earlier in this thread, once I have developed the process, I will write a "how to" article.

 

[Ken I]

Pete, I clearly never thought it through - sumps and diff cover etc. would be a nightmare to machine from solid - by this method you can create parts that will confound most onlookers - go for it - add draw marks and wrinkles to your model.
You can also scan and scale the real thing - lots of scope here.

Regards, Ken

 

[Steamchick]

Peter, you make me feel like I live in a 2-dimensional world and you live in 3d! But I'm happy and feel comfortable with my paper and drawing board. (For now). Good luck building a more uniform thickness on these shaped components. Please note: Modern cars are now using "stable plastics" for intake manifolds, so you can follow that idea, but for exhaust manifolds, I think you have good ideas! But watch out for thin sections where the electric field is weak. (Inside every curve). You'll need to make anodes to go in the middle of those curves to get some electric field to deposit the metal.
I think (never having done plating) that the theory says you can use any conductor for the anode, as the solution holds the ions of depositing material. So as long as some part of the anode is of the material to be deposited (of similar area or greater, than the depositing area) you can use parent metal or "other metal" (Stainless steel? Aluminium?) to make electric fields where there are otherwise none.
In your case, I think some anodes in the middle of any curved surfaces should work to keep the field where you want it.
Best if you get an electric field modelling software for the CAD system you use for modelling the parts. Then you can "teach yourself" where to put anodes to make the electric field more uniform around the component to be plated.
Working in the car industry, I always though it to be very clever how they manage to chrome plate onto plastic handles.... - by making the surface of the plastic conductive!
K2

 

[Peter Twissell]

The exhaust pipes were reasonably successful. After cleaning up, there is sufficient thickness of copper all over, but there are a number of pits and grooves in the surface. These will need filled with silver solder when I attach the end flanges, then the assembly will be nickel plated.
Yesterday I started plating the more complex induction manifold.
I made a shaped anode, in an attempt to even out the plating thickness.
After about 20 hours, the part looked like an octopus tentacle, with extensive "bobbles" over most of the surface.
I tried to file the bobbles down, to get back to a smooth surface, but found that the smooth plating was very thin and came away from the pattern.
I have now peeled all the plating off and I will start again.
I suspect the bobbling may be either due to the close proximity of the anode, or die to the anode being too large.

 

[Steamchick]

Hi Peter, not being an electroplating expert, I can only guess.... the electric field is too large? Drop the voltage...? Increase the gap to anode? It should be a 1/r-squared relationship (inverse square law). If you want to be technical. But surface radius (locally) increases the local field dramatically, so when you get a tiny crumb (dust size) of plating at some point, the electric field has instantly become bigger (a very small radius has appeared,, compared to the flat surface!) and encourages more plating at that point. Hence the bobbles! Stop after a tenth of the time, flat the slightly bobbled surface, then continue.
Or get an electric field programme and add your CAD models.
But really, I have no idea, except for the physics I remember.
K2
But maybe you need

 

[Peter Twissell]

Hi Ken,
Yes, I think you're right about the inverse square law and growth of bobbles.
I don't think there's anything I can do about the inside radii on the part. I've already established that the anode can't be too close to the part. With the anode away from the part, there is no way to increase the field at the inside radii.
That said, the difference didn't seem too bad on the exhaust pipes.

 

[Steamchick]

I was referring to the micro-radius of particles, rather than the macro radius of the tube diamer, or bend radius.
K2

 

[Peter Twissell]

Indeed so.
With the anode close to the part, the effect of the micro radii on the bobbles is amplified. So the anode must be further from the part, which precludes doing anything about the macro radii.

 

[Ken I]

Pete, yes those "bobbles" are because of too high a current density - which is caused by the anode being too close (inverse square rule). This leads to preferential growth points where the point current density is higher - a vicious circle.
The inverse square rule plays havoc when trying to get even distribution on complex parts - hence a mixture of anodes and thieves are used - but its something of a black art.
There are also chemical agents which work against over-current - I don't know what they are or how they work - but are used in solutions normally termed "self-leveling".
https://www.pfonline.com/articles/m...of-leveling-in-decorative-acid-copper-plating
Specifically "Self Levelling Copper" - typically used as the "undercoat" for Nickle & Chrome decorative finishes.

Image from the link above....
I mentioned a Hull Cell earlier - I suggest a trial flat part at an angle to a flat anode to determine the optimum current density for your solution.
I'll leave the math's to you - sum of inverse squares x dx = total amps - you can use calculus or a spreadsheet approximation via discrete "strips".
Then you can determine from the sum area of your components and thieves, how many amps you should be plating at.

Regards, Ken

 

[Steamchick]

Thanks Ken 1. I love to learn about something new! - Like this!
K2

 

[Peter Twissell]

Hi Ken1,

I've looked into levelling additives and I understand the mechanism, but the additives are not easily available and the process requires reversing the current direction to erode high spots away. This is beyond the level of complexity that I intend to invest.

In the meantime, I've made a Hull Cell, using a piece of plastic painted with graphite paint as the cathode to minimise the variables between the cell test and my part. I'll run the test as soon as the paint dries.

 

[Peter Twissell]

So I made a Hull cell and ran the test.
The cell is made from plastic and the cathode painted with graphite paint, so as to be representative of the part I want to plate.
From an online source, the test should be run for 5 minutes at 1 amp.
The photo shows the cell in the plating bath after 5 minutes. Plating had begun to deposit, spreading evenly from the location of connection.
Interestingly, a thick layer of plating developed quickly on the copper wire connection.
I left the cell to continue playing for a total of an hour, in the expectation that it might produce some more useful results.
The third picture shows the plated cathode.
There is some unevenness, but mostly around the connection point.
Certainly no clear distinction between the end closest to and furthest from the anode.

 

[Ken I]

Unusual result ? I suspect your (relatively) heavy copper connector was running interference.
As far as I know you should connect both anode and cathode at the wide end to minimize this.
The current needs to be high enough to induce bad plating at the narrow end. 1 A for what looks like about 2 square inches would be a bit low.
If I was running this test - I would (from the first test) take a stab at the current density - recalculate and run the test again.
I think I would also run the plate parallel for a while to develop an even layer over the conductive paint first - I suspect the paint is unable to distribute the total current well (initially) resulting in high current density about the connector simply because of losses in the resistive paint over distance.
Regards, Ken

 

[Peter Twissell]

Second attempt with the Hull cell, cathode stripped and repainted with graphite, connections moved to furthest ends, current increased.
5 minutes at 1 amp to cover entire surface of cathode with a layer of plating.
1 hour at 2 amps.
Evidence of "burning" (excess current) at the end closest to the anode, but otherwise the plating conforms to the brush marks from painting.
This was at several times the current density I was using for the part, so the burning was expected.
If I have learned anything from this, it is that I could be plating at higher current density (amps per square inch).
I am happy to stick with the current density I was using (0.1 amp per square inch).
I've now started another attempt at the part, but with the anode well separated from the cathode.

 

[Peter Twissell]

Finally some success with the intake manifold!
This one was run at just 0.2A, a fifth of the current which worked for the exhausts.
At the start of the process, even with the low current, some bobbles were beginning to appear on the areas closest to the anode.
I used the Hull cell parts to improvise a baffle between the anode and cathode, which appears to have worked, giving a more evenly distributed field at the cathode.
The part took most of the week to build, around 120 hours.
I think the lesson here is in the field distribution.
Ideally, I think the bath should have been much bigger, so that the size of the part is small by comparison with the distance to the anode.

 

[Peter Twissell]

A bit of cleaning up and melting out the pattern and the result is a useable part.
Note that the wall thickness is uneven at the small ends, where there are tight radii and high field density at the extremities of the part.
For this application, this is not a problem.

 

[Peter Twissell]

The electroformed manifold parts are soldered together, using a fixture to locate all the points of attachment to the engine.
The solder is a high melting point alloy which came with a boiler kit.

 

[Peter Twissell]

Manifold fitted to the engine.
Now to dismantle, fit the rings, set timing, reassemble and run...