Chromium plating

[Donald A]

I have now got to the driveshaft casing, in restoring a 1969 Featherweight (F811B9), and need to get it rechromed

The water pump housings I have are 1.120 in ID and 1.132 ID, and the uncorroded chrome end of the casing is 1.134 in OD, which is not a promising start.

Kempe 1970 ed tells me that a decorative chrome is 0.00002 in, but industrial chrome is
.0005 to .01 in , and decorative nickel is .0003 to 0012 in and industrial nickel is .001 to .1 in

I am told that the process for marine plating is triple - ie after stripping, make good the corrosion with heavy copper, finish back to smooth - then plate with nickel, for its anti corrosion properties, and then chrome, for its hardness. Chrome is almost twice as hard as nickel, so presumably that’s the reason why most people don’t stop at nickel.

I have tested the max and min ID of the housing, and only get a difference of .004 in ie 4 microns.

Going off at a temporary tangent, I once had a roadside chat with a Snap On salesman - I said I assume all your spanners are stainless? to which he replied “well we do make some things in stainless, but most of our stuff is deep chrome in other words deep enough to dent”.

I have approached a plater, but the girl doing the front end (ie administrative stuff) said that their chrome was 3 hundredths of a micron, even although she knew that we were talking about an outboard part which required marine specs - not a promising start, as that surely, (if I’ve translated the noughts correctly) puts me back into a decorative thickness

Add to the above that I don’t know the OD of the stripped tube, and therefore can’t work out the required thickness of the bottom 40 mm of the tube, to go into the housing.

One is pushed towards having a shoulder in the plating, so that the surface exposed to salt water can be thicker, and do a proper job. I then don’t know the permeability of the chrome/nickel (and presumably it is permeable, otherwise it wouldn’t have corroded in the first place - corrosion, on first principles, can only start when electrolysis starts on the ingress of water), and therefore can't work out the best value thicknesses

Hopefully, someone out there has done this exercise from a more knowledgeable starting point, and can help!

Regards
Donald A

PS I’ve looked through the threads on a search of this site, but none of these go into enough detail to answer the problem
PPS Duplex nickel (see Kempe) is attractive - first layer semi bright, levelling low sulphur content solution, and second layer fully bright levelling high sulphur content solution - but I suspect that takes me into impossible money....

[Keith.P]

I have only ever plated one drive tube, a 1942 seagull, that was plated, but not chrome plated, this was pretty much my only option, but the price of having the drive tube stripped and re-plated, when its just as easy and cheaper to replace it, especially on a late motor.

[headdownarseup]

Why not look out for a good second hand tube for sale.Quite a few about these days if you know where to look.
Much easier (and cheaper) than going down the replating route.


Jon

[Gannet]

Donald,
I would take a pragmatic approach.

Why not get it replated, hopefully with the traditional copper, nickel and chrome. Don't worry too much about the exact specification. Unless you are going to pay for it to be processed specially, it will probably be out of your control. If it is a tight fit into the pump housing, I am sure a flap wheel will rectify that in a few minutes.
In use and in storage, smear water proof grease over it. I do not know how long it will spend each year in salt water. Perhaps a fortnight? I expect it will then last a generation or two (if its greased).

I have had a couple of tubes replated (unknown spec) by Classic Seagulls in Cornwall. I have been satisfied with their service. Replating makes a huge difference to the visuals - even when smeared with grease! So far no sign of corrosion from the salt water!

Jeremy

[Oyster 49]

I've also had a SJM leg rechromed by classic seagulls. I think they charged me £25, which I thought was good value. My local platers in Derby are high quality, but the minimum charge is £75!

[Donald A]

Thanks guys - that's very helpful

I had had a chat with jackie at Sheridans, before posting the thread, and she said she did not have any featherweight legs at the moment - and even if she did, they would be plastic coated. She thought they would be made to fit immediately into the ends of the water housing, so therefore did not know the stripped OD of the steel tube. She also said they did some plating for the Freeman cruisers they service - but it came back replated, but still with the dents and corrosion marks in it.....

I like the idea of a flap wheel - I had not thought of that, and it means I don't need a shoulder.
Donald

[Oyster 49]

Part of the chrome plating process is to put the item in a pickling tank. Here the strong acids clean the metal and remove any corrosion. This will leave behind pits where the corrosion once was. The only way to avoid this is to dress out the corrosion first, which would be a big job on a rusty leg. If a really good finish is required then I would cut off the old tube, machine out the flange end and braze in a new tube, then get that rechromed.

Chromers also have a polishing shop as part of their operation, work is always polished first, and then between each plating op too. (Copper-Nickel-Chrome)