Metal Finishing

[Charlie]

I am making the attachment points for my Jordan Series drogue. I purchased some raw 316 3/8 x 3" Stainless steel that I am going to cut to length and drill for bolts etc. I have two questions. 1) How do you the SS. 2)Is it better for corrosion prevention to polish the parts that are not going to be visible?

[Charlie]

Originally Posted by Charlie

I am making the attachment points for my Jordan Series drogue. I purchased some raw 316 3/8 x 3" Stainless steel that I am going to cut to length and drill for bolts etc. I have two questions. 1) How do you polish the SS. 2)Is it better for corrosion prevention to polish the parts that are not going to be visible?

I hadn't asked the first question the question is How do you polish the stainless steel?

[Paul L]

Charlie,
Do a web search for stainless steel passivation. You'll find a fair amount of info on finishing ss. Here's one site with some good info:

Feature Article - How To Passivate Stainless Steel Parts


Paul L

[Charlie]

Thanks Paul

[delmarrey]

Originally Posted by Paul L

Charlie,
Do a web search for stainless steel passivation. You'll find a fair amount of info on finishing ss. Here's one site with some good info:

Feature Article - How To Passivate Stainless Steel Parts


Paul L

Dotto!

Polishing helps but the chemical treatment surpasses all else. You may want to do a polish first to get rid of the roughness and then the passivation will greatly improve it's resistance to corrosion.

[Charlie]

So is polishing the same as with wood. Start with a rough sandpaper and then work your way to progresively finer grits? I had some emery cloth laying around so I sanded a small section with 120 grit. It looks better but it also shows the imperfections. I'm thinking of hitting it with a belt sander with some 6o grit then moving my way up till it looks good and then hitting it with a buffing wheel. Is that the right thing to do?

[Steve Kidson]

While the theory and approach to polishing stainless (or any metal for that matter) is similar to timber finishing, a different type of abrasive material needs to be used.

To get the best results, take your parts to a professional who has the right belts, cutting/polishing compounds, and skill.

It is unlikely that an amatuer will be able to buy and use chemicals/equipment needed to electropolish for the final finish.

Fair winds

Steve

[David M]

I would not worry about it unless you are concerned about how something that others cannot see, looks. Stainless steel needs oxygen to not go active. I know that sounds counterintuitive for metals but stainless can go active in an oxygen free environment under the right conditions. I have bedded the roughest cuts of stainless with no consequences. Just keep the stainless clean and it should be fine.

[Charlie]

Thanks For all the advice. I am goiing to talk to the shop that sold me the SS and see what they say about polishing. The guy said to hit it with emery cloth and whether that is on a belt sander or in my had will make a difference in thte time it takes to do it.

David,

Thanks for the heads up on the rough SS that helps alot.

[Charlie]

Well I finallygot around to polishing the SS for my drogue attachement plates. They are hefty 3/8" by 3" by 30" long. I took 50 grit sandpaper and attached it to my 4 1/2" grinder. This did a good job of taking off the amount of metal needed to get rid of the pits left over from the manufacturing process. From there I changed down to 80 grit. Then I went to these scotch brite pads I don't know the grit but I used two different grits. The pads had a flexible sponge like backing which did a good job of not making divets (sp?) in the SS. I then applied a buffing compound to a wheel on the grinder and buffed the SS. It worked pretty good but I needed a stronger buffing compound. I'm goign to check the auto store tommorrow and see if they have it. It took me about two hours so far and I probably have another hour to go. I'll try to post some pix of the before and after.

[northerncat]

get a random orby and just work your way up through the grits till you get to about 400, then polish it will come up mirror finish if you use a cut then polish compoound, be aware that youll only get about 1m inute from each discbefore you need another one, its g\quick and cheap, you do need to fet rid of the mill scale though, a belt sander with zirconiated belts is good for this do this with 40g 80g 150g then move to the orby, takes about 15 to 20 minutes to do a chaine plate this way
sean

[Wotname]

Hmm... I am not sure that the hidden parts don't need polishing for corrosion resistance. The info. about SS needing O2 to maintain its corrosion resistance is quite correct; but as the hidden surfaces will most probably in an O2 deficent area but will still be damp (at least occasionally), then it will need all the protection it can get and a highly polished SS surface provides better corrosion resistance that a rough surface. Of course if the hidden surfaces are completely dry then maybe it is OK to leave them rough - but I have not found a completely dry area on my boat .

As for hand polishing, you seem on the right track, I normally go to 400 or 800 grit on the linishing belt before going to the cutting compound on the sisial buff. After that, a polishing compound on a stitched cotton buff and finished with fine polishing compound on a loose cotton buff. It is only then that you get a high polished finish.

But it is a lot easier to take it to a shop and get it electro-polished and that (I am told) is far superior for corrosion protection - and looks better too.

[Charlie]

Wotname Northern Cat:

I can see where I should have gone all the way up to 400 grit. I ddin't. I can still see the scratches from the scotchbrite pads. I'll have to see if I want to get rid of every scratch or not. It isn't what I call a mirror finish but I can see myself in the finish. I wish I had got your replies before I had started the project. It looks good but not 100%. Maybe 87%.

[northerncat]

the better you get it now the less maintenance in the future
sean

[Wotname]

Its all part of the learning curve. Well done for getting to 87% on first attempt