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I am working on this home machine and I soaked the feedscrew for 3 days and it looks good except one spot. Is there any other way besides using the feed screw nut to get this spot out.

The fastest rust remover I know of (save sandblasting)is hydrochloric(aka muriatic) acid. Hardware and pool supply item. Lung-ripping fumes and instant skin burns. Wear glasses and play outdoors. Have cleaned rusted tools and the like with it (dissolves rust quickly) but have never used it on something as fine as those feedscrew threads. I would try a small drop on good threads first. If the acid doesn't bubble, nothing is happening and you're ok to put it on the rusted areas where it will react and eat the rust away.
You have to completely remove the oil you put on the feedscrew as it will will keep the acid from reacting w/ the rust.

Also, keep the acid from getting onto anything that isn't steel; for example it will react very fast on pot metal!

The best and most non-invasive way to remove rust is by electrolysis. Here is a link on how to do it but you may want a smaller setup for fine parts.

rust removal by electrolysis: http://www.rowand.net/Shop/Tools/Electrolysis.htm
and a youtube video:http://www.youtube.com/watch?v=R5I5WBG5HPw
A Google search will give you many links.

Thin threads on a screw can be made up of mostly rust so be careful no matter what method. I just thought maybe electrolysis might work for this due to no scrubbing or chemicals.

I have heard that vinegar is a good rust remover but I haven't tried it yet. It might be a good place to start because it is always a good idea to start with the least radical method. If that doesn't work, move on the the next level. Also, I used to use commercial rust remover on my sidewalks to remove rust stains. I was told that the active ingredient in the remover was phosphoric acid, but I can't personally confirm that. The method linked in Sansenoi's post looks to be a good one because it won't turn your back yard into a toxic waste dump.

@Sansenoi: Thanks for the links. I have several very rusty Regina music box discs and have been looking for a way to clean them. This looks like my answer.

Jim

No problem with the links.. There are a lot of electrolytic rust removal tutorials on youtube.

No chemicals that can pit exposed good metal while removing rust and scrubbing the black oxide off is done after electrolysis with a plastic bristle instead of metal one in most cases.

It's just that with any method... if the thread of a screw or fine part is only held together with rust once the rust is gone the part is dissolved or the thread is bare.

You are correct in that once the rust is removed, there could be nothing left. It seems to me that someone offers dies for chasing feedscrew threads and perhaps some of the repairmen out there (George V or Ron Sitko for example) offer the service. This might be a good first step - to see what's actually there under the rust.

Jim

I would gently, but gently, go after it with a brass-bristle brush. Small ones, similar to toothbrushes, may be had at Harbor Freight. If a few gentle swipes reveal that the threads are mostly rust with little metal left, go no further but leave well enough alone.

Im a big fan of phosphoric acid too. It's a food grade acid (the stuff that was in cola & cleaned your pennies), and it will remove the rust without removing any metal.

Update: It cleaned up ok and operates as it should. Thank goodness.....

EdisonPhonographGuy wrote:Update: It cleaned up ok and operates as it should. Thank goodness.....

Which method did you end up using?