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25th Aug 2019, 09:38 PM #1Member
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Cleaning rust off a cast iron machine table
Hi all,
I am refurbishing a vertical bandsaw. The cast iron table is in good condition but orange with rust. What is the best way to get it near new condition again but without removing too much material?
I thought gentle abrasion with scotchbrite pads vs phosphoric acid but will the phosphoric acid etch into the surface and do some damage?
Ignore the parts in the pic, it's just to show the table.
TIA!
20190808_214806.jpg
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25th Aug 2019, 09:48 PM #2Most Valued Member
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The best thing I have found which removes all rust but very little (if any) metal is soaking the parts in a solution of 1 part molasses and 9 parts water.
Only down side is you need to soak it for about 2 weeks. However when you remove the part and wash it clean it's as clean as you will ever get. You need to remove any grease or oil first otherwise it won't work.
You can buy 5kg tubs of molasses at stock feed places for about $10. The solution can be used many times over.
I had a large part I wanted to clean (jointer planer table) so I made a box out of bricks in the backyard and lined it with a tarp. Pre-mixed the molasses in a bucket before pouring into the tarp and topping up with water.
Cheers.
Simon
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25th Aug 2019, 09:50 PM #3Philomath in training
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I'd be tempted to put an orbital sander on there. With gentle pressure and moving it uniformly across the table, I doubt that any variation in the finished surface would be noticeable. Plan B would be some Evaporust on paper towels.
Michael
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25th Aug 2019, 09:56 PM #4Gear expert in training
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My personal preference is a steel scouring ball (the ones you scrub pots with, NOT steel wool) because it leaves a nice patina behind which a) I like the look of and b) seems to resist re-rusting better than if you take it back to bright metal.
I think I've heard that citric acid solution works quite well, but it needs a while to soak which might not be practical if you have to try to find a container large enough for the table to fit in.
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25th Aug 2019, 10:17 PM #5Member
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Thanks everyone for the quick replies.
Simon... I've never tried molasses but have used electrolysis for rust removal. The catch is this is a big bandsaw (90cm throat) and I was hoping to leave the main table in place and work around it, however I'm probably just being lazy.
Michael... The orbital sander makes me nervous but I might be over protective.... It might actually help make it flatter after years of factory use. The Evaporust looks promising, it is rumoured to be EDTA and hence no acids etc. It's available in a gel form too so won't need the paper towels.
Elan.... Yeah I'm always puzzled why those scouring balls don't seem to scratch pots and pans, good idea.
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25th Aug 2019, 10:35 PM #6Member: Blue and white apron brigade
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If you want something a lot faster but just as safe as molasses, try citric acid, vinegar or oxalic acid. Oxalic is the industry standard - its fastest at converting the rust and produces the the most rust resistant surface behind. Citric and vinegar are slower but still quite effective. Phosphoric acid (PA) is also quick.
Any residues left behind by these acids are usually easily rubbed/washed off in these solutions.
Whatever you use DO NOT use any water to remove the residues or residual acid as this just restarts the rusting.
Let the excess acid drip off the part, blow dry the parts with a compressor, and then apply some light machine oil or wax.
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25th Aug 2019, 11:53 PM #7
Hi Guys,
I would second citric acid / Lemon juice ! I've tried it and I'm now a believer.
I'm sure you have seen my pictures of the number stamps that I found rusting in the local scrap yard and the rusty slitting saw blades that I bought last week. They had 36 hours in pure lemon juice. That stuff is great. here in the UK its 29p for 150 ml bottle from Aldi. I reckon that a paper towel soaked in the stuff would work just fine on your saw table.
10-07-2019_005.JPG 10-07-2019_006.jpg
This is the stuff, made in Italy.Best Regards:
Baron J.
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26th Aug 2019, 12:21 AM #8Golden Member
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I'd use a wire cup brush, get one of the less aggressive twist ones and run it against some scrap for a few minutes to flex the wires into shape then have at it on your table. Don't push too hard, go easy on the corners and you'll end up with a nice rust blued finish.
When your done rub on some linseed oil and it'll be as good as gold.
Cheers,
Greg.
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26th Aug 2019, 12:36 AM #9Senior Member
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26th Aug 2019, 01:00 AM #10Most Valued Member
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I use Inox and an orbital sander, on a lathe I had stored for a few months under a carport.
Prevents any further rusting too.
KrynTo grow old is mandatory, growing up is optional.
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26th Aug 2019, 08:02 PM #11Member
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Thanks everyone!
It seems there is more than one way to skin a cat (as long as it is a rusty cat). So we have:
Mechanical abrasion
sander
scouring ball
wire brush
Reducing agent
molasses
electrolysis
Chelation
Evapo-rust
Acid attack on rust
citric
acetic
oxalic
phosphoric
I would prefer to not remove the table and I might try the Evapo-rust on kitchen paper and see how it performs.
Thanks again!
Steve
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26th Aug 2019, 10:10 PM #12Using Tapatalk
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26th Aug 2019, 10:18 PM #13Member: Blue and white apron brigade
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Some corrections
Mechanical abrasion
sander
scouring ball
wire brush
Scotchbrite wheels - I love these, less damage than any of the above
Reducing agent
electrolysis
Chelation
Evapo-rust - I think it has EDTA in it.
molasses
citric
acetic
oxalic
phosphoric - depends on strength
Rust Conversion
Tannic acid
phosphoric - depends on strength
Rust dissolution
Strong acids like HCl and sulphuric
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26th Aug 2019, 10:22 PM #14Member
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thanks for cleaning that up Bob
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26th Aug 2019, 10:24 PM #15Member
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I've cleaned up a few woodworking machine tables and my technique is to use a razor blade scraper first. This will remove the majority of the rust, follow up with a scotch brite pad using wd40 as a lubricant then wipe down. Keep the razor blade at a lowish angle to the table as you would using it on any other surface and it wont scratch, use short pushing strokes, you soon get the feel for it. Where there is a bit of pitting I have used a random orbital sander with 240 or 320 grit. It takes a lot of effort to remove any measurable quantity metal off a flat surface like a cast iron table, that is to remove light pitting.
Be aware that some of the chemical rust converters can stain cast iron so it would pay to try a small area if that concerns you.
Tony
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