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Thread: Rust Removal from Precision Cast Iron Surfaces in 2020: techniques and when to stop

  1. #16
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    Quote Originally Posted by Mark e Kessler View Post
    Barkeepers friend and scotchbrite
    Now why didn't I think of that!

    I use BKF routinely for my stainless cookware. Never thought to use it for my machinery......

  2. #17
    just be sure to not let it sit to long, it works well because of the Oxalic acid just don’t leave it on to long or it will discolor the cast iron (which you can remove by reapplying). I use a little bit of water with it and red scotchbrite then clean up all the residue with water and rags and have found orange cleaner/degreaser cleans it up well too.

    Quote Originally Posted by Michael Drew View Post
    Now why didn't I think of that!

    I use BKF routinely for my stainless cookware. Never thought to use it for my machinery......

  3. #18
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    Yep, just found out how quickly it oxidizes cast iron to a weird green/yellow. I’d say less than 5 mins. I wasn’t sure if I was a dummy for using water as my lubricant. I don’t love the smell of solvents in an enclosed garage. Anyway, it did a bang up job with the scotchbrite pad, ROS, and the powder. I just wiped it clean with mineral spirits and a rag, but I think it will need polished again.

  4. #19
    Quote Originally Posted by Patrick Kane View Post
    Yep, just found out how quickly it oxidizes cast iron to a weird green/yellow. I’d say less than 5 mins. I wasn’t sure if I was a dummy for using water as my lubricant. I don’t love the smell of solvents in an enclosed garage. Anyway, it did a bang up job with the scotchbrite pad, ROS, and the powder. I just wiped it clean with mineral spirits and a rag, but I think it will need polished again.
    I always use WD-40 as the cutting fluid when buffing the tables. Wipe off with mineral spirits, then wax immediately.

    Erik
    Ex-SCM and Felder rep

  5. #20
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  6. #21
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    I also use wire brushes, like Lowell's Google link, wipe with mineral spirits, and wax. The wires aren't as hard as the tables, so only the rust is removed.

  7. #22
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    Thanks all for the great replies! Great info. Hope to have more time shortly to answer some replies individually, but here are a few pics of the table condition. Also notice the top of the ways are rusted a bit...bottoms are the same. For the table though, in a nutshell, looks like ?minor? pitting and a ~ 5 to 6 thou wallow in the center. Could easily get a 5 thou feeler gauge under the straightedge, 6 thou had some resistance, 7 nope. Powermatic's manuals for other/similar planers...say the 225 for instance...indicates that one should should set the knives to within 1 thou from end to end on the planer table. "Maximum deviation allowed for good planing is .001 (.025mm)." See 225 manual screenshot below. That'd be tough to do with a table off by 6 thou...yes it's a wallow and the ends of the table are probably at a similar height but this type of stuff irritates me...even if it might not visually impact a good portion of wood/projects that I'd build. The manual says it, and I want it. I'll clean it up as best I can with the advice you all have given, and then decide whether I want to have it reground or planed once I get it all apart.

    Cheers,

    Devin

    IMG-8771--Keep.jpg

    IMG-8777--Keep.jpg

    IMG-8775--Keep.jpg

    Capture.jpg

  8. #23
    Devin. I've seen a lot worse. If I were you, I would scotchbrite that table to give it some "grain", wax thoroughly with johnson's paste wax, then run some boards through it. See what it does before you make any decisions. Pulling the table and having it machined should be a last resort.

    Erik
    Ex-SCM and Felder rep

  9. #24
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    .006" would bug me, especially if i went through the hassle of repainting the machine, replacing other parts, and general cleanup. However, Erik is right, that level of dip really wont make a difference. That is a little less than 1/128", which is pretty slight if it transmits to the surface and thickness of a board. With that said, if you are already pulling the table, then i would be very hard pressed to not have the top reground. As an example, i havent dug into my Martin T17, but i know the bevel sprocket is missing a tooth. It doesnt affect the chain mechanism and beveling the blade, but its hard for me to leave that broken part in place knowing im going to spend 20-30 hours on this thing and another couple hundred bucks.

  10. #25
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    You really need to redefine precision. You are just talking the ground surfaces that the wood moves over. i thought you meant the sliding surfaces. I do not think I have ever heard of a wood machine having scraped in surfaces like many metal working machines will have. Any thing around 1/1000 is plenty good for wood working.
    Bil lD.

  11. #26
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    Quote Originally Posted by Eric Arnsdorff View Post
    My favorite is phosphoric acid (naval jelly as the product in a liquid gel form) with a brillo pad scrub. Following that cleaning with a brillo and some WD-40 has made pretty quick work of fairly rusted surfaces.
    I have no tools capable of detecting 2-3 thousandths runout over the length of my jointer table or table saw (or even my band saw or drill press table for that matter).
    I've cleaned up a couple of cast iron tables that were in rusty condition but not extreme long term rust. I do have height gages that claim accuracy to half a thousandth (I haven't verified my best one on a calibrated block in quite a while though). I could see no localized variation of even a thousandth of an inch after cleaning them. I don't know about the full table runout. All of my cast iron tables are at least as good and likely better than any of my straight edges that are long enough to span it.
    My take on it is rust removal of "typical" rust doesn't impact woodworking surfaces enough to matter. Extreme rust with large pitted areas could but I think it would have to be bad enough that it would already be obvious to you.
    Eric, thanks for the reply. Only recently heard about naval jelly. Glad to hear that works for you. And...

    "All of my cast iron tables are at least as good and likely better than any of my straight edges that are long enough to span it." <--that's also a good point.

    I do have a 48" Starrett straight edge (model 380-48) that claims an accuracy of +/-0.0002 per foot, or +/- 0.0008 over the whole thing with 1.6 thou worst case...but I have no way to measure that with a granite plate or anything. And the square I used to measure the table in a later response is .001 per inch advertised. Anyway, the more responses I get similar to yours, the less and less I'm caring about single-digit thousandths...I just thought why not aim for it if I can since they recommend setting your knives within 1 thou across the table anyway.

  12. #27
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    Quote Originally Posted by Timothy Orr View Post
    Here’s another way to think about it. The rusted surface certainly isn’t as precision as it was pre-rust, and it may not even be functional if moving parts are involved. So you sort of have no choice but to remove the rust.

    For the tolerances in woodworking, any of the typical methods are going to give you a surface that is as precise and as function at the original. Naval jelly, scotch brite, evapo rust, electrolysis etc may technically remove surface material but not in measurable amounts that would affect a wood working tool. If you are talking about the ways on a engine lathe where a couple of ten-thousandths would impact accuracy of the tool that is a different story.

    I’m talking about surface rust, now if you have actual pitting enough then you still to remove the rust then be thinking about how to repair the surface with fillers, re-machining etc.

    My 2 cents.

    Torr
    Thanks for the reply...and yea point taken about the rust..it'll have to come off no matter what I suppose and then I can assess where the table is at. As of right now when I measure it with the tools I have, it's showing a ~ 6 thou wallow in the center of the table that'll probably be there-to-stay unless I have it resurfaced. I may decide to live with the wallow though, tbd.

  13. #28
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    Quote Originally Posted by Bill Dufour View Post
    Electrolytic or EDTA are the easiest and reasonably fast. Do not use stainless with electrolytic just plain iron or steel. Stainless can make some bad stuff with chrome compounds in the waste.
    Bil lD
    Thanks for the reply...I will google it. Don't think anyone else brought this method up. How or on what have you used it before?

  14. #29
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    Quote Originally Posted by Jim Matthews View Post
    If you find the finished product (dimensioned boards) out if acceptable tolerances, a sled could be constructed to satisfy your requirements.

    My SWAG is that there will be more error induced by cutter runout, uneven roller pressure or blade alignment.

    Polish it until it shines!
    Another good point, I guess I'm just trying to control what I can. If I go to the trouble of taking it all apart, might as well try and make the bed all it can be. At any rate, as someone else already mentioned, I suppose the rust has to go no matter what so maybe I'll get aggressive with it

  15. #30
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    Quote Originally Posted by Richard Coers View Post
    I take off any heavier rust with a single edge razor blade scraper. Then buffing with maroon Scotchbrite. I never use sandpaper since I don't want to remove metal.
    Thank you. Yea the razor blade technique seems to be the most universally agreed-upon. Your Scotchbrite buffing is with an RO sander or buffer though right?

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