highly corrosive green wood? Red Oak

[Melvin Feng]

I chainsaw milled some red oak from a friend who had a tree taken down about 2 months ago. I made a couple large blocks to use as turning blanks, and I started turning one last night.

I noticed after turning last night, for probably around 20-30 minutes, that the chips that had landed on the lathe ways had already significantly discolored the metal. I keep everything coated in CRC 3-36 now, so this was surprising. I used CRC 3-36 with a green scotch pad to remove as much as I could, and left a film overnight. There was still some residual staining, but it wasn't too bad.

I also noticed that as I was turning, a black slurry was forming at the tips of my bowl gouges, and when I wiped it away, it stained my fingers.

I left it mounted in my chuck, and then completed the rough turning this afternoon. The chips once again stained the lathe ways, and some that fell on my bandsaw table also discolored it quickly, and I was using compressed air to clear them off regularly, so maybe on 5-10 minutes of them sitting on the table top, and there are still stains left.

I also noticed that some of the chips had black spots once they dried, which I didn't see while the chips were still wet right after being removed by the gouge.

On the chuck that had been touching the blank overnight, when I went to remove it, there was a black stain left on the tenon on the blank, and where the jaws had contacted the wood had turned black and had a layer of rust. These were brand new jaws, and this was the first time I had used them, so they still had the factory oil from Nova. I scrubbed off the rust and the black stain, and I believe they were already pitted some too. I also left these with a film of CRC 3-36 to help stop any further reaction.

This is only the second time I've turned green wood, the first was with some poplar, and it turned green very easily, and did not cause this type of corrosion at all. This red oak also seemed more abrasive, as I needed to sharpen my tooling quite often. I tried using both my 5/8" D-way as well as Crown Ellsworth, and they both dulled fairly quickly when turning the red oak, actually faster than when I have turned dried red oak.

Now, how normal is this?

Is this something I should be concerned about? It doesn't occur when I turn dried red oak, even ones that I've chainsaw milled from many years ago.

The tree had heart rot and some fungus growing on the outer sapwood layers and cambium, but I cut all that out with the chainsaw - could that still be a contributing factor?

General thoughts and suggestions?

[Don Stephan]

Green red oak and black walnut have done the same for me. One tip, keep a acid/glue brush on the headstock and always use it to wipe away the buildup in the flutes, Also, wash your hands well before reversing the blank, or your hands will leave dark smudges that are not easy to sand out,

[Rob Luter]

Red oak can be very acidic. Combine this with high moisture content and you have corrosive wood.

[Melvin Feng]

Green red oak and black walnut have done the same for me. One tip, keep a acid/glue brush on the headstock and always use it to wipe away the buildup in the flutes, Also, wash your hands well before reversing the blank, or your hands will leave dark smudges that are not easy to sand out,
That is a great tip about the acid brush, I keep a bag of those in my tool box! I'm glad to hear that others have had this issue, and that I don't have some crazy piece of wood that could be harmful to me!

[Melvin Feng]

Red oak can be very acidic. Combine this with high moisture content and you have corrosive wood.
Interesting, I didn't know that about the acidity of red oak. I may not keep turning these green blanks then, I have had to do a lot more cleanup after this one blank than what I typically need to do after turning most things.

[Perry Hilbert Jr]

here is a table of wood species ph values for future reference. https://www.researchgate.net/figure/Acidity-of-different-wood-species_tbl1_281295854

[John K Jordan]

What ever you do, don’t leave a block of wet oak on a cast iron bandsaw table for a few hours! Unless you like decorating the table with a nice rusty block-sized image.

[Melvin Feng]

What ever you do, don’t leave a block of wet oak on a cast iron bandsaw table for a few hours! Unless you like decorating the table with a nice rusty block-sized image.

Given this is my second time turning green wood, it amazed me how quickly the corrosion started, I can't imagine if I had left the wet shavings for a few hours or overnight!

[Reed Gray]

All of the oak trees do this. I keep concentrated lemon juice on hand to remove spots from my bowls. It also cuts what is on your hands, but hope you don't have any small cuts when you use it. If the spots dry on the wood, if you are twice turning, then it isn't a problem because it will turn off. If you once turn, the spots will show up from metal dust on your hands and on your tools from sharpening. I wipe my tools down with the green shavings, and my hands as well after a sharpening. My old 3520A had a very nice black patina to the lathe bed when I sold it. If the chips are not on long enough for the metal to pit out, then it is just color. I would wipe the ways off after turning.

robo hippy

[Rob Luter]

Interesting, I didn't know that about the acidity of red oak. I may not keep turning these green blanks then, I have had to do a lot more cleanup after this one blank than what I typically need to do after turning most things.

It can vary tree to tree. I've cut some down that smell so sour that it burns my nose. Smells like vinegar.

[Richard Coers]

My hands turn purple even handling kiln dried oak if I'm really sweating. I left some wet cherry curls sit on a big scraper one time. The steel was starting to pit the next morning. Hence the reason Robust and Oneway use stainless steel ways.

[Melvin Feng]

All of the oak trees do this. I keep concentrated lemon juice on hand to remove spots from my bowls. It also cuts what is on your hands, but hope you don't have any small cuts when you use it. If the spots dry on the wood, if you are twice turning, then it isn't a problem because it will turn off. If you once turn, the spots will show up from metal dust on your hands and on your tools from sharpening. I wipe my tools down with the green shavings, and my hands as well after a sharpening. My old 3520A had a very nice black patina to the lathe bed when I sold it. If the chips are not on long enough for the metal to pit out, then it is just color. I would wipe the ways off after turning.

robo hippy

That's good to know about turning oaks green, thanks! I do intend on twice turning, so I'm not too worried about the staining on the oak - I checked it today and there is definitely some blackstaining now, but I kept everything thick. I got into the habit of using compressed air on the ways every time I needed to clear out the hollowing, this kept it so that there was still some slight staining on the ways, but it wasn't too bad. I've also gotten into the habit of doing a wipe down with a cloth and some CRC 3-36 as part of my cleaning routine. I had honestly been hoping that the CRC would've held up better, but I suppose this is really rough on any surface treatment, and it is better than if the metal had been bare.

[Prashun Patel]

The staining isn't corrosion; it's oxidation . But it doesn't look nice, I agree.

The bigger functional problem is the actual rust caused by wet wood. That's not unique to red oak. You're lucky if any green wood turning doesnt rust a new lathe. Eventually, the ways do build up enough of a patina that they become mildly rust resistant (YMMV). But don't rely on that. Best practice is to blow off chips from all metal parts, wipe the ways, and then collect the wet chips out of the corners where it might touch drywall (DAMHIKT)

[Melvin Feng]

The staining isn't corrosion; it's oxidation . But it doesn't look nice, I agree.

The bigger functional problem is the actual rust caused by wet wood. That's not unique to red oak. You're lucky if any green wood turning doesnt rust a new lathe. Eventually, the ways do build up enough of a patina that they become mildly rust resistant (YMMV). But don't rely on that. Best practice is to blow off chips from all metal parts, wipe the ways, and then collect the wet chips out of the corners where it might touch drywall (DAMHIKT)

Isn't corrosion the same as oxidation in this case? I am not a metallurgist, but I'd be interested to know more about the difference here!

I did get in the habit of using compressed air to clear away the chips and I cleaned up everything at the end of the session, as well as emptied the dust collector. With the green turning, I noticed that the long strands of chips were getting caught on the impeller, so I ended up using a dust pan for most everything that fell on the floor and around - it is always entertaining to me how far the chips can fly with green turnings!

[Prashun Patel]

neither am I a metalurgist, and perhaps I am using the terms incorrectly.

I only meant to imply that the staining is a cosmetic nuisance but doesn't corrode it to the point of compromising the functionality. Water on the other hand...

[Melvin Feng]

neither am I a metalurgist, and perhaps I am using the terms incorrectly.

I only meant to imply that the staining is a cosmetic nuisance but doesn't corrode it to the point of compromising the functionality.

Ah! I see. Yes, there is only a stain left on the ways now, no rust that I can see. It was a bit worrisome. The chuck jaws though definitely look to have some pitting, so I'll need to be much more aware of these things when I am turning green wood in the future!

[Dave Mount]

The black color is from the interaction of iron with tannin's in the oak. Although it looks bad, the amount of iron lost to it is infinitesimal. Some people actually use this reaction to "weather" (think barnwood) oak and some other woods by dissolving some steel wool in vinegar then painting the solution onto the wood. The acidity is probably important to dissolving and keeping the iron in solution, as iron (Fe^3+) is not very soluble at higher pH.

I spent a period making green-bent chairs out of oak, and the thin back splats were bent into the chairs green. I'd rive the back splats out of green quartersawn (er. . .quarter split) oak then hand plane them to final thickness. I had to use a wood bodied jack plane for this, because iron-bodied planes would turn the whole thing grey (wet wood). Oxalic acid can be used to bleach the grey out if need be.

As far is actual pitting tools/lathe beds, I don't think (from my own observations, not science) oak is substantially worse than other woods with high moisture content -- any of those will get rust going if you leave them on unprotected surfaces. Oak just looks worse because of the grey/black color.

Beyond wiping down the ways of the lathe, one place it's easy to forget is the shaft of the tool rest and the hole in the banjo. Learned the hard way that when turning wood that is actively throwing water, it can seep down in there and cause a mess. Now after turning green wood I always remove the tool rest and wipe it down, then spray compressed air down the hole in the banjo.

Best,

Dave

[Reed Gray]

I am wondering about the lathe tools getting pitted. Never happened to me. I do get some coloration on the sludge that builds up on the tools, but nothing that actually discolors the metals. I turn pretty much only with Thompson and D Way tools.

robo hippy

[Peter Blair]

This is exactly why I don't turn green Oak. Was a bad experience for me and not worth the effort!

[Scott T Smith]

The black color is from the interaction of iron with tannin's in the oak. Although it looks bad, the amount of iron lost to it is infinitesimal. Some people actually use this reaction to "weather" (think barnwood) oak and some other woods by dissolving some steel wool in vinegar then painting the solution onto the wood. The acidity is probably important to dissolving and keeping the iron in solution, as iron (Fe^3+) is not very soluble at higher pH.

I spent a period making green-bent chairs out of oak, and the thin back splats were bent into the chairs green. I'd rive the back splats out of green quartersawn (er. . .quarter split) oak then hand plane them to final thickness. I had to use a wood bodied jack plane for this, because iron-bodied planes would turn the whole thing grey (wet wood). Oxalic acid can be used to bleach the grey out if need be.

As far is actual pitting tools/lathe beds, I don't think (from my own observations, not science) oak is substantially worse than other woods with high moisture content -- any of those will get rust going if you leave them on unprotected surfaces. Oak just looks worse because of the grey/black color.

Beyond wiping down the ways of the lathe, one place it's easy to forget is the shaft of the tool rest and the hole in the banjo. Learned the hard way that when turning wood that is actively throwing water, it can seep down in there and cause a mess. Now after turning green wood I always remove the tool rest and wipe it down, then spray compressed air down the hole in the banjo.

Best,

Dave

Excellent explanation Dave.

[Brice Rogers]

If I'm turning wet oak, I put a sheet of plastic over the ways and then dump it and air-spray the bed when finished turning. Pre-applying WD40 or Boshield, etc. to the ways before covering them also is a good idea.

Also, I will sometimes put some stretch wrap or saran wrap over the chuck jaws, especially if I'm going to leave the piece chucked up for a few days. The reason for that is that it keeps the chuck jaws from leaving a black stain on the tenon or mortise - - plus also keeps the jaws from turning black.

[Melvin Feng]

Those are some good tips. I did apply some CRC 3-36 before turning, but I still had staining issues. The saran wrap would have definitely helped the jaws though, there is some pitting, and it left the black stain on the tenon as well.