# Wood: Enemy of Metal?



## kevin (Mar 9, 2019)

Recently I happened to run across an interesting article on Corrosion of Metals by Wood (the article s from the National Physical Laboratory in England). 

As a person who enjoys woodworking as well as metal working, I often make tool holders (as in for storing on a shelf or in a drawer) out of wood. In addition, machine tools are frequently packed in wood storage boxes (still happens, though plastic is becoming more common). But the article above made me wonder if this is a good idea or not. 

The article is primarily directed at the use of wood for shipping and warehousing containers, but I think it has some application to the shop as well.

A few excerpts from the article:

Wood is a corrosive substance by nature, and can be made more corrosive by treatment given to it. Unlike most other corrosive substances, one of the corrosive chemicals in it, acetic acid, is volatile, and in an ill-ventilated space, wood can cause corrosion of metal nearby but not actually in contact.
Kiln drying accelerates the production of free acetic acid in wood, but most of the acid does not have time to escape. Kiln dried wood is more acid and more immediately corrosive than air dried wood, though it contains less combined acid that can be set free in later years.
Different woods have different acid content, some examples from a longer list:
Oak - high
Birch - fairly high
Spruce/elm - moderate

Unfortunately, no determinations have been made of the actual concentrations of acetic acid vapour inside wooden boxes, but it is clear that corrosion is caused by only very small quantities.
.  .  . even with well dried wood, a corroding humidity can be reached easily in a temperate climate, and all the time in a tropical one. If the wood becomes wetted, corrosive conditions can develop at any temperature, and be very severe at higher temperatures.
Avoid fresh wood. Avoid kiln dried wood. Avoid damp wood. Keep wood in a dry atmosphere for as long as possible before use.
The emission of acetic acid vapour from wood is retarded, but not stopped, by paint or lacquer applied to the wood. It must not be forgotten, however, that . . . paints . . . themselves emit corrosion vapours (formic and acetic acids). Choice of coating . . . preferably acrylics and two-pack epoxides and polyurethanes.
In my own experience, whenever I have something like a collet holder out of wood, I have always given it a polyurethane coating. I would expect that if there was a significant problem, I would see it where the tool directly contacts the wood, but I have not observed any unusual tarnishing or corrosion in this regard. I suspect the most important thing in this regard, as in general, is to keep the humidity low, but it is probably a good idea to avoid direct wood contact if possible, and if using wooden drawers make sure there is plenty of ventilation.


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## darkzero (Mar 9, 2019)

When I first got this chip brush, the day I got it I left it on the mill table overnight. It left a stain on the table in the shape of the handle. Came out with scotchbrite but lesson learned.

That's the only time I've ever experienced it but most everything else I have that comes in contact the wood is stained/cleared.


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## mikey (Mar 9, 2019)

Excellent post, Kevin. Thank you!


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## benmychree (Mar 9, 2019)

I have never seen any tendency to rust in my Gerstner tool box, nor any precision tools in wooden boxes,  Perhaps an issue in warehousing situations, but a tempest in a teapot on my world.


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## francist (Mar 9, 2019)

Early in my conservation training we were given an example of how not to store ancient coins. A museum had a collection of Roman coins (I want to say of lead, or similar alloy) and had made carefully fitted trays to hold them for exhibit. The trays were made of oak, and fitted into sealed drawers (sealed as in airtight). Within a short time, curators were horrified to find the coins covered with white corrosion product resulting from the acid content in the oak. 

Granted, museum conservation people tend to fuss about very small amounts with highly sensitive materials, and real-life tolerances can be somewhat different. However, if you've ever had occasion to turn woods like black walnut on the lathe, especially when it's freshly cut, you'll soon find your iron tool rests, bed ways, and even your fingers nicely purple or black from the reaction. 

I store a lot of my tools in wooden drawers and have for years without any problems. But, I'm still conscious of the potential and especially so if there's chance for moisture or higher than normal humidity. 

-frank


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## hman (Mar 9, 2019)

Kevin -
Great post!

Couple thoughts here ...

I definitely avoid oak.  Usually use plain ol' fir (as in a chunk of 2x4).  An example would be a rack for R8 collets.  After I've drilled the requisite holes, I saturate the wood with mineral oil or way oil.  Haven't kept any wood tool holders in sealed containers, so haven't had any issues yet.  Here in Arizona, moisture isn't much of a problem.  But even when I lived in Oregon, I don't recall any issues.

Having been a chemist in a previous life, and from the information in your post, I'm tempted to try dipping any future tool holders in ammonia, then drying thoroughly before oiling.

As for Gerstner tool boxes, the drawer bottoms are made of metal.  I've assumed it was for strength.  But it may well be that this reduces corrosion. I'm sure that if a Gerstner EVER caused corrosion of a precision measuring instrument, there'd have been a holy stink raised!


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## hman (Mar 9, 2019)

OOPS!  Maybe my idea of ammonia treatment is useless.  The article states that "Lime washing, which might be expected to absorb acetic acid vapours, has been found ineffective."  Ah, well ...

I did notice that elm has a pH close to neutral.  Might be worth considering, on this basis alone. Mahogany doesn' look too bad, either.  Ina I seem to recall a number of instrument boxes made of mahogany.

Lots and lots of info in that article!!!!


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## cbellanca (Mar 9, 2019)

Yes, wood has an acidic component. I coat on a regular basis all my bare metal  wood working surfaces including my table saw, planner, joiner, band saw, drill press. lathe and mill bed with *Johnson Paste Wax*. Even with the wax coating  I have had the most problem with treated lumber. Boards or saw dust from treated lumber Left over night will produce a hard to remove stain. The wax also provides protection with the normal room humidity.


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## Robo_Pi (Mar 9, 2019)

CAUTION ----- This post is kind of off topic ----- CAUTION

This is a story of wood versus metal in a slightly different way;

There used to be an 8 inch in diameter limb at the top of this Oak tree.



One very calm sunny day it decided to fall off the tree.   I was sitting out in the yard and heard it crack.  There was absolutely no wind.

I looked up and saw the limb break off the tree and begin it's 60 foot journey to the forest floor.

There was nothing that could be done to stop this limb from falling to the ground.

The problem was that my truck was parked directly under this limb!

All I could do was watch the event unfold before my very eyes.

I saw the rear window of the truck cap exploded into a frothy white sea of tiny glass particles.

I didn't think to take a picture while the branch was still on the truck.  It was a Y-branch and the smaller part of the Y was about 6 inches in diameter.

Miraculously the side windows survived.   And the windshield only cracked in the upper right corner on the passenger side.   So the major damage was to the obliterated rear window.




I actually laughed.   What else could I do?  Getting upset about it wouldn't solve a darn thing.  At that instant I just resigned myself to having one more unwanted project on my to-do list. 

So with great patience and calm, I got the chainsaw out and cut the branch up to remove it from the truck.  It was way too heavy to even budge in once piece.   It wasn't a dead branch.  It was perfectly live.  I have no idea what made it fall off the tree.  It must have been struck by lightening at one point is all I can figure.

In any case, I put the branch on the sawmill and cut it into lumber.   Then I used some floor jacks inside the cab to jack the roof back up.  Did a little hammer and dolly work.   And then set about building a new rear window frame using the oak from the very branch that smashed in the roof. 

Here's the final repair job.    Now I call this truck my "woodie".


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## silence dogood (Mar 9, 2019)

I read the article about the corrosion of metal by wood.  However, there is a lot more to this.  Salt based chemicals are used as a preservative for wood.  That's why you use special coated fasteners and metal when you buy treated lumber.  And yes there is acetic acid in oak.  But there is also a lot of tannic  acid  in oak, which is used as a preservative for iron.  The metal was also put in a sealed box for testing purposes, hmm.  The wooden tool boxes use drawers so the wood can breath. Last, my house is made out of either fir or pine 2by's and sheathed with cedar ship lap fastened together with steel nails.  My house should be a pile of rotting lumber with brown stains.  Funny, it's still in one piece after 70+ years.   I make wood handles and wood boxes for my metal tools. Never had a problem.  Come to think about it.  I have tools and knives with wood handles that are over 50 years old.  The metal and wood are just fine. Sorry about overdoing my 3 cents worth.


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## 682bear (Mar 9, 2019)

They have been using wood stocks on firearms since firearms were invented...

With the exception of a certain manufacturer using salt to cure the wood... I don't know of any common problems unless other factors are introduced (such as storing in damp conditions).

-Bear


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## Robo_Pi (Mar 9, 2019)

kevin said:


> The article is primarily directed at the use of wood for shipping and warehousing containers, but I think it has some application to the shop as well.



This little tid bit of information is most likely paramount. 

It could be the green uncured wood is being used to make shipping containers etc.  I would imagine that green uncured wood may very well contain juices that aren't going to be metal friendly.    But after wood has been properly dried and cured these concerns most likely no longer apply.


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## pstemari (Mar 9, 2019)

The argument above was that drying the wood producers acetic acid (ie vinegar), which doesn't disapate immediately.

Dunno. Never had any issues with my Gerstners, but I also keep VCI emitters (Zerust or Bullfrog) in each drawer of both the Gerstners and the Kennedy chests.

I think the steel bottomed drawers are just to increase useful volume. The steel takes effectively no vertical space, while a wood bottom would require at least a 1/4" for the thickness of the bottom and enough meat on the sides to hold it. With all the 1/2” deep drawers, that would be a lot of wasted volume.

Sent from my Pixel XL using Tapatalk


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## cathead (Mar 10, 2019)

Strong acids in the shop even in closed containers cause a lot of rust on machine tools too.  Due to pressure and temperature
changes, gasses slowly escape and rust up the area around the container.  Car batteries(sulfuric acid) are guilty of this also.    
A gallon container of muriatic acid(20% hydrochloric acid) is responsible for causing a lot of rust if left anywhere near iron.  It's best
to keep acids out of the shop if at all possible. Green oak wood or oak sawdust on cast iron or steel causes rust quickly because it has
both the acid and moisture present to form oxidation quickly right where you don't want it.


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## MarkM (Mar 10, 2019)

I tend to differ.  Living on the East Coast by the ocean I try to use wood as much as I can in my shop.  I have found the wood draws the moisture out and have had no issues with rust.  Mostly pine with some oak but all dry before used.


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## stupoty (Mar 10, 2019)

I have gauge blocks that are in tight fitting wooden boxes, they seem to be ok , but i do tend to use food safe mineral oil on the standards to protect them.

I have found wood dust and chips to be bad for a little corrosion.

My biggest corrosion foux pas, was using some anti slip matting, it has a pattern somewhat like an air tex fabric.  I put it at the bottom of my roll cab draws and everything I layed on it picked up the patern of the "rubber" mating in a light rust.  I'm guessing it has some sort of acid that is in it.

Stuart


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## hman (Mar 10, 2019)

I've noticed that a lot of Chinese rubber has a pretty strong smell- MUCH more so than American rubber used to.  

Wild-a$$ theory - incomplete vulcanization (which uses sulfur).  This would leave uncombined (smelly) sulfur compounds in the rubber.  These plus moisture might well produce sulfuric acid.


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## ThinWoodsman (Mar 10, 2019)

darkzero said:


> When I first got this chip brush, the day I got it I left it on the mill table overnight. It left a stain on the table in the shape of the handle. Came out with scotchbrite but lesson learned.
> 
> That's the only time I've ever experienced it but most everything else I have that comes in contact the wood is stained/cleared.



The Bridgeport I bought came with two hardboard (/masonite) table covers that were shaped to fit around the vise, so naturally I put them on the table right away. Probably just fine in a climate-controlled shop, but after sitting for a couple of months during a very wet summer while I completed the shop and got the wiring sorted, there was rust all over the table surface. Easy to clean up, as with yours, but I never but the covers back on. Might make some new ones with corrugated plastic on the base, cut to a new shape (I keep the vise on one side, an angle table on the other).

That said, I keep a chuck board on the lathe ways (by the tailstock when not in use) and it hasn't caused any problems. So it was likely just the ludicrous humidity last year.

Man, I wish my wish my Nupla fit in that part of the table. Pretty handy place for it.


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## diamond (Mar 10, 2019)

I don't know how much wood may have contributed to this but perhaps a similar experience that taught me a lesson.  I built an enclosed shop room inside my 40x50 metal building last fall and it houses my shiny new PM lathe and a bit less shiny and much less new Bridgeport mill.   I built it out of wood, all stuff you get from the Depot.  It's a lot of wood, including the sheathing on the walls (chipboard).  Where it contacts the concrete floor it's treated, otherwise all pine/fir stuff.   We've been having a particularly wet late winter/spring here in Northern California.   The humidity has been very high.  The shop isn't climate controlled (except when I'm using it).  

I recently went on a trip to Europe for a coupe weeks during this wet weather and that's when I learned a lesson.   

I did not coat the shiny bits on my machines.  That was a mistake.   I came home to find a nice orange/brown color on much of those highly polished surfaces.   My chuck, carriage and even on the ways had a film of rust.  The chuck was particularly bad.  I was horrified!   I should have snapped some pictures but all I could think about was cleaning that off.   Some WD40 and a bit of elbow grease and it is all ok.  Thankfully on the ways it was just a slight surface discoloration.  Much longer and I bet there would have been some pitting starting.   I'm sure the humidity is/was the major culprit.

I now know I need to coat it if I'm going to be away any length of time.  I don't use my machine daily so I do it pretty often.   I really like LPS-2.   I spray all the shiny bits and it leaves a pretty heavy coat that doesn't seem to disappear easily.  Just a few quick sprays is all it takes.   Easy to wipe off when I'm ready to resume using the machine.  I spray my mill table, Kurt and other surfaces with it too.   There's probably other (and maybe cheaper) options but I like this stuff.


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## Reddinr (Mar 10, 2019)

I once left a small piece of freshly planed oak on my planer table.  Came back after being away for 2 weeks and there was a board shaped area of dark rust on the surface right under the board.  Last time I did that...  You can smell the acetic acid or maybe the tannin when you plane the stuff.  On the other hand, when I was younger I made a bench top out of laminated chunks of pallet hard wood.  There was quite a bit of oak and some mystery hardwood.  I dried and planed the pieces and gorrilla glued them all together to make a >200 Lb. 2.5" thick table top.  It took a while.  Like I said, I was young.  I varnished it with a few coats.  Long story short, no rusting problems with tools left on the table top still today.  So moisture content and coatings seem to make a big difference.


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## ThinWoodsman (Mar 10, 2019)

diamond said:


> I built an enclosed shop room inside my 40x50 metal building last fall and it houses my shiny new PM lathe and a bit less shiny and much less new Bridgeport mill.   I built it out of wood, all stuff you get from the Depot.  It's a lot of wood, including the sheathing on the walls (chipboard).  Where it contacts the concrete floor it's treated, otherwise all pine/fir stuff.  ...



Heh, sounds like we went through the same experience, only mine was built in a wood barn. I picked up a GE dehumidifier at Lowes or Home Depot or something, around a hundred bucks. Plugged it into a timer, so it kicks in for an hour twice a day: at 3pm and 3am. Those times seem to be when the temperature in the air changes the most drastically. The hit to the power bill wasn't that bad (we're talking a couple dollars a month) and it sure did the trick.

I like LPS as well, but made some of (Bob's) Ed's Red and have been using that in a Sure Shot mister. Leaves things a bit less sticky.


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## bill70j (Mar 10, 2019)

A potential problem with using wood storage boxes is the type of adhesive you use on the joints.  Regardless of the wood you use, If you use a yellow glue (Titebond, for example), it's important to apply a good sealer, like polyurethane, to cover the joints.

Yellow glue is a polyvinyl acetate adhesive.  And acetate is an ester of acetic acid, which will stain un-coated metal in an instant.


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## john.k (Mar 11, 2019)

oak is notorious for causing rust of steel/iron,as well as splitting ........this is why oak pegs were used to secure oak frames ,not bolts or nails..........one time a GTD tap and die set came in a wood box,with a little compartment for every piece.......oregon pine.or red spruce ?......100 years on the steel is still unrusted ,and the box has held together unlike plastic,which disintegrates into corrosive crumble.


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## yendor (Mar 11, 2019)

Lots of stories here about Wood & Rust from both sides.

As concept I haven't gotten to it yet but I plan is to make a couple of storage boxes for a few of my tools out of TREX Trim material.
It is essentially recycled plastics but machines a lot like wood. I am hoping to avoid the wood = rust problem.

The trim peices come in nice 3/4" thickness and can be glued together.


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## stupoty (Apr 27, 2019)

Randomly I had to use my surface plate which I havn't used for about 6 monthes maybe a little longer(yeah I should do more high precision stuff  ), the wood cover is 1/2 inch ply wood I have oild with mineral oil (baby oil) the edge pieces are glued and nailed (PVA glue).  Their wasnn't any rust issues with it (phew).

My workshop is in a below ground room which is open to the elements (their is a door but it doesn't air seal, like a lose barn door situation).




Stu


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## MarkM (Apr 27, 2019)

Crafty.  Never thought but makes total sense and mineral oil can be had so cheap when you buy it in non scented baby oil.  Very impressive knowing your weather.  Spent a year in Basingstoke.  
Did you seal the bottom perimeter at all or just rest on as is?


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## stupoty (Apr 27, 2019)

MarkM said:


> Crafty.  Never thought but makes total sense and mineral oil can be had so cheap when you buy it in non scented baby oil.  Very impressive knowing your weather.  Spent a year in Basingstoke.
> Did you seal the bottom perimeter at all or just rest on as is?



I oiled the ply in side and out , was left to soak in a bit and gave it a bit of a rub with a cloth.

The wood top just rests on the top of the surface plate. I use the height gauge on the ply for low precision marking sometimes.

Stu


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## ThinWoodsman (Apr 27, 2019)

I made a wood cover for my granite surface plate. Put a felt lining on both top and bottom: bottom to act as a sort of duster for the surface plate, top to give me a safe place to park delicate instruments, newly-polished parts, etc.

I forget where I saw the idea about making a wooden felt-lined tray with a key for holding in the vise. Gave me the idea for the cover, though I still haven't got around to making just a tray.


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## benmychree (Apr 27, 2019)

I just lay a well oiled rag on the surface plate then put the plywood cover over that; the plywood having been varnished.


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## KBeitz (May 5, 2019)

I'm both into wood and metal working. I save my lathe and mill metal chips for staining my wood slab benches.
I sprinkle on the chips and water it down for the night. The next day I brush the chips off. Great looking stain..


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## rwm (May 5, 2019)

I have recently been making tool storage boxes out of teak, which is a reasonably oily wood. Do you think this will be a problem? Am I wasting my time with this? Should I oil the teak with mineral oil? Or even and anti-rust product like Boeshield?
Robert


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## Hellkell (May 7, 2019)

The report, which has been moved but can be found with a search on the site, says teak is on the higher end of the corrosion scale. 

I just made about 15 wood boxes for tools myself. I did coat them with polyurethane. 

I read an article about the rust inhibiting properties of lanolin. That is a grease made from lambs wool. I thin it with paint thinner or diesel and brush the stuff on my metal tools. I think it’s about the best product I’ve come across. I bought a tub of it on eBay.


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## rwm (May 7, 2019)

I think I am going to soak my teak holders in Boeshield and see how that goes. I will report back if I see any corrosion. 
Robert


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## stupoty (May 8, 2019)

Hellkell said:


> The report, which has been moved but can be found with a search on the site, says teak is on the higher end of the corrosion scale.
> 
> I just made about 15 wood boxes for tools myself. I did coat them with polyurethane.
> 
> I read an article about the rust inhibiting properties of lanolin. That is a grease made from lambs wool. I thin it with paint thinner or diesel and brush the stuff on my metal tools. I think it’s about the best product I’ve come across. I bought a tub of it on eBay.




Does not the combination of lanolin and diesel smell a little ?

Stu


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## ThinWoodsman (May 8, 2019)

Indeed it does. Odorless mineral spirits work better.


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## Hellkell (May 12, 2019)

Diesel is what I had at the time but I’ve used paint thinner and lacquer thinner with good results.


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## Calandrod (Dec 13, 2022)

KBeitz said:


> I'm both into wood and metal working. I save my lathe and mill metal chips for staining my wood slab benches.
> I sprinkle on the chips and water it down for the night. The next day I brush the chips off. Great looking stain..


I’d love to see a picture of that if you have it.


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## rwm (Dec 13, 2022)

Since this thread has been revived I will report back that there has been no identifiable corrosion on my steel parts stored in teak treated with Boeshield.
It seems the original link to the reference article is now broken. Here is a similar article:





						Corrosion of metals associated with wood - Victoria and Albert Museum
					

Wood and metal are usually regarded as highly compatible materials.  However, interactions between certain metals and woods can take place under adverse conditions, or as a result of using unsuitable materials.




					www.vam.ac.uk
				




Also


			http://resource.npl.co.uk/docs/science_technology/materials/life_management_of_materials/publications/online_guides/pdf/corrosion_of_metals_by_wood.pdf


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## silence dogood (Dec 14, 2022)

I have tuned pianos that have wood soundboards, wood pin blocks, with steel strings, steel pins, and cast-iron frame for a living. Shot steel barrel rifles that had wooden stocks. Own wooden toolboxes that held tools made of steel and brass. In just about in every case if there was a problem, it was high humidity over a period of time. Although recently, I've learned to be careful of certain glues especially the PVAs (white or yellow wood glues) have a gassing off problem. 
Many of you have replace those funky plastic handles on your machines with metal. I prefer to replace mine with wood, because it has a wonderful feel to it. The tool that I had for tuning pianos has a rosewood handle. This was not just because it is pretty (which it is, in fact it is beautiful), but because wood is easy on the hand and less tiring than other materials. When you spend two or three hours tuning a piano, it can be quite a strain. 
My conclusion is that the real problem is high humidity, and I might add is neglect. Keep these things clean and oiled or waxed or whatever it takes.


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