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Protect original iron mill bed under aluminum tooling plate? Cathodic protection?

nickparkerprint

Plastic
Joined
Jan 3, 2021
Location
Bay Area, California
Hi all, sorry if this is the wrong category.

I have a Shizuoka ST-N knee mill in beautiful condition that I've converted to modern control. Unfortunately it lives in a woodshop so I have to use water based coolant on it, and if I'm not religious about wiping it down with oil each use the iron bed gets rust spots.

I want to put aluminum tooling plate on my iron bed and leave it there, but I'm worried about corrosion underneath. What should I do?

I have a few ideas I'm considering but I want to get your opinions because, aside from foolishly using water as coolant, my problem seems like a common one. My thoughts:
  • Put a thin plastic layer under the tooling plate and plastic washers under the mount bolts to prevent a corrosive circuit forming, and keep water out from under.
  • Use a thick coat of grease instead of plastic, and just check on it every week at first to see if anything's corroding.
  • Bolt sacrificial zinc blocks to the underside of the tooling plate in the bed T-slots to protect the iron?

The zinc seems like the most robust solution if it would work the way I'm imagining, but like I said this must be a solved problem in the community so I'd love to hear what others have done. Thanks!
-Nick
 

Rudd

Stainless
Joined
Jul 30, 2003
Location
savannah, jaw-ja
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[*]Bolt sacrificial zinc blocks to the underside of the tooling plate in the bed T-slots to protect the iron?
[/LIST]


-Nick

You do realize that aluminum is only a couple tiny steps up the galvanic food chain from zinc?

I'd be more worried about the fact that there is going to be wet iron under there that won't get wiped down. Iron vise on iron table will get rust under it.
The grease idea - that could be real entertaining on the first heavy cut.
 

winger

Stainless
Joined
Dec 28, 2005
Location
portage county, wisconsin
We use this on the press bed under the die set.

Roll Over to Zoom
LPS Corrosion Inhibitor 11 oz. LPS Corrosion Inhibitor 11 oz.
LPS Corrosion Inhibitor 11 oz.Item no.13555|00316

water soluble lube is wiped on the plate but not flooded. Still probably best to renew it every few months.

Dave
 

jwearing

Cast Iron
Joined
Aug 26, 2017
Location
Bay Area, California
What coolant are you using exactly? I'm no expert but my understanding is that they can be made alkalyne enough so that they don't cause rust.

I use water + washing soda in my parts washer, nothing rusts (until I rinse it off).
 

nickparkerprint

Plastic
Joined
Jan 3, 2021
Location
Bay Area, California
Sorry I worded my post poorly - the 'coolant' right now is plain tap water, and all I can switch to in the future is water based stuff for the sake of all the wood in the room. I've been meaning to try a few different brands but I've been reluctant because I know I'll end up with liters left over of my second choices.

I'll definitely try mixing some washing soda in, thanks! That'd be a wonderful solution if it's good enough.

>You do realize that aluminum is only a couple tiny steps up the galvanic food chain from zinc?

My understanding is that aluminum forms a nonporous oxide layer and then largely stops corroding, while zinc doesn't. My thinking was that the zinc would protect the iron from the water, not from the aluminum. Although after some more reading it sounds like the zinc and iron would both need to be touching a given drop of water for it to work that way, so probably not a good option. There's also some frightening stuff about hydrogen embrittlement with zinc anodic protection.

The grease would just be a squeezed out barrier around the edges and in any pits or cracks. The expectation isn't that there'd be a lubricating film across the whole surface, so with enough bolts I don't think it would slide around? The grease solution is what the career machinist who I got the mill from recommended.
 

thermite

Diamond
My understanding is that aluminum forms a nonporous oxide layer and then largely stops corroding, while zinc doesn't. My thinking was that the zinc would protect the iron from the water, not from the aluminum. Although after some more reading it sounds like the zinc and iron would both need to be touching a given drop of water for it to work that way,

I have been "playing with" research on all this for months in re an Aluminum roof the maker wants steel nails double-dipped hot galvanized used with.

Mind we are looking at 40 to 50 years service, and they have been GETTING that since 1976, "for real" not as adverhooring BS.

It isn't that big of a deal.

Shed the tap water.

Adopt a known low-hassle coolant that helps REDUCE the chance of galvanic reaction. You are not the first person to ever need such of a thing.

Turn your attention to not having to WORRY about "all the wood in the room".

As-in shield the mill's splash. And/or shield the wood.

Much less work than re-engineering the electronegativity side of the Periodic Table of the Elements for the whole damned universe to eliminate galvanic potentials, yah? I mean.. GOD tried it.. had to give it up and take the day off!

Done?
 

Mark Rand

Diamond
Joined
Jul 9, 2007
Location
UK Rugby Warwickshire
three thoughts, use one or more:-

Run air if you need chip evacuation and carbide cutters so you don't need coolant.

If you must use plain water, paint the entire table with a zink rich 'cold galvanizing' spray paint before bolting the tooling plate on, it'll protect the T slots, where the water would also gather. skim the tooling plate for flatness before using. Also make the water de-ionized.

Build an enclosure around the mill/metal work area, with separate air supply and extraction

Tell your significant other that you need to buy an additional workshop...
 
Last edited:

DDoug

Diamond
Joined
Oct 18, 2005
Location
NW Pa
Sorry I worded my post poorly - the 'coolant' right now is plain tap water, and all I can switch to in the future is water based stuff for the sake of all the wood in the room. I've been meaning to try a few different brands but I've been reluctant because I know I'll end up with liters left over of my second choices.

Ask a local machine shop to spill you off a gallon of their coolant, toss them $20 or so.
 
Joined
Jan 11, 2005
Location
Duluth, MN
I worked in cathodic protection for 15 yrs. You're right--the anode (zinc or magnesium) must be in the same electrolyte(coolant) as the cathode(machine table). Coatings(paint, epoxy, coal tar enamel) are almost always the first line of protection. I'd try the LPS or the grease.
 

nickparkerprint

Plastic
Joined
Jan 3, 2021
Location
Bay Area, California
Thanks for the advice everybody!

I'll talk to the mill's original owner about cold galvanize spraying it before throwing grease and the aluminum on there. That looks like a great long term solution, and I'll suck it up and buy some real coolant as well. I'm glad I came and asked y'all before doing anything...
 

thermite

Diamond
Thanks for the advice everybody!

I'll talk to the mill's original owner about cold galvanize spraying it before throwing grease and the aluminum on there. That looks like a great long term solution, and I'll suck it up and buy some real coolant as well. I'm glad I came and asked y'all before doing anything...

"Great(er) long term solution" is prolly to use Iron, steel, linen bakelite, laminated "fossilized" bamboo, FR4/G10, or Carbon fibre for fixture plates instead of shiney-wood!

:D
 

Tony Quiring

Titanium
Joined
Nov 5, 2008
Location
Madera county california usa
Was going to suggest clear lacquer on the table to seal it but saw mention f cold galvanize, much better.

10 ft windmill in back yard with bullet holes in sales when we got it more than 15 years ago.

Sprayed cold galvanize on it and still there.

We use it on cell and comm towers and it stays put.

It can be removed with effort.

So clean with solvent.

Test on a scrap to see that it sticks after solvent clean, if not clean solvent off with acetone and the it a good coat.

Get it in brush on can and brush in the table area t slots.

With acetone on rag wipe bottom of vice and area on table where it goes then spray both light coat and clamp it down.

For extra protection brush on where try meet



Sent from my SAMSUNG-SM-G930A using Tapatalk
 

dgfoster

Diamond
Joined
Jun 14, 2008
Location
Bellingham, WA
Having worked with aluminum/steel combinations in a salt water environment I think you are spot-on to be concerned about galvanic corrosion. I would spray a coat of zinc paint on the table and the plate.. I would not hesitate to use oil or grease in between the table and the plate. Grease causes a mechanical linking of table to plate---I cited a paper that showed this a few years ago.

Take it off in a few days or a week or so and then at progressively longer intervals. A single coat of paint on both the table and the plate might also be a good solution. Proper etching prep with phosphoric acid metal prep will much improve paint adhesion and a final wipe down with isopropyl alcohol (NOT a petro distillate of some sort) will also help the paint to really stick well.

Denis
 








 
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