Millscale:

[TurnipTruck]

It’s a *****.


This is forty minutes of grinding so far:


This was an unused 1/2” thick table stored outside under spruce and birch trees for a decade before it was given to me. I’m trying to clean it up cuz it dirties everything I put on it, can’t wipe dust off, and occasionally doesn’t conduct.

Anything better than a cup grinder? Eighty grit in a belt sander doesn’t touch it.

 

[mike93lx]

Maybe build a dam around the edge and pour on muriatic acid? Less effort, but not exactly simple would need to keep it there for a solid day then clean it up

 

[bb29510]

except where you are welding, leave it

 

[jeepinerdeep]

I feel like coarse type 29 ceramic flap discs do better than a hard rock for me. But you may be in it for a half dozen decent discs.

I use stripper discs on tubing scale, but that is much lighter than what you have in front of you.

I have read about a scale disc from walter that is supposed to be good, no experience.

 

[mogandave]

i would throw a blanket over it and soak it with rubbing alcohol for a half hour then hit it with a cup-brush

 

[MadeByMiller]

Jason from Fireball Tools did some testing and found THESE Walter discs to perform the best.

 

[nadogail]

I think you have more Oxide than Mill Scale.

 

[Firebrick43]

I think you have more Oxide than Mill Scale.

I agree, If I plan I get rid of mill scale by letting it rust some, as the rust pops the mill scale loose, and then knock both off with the surface conditioner or a wire wheel and treat with ospho.

 

[mogandave]

I agree, If I plan I get rid of mill scale by letting it rust some, as the rust pops the mill scale loose, and then knock both off with the surface conditioner or a wire wheel and treat with ospho.

It does not look like rust. Ten years outside under a tree I’m guessing it’s sap.

If it’s rust, I agree with a coat of OSPHO.

 

[TurnipTruck]

It’s too even to be rust and too hard to be sap. It’s actually too smooth to match the mill scale I’ve seen on box tube. Maybe they put some sort of epoxy just on the top surface? I’ve inadvertently soaked the top in ATF and gasoline for months during construction with no lifting or even resembling a coating, tho.

 

[PCustoms]

80 grit? Lol

Got to be way more aggressive.

I like the non-woven metal prep discs:



I stole that image from Amazon. Usually I order 3m, or get Avanti brand at the orange store.

 

[Snip's]

If its been outside for 10 years exposed to the elements, I doubt there is any mill scale left on the top.

Pine trees will drop sap, lots of it.... I have two huge pine trees next to my driveway and I have to be carefull parking cars close to them....

You might do a test area where you wipe down a patch with turpentine to remove any accumulated debris, dry it off. Then lay a cotton diaper and saturate it with muriatic acid.... Once clean, follow it up with a slurry of water with baking soda, dry, follow with a light coating of oil. We like to use Weld-Aid anti spatter in the shop.

My welding table in the shop...

 

[Juiced06GTO]

How about one of those eastwood surface strippers, they seem to do some damage at cleaning stuff up.

 

[WillyBoy]

I agree that it's not all mill scale. Try a belt sander if you have one. You may need to replace a few belts before you're finished but you'll cover a lot more area in 40 minutes.

 

[Garcky]

I agree that it's not all mill scale. Try a belt sander if you have one. You may need to replace a few belts before you're finished but you'll cover a lot more area in 40 minutes.

I second the belt sander idea. It'll end up looking better, too.

 

[rpcraft]

Try pouring some muriatic acid on in areas and let it sit for about 20 minutes to an hour and then just wipe away. If you just start from the middle and pour enough so it doesn't run off the edge you can probably just put some shop rags around the edges to help with spillage. Just use rags you will be throwing away. Once you have done the bulk of removal you can use some Metal and Concrete prep from Klean-Strip (get it from home depot) and that will help finish it up and also if you wipe on and let air dry will help protect it in between uses. I just do that and then wipe with acetone before using again.

 

[PCustoms]

Word of caution: acid fumes may rust any adjacent metals

 

[TurnipTruck]

I have tried a 3x21 belt sander; all it did was polish the surface to black. I will try some white vinegar to try to narrow down what is on the surface, before purchasing other chemicals.

 

[rpcraft]

Word of caution: acid fumes may rust any adjacent metals

That is wise advice. I wasn't thinking about that.

 

[NORTON'S SHOP]

Sand blasting won't work?

 

[TurnipTruck]

White vinegar only rusted where the grinder was used.
Sandblasting would require unwiring the welder underneath and lifting the table off the anchors.
I will try some paint stripper next to see if it is an applied coating.

 

[PCustoms]

White vinegar only rusted where the grinder was used.

It's going to need to sit for at least a day.....

Get a closeup pic of the surface.

Any chance it's an AR plate?

I still think an aggressive strip disc is your best bet.

 

[lilredex]

Don't discount the vinegar solution.....

Jump ahead to 14:33 for details.

 

[rpcraft]

Sand blasting won't work?

It's kind of cumbersome and heavy to fit a sheet of metal that is 1/2 inch or so thick into a blast cabinet and also it would need to be a really big blast cabinet, and then also it would just rust pretty quickly afterwards as well unless you treat it with something.

 

[mogandave]

It's kind of cumbersome and heavy to fit a sheet of metal that is 1/2 inch or so thick into a blast cabinet and also it would need to be a really big blast cabinet, and then also it would just rust pretty quickly afterwards as well unless you treat it with something.

You don't need a cabinet to sandblast.

 

[NORTON'S SHOP]

It's kind of cumbersome and heavy to fit a sheet of metal that is 1/2 inch or so thick into a blast cabinet and also it would need to be a really big blast cabinet, and then also it would just rust pretty quickly afterwards as well unless you treat it with something.

Not all sandblasting is done in a cabinet.

 

[rpcraft]

Not all sandblasting is done in a cabinet.

That is true but once you start getting larger than a blast cabinet size you won't want to be doing it at home. Those cheap harbor blast pots will cost you a lot of time and frustration trying to blast something bigger than 2 foot square and you won't want to do it indoors or in your driveway if you have vehicles parked around either.

 

[mogandave]

That is true but once you start getting larger than a blast cabinet size you won't want to be doing it at home. Those cheap harbor blast pots will cost you a lot of time and frustration trying to blast something bigger than 2 foot square and you won't want to do it indoors or in your driveway if you have vehicles parked around either.

Actually, blasting outside is pretty manageable if you pay attention.

 

[NORTON'S SHOP]

That is true but once you start getting larger than a blast cabinet size you won't want to be doing it at home. Those cheap harbor blast pots will cost you a lot of time and frustration trying to blast something bigger than 2 foot square and you won't want to do it indoors or in your driveway if you have vehicles parked around either.

Take it to a business that does that sort of thing. I like doing things myself, but there are some things that just aren't worth the time and effort. I live in a fairly small town and there are a least three businesses that will do this.

 

[Innovate1]

I have a somewhat similar issue. I have some 4140HT (Rc 30) that is not decarb free. No experience with this material but needing to machine it. I have carbide end mills and think I have the machining covered. But my understanding is there is a hard surface layer that is hard on cutting tools. Not sure how thick it is but surface looks pretty good. Options suggested so far are surface milling to below the surface (how do I know how deep it goes?) so cutting is mostly in the core not the surface (with climb milling). Other option suggested was to grind. Belt sander might work well. What sort of belts for this type work? Have used it for only wood work so far. I have a small sand blaster so that is also an option.

 

[rpcraft]

Actually, blasting outside is pretty manageable if you pay attention

If you have a blast pot, and a compressor that can run it, as well as a good drier system, then yes, it's pretty easy. Even if you don't pay attention.

 

[housewolf]

Don't discount the vinegar solution.....

Jump ahead to 14:33 for details.

OP inspired me to at least try to clean up an old table I built ~ 20 years ago. I tried a little last night with a belt sander then tiger paws on a grinder it was very time consuming & I wasn’t happy at all with the results.

. I saw this video this morning and sure as hell wasn’t going to build a dam around my table. I took an old towel, laid it over (most of) the table and saturated it with vinegar. I’m not the patient sort so wouldn’t wait “overnight”. Soaking about 3 hours, I was able to do this “wet sanding” with the vinegar using an orbital & 80 grit. You can see a distinct line on the right side where the towel ended. I’m going to let it “soak” longer and see if it isn’t even easier.

 

[housewolf]

I wish I had a complete before & after ‘cause the top came out so good, I painted the frame. Yea, cover the top & soak in vinegar, orbital sander with 60 or 80 grit then go over it again with 120

ETA: I found a (not very good) “before” pic

 

[TurnipTruck]

It's going to need to sit for at least a day.....

Get a closeup pic of the surface.

I still think an aggressive strip disc is your best bet.

I found a “paint removal disc” and gave it a try. It cleaned 3/4 of the table before it wore down to the nut.

I used the cup grinder to clean off all the tacks and to flatten the birdshit holding the angle to the table edge. I think the grinding wheel got dulled or clogged because it cut much better after hogging out an especially crappy weld. If I had a concrete paver I could try sharpening the wheel occasionally.

The lighter colored area above the blue grinder is where I tried some paint stripper; all it did was change the color of the coating /oxide, whatever it is.

Then I cut loose some poorly welded lower struts between legs to unbanana the table. I may have to fork an engine or two on top to hurry the flattening.

 

[dave_dj1]

Next time order pickled and oiled steel

 

[zmotorsports]

@housewolf , your table turned out awesome. I am definitely going to give soaking a towel in vinegar a try on my fabrication table.

 

[TurnipTruck]

Then I cut loose some poorly welded lower struts between legs to unbanana the table. I may have to fork an engine or two on top to hurry the flattening.

Or instead of a lot of weight, I could try some post weld tensioning.
I only need 3/16” of banana flattened.


Should I use a weed burner underneath to normalize the table top while tensioned?

 

[nadogail]

You could heat the top side ans spray water on the lower surface to "Shrink" it back to flat. After which then add braces to keep it that way.

 

[Snip]

Jason from Fireball Tools did some testing and found THESE Walter discs to perform the best.

I bought one of these millscale discs, they are amazing on mill scale. For such a large flat area like the oP's table top I would try an auto body type dual action sander starting out with course and working finer discs until you got the finish you would like. works faster than you would think.

 

[TurnipTruck]

Continuing on with the side weld bench:


This looks rusty, and is more pitted than I suspected. I stitch welded the seam and prepared to stink up the shop again grinding down to shiny.

I got one third of the side bench sorta ground down using a frequently-sharpened cup grinder. After numbing most of my fingers grinding for two hours, I said Screw This and tried a whole gallon of white vinegar to see if this coating is different from the central table. After notifying the wife that her vinegar is depleted, she mentioned that the gallon I used is cooking grade and is only 5%. Looking around, Depot has a lot of 30%. Maybe that is why my chemical method has been unsuccessful.