derusting a Crozier surface plate

Hello all, I rescued an 18 x 30 130 lb. cast iron surface plate from a friend before it went to the scrap yard. It unfortunately sat out in the weather and has some pretty good rust on its surface. I am razor blading it off and so far no major pits. Any suggestions on bringing it back to a workable condition would be appreciated. Thanks, Jim

I purchased a Milling machine that was all orange rust from being outside for a year in the weather...
I took hydrochloric acid.. Muratic... is the same.. I think 25% concentration and painted it on there.
The rust came off in a cloud of smoke. Completely.
But, full safety gear, do it out-doors... as I found when I did it in my shop, that airborne rust condensed on every piece of metal in the shop... yellowed my tool-holders..
The acid, I think I bought a gallon for $25 or so.
It worked wonderfully.

i think you will find it is the fumes from the acid that does it.

I did some tool steel parts and within a metre i had some other parts it ended up putting spots on those parts.

So be careful with acid and do it in a well ventilated area.

What type of workable condition? To use it as a lapping plate, and inspection plate, a scraping master? How about a few pictures too. Top and bottom. Scraping plates need a really good ribbed bottom and 3 points to make the grade.

I would get the most use out of it as an inspection plate I think, I hope there is some life left in it.

Looks like a Challenge and its a scraping or inspection plate. I have found over the years the seem to rust evenly unless something was sitting on there. A real fast and more dangerous way is to used some acid on it that they sell in pait stores for cleaning concrete. Industrial grade rubber gloves and not those thing surgical ones. Have to wear goggle safety glasses and an aerator rub it on and let it sit 10 minutes and garden hose it off. like I said t Then use a wood sanding block with 100 grit paper and rub it evenly. A slower but works way is to use brake fluid. and scotch brite pad in a drill or round one in a air grinder. Then scrape it and I know someone who can help with that :-)

If you use any acid products on this plate, be sure to neutralize the acid before considering yourself "done". A sodium bicarbonate/baking soda mix with water, brushed or sprayed on evenly and allowed to fizz until all the acid is dealt with should work, but others may have better methods. And yeah, do all this outside and away from other metals (like, not next to the car!).

Wipe off the compound, and then you can coat exposed surfaces with a preservative oil. The oil won't affect any future scraping (it can be removed), but if you'll be painting any areas then use an appropriate prep compound on those surfaces, then paint as needed. Oil bare metal when the paint is fully set.

jmm03 said:

Hello all, I rescued an 18 x 30 130 lb. cast iron surface plate from a friend before it went to the scrap yard. It unfortunately sat out in the weather and has some pretty good rust on its surface. I am razor blading it off and so far no major pits. Any suggestions on bringing it back to a workable condition would be appreciated. Thanks, Jim

Click to expand...

1) its rusted so already not flat to high precision
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2) take nylon abrasive cloth or scrubbing pad and mineral spirits and rub rust off
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3) then take some stikit abrasive sandpaper and stick it to a flat ground block and sand it. it will show shiny high spots. if you got a flat abrasive stone you can try same thing. you can indicate surface to measure how bad it is.
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every week large fixtures are removed and pallet table and fixture needs cleaning often is rusted and pitted. you just have to decide how much effort you want to do to put it in good enough condition. takes a lot of time to remove even .0002" from large surfaces. often if you make a magic marker mark and sand it off it removes .0001" to .00005" depending on how rough surface is and how coarse the sandpaper or abrasive stone is. deep rust pitting can easily be over .0010"

If your goal is to bring it back to life with a decent freshly-scraped surface, you can ignore the rust, since it will be gone completely with the first few passes of scraping.
Even with de-rusting* you won't be sure about how flat it is and, likely, it will need some touch-up by scraping. Yes, scraping a 18x30" surface is not a quick job. However, to use it only as inspection plate, you don't need to fight till the last tenth f thousand and you don't need to get it to too many points per square inch, as long as the bearing is more or less uniform.
The added advantage of a scraped surface is that you can slide your gages without any significant stiction.

Paolo

*About rust removal: any acid is rather effective, but it has the disadvantage of keep digging into the metal: they don't stop at the interface between rust and metal. If you choose to use an acid nevertheless, I'd suggest you use vinegar, instead: a bit slower acting, much more controllable and not harmful at all. Use it outside, since the same vapor issues apply.
Molasses removes just the rust, stopping at the interface with raw metal. Similar, faster action is obtained using EvapoRust and similar chemicals.
Be aware that some rust converters based on phosphoric acid will leave a hard layer of iron phosphates, which is rather abrasive: a great idea if you want to paint over, not so great on a reference surface, where you'll slide some precision instruments.

Thank you all so far. I am leaning toward the acetic acid method mainly because I am not a fan of anything stronger,and disposal becomes an issue. (I work in a plating and anodizing facility and deal with nastiness every day...)I mainly did not want to cause more work to myself than necessary,but at least now I have a better idea of how to proceed. (Mr. King, do you ever think you will have a scraping class in southern California? ) Jim

i never use chemicals cause no need
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extremely rusted fixtures and pallet/tables if nylon abrasive scrubbing cloth feels rust is heavy , then a 5" air sander with nylon abrasive pad is used with hand stone in other hand. you rub stone across and if you "feel" stone hit rust spot i use air sander with nylon abrasive a few seconds and test with stone hand rub across. hard to describe. back and forth with air sander and stone many times. this is after mineral spirits and alcohol to remove oily residue. all told normally stone, hand nylon abrasive pad and air sander with nylon abrasive pad takes about 2 minutes a square foot to get to point where stone feels rust sticking up is mostly gone where hand stone can finish. a meter square pallet can take 10 to 20 minutes. usually takes longer to get chips out of the tee slots which gets hard like concrete.
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obviously if stone feels like its going over rust it needs to be removed and until rust gone stone not doing much on the metal left. usually use coarse and fine stone. until rust gone usually need a coarse stone. basically most times its a 5 to 20 minute job depends on how rusty and how big.
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sure i have seen brand new 50" square pallet tables hand scraped on new machine you can see hand scraping marks getting worn off in a few months even with just a ultra fine arkansas stone. obviously just heavy metal fixtures rubbing on it will burnish the scraping marks off and surface will rust or tarnish eventually just sitting in a shop unless coated with oil or something heavier. stuff can rust just sitting in a storage rack and can rust being in a machine and storage racks for months.
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basically i aint seen any large metal surface weekly not need a fine stone rubbed across to check for rust and oily spots (if it smears it aint clean yet). sure you can indicate surface if you want to see how much not flat any longer. obviously with some tolerances you would be doing this weekly

I actually saw progress from just scraping the rust off with a razor knife blade, tedious but effective. I used some vinegar out of curiosity but i could see that it would need some serious soaking to really work. I neutralized the acetic and oiled it up and will do the scotchbite or oiled sandpaper next. Appreciate the help. Jim

If your going to plan on scraping it, I agree with Paolo,the rust will be gone long before you get it to inspection quality. I'd do a quick wd40/steel wool/scotch brite job to knock off the heavy/dust rust and start scraping. Start with 2 or 4 cross cut passes, maybe 60-90mm/ 3/8"/1/2" or so long cuts. After that you should be pretty close to rust free and a nice, printable surface to start scraping for real. Save yourself the heavy lifting for scraping instead of rust removal, you'll need the energy!

Corey

I recently cleaned up and re-scraped a series of SE and a 18x18 SP which had suffered from poor storage. Rust pitting was in places 0.030" deep with odd small pits past that. I scraped off the worst with an old HSS saw blade to save the carbide.
I made a couple of attempts with an evaporust type commercial treatment - which was great at removing the rust but it changed the surface properties and to my mind caused faster degrading of the carbide edge when I started scraping - or it may have just been the remaining rust in the last few thou' of surface.
For my money / time - if you cant get the plate re-machined, then get at it with a wide scraper blade and get the surface down below the rust - then scrape it back to good.