Rust removal from surface plate

[inchpincher]

Another great drunken eBay purchase which has sat in my workshop for the last six months is a rusty 3'x2' surface plate which I won for £7. I'm not expecting an A1 finish (like hand scraping it etc) but how should I least abrasively remove the rust, normally I just use the strip wheel in my die grinder but it think it's a little harsh. Never had good results from liquids or gels for rust removal

I'll build a frame for this one day out of 50mm angle. One day

 

[rikrobson]

liquids and gels are rust converters not removers. they chemically change the composition of the rust.
To get a decent finish use a grinder with a flap wheel. you can get various grit grages from 36 down to 120.

With all the rust on it its never going to be accurate unless you get it machined

Another way to remove the rust would be to use the electrolysis technique.

you will need:
a plastic tub big enough to take the item
a spare lump of steel/iron for sacrificial anode
battery charger
washing soda.

Method.
connect a wire to the item to be cleaned.
place the item in the tub and the lump of iron so that the they don't touch.
fill with enough water to cover the item. the lump or anode can stick out of the water and is easier to connect. if it is submerged you will need to add a wite otherwise you will loose your charger terminal.
add a scoop of washing soda, this can be added to the water prior if its easier. it will mix and disolve anyway and will be quicker in hot water.
connect the red lead of the charger to the lump/anode and NOT the item.
connect the negative lead to the wire attached to the item.
turn on the juice and wait 24 hours. bubble should start to appear.
there will be a rusty scum and the water will go browny green
after 24 hours the magic should have taken place.

turn of and take out the item. this should now be rust free. you will have pitting where the rust was an this process does not add fresh iron in place of the rust.
hte lump look like its been in the sea and covered in rust.

 

[Chipper]

Strip & clean disc will clean it up OK. Or if you could dunk it, citric acid would be another way, leaves a light grey finish.

 

[mike os]

go anywhere near it with mechanical cleaner/sander/grinder & you can forget using it as a surface plate..

wire wool or scotchbrite & a little light oil will soon have it clean & not compromise surface flatness.

 

[Engineer]

Knotted wire wheel in an angle grinder will work well, and is fast and easy. If there is any other than very light surface corrosion though, its had its day as a surface plate, and worth bearing in mind you can sometimes find perfect surface plates for very reasonable money.

 

[gordon stephenson]

I use diluted sulphuric acid for jobs like that, Taking all safety precautions of course, rubber gloves, goggles and face shield etc, Set the table top level and brush on the acid,keeping it wet for an hour or so, then rinse off and dry.If all the rust has not gone just repeat,
then use a wire wheel to give it a little polish,finish off by going over it with an oilstone and plenty of oil. As mentioned above will not be as good as new but will do for 99% of jobs,

 

[stormin]

liquids and gels are rust converters not removers. they chemically change the composition of the rust.
To get a decent finish use a grinder with a flap wheel. you can get various grit grages from 36 down to 120.

With all the rust on it its never going to be accurate unless you get it machined

Another way to remove the rust would be to use the electrolysis technique.

you will need:
a plastic tub big enough to take the item
a spare lump of steel/iron for sacrificial anode
battery charger
washing soda.

Method.
connect a wire to the item to be cleaned.
place the item in the tub and the lump of iron so that the they don't touch.
fill with enough water to cover the item. the lump or anode can stick out of the water and is easier to connect. if it is submerged you will need to add a wite otherwise you will loose your charger terminal.
add a scoop of washing soda, this can be added to the water prior if its easier. it will mix and disolve anyway and will be quicker in hot water.
connect the red lead of the charger to the lump/anode and NOT the item.
connect the negative lead to the wire attached to the item.
turn on the juice and wait 24 hours. bubble should start to appear.
there will be a rusty scum and the water will go browny green
after 24 hours the magic should have taken place.

turn of and take out the item. this should now be rust free. you will have pitting where the rust was an this process does not add fresh iron in place of the rust.
hte lump look like its been in the sea and covered in rust.

I'll second the electrolytic rust removal technique but suggest if you haven't a tub large enough to take the surface plate try putting the electrolyte on an old towel and place it on top surface of plate, soak in the washing soda. Place another large plate on top of the towel to act as the anode. Saw this method suggested for cleaning up the table of a milling machine that was covered in rust and obviously too big to dip in a large tub.

 

[steveo3002]

bilt hamber deox gel and liquids do work as advertised , they do remove not convert

some have said its just acid powder avail on ebay..i have no idea , but its good and doesnt touch the good metal

 

[inchpincher]

thanks gents, i will mull it over. I tried the wire wool and paraffin previously (as seen in the pic) but soon realised it would take about 2 weeks solid and not to a very satisfying finish. I think i have various acids and bilt hammer products kicking around from cleaning old fuel tanks, may experiment time permitting.

As mike os said, i'd rather keep any tool too aggressive on the bench because although the plate is well past it's best i would still like to keep it reletively flat! Like the electolysis idea although maybe a bit too much faff for a seven quid lump of rusty iron when a perfectly usable surface table can be had for 50-100 on the dreaded ebay... It takes two guys to drag it around the workshop too so prefer not to move it much!!

ta

 

[subarc boy]

rust

use a 9 inch grinder with with a flap disc take you about 10 mins
or buy a new bit of plate and weld it ontop ??

 

[brightspark]

use a 9 inch grinder with with a flap disc take you about 10 mins
or buy a new bit of plate and weld it ontop ??

ITS A SURFACE PLATE not a welding bench top. a piece of float glass or granite will be more acurate than that

 

[inchpincher]

use a 9 inch grinder with with a flap disc take you about 10 mins
or buy a new bit of plate and weld it ontop ??

I wanted to use this as an 'engineers surface plate' when the rust is gone, ie a very flat surface for marking and referencing so I'm trying to curb my power tool enthusiasm, please don't encourage me

 

[inchpincher]

ITS A SURFACE PLATE not a welding bench top. a piece of float glass or granite will be more acurate than that

Beat me to it!

So is it common opinion this plate is fecked then? I'm not a precision engineer by any stretch but a large flat surface would be useful...

 

[penfold]

I wanted to use this as an 'engineers surface plate' when the rust is gone, ie a very flat surface for marking and referencing so I'm trying to curb my power tool enthusiasm, please don't encourage me

Sorry, but you have 2 hopes of that and one of them is Bob.

ITS A SURFACE PLATE not a welding bench top. a piece of float glass or granite will be more acurate than that

I beg to differ; a welding bench is nearly all it's good for now. I got a 18"x24" granite surface plate for £35; bide your time and similar things will appear.

Beat me to it!

So is it common opinion this plate is fecked then? I'm not a precision engineer by any stretch but a large flat surface would be useful...

Sorry but yes it's ******ed. It will still be pretty flat though, just flat with rust pits. The least worst option for de-rusting are the citric acid or electrolysis methods. Scotchbrite on such a large area will bore you to death and powertools will reduce the already poor flatness even further.

 

[scott0031]

It will be exceptionally hard to get it back to a totally clean looking finish. I cant speak for the chemical and electro chemical means mentioned as i have little and no experience respectively.

Pics are are always hard to define how good or bad the actual condition is. That said it looks like its surface only. From what i can see assuming the plate was fairly flat to start with, then i think you have a pretty good chance making it perfectly usable again for what you need, unless you need something super good and are in high end precision work. If that's the case then look at a granite surface plate. They are pretty cheap these days from the right source.


My advice would be, what ever you do, do it by hand and not by any mechanical means. It will be time consuming, but that's the fun of the challenge inst it? Use a scraper to remove the surface rust. A broken hack saw blade ground to a knife edge works well. Use the end of the blade so the bit you grind is the half inch dimension, grind to about 10 degree or less so it becomes a flat scraper. use the scraper as flat as you can keep it with only a small inclination. Have a go and i think you will be surprised how easily the surface rust comes away. Its down to you to do it with finesse and care, so you don't dig in the plate, you will actually find it wont dig in if you use the right technique. Don't keep going over the same area time after time, scrape remove the surface rust and move on to the next patch. You can use a soft mild steel scraper ground up if you prefer to get familiar with the process. It will blunt pretty fast and need re-grinding regularly. The smaller surface area of a hack saw blade is ideal as it allows you to get under the rust and lift it off easier than something with a bigger surface area. trial and error might be the key to find the right combo for you.


After that use a hand scotch bright pad by hand or wire wool with either paraffin or white spirit. The scotch pads are good as they can be used with a flat wooden rubbing block. Using a block will prevent you putting pressure in one area only, which will happen if you use fingers. Fingers and hands are fine More lighter strokes is better than hard vigorous ones.

You may find small areas of pitted/ stained iron underneath, this does not mean it the end of the world. Often with something like this after the rust is removed you will find clean iron, Those clean iron areas are the bit you are interested in, as those are the high points any tools used on the surface plate will run on, so those stained slightly pitted looking areas does not mean the death of the plate. It may not look pretty, but it will still function as good as a clean looking plate.


Try a small area using this method see how you get on. A good bit of elbow grease wont kill you




Kind regards.



Scott

 

[Engineer]

Removing rust from a surface plate is not going to restore its accuracy, and the best thing to do would be to get the rust off using a rotary wire brush, relist on Ebay, and wait till an undamaged one comes long for reasonable money.

 

[breezer]

Probably not worth all that aggro for £7.

Weigh it in, or make it into a welding bench.

 

[Pete.]

I'd be over the moon if I scored that for £7. It would make a very nice assembly bench, and even if fairly rough methods were used such as running a DA sander over the whole surface it would still make a passable marking-out bench for a home workshop. I wouldn't want the job of removing a couple of thou of material off it with a sander that's for sure.

THe proper way to fix it would be have it scraped but you could have it ground to a good finish.

 

[Shox Dr]

I'm surprised no one has suggested having it reground? It's only a telephone call to find out the cost

 

[Pete.]

Yes a Blanchard would make a nice job of it. I thought about suggesting it but figured the cost would be prohibitive.