What is the best tool for..

[gazelle]

I regularly need to grind rusted steel in small areas (at least 2cm diameter)to measure remaining thickness with an Ultrasonic Thickness meter. The plating is between 4 and 10mm thick (when new). The rust can be 10mm in thickness.

A 240V supply is not necessarily available.

What is the most appropriate tool for removing the rust leaving a relatively smooth finish, without the risk of taking too much good material with it?

Cheers

Martin

[western]

reckon a rotary wire brush would do & not remove any good material, but without a good power source, your a bit stuffed.

[redneck]

For thick rust use a welders chipping hammer or a geologists hammer to get the bulk of it off. Once you have the thick rust off then use either a Flap disc or wire cup brush in an angle grinder, or use coarse Scotch-brite discs in a battery drill.

I've used these methods in prepping for U/T testing where material removal had to kept to an absolute minimum.

The scotch-brite discs provide a very good finish for U/T.

[Night Train]

With no mains power you can use a battery powered grinder with a wire cup brush to clean it up, after chipping off the worst. A Dremmel will be a bit too small I guess.

[gazelle]

Thanks guys,

Is there a recommended cordless grinder?

I will have a go with the scotch-brite pads with the drill.

Are there flap disks that can be used with a drill?

Cheers

Martin

[ahebron]

An angle grinder plus a small generator to power it when mains voltage is not available. Seesm to be the best method to me!

[gazelle]

Two examples of the the type of surface I need to clean for measurement.

[sotal]

I'd go with the suggestion above using a small generator and a small angle grinder. Flap disc in the grinder is the quickest way I've got of removing rust. You could though get a fairly decent battery powered drill (Makita etc) and a variety of wire wheels (cups, wheels etc) then once the bulk of the rust is chipped away that should clean it up within a few minutes - probably the cheapest way

[bishbosh]

As you state you don't want to remove any good material I would stay away from flap wheels - they are in my experience extremely good at removing competent material!

I would stick to using wire brushes.

[Night Train]

Ditto about flap wheels. I use them at 80 grit for shaping metal, very effective.

Have you thought about an inverter? I have one in my car for just these sorts of occasions where I have to work outdoors without a power supply.

It was really useful when I was staying at the Centre for Alternative Technology in Wales. They had a power cut one evening and while everyone else was being all green and huddled around a candle I drove my car up to the digs, plugged in my music, my laptop and some lighting and carried on work. I even managed to brew up.

[gazelle]

Thanks for the continued advice guys.

I have two applications in mind for this cleaning requirement:

1 - (LR related) Under the truck to clean off rust prior to protection without loosing to much of the tin foil used to make the td5 Defender chassis. (This is too thin to measure with my UT when new (esp rear x-member!)

2 - (LR related in that the LR gets me to the job!) Measurement of the thickness of Narrow boat hulls, often in the wet bottom of the "dry" dock, on my back in a 20 inch space below the boat.

I am looking for one tool to work with both of these similar cleaning requirements.

It is the second of these applications that makes battery power so compelling. The picture below shows the typical environment that I will need to be using it in!

In most cases there will be 240V power, so I will investigate this and look at a suitable inverter/cheap generator when this is not available.

Where do you guys get your brushes and scotch-brite disks from?

Cheers

Martin

[disco_al]

Sealey do a cordless grinder for about £85 plus vat, that uses li-ion batteries i think.

[FridgeFreezer]

12-14v cordless drill or grinder, smash the battery pack & stick jumpleads on to a car battery (~2mmsq cable will often do). Will last for ages compared to battery packs, even on a shagged out battery.

[LandyManLuke]

It's not like you have to smash up a battery pack, I made a plug out of a bit of wood that slots in to the drill in place of the battery, and does exactly the same thing.

The idea does work very well, one warning - where as a battery drill will run out of current and stall if you over-work it, one wired to a car battery will keep on running, over heating or killing itself etc.

[gazelle]

For the next one I am looking to use a 115x22 grinder which I have already, and use these scotch brite disks to clean off the rust.

Do I need anything else, like some form of mandrel or plate?

Martin

[steve b]

Have you got compressed air available?

The trade tool would be a needle gun or descaler

There may even be a battery version ...

cheers

Steveb

[gazelle]

I have ordered some Scotchbrite purple Clean and Strip disks for the drill and some SC-DB Scotchbrite Fibre Backed Metal Conditioning Discs for the grinder.

There are no wires to fly off on me when underneath, so hopefully a better/safer bet than the wire brushes. I will still be wearing work gloves and eye protection though!

I will report back on how I get on with them.

Martin

[RobotMan]

When I was at sea air driven needle guns where the weapons of choice for deck or Hull prep.

[M&S]

Keep it simple.

I still reckon a cordless drill/grinder with wire brush cup would be best. I've shifted loads of rust with this method over the years. Never had any wire come out either.

Get a couple of batteries and you're sorted. One can be on charge in an office/mess room/etc For what you are doing I don't imagine you'll even use one fully charged battery anyway.

No need for anything more than this, and certainly no need to be carrying larger power supplies around with you as you'll only be using it for a few minutes at a time.

[CBolton]

Hi mate....my suggestion after taking the entire under side of my Ford Capri to bare metal would be these

My link

if you are just doing a small or large area that is devoid of mountings or fixings sticking out...ie the hull of a boat then these are superb, will remove rust down to shiny bare metal very quickly, you can get them for angle grinders or for a drill both of which you can buy cordless.....and no wire bristles to get stuck in your skin......oh and you will not damage the underlying metal at all

the discs went through rust/paint/primer very quickly highly recommend them

[gazelle]

The coarse Clean and Strip disks on an electric drill did a fantastic job of taking the surface rubbish off. It took the rust off without taking any underlying steel.

No flying wire bristles. It is easy and effective. Highly recommended.

Cheers

Martin

[Range Rover Blues]

How accurate is the Ultrasonic Thickness guage when the steel is pitted?

[gazelle]

How accurate is the Ultrasonic Thickness guage when the steel is pitted?

+-0.05mm. It takes a surface to surface 3 echo measurement which ignores the small pits.

If the pits are larger then it could affect the readings, but I would suspect that the pits would tend to reduce the reading.

Have a look at this web page for more information

[gazelle]

I have now had an opportunity to use both of the products I bought on the same structure.

The strip and clean disks work with an electric drill and clean back to bright steel. Existing pits are clear but unlike grinding, no clean steel is taken off.

The Fibre backed disks are designed for blending. On the grinder they clean very quickly and give a very clean finish - but..... you do go through them very quickly.

For example on a 30ft narrowboat (scale, old paint, rust) one strip and clean disk is only half used for cleaning the UT points - whereas one fibre backed disk only does one side.

In conclusion: the strip and clean disks clean well enough, and last, the fibre backed disks work faster, last less long, but clean better.

The structure in these pictures was cleaned with the fibre backed disks:

And this was the strip and clean disks:

Hope that helps someone.

Best regards

Martin