metal sanding

After spending best part of the day on cleaning rear wheel with flap wheels/angle grinder ,wire brush attachments,and good old emery cloths to clean black coating off, I have to ask the question Is it necessary to clean every part of it away prior to painting ??

In a word 'yes'. (Speaking as a paint supplier). Everything should ideally be wire wheeled, filed so that there are no sharp edges or any contamination. Its a long and labourious process - I've just expereinced 6" Foden Chassis Rails. If you dont get all the loose rust, mill scale, oil, grease and dirt off you risk the primer being unable to adhere to the substrate. Thats a posh way of saying the paint won't stick. Painting is all about the prep - if you skimp on that area you can be the best painter in the world but its fairly meaninless when it all flakes off.

Its not all doom and won't needfully go that bad but if in doubt spend a bit longer cleaning and sanding its worth it in the long run

If you want to munch of a lot of mill scale the first thing i will say is don't use cheap abrasive's they just don't cut it pay up now and save your self a lot of time.

http://www.shop3m.com/61500111804.html?WT.mc_ev=clickthrough&WT.mc_id=shop3m-AtoZ-3M-Scotch-Brite-Surface-Conditioning-Disc

I use these disc's on mill scale all the time but the key here is your grinder i use a variable speed machine a car polisher is about the same. The more speed you have the more damage you will do to the part the next bit is heat the more heat you put in to your flap wheel the faster you will lose it's ability to remover the hard shinny scale i'm sure you have noticed when you turn it over and look at your disc the edge is just white fabric no abrasive at the cutting edge and remember you are trying to grind some thing that is super smooth and hard. Slow you grinder down and you will over come all this. I did both my rear wheel spokes in under a hr or so and that was with giving them a bevel all over with a power sander and then a going over with a 240 grit DA on a 8mm orbit to blend al my radius in.

Witch is one more thing you will never get scale of with a sander you need a DA with a high orbit and 60 or 40 grit paper.

Grinding a weld on steel is very different from removing mill scale just like there is different sand paper for wood and paint.

Hope im not teaching you to suck eggs my job is sorting stuff out like this every day at work my poor 3M rep has got me just about a sample of every thign they do over the years to over come this problem.

That's helpful hudmut, thanks. I was wondering if anyone has used a needle scaler on the rear rims? I'm thinking of getting a cheapy from machine mart this avo.

Dan

Simple solution is sand blasting. I had my road loco rear wheels done to get all the excess rubber off from the vulcanising process and you won't get a cleaner surface than that. Well worth the investment.

Brian

bjwlancashire wrote:
Simple solution is sand blasting. I had my road loco rear wheels done to get all the excess rubber off from the vulcanising process and you won't get a cleaner surface than that. Well worth the investment.

I've thought about that Brian but I don't want to make a sand blasting cabinet in my already cramped workshop. Plus doing it this way will result in less dust (hopefully)!

Dan

I paid someone to do it who has the kit already, you will find someone local. It gets the job done quick and easy with no mess in your workshop - even all that sanding creates loads of dust.

Brian

bjwlancashire wrote:I paid someone to do it who has the kit already, you will find someone local. It gets the job done quick and easy with no mess in your workshop - even all that sanding creates loads of dust.

Tell me about the dust!!!! Last year I was using a power-filer in the workshop for 2 weeks before Christmas. I regretted it - so nicer to do stuff like that outdoors. No respirator can save you from it 100%! Well, no cheapo respirator that I buy can

The needle scaler arrives tomorrow so I will report back when I use it (going away with work for a few days though so it will probably be next week).

However, I was chatting with a friend the other day and he primes directly on mill scale having removed all loose rust and welding scale. His jobs are for the MOD so if it passes the tests for them then sometimes as model engineers I think we go waaaay to far!

Dan wrote: However, I was chatting with a friend the other day and he primes directly on mill scale having removed all loose rust and welding scale. His jobs are for the MOD so if it passes the tests for them then sometimes as model engineers I think we go waaaay to far!

Must be an engineers fetish!!

Brian

Agreed! Sometimes I go way overboard!

But seriously I think that we need to learn to relax sometimes. I own a copy of 'How (not) to paint a locomotive' and although there are many good tips in the book, I'm not going to let it rule the paint job on my STW engine.

Indeed - Only I can balls up my paint job immeasurably

Going over board is some thing I totally excel at every thing of mine is done as good on the in side as it is the out side or I just cant sleep at night no joke that i had a brand new lathe and because the paint was not as i wanted i repainted the hole thing.

Iv got a blaster and did my front wheels in that but I just like to do every thing my self I never trust any body else to do me the job I want and because my rear wheels wont fit in my blaster I did mine that way.

Got one more trick to give away after cleaning a casting for its first cote of paint go over it with a gas torch it will burn off all the bits of lint that was left behind from your degreasing rag. Because castings all ways pick up and hold things when wiping them down for paint

I have it on good authority that it's quite in order to paint over good, sound mill scale! However,should you wish to remove it easily and without effort go to B&Q and buy 5 litres of Patio and Concrete Cleaner (less than £10). Place the item in a plastic container and soak in the cleaner for 20-30 mins. On removal, clean item with an abrasive sponge and the mill scale will just dissolve away without any effort. Wash with clean water. You then have bright,clean metal. I found this on the internet and couldn't believe how easy it was.

Great tip Steve

Used this method with concrete etcher (hydrochloric acid) at the weekend. Could not believe how quick it was. Did 16 spkokes in an afternoon.Saved heaps of time. Beats using a flap wheel. Just don't get this stuff on your skin or in your eyes, wear protection.
Phil

Sounds good! I should update everyone with the needle scaler - it didn't really work! In the end I used angle grinder flap discs and the powerfiler. Those powerfilers are blooming marvelous

Couldn't agree more the power file is brilliant. One of those gadgets you wonder if it is as good as you hope and often dissapoint. But the powerfile doesn't - essential STW builder equipment.

Simon

I have an air power file too,I agree its a must have.


Kev

I must admit I have removed anything loose, degreased, and gave everything a rub over before painting, but I've got cleaned everything back to shiny metal. I may regret it in years to come I accept, but about 15 years ago structural engineers insisted on everything being bright and shiny, (I remember having rebar shot plasted more then once before use) in recent years they have wanted the steel to have a level of corrosion on to help provide a key.

Everyone will have their own way of doing it mind you and all will be equally right.

Steve A wrote:I have it on good authority that it's quite in order to paint over good, sound mill scale! However,should you wish to remove it easily and without effort go to B&Q and buy 5 litres of Patio and Concrete Cleaner (less than £10). Place the item in a plastic container and soak in the cleaner for 20-30 mins. On removal, clean item with an abrasive sponge and the mill scale will just dissolve away without any effort. Wash with clean water. You then have bright,clean metal. I found this on the internet and couldn't believe how easy it was.

Thanks Steve - you are a star for posting this bit of advice. I had blisters by the time I'd finished sanding the B-spokes for my front wheels, so wasn't relishing having to do the A-spokes. Thankfully I read your post and tried soaking them in patio cleaner and the spokes came up beautifully. I hardly had to do any sanding - you have saved me hours of time, lots of mess and more blisters - Thank you!!! I think I'll be putting everything in this stuff from now on.

Couldn't find the patio & concrete cleaner at my small local B&Q. Is it a B&Q product or is it made by someone else?

John

I used this stuff, worked fine. Get some plastic seed trays while your there if you don't have any. They are long and shallow so you dont need to use as much cleaner, you can also cover the whole spokes at once.

http://www.diy.com/nav/build/building-materials/building-chemicals/cleaning___sealing/Cementone-Brick-and-Patio-Cleaner-5L-10487601?skuId=10978308

Or if you want some really good stuff then use this.

http://www.bilthamber.com/deox-c

Brilliant. Thanks for that. I shall get some tomorrow.

John

If it helps you find it at B&Q, it wasnt with the normal cleaners, it was in the Builders Yard bit. Yes its a B&Q product, in a big white bottle. C

Some millscale comes off easy with a flap wheel and some doesn't, I use a tungsten tipped rubber wheel I got at Dorset, very good at removing rust & millscale. You just have to hold it lightly as otherwise it cuts grooves in the steel, it also doesn't like going into an edge or across a hole as the tips break off! Good on flat surfaces though.