Sufrcae Prep of Aluminium

Hi all, i'm looking for advice as to how to surface prep thin sheet aluminium.

The material will be aluminium sheet between 1 & 2 mm thick, in squares up to 400mm square (approx 16"

The requirement is to get the sheet material as flat as possible, and reasonably smooth, so there are no dents or blemishes. Also to provide a key for later coating, so ideally the process would leave the plate as clean as possible.

What machinery could be used to achieve this?

My knowledge of modern machinery is limited so any help would be much appreciated.

Many Thanks

Rog.

Hello Roger. I should say that the only way to avoid dents is to not inflict them. Once in, virtually impossible to remove. I'd suggest belt or orbital sanding to clean surfaces and remove small blemishes, flipping the material frequently to treat both sides in parallel (no pun intended). If you can find a vacuum pump and make a simple, flat, vacuum hold-down table it will be well worth doing for the convenience it brings. Suprisingly, supported thinnish MDF provides a good surface and allows sufficient airflow through its structure to act as desired without the need to drill perforations. Just mask off the area outside your job with parcel tape or similar.

Sanding, particularly with fine grades, will harden the aluminium surfaces somewhat, which can be useful or annoying, depending upon your intentions.

Good luck,

Ken.

Ideally i would be looking for an automated method of achieving this. Getting someone to do it for me, rather than equipping myself - at this stage anyway.

I would need a reasonably large quantity of plates.

So the question should perhaps be "how would this be done in a production environment?"

I am aware that i would need to start with essentially flat material.

In which case you need to talk to metal polishing companies.

Tell them what you want and let them sort the machinery out, after all they should know their job better than you.

You may be better off buying it with a brushed or annodised surface with a plastic protective sheet on the top.

J

I take it you want a soft surface for your blank disks?

If so you will want an unanodised (soft) polished plate. You should be able to get this. Leave the plastic on until the moment you need it.

Neil

Can you buy pre-ground aluminium sheet that's suitable for my purpose.

If so who does it??

Thanks

R.

Why do you want it ground? Is the surface of virgin sheet aluminium not flat enough? At 1 to 2mm thick, it is going to flex all over the place anyhow. And you are going to paint it anyway, which is not going to be any flatter than unmachined sheet if paint is thicker in one place than another.

Tell us a bit more about the application for the these plates and someone might know just what you need.

All I recall about grinding and aluminium is being told very forcefully that it should never be done - soft metal clogs the stone and can lead to it shattering. Now there may be some specialist process that avoids that - others may know?

Rolled aluminium will be flat to a pretty high standard. Keeping protective coating in place until late in the day will reduce chances of marking.

You don't mention what coating is planned - for paint an etch primer is typical on aluminium. Others have already suggested anodising, which might work well for some coatings (be aware there are several variations on anodising with differing end properties).

The cutting technique used may introduce variations in flatness.

Hi Roger talk to Orion alloys as they fairly near to you

**LINK**

Paul

Roger, you won't improve on the plate as bought, and unless it is going to be anodised, or painted with some sort of coating, a layer of oxide will form on exposure to air. Ian S C

Apparently it is possible to grind aluminium. Its just one of the processes that can be used preparing ultra flat aluminium platters for computer hard disks.

This link briefly outlines one process of one maufacturer of HDDs, I once read a very detailed description of every stage or making a platter but I cannot find the link.

**LINK** (Its safe to click on)

One thing I have never quite understood is why two platters dont 'wring' together. The surface finish and flatness is surely equal to guage blocks? but I cannot detect any grip between any of the ones I have removed from old drives.

Ian P

Edited By Ian Phillips on 11/08/2013 11:04:31

Ian, just had a try with the 4 platters I have here, I can just about detect some indication that they might wring together , and they might if they were absolutely clean, and dust free. It might be either the magnetic properties in the disc, or the teflon type lubricant layer on the surface of the disc that keeps them apart.     Ian S C

Edited By Ian S C on 11/08/2013 14:34:35

One of the ways we "polished" aluminium in the aircraft factory was to put the component onto a large bed , loaded water and marble chips on top of it and then the table was mechanically 'shaken'. The marble gently polished the surface to remove stress raisers etc. - The panels were about 40 ft x 5ft and saved a lot of time than some of the other processes available.

Just noticed the posting by Ken King where he mentioned using thin MDF board for making a vacuum table. How thin are we talking about here and how much grip do these tables give? Is it possible to do light milling on an aluminium sheet or would that be rather dodgy.

Doug

The reason for not grinding Aluminium is that many people have been injured by trying to grind on a conventional bench grinder. The soft metal very rapidly cloggs the stone then can weld to the job so the stone can shatter and do a lot of damage to the people around the machine. The spinning stone has a lot of kinetic energy that gets released in miliseconds.

Specialists know exactly how to grind Alloys but they do it under carefully controlled conditions which are not available in the home workshop.

The OP is looking to produce Ali blanks for direct disc cutting - LP style. So the requirement is to have the surface locally smooth to idealy well under a tenth of a micron. Milling or turning might not quite do...!!!!

Billy.

Not much help here, but this is interesting info on the mastering process: **LINK**

Neil

I'm not sure Roger mentioned what he was using the plates for ?

Sheet ally is "reasonably" flat as is.

• Anodizing would require a polished surface if scratches/blemishes are not to be visible. Probably the same for powder coating.
• For painting I'd use a self etch primer and wet sand and polish the painted finish.
• If it's for recording onto i'd be looking at chemical degreasing and sonic water cleaning before an electrolytic coating process. But I'd question the size of the plate if it's spinning. It would require some pretty fine balancing if mounted on a spindle.

My first job at HP was building disk drives and all parts for the drives except the platters and circuit boards were cleaned using sonic water tanks and surfactants. The platters were bought in already plated with the magnetic coating.

Turn his 16"sq into a disc, and you have the size of the old 16" recording disc that Dad was using when he was a technician with the NZ Broadcasting service in the 1940/50s after his Air Force service during WW2. These discs were coated with a layer of wax, and the recording made on that. There's one out in the workshop that Mum used as a lid on the jam pan. Ian S C