Sheet metal flatness / availability

[peter brooks]

I'm starting a bit of metal work. I've been a woodworker in the past and have always made things but my knowledge of metal raw materials is next to nothing.

In terms of sheet materials I think aluminium (aka aluminum) will be the most readily available and the easiest to work. I want to avoid plastics if possible.

I've bought a small modelmaking lathe (an Emco Unimat 3 with the milling / drilling attachment), while this will be great for turning, drilling and light milling I don't think it would be up to milling a larger surface - say the film plane for a 617 back.

So the query is - are there different grades / qualities of aluminium available that would exhibit better flatness and surface quality 'out of the box'? What am I likely to get buying from an online metal retailer (for example in the UK themetalstore.co.uk)? Are there specific 'scientific' suppliers etc. who would sell better quality? Or other sources? I just don't know what is available.

Any suggestions very welcome (apart from 'don't bother' ).

(I'm aware that there are plenty of people on this forum that have worked in precision engineering, the various sciences etc. We wouldn't be talking NASA in terms of accuracy, so it is very much 'horses for courses' with the aim to getting a sufficiently good result!).

Thanks!

[Tin Can]

I have 2 Unimats. never use them, too small

Study this source which I don't think will ship to you, however no order is too small and they deliver to me ASAP

https://www.mcmaster.com/

but they have all kinds of data on materials

I used them everyday in our huge factory

Why Mill to size, buy the exact thickness

Try eBay, they sell a lot

[peter brooks]

Thanks for the reply and link Randy - wow! McMaster-Carr look like a great resource. I see that their aluminum range includes tight-tolerance and anodized. I need to find something similar in the UK.

I have 2 Unimats. never use them, too small

Ha ha, yes, tiny in fact. I only want to make very small parts though, and my workshop space is really limited, so I think it will suit well.

Why Mill to size, buy the exact thickness

It wasn't milling to size but facing (if required) to remove scratches / gouges and/or to make it truly flat. I really have no idea on the quality I could expect from a general-purpose stockholder (I was going to call this post 'How flat is flat?' but thought that might be misleading!).

Cheers,
Peter

[Tin Can]

FLAT

Most of my working life was confirming FLAT on cast iron and Alu engine head and block

I used calibrated McMaster Carr Straight edges with constant rechecks before and after ANY usage

Probably Starrett https://www.mcmaster.com/precision-straightedges/

If out of spec, all tests were discarded from that batch, a nick can ruin your day

We found it cheaper to buy NEW rather than fix any straight edge

We also tested surface roughness of the parts every clamp up

I cleaned the parts with new often, straight razor blades hand held, not easy removing baked on Teflon, paper, goo, asbestos, and worse

Of interest to our hobby, is a Fuji Product, I also used after the above.

https://fujiprescalefilm.com/

Think real hard how to simplify you project!

Thanks for the reply and link Randy - wow! McMaster-Carr look like a great resource. I see that their aluminum range includes tight-tolerance and anodized. I need to find something similar in the UK.



Ha ha, yes, tiny in fact. I only want to make very small parts though, and my workshop space is really limited, so I think it will suit well.



It wasn't milling to size but facing (if required) to remove scratches / gouges and/or to make it truly flat. I really have no idea on the quality I could expect from a general-purpose stockholder (I was going to call this post 'How flat is flat?' but thought that might be misleading!).

Cheers,
Peter

[bmikiten]

Metal is subject to several factors when it goes through the manufacturing process and as a result, you'll see not only "flatness" issues (relative from point to point) but often surface anomalies that show up as high and low points across the total surface area. As a woodworker, you'll be familiar with the idea of a drum sander or jointer being used to achieve a flat surface but also having to deal with small surface issues due to temperature, humidity, etc. Milling the metal with a surface mill is probably your best bet as long as you understand the work holding requirements and have adequate reference points. You could also rough size the material and take it to a local machine shop for finish refinement. In the end, how flat does it need to be across the active surface? Sheet metal (as you noted) is inherently not flat and you'd need to look at bar stock which is then milled flat.

[BrianShaw]

For thin or stamped sheet metal parts, it is sometimes necessary to have a machine shop "double disk" the parts to relieve stresses and achieve flatness.

https://metalcutting.com/knowledge-c...disk-grinding/

[LabRat]

For thin materials, a rolling mill is used to even out thickness of sheets (looks like the rollers from the wringer on old washing machines), but require skill to set roller tensions correctly (or easy to set perfect curves into flat material...

Most materials are rolled reasonably flat during manufacturing, but can get distorted in process, but usually can be re-flattened by sandwiching between two pieces of flat material (thick aluminum, steel, even multi layers of thick MDF bonded together) and beating both sides with a mallet... (This works well for wavy old neg carriers...)

Steve K

[nolindan]

An interesting read - The Foundations of Mechanical Accuracy by Wayne R. Moore (of the Moore machine tool company):

https://ia800104.us.archive.org/20/i...l_Accuracy.pdf

It is all rather Zen... See page 21 for making a flat surface: pressure plates are best made in three's.

[peter brooks]

Thanks all for your contributions, very useful information and suggestions, a real education!

When I had a fully equipped workshop the hefty cast iron beds of the planer/thickneser or bandsaw were invaluable for their flatness (it is all relative of course). I think I'll have to get one of those granite surface plates for setting out metalwork, plywood or kitchen worktop material just can't be trusted to be flat.

I am going to order some 2mm alumin(i)um sheet from a normal stockholder (to make some picture-frame style bellows fixings - my somewhat unloved thread on that is here), so I'll see what that is like in sheet form when it arrives.

Milling by a local machine shop sounds like probably the best route to an acceptably flat surface though.

[jp]

If it's thin sheet, bending the edges >=90 degrees should also straighten things out (like a pacemaker speed/crown graphic lensboard)