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Thread: Sheet metal flatness / availability

  1. #1

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    Sheet metal flatness / availability

    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!

  2. #2
    Tin Can's Avatar
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    Re: Sheet metal flatness / availability

    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
    Last edited by Tin Can; 21-Nov-2022 at 05:00. Reason: eBAY
    Tin Can

  3. #3

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    Re: Sheet metal flatness / availability

    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.

    Quote Originally Posted by Tin Can View Post
    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.

    Quote Originally Posted by Tin Can View Post
    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

  4. #4
    Tin Can's Avatar
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    Re: Sheet metal flatness / availability

    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!


    Quote Originally Posted by peter brooks View Post
    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
    Tin Can

  5. #5

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    Re: Sheet metal flatness / availability

    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.

  6. #6

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    Re: Sheet metal flatness / availability

    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/

  7. #7

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    Re: Sheet metal flatness / availability

    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

  8. #8
    Nicholas O. Lindan
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    Re: Sheet metal flatness / availability

    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.
    Darkroom Automation / Cleveland Engineering Design, LLC
    f-Stop Timers & Enlarging meters http://www.darkroomautomation.com/da-main.htm

  9. #9

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    Re: Sheet metal flatness / availability

    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.

  10. #10
    jp's Avatar
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    Re: Sheet metal flatness / availability

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

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