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Scraping an aluminum straight edge -- worth it?

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  • Scraping an aluminum straight edge -- worth it?

    So I've gone ahead an purchased a granite plate. Waiting on delivery.
    In the meantime am looking around for things to scratch. I mean scrape.

    I have a CI angle plate about 6x6x6 or so but i dont know if i want
    to learn on that as I'd hate to really mess it up.

    ever try making a wooden table? and the legs don't quite hit the ground
    at the same time? you go round and round till the table sits level but the
    legs are only 1/2 as long as when you started?

    I have a 24" aluminum straight edge, Veritas brand, Canadian.

    http://www.leevalley.com/en/wood/page.aspx?c=&p=50074

    Claims its good to 0.003" over its length. Soon enough I'll have a chance
    to test how good it is, but i'm wondering:

    Is it worth scraping aluminum? Meaning, will it move on me, etc etc?

    Tony

  • #2
    Yes its worth scraping you'll be able to check your wood working and see how close you can get.

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    • #3
      For practice? yes it's worth it.

      I really don't know how durable it would be though. Think it would depend on how thick the aluminum is.
      I have an older (12-15 years old) aluminum box beam level, and an ancient craftsman 2ft I beam type that is a very heavy, and both have held up extremely well as far as straightness and accuracy go (cosmetics is a different story!) Also have a good quality, but lightweight extruded I beam level, with that one, the readings and straightness change if you hold it a while

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      • #4
        Thanks kendall. Thats about what I imagined. It's about 1/2" thick or so and necks in the middle (hourglass cross section) down to maybe 1/4". I don't mind
        messing it up. But I suppose for that matter I could flycut some Al and then scrape. Slowly I'll graduate to cast. My assumption is alum will be easier / faster to scrape during the learning curve.

        duck, yes its my straightedge for woodworking. I have a nice #7 jointer
        plane that puts that straightedge through its paces.

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        • #5
          Originally posted by Tony
          duck, yes its my straightedge for woodworking. I have a nice #7 jointer
          plane that puts that straightedge through its paces.
          I suppose anything for practice is ok, personally i wouldn't bother though as the AL won't stand up as a reference. I suggest getting a 12" section of 1"x2" durabar, shouldn't cost much and you end up with a useful reference, mill a bevel on it and you can use it for small dovetails

          I hope you're not using a plane sole as a reference they are not at all flat
          in Toronto Ontario - where are you?

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          • #6
            Thanks Mcgyver.

            No I didn't mean to say I was using the plane sole.. I meant the
            surfaces I can plane with my #7 come our flatter than my veritas straight
            edge if I take my time.

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            • #7
              You can certainly scrape or even just file aluminum to a very straight edge. It does warp a lot more from hand heat unless you use an insulated handle. The table on my mill is hand filed/scraped aluminum and it measures around .0001" flatness overall using my "patented" laser measuring method.

              See here: http://ixian.ca/gallery/laser/flattest.htm
              Free software for calculating bolt circles and similar: Click Here

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              • #8
                I dunno about scraping aluminum..... might depend on the alloy.....

                the scraping process pretty well was developed for cast iron, because it "fractures off" nicely. The scraping tool is optimized to fracture off thin shavings of cast iron. It does not "cut", it pretty much "bulldozes", relying on the material to fracture in order to complete the removal of the chip.

                many alloys of aluminum are gummy, and would be heck to scrape, you'd really turn up burrs that you'd have to file off. Dunno if that is scraping or filing. I'd suspect that any "experience" or "practice" you got in on aluminum would not be very useful on the more usual materials that are scraped.

                Also, the size of item you referred to, 1/2" in one dimension, and 1.75" in the other, is typically not worth scraping, as it is too floppy if of any size, as those are. But I am not clear on what your goal is, nor what you propose to use as a reference before the flat gets to you.
                CNC machines only go through the motions.

                Ideas expressed may be mine, or from anyone else in the universe.
                Not responsible for clerical errors. Or those made by lay people either.
                Number formats and units may be chosen at random depending on what day it is.
                I reserve the right to use a number system with any integer base without prior notice.
                Generalizations are understood to be "often" true, but not true in every case.

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                • #9
                  Just picked up a like new 18"x24"x6" pink Starrett Granite plate for $75. My question is do I support the whole underside or just around the edge? I assume the entire bottom because it came with round rubber pads on the underside.
                  On a side note I rescued a 4x8 do-all cast iron table tagged guaranteed to .0001 that weighs 8000# without the 5 legs, also it's 3x6 little brother & a 3x6 die table with at least 120 threaded holes I'll use for a welding table. They we're going to scrap these & i just couldn't let it happen. It's really sad what's sold for scrap in the US.

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                  • #10
                    I believe that surface plates generally come with pre-described mounting areas on the bottom. Three on my plate. Add a rubber disc, a felt washer, a folded napkin- set it on something fairly stable and make it level if you need to. Level is nice but not particularly important. If it came with pads factory attached, those are the points where it's expected to rest on. I think that supporting it all around the perimeter is probably a mistake.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                    • #11
                      I think I'd just as soon scrape rubber, AL just responds too much to temperature changes
                      I cut it twice, and it's still too short!
                      Scott

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