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Project: Angle grinder guide mechanism to cut sheet straight

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  • Project: Angle grinder guide mechanism to cut sheet straight

    Here is a project that has been in gestation for some time. It is a guide for cutting metal sheets of various thickness using an angle grinder.

    I have started some of the fabrication and already have some things to share and questions to ask. The need to workout how to calculate for, reduce or prevent "shrinkage" during welding is something I'd really like to know how to do; one weld caused my carefully sized parts to get seriously "slurped" to smaller size; and another plain went banana shaped. Will post photos of those early steps when I can get the images off my phone. Please feel free to give of your wisdoms as I go about the task.

    The project came about, as these things do, due to the need to have this tool in my arsenal BEFORE I felt able to progress other projects.

    Short story; I needed a tidier way to accurately cut hot rolled sheet; here are some examples:
    a) 13mm hot rolled squares of about 350mm (12 inch) width; I acquired about 20 of these for $9; they are too big to go in my power hacksaw.
    b) 1200 x 2400mm (4ft x 8ft) x 3.5mm cold rolled galvanized sheet; this I purchased new and need to render it down to make a water jacket to surround a fire box to heat my pool.
    c) 6mm x 300mm hot rolled sheet; I use 6mm in many of my projects; the 200mm ones I can cut ok in the power hacksaw; the 300mm ones don't fit.

    Existing cutting approach is:
    * Scribe as tidy and as visible a line as I can muster in the target to be cut.
    * Then with grinder in hand try to guide the grinder along line; to left-of-line, right-of-line or right-on-line depending.
    * Keep up a too and fro motion along the ever deepening line till the target becomes two pieces.

    Downfall of current approach is that the cut line is always wobbly. For some things this does not matter too much; but for others it is a pain and I find need to allow extra for cleanup to fit.

    The images below are screenshots from the CAD package I used to get the core design working.







    Cheers,
    Norman
    Last edited by Norman Bain; 04-25-2013, 05:44 PM.

  • #2
    I think that is a very pregnant idea! When are you going to build this thing?
    Location: The Black Forest in Germany

    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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    • #3
      what I have done is to clamp a board or chunk of metal to the piece I want to cut. I let the blade guard run along side the clamped straight edge. I also do the same with a torch if it has to be relatively straight. Soon this will be no problem when I have finished my CNC plasma table.
      Location: The Black Forest in Germany

      How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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      • #4
        If you are trying to cut 4x8 pieces of sheet steel,
        why not use a circular saw (Skillsaw) with a abrasive
        blade to cut it? Clamp on a straight edge as a fence
        and you get a straight cut. Do you want to make stuff
        or make tools to make stuff? (Probably not a good question
        to ask around here, LOL).

        --Doozer
        DZER

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        • #5
          Or find a fab shop with a shear to cut the 4x8 sheet for you. The cutting guide in the pictures is pretty clever though, I can see it having uses.

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          • #6
            Originally posted by Doozer View Post
            If you are trying to cut 4x8 pieces of sheet steel,
            why not use a circular saw (Skillsaw) with a abrasive
            blade to cut it? Clamp on a straight edge as a fence
            and you get a straight cut. Do you want to make stuff
            or make tools to make stuff? (Probably not a good question
            to ask around here, LOL).

            --Doozer
            This works for me too. I've also used a table saw while using an appropriate abrasive blade, both work great for holding a straight line.
            Including the above I also feel a plasma cutter or a good old oxy/acetylene torch are hard to beat when cutting a lot of sheet metal.

            I only use an angle grinder for short pieces as the smaller diameter wheels are slow in comparison to the other alternatives. 13mm sheet will be slooow.

            Careful with the galvanized sheet as the fumes from welding are not very good for living things.

            Distortion control while welding is the subject matter of many books as it's a very broad topic, but do a quick internet search and you will find lots of good info on the subject. Experience and practice will give one a good basis of knowledge as well.
            Here's a link with a few good pointers.

            http://weldingdesign.com/archive/avo...ion-thin-sheet
            Home, down in the valley behind the Red Angus
            Bad Decisions Make Good Stories​

            Location: British Columbia

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            • #7
              With the intent of not being a buzz kill,
              If you do decide to build your cutting machine,
              take note that abrasive grit and linear slide bearings
              do not live well together. Even guarding the wheel,
              dust tends to go everywhere. A vacuum helps some,
              but not perfect. One semi-dirt tolerant design is the
              Vee-roller type of linear bearing system. Most radial
              arm saws use this design. The Vee tends to exclude
              debris from the path of the wheels. Look up
              Bishop-Wisecarver. They make track of this type.
              Also, a good thin wheel I have found is the Metabo
              Razor Blade series of wheels. They are .040" thick
              as opposed to 1/16", and they cut super well.

              --Doozer
              Last edited by Doozer; 04-22-2013, 09:52 AM.
              DZER

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              • #8
                I feel your pain and do a lot of "free hand" cutting with my grinder. I try when ever possible to MAKE the thing I want cut fit my 4 1/2" bandsaw (can go to baout 12" max) but sometimes a grinder is the only way. Dont do a lot a sheet steel work, and when I do I use a plasma cutter (best toy I ever bought, cuts up to 1/2" plate)
                As for welding, I try to NEVER if at all possible weld finished bits together, but weld and THEN finish (which can get a bit interesting when trying to lathe something up). Not sure how other deal with this (and would LOVE to here) but when I weld I am never looking for 0.005" accuracy (usually 0.5" lol). I would gather TIG welding would be a lot less "cruel" to machined parts over stick (which is mostly what I use as I ran dry of Argon )

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                • #9
                  Originally posted by Stern View Post
                  As for welding, I try to NEVER if at all possible weld finished bits together, but weld and THEN finish (which can get a bit interesting when trying to lathe something up).
                  That is how it is typically done in industry. BTW, when I cut metal sheets I'll use the shear at work, an oxy/acty torch & angle iron as a straight edge, my Skill saw with a metal cutting blade & straight edge, or my Milwaukee sheet metal nibbler.

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                  • #10
                    I use an old table saw with an abrasive wheel.
                    Two problem areas are - I had to make a sheet metal guard to cover the motor to keep the spark away
                    Sometimes very thin material will go under the fence.
                    I'm sure the fence could be modified with a piece of flat bar that fits tighter to the table.
                    I usually use it to cut stainless steel.
                    Larry - west coast of Canada

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                    • #11
                      Thanks for the feedback.

                      Willy; I did go look at the welding site you posted. There was good info there but I am not sure how I should have applied it.

                      Some photos have been "extracted" from my phone. Most are not too bad.

                      These photos are of the portion of the front and rear clamps that hold the rods. I was real keen to get this right. Sorta had it in my head if all was not really true and parallel in this step I'd not have a sliding jig at all; so set about making the pair together. Plan was to weld and drill them together then cut them in half to make the two ends.







                      Last edited by Norman Bain; 04-25-2013, 05:43 PM.

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                      • #12




                        Here I share a bad experience I walked myself into. I had used a 60 degree center drill to accurately position the holes. Normally I would only just touch (not drill) the work with the center drill to make a mark there for next drill to follow. However on this occasion as the center drill point was exactly the same diameter as the first drill to be used I went much deeper. This was fatal; I was wrestling with chips in the hole the whole way.

                        Because of the depth I had to peck drill; but the chips did not clear the hole when I raised the drill; this left some UNDER the drill tip. I got there by not quite lifting the drill clear of the work; but even then the sound during drilling was ugly due to the flutes being grabbed by the chips and I was dead scared I'd break a drill ... especially the long ones.



                        Last edited by Norman Bain; 04-25-2013, 05:42 PM.

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                        • #13
                          This for me was "stage one" complete.

                          Last edited by Norman Bain; 04-25-2013, 05:43 PM.

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                          • #14
                            Thanks for the update..looking forward to your progress

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                            • #15
                              Next step is to put some "feet" on the risers. The risers (which hold the long rods) are still "together"; that is, I have yet to cut them into two parts.

                              Plan is to attach the feet (the upper clamp portions) then machine it all to be aligned before parting with hacksaw.



                              First I need some "strips" to be extracted from the 13mm sheet that is available to me. I often use the slitting saw to cut stuff. However this sheet was "tall" and when I tried to cut a strip from it WITHOUT added support it caused a big wakeup. I don't have a photo; but the sheet was vibrating like crazy as the slitting saw started its work. I thought I wonder if I put my hand on the sheet would that stop some of the terrible noise I am observing. Upon putting hand on the sheet and applying a bit of pressure the saw blade broke into a considerable number of pieces and I had some sticky red stuff running down my forehead. I was wearing safety classes but it was not nice.

                              I now have great distrust of the slitting saw and ALWAYS use full face protection if I am close.

                              The rig below was aimed at reducing the vibration while cutting. It did work though just; as the vice was unable to hold the plate even though there were jacks positioned at each end of the sheet to stop it tipping. I did get there in the end by keeping to shallow cuts.

                              I did read with great interest a whole thread here recently on use of slitting saws. I agree with most of what was said; though do find that if the part is really really well held, so that it does not vibrate, a full depth cut (13mm 0.5") is quite achievable.



                              Ok; now have the slices. Need to face them up a bit to be of consistent size. I figured the actual size was not mission critical so long as they are all the same.



                              The clamp bars bend like bananas when I welded them. Gave them a good smack with a hammer to get them back to somewhere near where they needed to be.

                              Last edited by Norman Bain; 04-25-2013, 05:46 PM.

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