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Machining hot-roll steel - just complaining

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  • Machining hot-roll steel - just complaining

    This morning I squared up a 3" x 3" x 1/2# piece of hot-roll angle on the lather, by clamping it to a faceplate against another square angle that was store bought.

    I remember reading somewhere that hot-roll was in effect case-hardened by the production process. But I wasn't prepared for exactly how difficult it was to machine. It was throwing off painfully hot chips that kept burning my arm, just like trying to machine a hardened bolt.

    On the first surface I completely destroyed a HSS bit. Then I switched to carbide and things went a little better but I could only get a mediocre surface finish that wasn't particularly flat.

    Keep in mind this is all on a 7x10 mini lathe that flops around like wet noodle whenever it grabs. I can actually SEE it twist.

    Right now I'm doing this to make a jig for machining another part. Later I've got to go through this all again after I weld triangular support braces to it, as this piece of angle is going to be a core component of my milling attachment.

    Just complaining.
    Lee

  • #2
    whats the material? regular old mild steel? Its not casehardened, there's not enough carbon in it for that, but the scale can be tought on tooling. its also difficult to get a a good finish unless you're going fast with carbide.

    How fast were you going? It shouldn't eat tooling like you described....i'm wondering if you were going a little too fast
    .

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    • #3
      Don`t know what you doing wrong ,but hot roll steel called 1020 cuts like butter . Very easy to machine.
      You must have hot roll something else .
      Every Mans Work Is A Portrait of Him Self
      http://sites.google.com/site/machinistsite/TWO-BUDDIES
      http://s178.photobucket.com/user/lan...?sort=3&page=1

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      • #4
        It was A36, and there definitely is some hardening of the surface beyond just the scale. I can tell when I'm drilling it, it's hard going at first, then easy, then hard again before breaking through. Also, even after the scale was gone, it was still machining like hardened steel (tiny chips, very hot).

        I couldn't go over about 300 RPM absolute max, because it wasn't well balanced. I don't have a lot of options here for heavy things to bolt to the faceplate.

        The finish and chatter definitely got worse towards the center as the surface feet per minute slowed down. I found that I got a lot less chatter with the 3/8" carbide tooling than I did with the 1/4" HSS tooling. I might try switching to 3/8" HSS in the future now that I know how to grind my own bits.

        I'll look for 1020 in the future.
        Lee

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        • #5
          you're going way too fast, that's what smoking your tools. For ANY machining, drilling, milling, turning, figure out your max speed - RPM's = 4*CS/Dia. Cutting speed for HSS on mild steel is 80-100 sfm .... therefore max rpm = 4*100/4.25" (4.25" = the hypotenuse of the 3x3)...slow it down to under 100 rpm.

          A36 is kind of bottom of the barrel structural steel, thats some bad ass stuff to make 1018/1020 look good but I don't think a36 machine much differently than 1020, its realitive easy to machine, but tough to get a great finish. use a sharp stoned tool with rake.

          imo stick with 1/4, and put some packing under them...they;re easier to grind than 3/8"
          Last edited by Mcgyver; 07-31-2010, 06:20 PM.
          .

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          • #6
            This may not apply in this case, but I've had times when the piece got hot, it didn't turn as well. Let it cool, it goes better again.

            Removing the scale is a bit of a chore when you consider the life of the cutter. If you're prepared to sharpen a suitable carbide cutter enough times to get you through the job, you can then switch to a fresh insert to clean up after that. With proper speeds you can get an acceptable finish and will be able to make a fairly accurate part. One thing I like to do is sand the surface after turning it.

            With some sandpaper laying on a flat, you skid the workpiece over it while keeping the pressure more or less centered on the surface facing the paper. The more you work at it, the better looking it will get, but you do run the risk of rounding over the edges. It doesn't usually take much though to remove high spots and arrive at a perfectly usable surface.

            I have not used any chemical means to remove scale from hot rolled, but it might be an option, depending on the application for the part you'd be making. Another idea I'll bring up is that of annealing the part after scale removal, but before final surface turning. I haven't done this either, but it could make sense. Someone might have some input on this-

            Another suggestion I can make- hot rolled is often not flat or round. When you first clamp a piece of angle to a fixture so you can turn one face, it may not sit so solidly. This could easily affect how well it machines and what the surface looks like after. It's easy enough to de-scale one surface, the turn the piece in the fixture and de-scale the other surface. A few strokes on the sandpaper on a flat will show how flat the surfaces have become. Once you can get a better contact area against your fixture, the results might improve. Don't forget the edges of the piece of angle iron. If those edges don't fully contact against the faceplate, the workpiece might rock slightly during the machining, similar to what happens when the surface is slightly rounded and can't sit flush against the fixture. The workpiece should be constrained from moving in any way to be most solidly held- and this sometimes includes putting a support strut under the overhanging side, which is the side being machined. Flex in the material will affect how well it all goes, and with the high cutting forces generated when removing scale it can be a significant factor.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #7
              Originally posted by Mcgyver
              you're going way too fast, that's what smoking your tools. For ANY machining, drilling, milling, turning, figure out your max speed - RPM's = 4*CS/Dia. Cutting speed for HSS on mild steel is 80-100 sfm .... therefore max rpm = 4*100/4.25" (4.25" = the hypotenuse of the 3x3)...slow it down to under 100 rpm.
              Thanks for posting that info and equation, I knew it was important to know but I didn't know it yet.

              The lathe has a motor with a speed control, thus when I go slow there is no power and I don't have enough momentum to compensate and the machine just stops when it hits a tough spot, even with the lightest of cuts.

              I know, it's a piece of junk.

              By the way, what is "packing"? Just another piece of steel underneath to help keep the tool from flexing downward?
              Lee

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              • #8
                Originally posted by darryl
                Another suggestion I can make- hot rolled is often not flat or round. When you first clamp a piece of angle to a fixture so you can turn one face, it may not sit so solidly. This could easily affect how well it machines and what the surface looks like after.
                That would explain a lot about why it was easier to do the second side after I did the first.

                I bet the fact that it had a 2.5 inch overhang didn't help either, although I can't imagine there would be much flex in 1/2" steel over 2.5".
                Lee

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                • #9
                  Packing is just a strip of metal to bring the 1/4 inch bit's cutting edge up to center height. That's needed if you have s toolpost designed for larger bits.

                  Dan
                  At the end of the project, there is a profound difference between spare parts and extra parts.

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                  • #10
                    Structural steels such as A36 and beams, channels, and other shapes are not intended to be machined, other than sawing and some drilling. Most fab shops punch holes. So you have the wrong material from the start.
                    There is no such thing as "hot roll" steel. It is "hot rolled". Our language is in a shambles. Go to the supermarket and see "skim milk" . Wonder how to milk a skim? Or is it milk with the cream skimmed from it and properly known as "skimmed milk"?

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                    • #11
                      I think tdmidget has it right. That sounds like the same steel they use for the angle to make bed frames. I despise the stuff, personally. It's does the job it's intended, but isn't much good for machining. Although it looks like nice stock to fabricate things from it doesn't weld very well either.
                      Unfortunately there are quite a few things out there that are inviting to the HSM because they are plentiful, free or inexpensive, but don't work out so well. Cast iron weights from exercise equipment look like they might make a good faceplate or chuck backplate and cast iron window sash weights also look like a good source of cast iron bar. Neither are really much good, usually.

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                      • #12
                        Hot rolled steel machines like a dream, if it gives you fits then you are not much of a machinist.

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                        • #13
                          He needs to get a bigger lathe.

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                          • #14
                            Originally posted by gwilson
                            He needs to get a bigger lathe.
                            No he needs the right tool for the job, a milling machine.

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                            • #15
                              Originally posted by firbikrhd1
                              I think tdmidget has it right. That sounds like the same steel they use for the angle to make bed frames. I despise the stuff, personally. It's does the job it's intended, but isn't much good for machining. Although it looks like nice stock to fabricate things from it doesn't weld very well either.
                              Unfortunately there are quite a few things out there that are inviting to the HSM because they are plentiful, free or inexpensive, but don't work out so well. Cast iron weights from exercise equipment look like they might make a good faceplate or chuck backplate and cast iron window sash weights also look like a good source of cast iron bar. Neither are really much good, usually.
                              actually, A36 is nothing like bed frame angle. A36 is the most common grade of hot rolled steel used in the construction of large buildings (and lots of other stuff). it has a yield strength of 36ksi (36,000psi) and a tensile strength of 58ksi(+) it is the grade that you will find for most angles, channels, flats and plates. A36 is extremely weldable and drillable, though as mentioned, the most favored way of working it is by punching and shearing, or flame/plasma cutting. it has very loose rolling tolerances so you are likely to find it not always completely dimensionally accurate and often out of square. in its intended industry, dimensional accuracy doesn't really go below sixteenths of an inch.

                              i don't know what bed frame angle is specifically, but it is near impossible to drill, and after welding, it can usually be broken near the weld by striking it with a hammer. it's very hard and brittle.

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