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Confusion with finding correct rake angle on lathe bits

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  • #31
    You might consider 1/4" bits. stack two together if you want a bit of extra support/height. they'll be cheaper and oh so much faster to grind. keep in mind you'll use one hss bit for maybe a decade or more....there's a lot sharpenings in one
    in Toronto Ontario - where are you?

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    • #32
      If you go the HSS route, there are a few things to note / remember.

      First is that even though you can regrind a bit dozens of times to use it different ways, most people don't. It's just a lot of hassle to regrind a perfectly good threading tool into a parting tool and then into a roughing tool. You end up with a drawer or box of tools with specific grinds on each one, just as you do with carbide inserts. That's not a bad thing, it just means that you can't buy just one HSS blank and use it for everything.

      Second is that you have to resharpen or at least touch up the HSS edge each time you use it. That can change the edge height, so you need to check the cutting edge height each time that you refresh the edge.

      That brings up the subject of shims. Unless you have a QCTP, you need to adjust the height of the tool to bring the cutting edge up to center height by stacking shims under the tool. It's a good practice to store the shim stack with each tool to make it quicker to mount.
      At the end of the project, there is a profound difference between spare parts and left over parts.

      Location: SF East Bay.

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      • #33
        For most stuff , I use 1/4. And. 5/16 inch.. Some 3/8. And the odd 1/2 inch seldom gets used.
        The rex red cut I use is a cast finish, not ground..so it looks ancient and perhaps unuseable. The opposite though is true, quite tough.
        Keep in mind as a part or full box may show up on ebay, the seller thinking it is crap..

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        • #34
          personally I'd suggest just buying a SCLCR10 turning tool and a pack of CCGT inserts from ebay or Banggood. The inserts are sharper and better ground than anything you can do by hand, there's a 2nd tip for when you screw up the first one, no tip build up with alu and you can just get on with making chips rather than trying to figure out why your finish is crap. Remove the most variable variable. After you've gotten used to using the lathe and making chips, then start playing around with grinding HSS.

          I started out with HSS, spent ages learning how to grind it, hone it, get the right angles, muck around with toolpost angle for different cuts, used 2 different bits for turning and facing, cursed tip build up cutting aluminium, watched cast iron wipe the tip off my tool. Then I bought some SCLCx holders and CCGT inserts and now use HSS only for special jobs and parting. I think I'd busted 2 tips in a couple of years. Easy peasy to use, turn and face with the same tool, turn to a shoulder without angling the toolpost etc etc. I probably have as much in my tooling as Victor does in his bench grinder.

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          • #35
            First, there is no "correct" rake angle for steel and brass. The selection of a rake angle is made from a number of factors and you, as a beginner, are far from understanding them. I have been machining for many years and do not understand all of them, but I am still learning. I worried a lot about selecting tool bits when I started. Fortunately my first lathe came with some and I just started with those. My point is, don't get excessively worried about rake angle at this point. It is a thing that an experienced machinist will consider to solve a problem he is having or to maximize some factor, like tool life, surface finish, rate of production, or whatever.

            The main thing you need to consider when purchasing already ground tools is the angle at which your tool holder will hold them. Most modern tool holders, including the one pictured on the machine in your link, hold the tools in a horizontal position and most pre-ground tool will be correctly angled for that angle. The older, Armstrong style holders are designed to hold the tool at an upward angle to begin and tools for those holders will have smaller rake angles; in some cases, the rake angle on the tool will actually be negative while still providing a positive effective rake while cutting. I worried about this a lot when I was starting but found that most of that worry was not needed.

            OK, I looked at the Grizzly tool set you are considering and the tools in it probably have a rake angle somewhere between 5 and 10 degrees. They will be suitable for general work. Most other pre-ground tools will also be in this general range and they will work in your lathe.

            I know others have said otherwise, but I will give you some information on my early use of carbide tools. While learning to use my lathes I did purchase some braised carbide tools similar to the ones you are considering. My first carbide tool was broken on the second cut. My fault, not the tool's. The second one lasted a bit longer, but it also did not even finish one part. I know that others have boasted about their use of carbide tools in their lathes, but I feel that a beginner should start with HSS tool bits and become familiar with turning for some time. Now I do use carbide tools when the situation seems to call for them. But I still also use HSS a lot.

            Another thing about carbide tools is they are more difficult to sharpen. I like tools that are dead sharp. I have not seen a single braised carbide tool that I considered sharp enough out of the package. I like to touch them up by hand with a diamond stone. You can do this because you do not need to remove much carbide for a touch-up. But if you chip them and need to grind them back to get an edge, you will need a diamond wheel on your grinder and they are expensive.

            If you need to learn how to grind tools, I suspect you will get more experience if you are using carbide tools. But it is easier and less expensive to learn with HSS. Have fun.
            Paul A.
            SE Texas

            And if you look REAL close at an analog signal,
            You will find that it has discrete steps.

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            • #36
              Originally posted by Paul Alciatore View Post
              First, there is no "correct" rake angle for steel and brass. The selection of a rake angle is made from a number of factors and you, as a beginner, are far from understanding them. I have been machining for many years and do not understand all of them, but I am still learning. I worried a lot about selecting tool bits when I started. Fortunately my first lathe came with some and I just started with those. My point is, don't get excessively worried about rake angle at this point. It is a thing that an experienced machinist will consider to solve a problem he is having or to maximize some factor, like tool life, surface finish, rate of production, or whatever.

              The main thing you need to consider when purchasing already ground tools is the angle at which your tool holder will hold them. Most modern tool holders, including the one pictured on the machine in your link, hold the tools in a horizontal position and most pre-ground tool will be correctly angled for that angle. The older, Armstrong style holders are designed to hold the tool at an upward angle to begin and tools for those holders will have smaller rake angles; in some cases, the rake angle on the tool will actually be negative while still providing a positive effective rake while cutting. I worried about this a lot when I was starting but found that most of that worry was not needed.

              OK, I looked at the Grizzly tool set you are considering and the tools in it probably have a rake angle somewhere between 5 and 10 degrees. They will be suitable for general work. Most other pre-ground tools will also be in this general range and they will work in your lathe.

              I know others have said otherwise, but I will give you some information on my early use of carbide tools. While learning to use my lathes I did purchase some braised carbide tools similar to the ones you are considering. My first carbide tool was broken on the second cut. My fault, not the tool's. The second one lasted a bit longer, but it also did not even finish one part. I know that others have boasted about their use of carbide tools in their lathes, but I feel that a beginner should start with HSS tool bits and become familiar with turning for some time. Now I do use carbide tools when the situation seems to call for them. But I still also use HSS a lot.

              Another thing about carbide tools is they are more difficult to sharpen. I like tools that are dead sharp. I have not seen a single braised carbide tool that I considered sharp enough out of the package. I like to touch them up by hand with a diamond stone. You can do this because you do not need to remove much carbide for a touch-up. But if you chip them and need to grind them back to get an edge, you will need a diamond wheel on your grinder and they are expensive.

              If you need to learn how to grind tools, I suspect you will get more experience if you are using carbide tools. But it is easier and less expensive to learn with HSS. Have fun.
              Decent 8" diamond disks are like 8 dollars per piece from ebay so that is not reason to avoid brazed (hopefully not braised) carbide tools.
              But hobby quality carbide insert tooling is so cheap that brazed carbide is suited only for very specific cases like hand scrapers, just like many of us only use HSS only for oddball jobs.
              Location: Helsinki, Finland, Europe

              Comment


              • #37
                Get both. It's not that expensive, and they both have their place. You can try them both in an afternoon, and I bet you will get better results with the carbide. I'm talking about inserts, not brazed. Practice on some aluminium, it's more forgiving.

                I disagree with the "you must learn to grind first" philosophy. Learning to grind tools is a skill worth having, but you can make plenty of chips without that skill these days (not true in the past). Millions of people drill holes without knowing how to sharpen a drill bit, or even how a drill bit works. You can make neat stuff and learn lots without sharpening a single HSS blank. Just be aware what HSS is for, and be ready to learn when you need it. There is plenty of educational material on carbide tooling, so you can still learn how chips form, break, etc without grinding tools. Should you learn to grind tools? Yes! Does it have to come before you make your first thing? No.

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                • #38
                  MattiJ, are you saying you dont form cut, dont snapring groove, cut keyways, cut Acme butress ir Whitworth thread, various radii, etc? What happens then ?

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                  • #39
                    Originally posted by MattiJ View Post
                    Decent 8" diamond disks are like 8 dollars per piece from ebay so that is not reason to avoid brazed (hopefully not braised) carbide tools.
                    .
                    Brazed and braised are the same word at root, and both brazing and braising can be, and were done on a brazier. No need to make too fine a distinction between them.

                    And don't let the dictionaries tell you differently.
                    Last edited by cameron; 05-26-2017, 04:59 PM.

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                    • #40
                      Originally posted by pinstripe View Post
                      ...
                      Practice on some aluminium, it's more forgiving.
                      ...
                      I disagree with the "you must learn to grind first" philosophy. Learning to grind tools is a skill worth having, but you can make plenty of chips without that skill these days (not true in the past). Millions of people drill holes without knowing how to sharpen a drill bit, or even how a drill bit works.
                      ...
                      I agree with both these statements.

                      When I started out there were lots of "balls in the air" on lots of the topics surrounding how to make chips and parts. A lot of that went away when I purchased my first carbide insert tool.

                      Now that I am further along in the journey I have high confidence I could (if I wished) create a HSS tool in a flash. Like others here have said; just give it some front and side clearance and be aware there is a point (two faces really) that need to be clear of the work so they do not rub.

                      The tool height (I suggest just a tad initially) should be at or below the centre of the spinning round surface. Do a facing cut and watch the "pip" form as it gets close to the centre of the part is the best way to gain confidence you have the height right.

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                      • #41
                        Originally posted by victor View Post
                        Hi, I am new to this forum so sorry if I make any mistakes. So I am purchasing a lathe to learn on http://littlemachineshop.com/product...ory=1271799306. I was looking for bits for it and came across this pack https://www.grizzly.com/products/11-...ce=grizzly.com. I want to turn steel and brass, but it does not mention the rake angle. I am also getting this tooling package that includes bits but still does not mention rake angles http://littlemachineshop.com/product...5207&category=. Am I missing something?
                        That tooling package from littlemachineshop should provide you with most of what you will need, so I would skip the 11 piece set from Grizzly. The inserts from littlemachine shop have a 7 degree positive rake angle that works well in steel. If you find that the inserts are pulling into the work when turning brass, then try a HSS tool bit that has side and end clearance ground, but leave the top surface alone. This will give you a 0 degree rake angle, which is preferred when cutting soft brass, when the HSS is mounted in the quick change tool post holder.
                        Last edited by tom_d; 05-26-2017, 05:46 PM.

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                        • #42
                          Originally posted by 754 View Post
                          MattiJ, are you saying you dont form cut, dont snapring groove, cut keyways, cut Acme butress ir Whitworth thread, various radii, etc? What happens then ?
                          Grooves = carbide parting inserts grinded to correct width as HSS is pretty useless in making grooves to hardened rod. keyways =not many but used scrapped carbide endmill "blancks", buttress threads = HSS so far, withworth= carbide inserts, radii = usually carbide inserts. Never used brazed tools on (metal)lathe.
                          Oddballs like I said.

                          Then if I want to move some metal and not just waste my time its 100% carbide insert tooling. OK, I also use cermet and ceramic inserts
                          Location: Helsinki, Finland, Europe

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