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  • Advise to newbies from a newbie

    Hi guys,

    Had an interesting thing happen a while ago (Sunday afternoon). I was attempting to turn some stainless to make some new axles for a sheave on a friend’s sailboat.

    These axles are 3/8” in diameter and about ¾” long with a turn down on each end about ¼” in diameter and ¼” long.

    I found some 3/8” X 3” stainless steel hex bolts at Tractor Supply for cheap and bought 2, one for each axle. I cut off the head and the threads on the bandsaw (they cut real easy) leaving about a 1-3/4” blank. The bolts were made by the Hamilton Group. Just for grins I looked up the Hamilton Group website to find out what kind of stainless I was dealing with. No luck.

    So I chucked up one of the blanks on the lathe to turn down one of the ends. RPM was 460, feed was .0018 and doc was about .005. The tool was one of those premium harbor freight carbide ¼” tools. The finish was horrible!! It looked like it was cut with a hammer and cold chisel. I decided to speed it up a little so I tried 2000 rpm. Same feed and doc. I was feeding towards the headstock. The tool melted the stock and pushed it up into a ridge like it was plastic. While exciting, (things happen real fast at 2000 rpm) the finish was still horrible.

    I decided that I had better try and find out what kind of stainless I was dealing with so that I could determine a proper feed and speed. Internet research leads me to believe that the bolts are 18-8 (304 or more likely 316).

    I called customer service at the Hillman Group this morning (Monday), Brenda there said that the bolts were 18-8 304. Then I looked in Machinery’s Handbook for feeds and speeds. For 304 they recommended 75 sfm, .012 ipr and a .125 doc when using HSS.

    Went out to the shop this morning, ground a new HSS bit and tried at the recommended settings except only used a light doc, about .005. The finish was better but still rough. I backed off the feed to .0018 ipr and turned a much better (acceptable) finish.

    The point of this diatribe is: If you are a newbie like I am, a turning or milling project with materials or tools that are new to you will usually turn out better (and time will be saved) if a little research is done prior to energizing the machine .








  • #2
    I think the main moral of the story is rather that the Harbor freight tools suck. Or a more sophisticated lesson is learning about using the proper carbide insert.

    Comment


    • #3
      A little knowledge needed

      Looks like you're in the same boat that all of us have been in and your haveing to learn a little bit about bailing...

      Did you put a slight radius on the end of your tool bit? If you leave a sharp point at the tip you will get a rough finish, where if you radius the tip it will generally give a better finish.

      How far out of the chuck was the piece sticking? the farther from the chuck the more flex you are apt to get and the finish quality goes down.

      And you might try putting just a drop of oil on the workpiece (10w40 works at my house and I just happen to have some in my oil can...) may also help with finish.

      There are better ways, to do things, but when you are doing it for the first time you get to learn a lot, and to learn wht will work to get the job done.

      Generally - if it is not working well, a little less speed will give better results that a lot more... But then I think you already paid for that lesson. Keep it up, you get the hang of it.

      Comment


      • #4
        It has been discussed several times in other threads but there are better ceramic inserts that fit those tool holders.
        Byron Boucher
        Burnet, TX

        Comment


        • #5
          Beanbag,

          As a general rule, I would agree that Harbor Freight tools suck, however I have gotten some pretty good results with these in aluminum and fair results in mild steel. I am sure you are correct that there are inserts that are more appropriate for turning SS. The top speed on my lathe is 2000 RPM. When turning small diameters like this I just don't think my lathe is fast enough for carbide.

          Kfq2d

          I ground the tip of my HSS tool to a point as I wanted a flat shoulder at the transition. The part was sticking out only a little more than 3/8". I did not notice much flex. I agree that some cutting fluid would probably help. I have another axle to go, so I will try some 10W40 and see if it helps.

          If anyone has another suggestion as to cutting fluid to use for 304 stainless, I am all ears.

          I am very satisfied with the finish as it is. I only turned the smaller diameters, the 3/8" diameter is as it came from the manufacturer.


          Thanks,

          Tim

          Comment


          • #6
            Originally posted by tmc_31
            Beanbag,

            As a general rule, I would agree that Harbor Freight tools suck, however I have gotten some pretty good results with these in aluminum and fair results in mild steel. I am sure you are correct that there are inserts that are more appropriate for turning SS. The top speed on my lathe is 2000 RPM. When turning small diameters like this I just don't think my lathe is fast enough for carbide.
            You don't need high surface speeds for carbide to work. What you need for SS is an insert that has a sharp edge and some positive rake. It works fine at "slow" speeds also.

            Comment


            • #7
              Agree with the other suggestions, also 10w40 is not a cutting oil, it is an automotive lubricant. Go to the local hardware and get some dark cutting oil, or lard oil, or use crisco or bacon fat from the kitchen if you have nothing else.
              James

              Comment


              • #8
                also 10w40 is not a cutting oil, it is an automotive lubricant.
                Not a lubricant at all!
                WD stands for "Water Displacement" + "We gave up after 40 tries".
                I think what they mean is if you pour it into water, it will be displaced. But even that is wrong, as it is lighter than water. That's why they gave up and decided to sell it


                Nick

                Comment


                • #9
                  Some Confusion Here?

                  WD-40 is as Nick described. However, 10W40 is an automotive multi-viscosity motor oil.

                  Get the cutting oil. Used judiciously, a little goes a long way.
                  Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                  ~Practitioner of the Electromechanical Arts~

                  Comment


                  • #10
                    However, 10W40 is an automotive multi-viscosity motor oil.
                    I already cleaned my glasses.


                    Nick

                    Comment


                    • #11
                      I have some sulfur based Rigid Dark cutting oil which I will apply with an acid brush. I have used it before with good results.

                      Thanks guys,

                      Tim

                      Comment


                      • #12
                        Since nobody else has said it, I'd like to point out that your feed and depth of cut was rather anemic. Stainless work hardens if the tool is allowed to rub so you need to be more aggressive with feeds and depth of cut. Most carbide inserts aren't as sharp as HSS so they tend to rub more and also prefer deeper cuts. Also, Stainless needs to be run pretty slowly compared to mild steel and certainly Aluminum. A 3/8" bolt running at 2000 rpm was cooking along at 196.5sfm (SFM = .262 x diameter x RPM). For HSS tools, I tell my students to use 40 SFM, which is a very conservative number, but it keeps them from burning up their tools. Your 196.5 would probably be ok for carbide if you were using an insert meant for stainless although you should check with the insert manufacturer for recommended speed/feed/d.o.c.
                        Stuart de Haro

                        Comment


                        • #13
                          Originally posted by tmc_31
                          I just don't think my lathe is fast enough for carbide.
                          Not picking on the OP, but I am starting to think that this might be one of the biggest old wives' tales out there.

                          I have a 7x lathe, which is pretty sorry in most respects except that it can go pretty fast and has a nice variable-speed drive which makes experimenting easy. Power feed is either "on" or "off" so not flexible there. Anyway, I kept reading old guys saying that you can't use carbide on lathe this small, that HSS is much better, etc.

                          Anyway, I started experimenting about a year ago with insert tools and have never looked back. Here's what I found:

                          1. The 5-piece triangular tool holders stink. Don't buy them. The cheap (~$30 each) diamond tool holders seem pretty decent, though. I spent $100 for a 3/8" set from A.R. Warner and have no regrets.

                          2. Use the right kind of insert for your material. A lot of places will sell you single inserts, so it's possible to get a half-dozen and have a couple of each major flavor.

                          3. The right feeds/speed is the one which works best, not what the book or some yahoo on the internet (e.g. me) says is best. I found that I got good results on a 1.5" piece of O-6 tool steel all the way up to 1500RPM which is a lot faster than most guys will run a 7x lathe even in aluminum. I've had good results on stuff under .500" at 1000-1500RPM so I think you should be fine with a top speed of 2000.

                          Since I switched to CCGX inserts for aluminum, I rarely reach for HSS anymore. The CCGX inserts give me as good a finish as the HSS did, and for those who wonder if I was doing it right, I finished all my HSS tools on the same #4000 Japanese water stone I use to touch up my Shun Kaji chef's knife. I do sometimes feel like I get better results with HSS in cast iron, and so I do have some HSS inserts that fit my SCLC tool as well as a few HSS blanks in case. And I still use HSS for threading since it works fine for me there.

                          I don't have anything against HSS and it is definitely cheaper. However, I get far better results with carbide, particularly in harder steels, and I love the convenience.

                          I haven't really tried carbide endmills out yet on my benchtop mini-mill, mostly because I'm happy with the results I've gotten with HSS so far. But I'm starting to think that a lot of the talk about small machines not being able to use carbide well is mostly guys on the web repeating the same stuff they heard other internet experts say.

                          What is true for sure is that I am not able to get anywhere near the *maximum* performance of carbide tooling on my little toy machines. So what? In most cases, I'm not operating anywhere near the maximum potential of HSS, either, that doesn't mean I'd get better results with carbon-steel tooling from the early 1900s.

                          FWIW, I think Bob Warfield had much the same experience and I think he's taken as scientific an approach to this problem as anyone out there. YMMV.

                          Comment


                          • #14
                            You need a dead sharp insert. Your problem looks like the result of using an insert with a honed edge, weather it be a cheap low quality one or not. Instead of cutting your just pushing.


                            JL................

                            Comment


                            • #15
                              Ceramic vs Carbide

                              I can't remember who said it first. "If you like carbide you are going to love Ceramic." Take a good look at this:
                              This is the 3/8" version of the import holder. With the Ceramic insert it is a good and usefull tool.

                              There is nothing wrong with HSS if it is sharpened correctly. It does need the angle to be right and to be honed to a sharp edge but that is easy to do on a small tool.
                              Byron Boucher
                              Burnet, TX

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