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How fast can a lathe or mill be speeded up

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  • How fast can a lathe or mill be speeded up

    I am a retired engineer whose last hands on experience with metal machining was a metal shop course in '67. I have been following this forum for a couple of months now, and it has been a valuable source of information.

    I recently purchased a PM 45 mill and a 1236 lathe from Matt, based on the positive reviews he has here and elsewhere, and after paying him a visit (with a stop at grizzly on the way). I rented a 600 sf industrial space in Montreal where I am setting up my retirement hobby workshop.

    I have already installed the machines and started making chips. I have done a few mods, namely:
    X axis table feed
    3 axis DRO on the mill, (he did not have it in stock).
    Spindle DRO on the mill, the z axis DRO is useless imho.
    Z axis lift motor.

    I would like to add photos, but I have not figured it out yet.

    Today I will be receiving a couple of 2 HP motors and two Hitachi sj200 vfds and my question is, based on your experience what would be a safe maximum speed to run the machines. Would 120 hz, i.e double the actual speed be OK, or is there a risk of some thing flying apart.

  • #2
    For the mill I would look on CNC zone. Just look a different machines with the 45 number as they are all the same machine but called different names. From memory one guy runs his up to 4000 rpm on standard taper bearings.
    As for the lathe, mine is a 12 x 36 and goes up to 2000 rpm and I don't see a need to go any faster. One thing to think about is the maximum speed of the chucks, you may have to upgrade to a better quality one if you are going any faster.



    • #3
      I agree, unless you're working on incredibly small stuff, I wouldn't worry about spinning them much faster, rather you'll end up usually running in the 25 to 60 Hz range.

      Remember, you can always run a cutter slower than recomended, but you just about never want to run it faster.

      (I've had the 12x36 gear head for a couple years now and I don't think I've ever had it in top gear once.


      • #4
        in my world you can go as fast as you darn well please but you will have to make some other adjustmens for the speed up better chuck for 1, 2 better lube systems for thoes with gear head lathes,3make new gears for the carrage so it does not go to fast and slam into the head or worse your chuck,youll need to make some other changes as well iam sure..really who needs to go that fast any how,


        • #5
          2k is plenty of RPM on a manual unguarded machine, that is a heck of a lot of kinetic energy. Besides mechanical stress the other limiting factor is feedrate. If you plot out your chip load & RPM you'll see it does not have enough feedrate to utilize higher spindle speed. I have seen several CNC (non of ours thank goodness) lathes that have launched parts at high RPM and it is lethal, if you have personally seen the viewing port hole on a lathe busted you'll gain respect for it.
          Last edited by squirrel; 02-26-2011, 11:16 AM.


          • #6
            My Babbitt bearing lathe has 1,000 RPMs as its recommended max.


            • #7
              I would guess the biggest concern with speeding up too much would be whether the bearings can do it. Doubling the speed might not be an issue, especially if your high end is only around 1200 or so (that's what mine is on my 12x36), but you never know. Keep in mind that the faster your lathe is turning, the faster your carriage will move towards the headstock, so your reaction time will need to be quick. Unless you're doing lots of small work (1/2" and less) or plan on using lots of carbide (needs higher cutting speeds) you probably won't need more speed.

              With metals, speed isn't everything. Your RPM should be based on the diameter and material. The formula is RPM = (SFM x 4)/Diameter. On the mill, the diameter will always be the size of your cutter or the hole you're boring. On the lathe, the diameter is the size of the stock UNLESS you are drilling or boring a hole, then it's the size of the hole. The SFM (surface feet per minute) depends on the material you're cutting and what your cutting tool is made of. There are lots of speed and feed charts out there, but make sure you're looking at one for the correct cutter material. High Speed Steel won't last long at carbide speeds. For HSS, I use 90 for mild steel, 50 for tool steel and mystery steel, 150 for brass and aluminum, 40 for stainless, and 100 for bronze. These are conservative numbers, but they work well on slower machines and will keep your tools in good shape. That's probably a bit of a tangent to your original question, but I hope it helps anyway.
              Stuart de Haro


              • #8
                Unless you are going to be chewing up a lot of Aluminum for commercial purposes, why would you need to go that fast.
                The shortest distance between two points is a circle of infinite diameter.

                Bluewater Model Engineering Society at

                Southwestern Ontario. Canada


                • #9
                  maybe you mean how fast to run the motor. double the original speed is fine (have been doing that for years), maybe a little more for a short period of time.
                  Last edited by dian; 02-26-2011, 03:22 PM.


                  • #10
                    Since your an engineer and some other engineer designed your machines and set the speeds on them why would you think he didn't know what he was doing? Why would you think you could improve by running them faster?

                    I have been doing machine work for most of my life and I have never found it necessary to run a lathe or mill at it's maximum speed very often. I have wished for more speed on the older babbit or bronze bearing lathes but had enough sense not to do it after one experiment that turned out bad. In fact I locked up the headstock on a babbit bearing lathe once never to try that again.

                    When I worked for a living we almost always used brazed carbide and seldom ran it at max speeds, we just didn't need to and got good results at reasonable speeds. Sometimes you run fast and sometimes slow depending on what results you want.

                    Maximum speed/feed is best used on CNC with flood coolant to take full advantage of it, not on manual machines with air as a coolant.

                    Let me repeat, it is NOT NECESSARY to run the high speeds some charts recommend for carbide. Good results can be had at lower speeds and feeds by LEARNING HOW to use your cutters and not just plunging FULL SPEED AHEAD without knowledge and experience.

                    Now I use mostly brazed carbide and some indexable carbide holders at home. Sometimes I use HSS but mostly for formed shape cuts and threading. Sometimes I run fast and sometimes slow but experience has taught me when and where to do it.
                    Last edited by Carld; 02-26-2011, 03:01 PM.
                    It's only ink and paper


                    • #11
                      Thanks for your replies, I have mostly used the mill since I got the machines, and I definitely felt the need for higher speed e.g. when using 1/8" end mill. As for the lathe I tend to agree that 2000 rpm is plenty. My question was mainly to seek guidance in programming the VFD, setting maximum allowable Hz to remain safe. I know from research that the motor will be ok at 120 Hz and maybe more, but I would not be going any faster.

                      Carld: having worked with engineers for 40 years, and being one myself, I've learned that engineers like all humans make mistakes, sometimes colossal ones that lead to loss of limb or life, not to mention poor design which is all too common.

                      Btw how to post pictures, in my posting rules it says you may not post attachments.


                      • #12
                        Not trying to make you mad, just pointing out reality.

                        If you want to post a photo use Photo Bucket or some such site. copy and paste the img link to the post and it should come up in the post. In Photo Bucket it is the bottom link in the dropdown under the photo. When you click on it it is automatically saved and all you have to do is open the reply window and use ctrl/V to put the photo link in the post.

                        This site won't let you cut and paste directly from your computer. Photo Bucket also resizes the photo to the correct size for posting.
                        It's only ink and paper


                        • #13
                          I wonder why Monarch engineers decided to give the 10EE a maximum spindle speed of 4,000 rpm.



                          • #14
                            Originally posted by philbur
                            I wonder why Monarch engineers decided to give the 10EE a maximum spindle speed of 4,000 rpm.

                            To do those tiny parts that you need 10,000 RPM for.


                            • #15
                              Originally posted by philbur
                              I wonder why Monarch engineers decided to give the 10EE a maximum spindle speed of 4,000 rpm.

                              I don't mean to hijack this thread ,but long ago I was running a brand new monarch 10 ee at top speed,it was equipt with a jacobs rubber flex collet.DANGER the 2 peice interlocking retaining rings opened up from centrifical force and hit me hard.I was young and dumb and just put it back together and ran it slower.I dont remember if the collet system had a max rpm warning or not .I have just instaled a vfd on my 1340 lathe(see ''My vfd lathe conversion'' general) and am drilling 1/16 holes in aluminum ,I am at 2200 rpm spindle speed and could easily go to 6000 but the gears and or bearings are making pretty much noise so I wont go faster.
                              Last edited by Edwin Dirnbeck; 02-26-2011, 05:06 PM.