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  • Pulley mass

    I am ending another thread where I was asking about extending and possibly
    enlarging the shaft of a treadmill motor to power a mill.

    I had a big head slap moment and realized that because the treadmill motor will
    be var speed, that I really don't need the huge 6 step pulley. I mean, if it just
    fit right on, I would use it but, altering a bunch of stuff to use it .. isn't necessarily.

    The new motor is 2HP and is stamped at 8200 rpm. No matter what I decide
    on for the motor pulley, the spindle pulley is still a huge 6 step.

    You may be a able to see my question coming .. but .. is that pulley capable, or
    is it a bad idea, etc etc of that speed .. the spindle itself has Timken bearings.

    Of course I will stepping it down somewhat, but may still end up getting 4000
    to the spindle.

    Mike
    John Titor, when are you.

  • #2
    Remember that the pulley system does more than just control speed; speed and torque go hand in hand, or would it be hand in glove since it is an inverse relationship? And since the title is pulley mass, are you concerned or desirous of a flywheel effect? I can't imagine what you would want to mill at 8000 rpm, so I'd pick my top desired speed, the slowest step on the spindle pulley, and determine the required single step for the motor.

    Hope that wasn't too rambling to follow.
    Kevin

    More tools than sense.

    Comment


    • #3
      Also remember that these motors are not rated for continuous duty so you may need a fan to keep it cool.

      I would rather have a three phase motor with a vfd. Depending on your DC drive, some have pretty rough low speed operation.

      Comment


      • #4
        Ok .. sorry .. my question must have been confusing.

        I'm just saying that the motor I am going to use is a pretty high speed motor .. and I was
        wondering if a pretty large pulley minds going that fast .. thats all.

        And now I am a little confused because I always thought that when you use very small
        endmills and such .. that the faster the better. Why do they make 10,000 rpm mills if
        the extra speed is useless ?

        and if you reply .. that .. well they have special bearings and are direct drive .. etc ..
        well .. there ya go .. thats exactly what the heck I am trying to find out ..
        a REASON .. I can't run my setup at high speed.

        Hey .. I'm just learning here and the answer may be obvious .. but not to me.

        Also the motor is a treadmill motor .. not sure how you can get anymore continuous
        use than that. Unless I'm on the one on the treadmill, I can only go for about 5 mins .. grin
        Last edited by Mike Amick; 11-12-2013, 08:25 PM.
        John Titor, when are you.

        Comment


        • #5
          I've been using a treadmill motor on my 8x18 for years now. I've often had it running for 1/2 hour at a time, and perhaps an hour or so over a 3 hr period. It doesn't get much past warm. I use the original 3 step pulley on the spindle and the mating pulley, which is stepped down about 1.5 to 1 from the motor. I don't use the back gears anymore. For speed control it's basically a variac with a bridge rectifier and capacitor.

          I seldom even change the belt to different ratios. For 99% of what I do, I just turn it on and dial the variac for the rpm I want. To be fair, I have also made up a rather large pulley which can mount directly to the spindle pulley, and that gets driven by a geared motor which originally ran a mobility scooter. That's my setup for when I want very slow speeds and/or higher torque.

          Varying pulley ratios would not give me the range of speeds I'd be happy with, and to be honest I haven't tried running it from an electronic speed control- maybe that would show up a loss of torque at slower speeds, I don't know.

          As far as a 'pretty large pulley' going at 8000 rpm- I'd think you have a mismatch in your setup if that's what's going to happen. First of all, what are you going to do with the belt on the large step- it's going to go to a smaller step on another pulley, so you'd be getting a step-up in rpm. You won't be running any normal spindle at those speeds, so setting up your ratios like that would be an error. If you are running a high speed spindle with your setup, then mechanically the parts ( like the 'large' pulley at 8000 rpm) aren't going to be the problem.

          For the most part you need to define the range of input rpm that you can provide in whatever way, and the range of output rpms you want. If your existing pulleys can't give you the range, then you need to rethink the pulley system.
          Last edited by darryl; 11-12-2013, 10:26 PM.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

          Comment


          • #6
            Common pulleys used on lathes and mills would almost surely vibrate like crazy and possibly fly apart if run at 8000 RPM. High speed can be very useful for small work or cutters but the spindle would need to have bearings, pulleys, and balance suitable for those speeds.
            Don Young

            Comment


            • #7
              But the motor pulley would run at the motor's speed, which may not be constant, but it will be a lot less than 8000 RPM. It is the spindle pulley that would run at the higher speed. And it would necessarily be of a smaller diameter so the centrifugal force would be less. Now if the spindle pulley also had some large diameter steps, then you should worry.

              For a point of reference, my Unimat has a three step, aluminum spindle pulley and the largest step is around 3.5" OD. It is machined, but no extra steps were taken to balance it. It is mounted with an axial nut, not a set screw so that does avoid one possible source of vibration. It runs up to 10,000 RPM with no discernible vibration and although it is about 50 years old, it has not flown apart yet. Now, a 6" or 8" pulley may be a different story.

              10,000 RPM is not all that scary.



              Originally posted by Don Young View Post
              Common pulleys used on lathes and mills would almost surely vibrate like crazy and possibly fly apart if run at 8000 RPM. High speed can be very useful for small work or cutters but the spindle would need to have bearings, pulleys, and balance suitable for those speeds.
              Last edited by Paul Alciatore; 11-12-2013, 10:59 PM.
              Paul A.
              SE Texas

              Make it fit.
              You can't win and there is a penalty for trying!

              Comment


              • #8
                Re-reading the first post- the spindle pulley is a large six step, and has timken bearings. What is the machine? It's unlikely that you'd want to run that spindle past about 3000 rpm, so your motor pulley would be about 1/3 or so the diameter of the smallest step on the spindle pulley. Does that make sense mechanically? I mean, maybe the motor pulley would be way too small in this case, and an intermediate stage of reduction would then make sense.

                At the same time, it's unlikely that you'd want to run the motor at full rpm. Chances are it will deliver plenty of power at around 5000 rpm, which is a more reasonable speed to deal with. I never run mine at full voltage, and at any rate the full rated rpm is at full rated voltage and no load. The no load part won't be seen anyway as there will be losses in the belt and pulleys, even before any cutting action draws power.

                You will want to ensure that enough power is available to the cutting application, so do plan on being able to power the motor with enough voltage so it is capable of turning at 5000 rpm or so. If you can only get it up to say 2 or 3000 rpm, then you may be limiting the work it can do for you.

                As I see it, you have a few variables to consider- what is the fastest you can safely turn your spindle, what is the fastest you wish to be able to run the motor, what is the smallest pulley that will work properly with the type of belt in use, and what range of speeds do you wish to provide through the pulley system. To begin with, choose 5000 rpm for the motor and the smallest pulley size. Then work out what spindle speeds you'll get with the existing 6 step pulley using only the small drive pulley size.

                I think you'll find that you are in the ballpark for the higher spindle speeds, but that you won't be able to get slow enough speeds without also reducing the motor rpm. Then consider that the slower you run the motor, the less ultimate power you'll be able to deliver to the spindle. If you do need power (torque is the better word here) at slower speeds, then you will have to add an intermediate pulley and belt stage. That's what I've done with my setup, and my intermediate step down is about 1.5 to 1. I think it's quite realistic to plan to have that intermediate step in the system. Then you also add electronic motor speed control and you end up with a nice system.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                Comment


                • #9
                  Ok .. here is the mill its going on. As you can see, not much choice in the spindle pulley, its
                  designed around the pulley sleeve. And I laid the OEM motor pulley there beside it.

                  As previously stated, the motor is a big ol 2HP Baldor, tagged 8200 RPM. I do not have
                  an rpm target. I do know that I can get this thing down to about 100 rpm with the big
                  flywheel on it and I can't stop it. OOoogoles of torque or whatever we want to call it.

                  So .. if I step it down to where it is running the spindle at 5000, it should have lots of
                  power even a creeping speed. I just wanted to hear from you guys that pulleys this
                  big don't mind going that fast.

                  Using a KB speed control for var speed.

                  John Titor, when are you.

                  Comment


                  • #10
                    The KB SCR drives kind suck at lower speeds. KB PWM drives are good. Your hand is not a good judge of torque. I can't stop a RC car motor by hand but I wouldn't put it on a mill.

                    What is the difference between a 3000 rpm spindle and a 10000 rpm spindle? Lots. Lubrication and preload to name a couple. A typical R8 spindle can do about 4500 - 5000 RPM without any problem. Go past that and you might be asking for problems.

                    Comment


                    • #11
                      I know this isn't helpful, but MAN! That mill really shouts "LOOK AT ME!" And I keep doing just that

                      Comment


                      • #12
                        Great looking paint job on that mill. I suspect you would be happy with just a 1 1/2 or 2 inch pulley on the new motor lined up with the largest pulley on the cone. The resulting speed reduction and torque increase would give lots of cutting power for most uses. The lowest speed stuff you may do, like wanting to run a 4 inch diameter fly cutter at 50 rpm is the only time I can think of where you may wish you had more mechanical reduction because the motor may not let you take as deep a cut as that Millrite might otherwise be capable of.

                        Comment


                        • #13
                          Re-motoring and selecting puleys ratios etc. starts and ends with getting the desired spindle speeds right.

                          It doesn't take a rocket scientist to look at the photo (nice paint by the way) and see if the belt was shifted to the top speed-up step and the motor run at 8000 RPM the spindle would exceed 20,000 RPM. Is that what you want?

                          You can't bolt a high speed motor on a machine tool and just hope for the best. If you don't and just throw things together, odds are you will wind up with a lame combination of speeds, some you can use, some may overlap excessively, and some that may be plain unusable. You have to work out the desired range of spindle speeds and from that the ratios of the step pulley and/or gearing step by step back to the motor.

                          Do the math first. None of this "pretty fast" or "close enough" or "maybe a 1 1/2" pulley here." You need actual numbers you can have sonfidence in. Objective data.

                          It's all ratio and proportion like you learned in high school. Get it right and you finish with a range of spindle speeds with a little overlap and each well defined and suited for the work you wish to perform. This does not happen by accident. Expect to spend a couple of hours with the calculator and the step pulleys patiently working the problem until you get a speed chart based on the 8000 RPM treadmill motor's performance and the spindle speeds you desire.

                          The relationship of HP to motor RPM has been alluded to but not clarified. Electric PM and induction motors may be called constant torque sources. Slow your 8000 RPM 2 HP motor to half speed (4000 RPM) and you get 1 HP. Slow it to 1/4 (2000) RPM and you get 1/2" HP. Will that do your job?

                          I predict your best bet would be to leave the existing motor in place to run un-powered as a counter-shaft. The treadmill motor would mount outboard and drive the existing motor pulley's largest step with a 1:3 belted reduction. Lame looking maybe but very effective.

                          If it was me and your existing motor was three phase I'd park the treadmill motor on the shelf for another project and get a VFD. No calculations, no sweating pulley ratios, no kludgy motor brackets hanging off the machine, just a nice tidy box mounted handy to the operator position running the existing motor up and down, smoothly and efficiently.
                          Last edited by Forrest Addy; 11-13-2013, 05:14 PM.

                          Comment


                          • #14
                            What Forrest said! +1

                            Comment


                            • #15
                              Originally posted by Forrest Addy View Post
                              You can't bolt a high speed motor on a machine tool and just hope for the best. You have to work out the desired range of spindle speeds and from that the ratios of the step pulley and/or gearing step by step back to the motor. If you don't and just throw things together, odds are you will wind up with a lame combination of speeds, some you can use, some may overlap excessively, and some that may be plain unusable.

                              Do the math first. None of this "pretty fast" or close enough" or maybe a 1 1/2" pulley here." You need actual numbers you can have sonfidence in. Objective data.
                              Forest .. I would love to have you in my corner, looking over my shoulder .. grin

                              Let me try and straighten this out a bit ..

                              Here are my misconceptions and concerns ... gathered from pure observations
                              and post reading.

                              High speed can be useful. When using very small "tools" EM's etc the faster
                              the better. I have a motor that can give me all the speed I'll need but I don't
                              have a clue as to the limitations of the bearings and pulleys.

                              THATS WHAT MY QUESTION IS. cough cough .. sorry shouting bothers my throat
                              And ... I was smiling while shouting .. no offense intended .. grin

                              Yes .. lower speed with power will be my main objective, but with a couple of
                              these six step pulleys that's not that hard. Using 2 of these 6 step pulleys and
                              a good PWM controller, I can have the best of both worlds. I should be able to
                              go from 50 rpm to 10,000 rpm.

                              Do I have very specific RPM's in mind ? no Not sure if that is really that
                              important. What is important is the limitations of the equipment .. that will
                              dictate the target RPM's.

                              Macona helped a lot by saying that 5 or 6 thou rpm is about the comfortable
                              limit for an R8 type arbor .. so if others agree on that ... that will be my upper
                              target.

                              As far as the lower target ... as slow and as powerful as I can get.

                              As you said .. it ain't rocket science.

                              Mike

                              ps .. thanks for the compliments on the paint job. I am just completing a complete
                              tear down all documented with a zillion pics. Creating a web page to act as a
                              pictorial instruction for dummies like me.

                              Real machinists are surrounded by drab grey's and green's .. Not in my world !
                              Last edited by Mike Amick; 11-13-2013, 05:30 PM.
                              John Titor, when are you.

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