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Increase the spindle speed of a old Sidney Lathe

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  • Increase the spindle speed of a old Sidney Lathe

    Hello everyone
    I want to up the spindle speed of my 1941 Sidney lathe. its a big monster 14 swing x 32 centres with what I beleive to be a 5hp 3phase motor. Pics of the lathe can be seen on this site by shearching for 1941 Sidney Lathe. This old girl tops out at 860 RPM, and want to get the speed up to 1200-1500 RPM.
    I would like to hear from anyone that has done the same on a simular machine of this size. What was your method of doing this? I was thinking of making up a new sheave/ pully for the motor its self, as the top has a clutch and don,t want to mess with that end of it. Or,,what say you,,on how you would do this? This Lathe should no doubt handle the increase in RPM, and the chucks should allso easly take a top speed of 1500rpm , so Machine and chucks should be fine as far as I can see.

    The lathe will run up to 860 now and Im not trying to go any more than 1500- tops so, if there is any thing im over looking here,, by all means,lets hear it.
    If you guys know of a better way to do this, or different way, Im all ears


  • #2
    By far the easiest way is to use a VFD to drive that motor at up to 2x its nameplate rpm. This can cause problems in some motors . Keep in mind that the spindle bearings will need close attention, particularly if they're babbit.

    1200 rpm should be a piece of cake... that's 50% overspeed. The other neat part of the VFD is of course the "dial a speed" knob; my 5 Hp YMZ will just crawl along at 5% of rated rpm, handy for killing corners w/ a file w/o stopping and switching gears. I hooked up the original jog button to generate a similar slow speed crawl...
    Bart Smaalders


    • #3
      As you already have 3 phase you can probably pick up 3Ph to 3Ph VFDs quite cheap as they are of little use to the hobby market.
      Depending on your motor's capability this could get you part or all of the way prior to modifying transmission components.
      Check your bearings, chucks & backplates will take the increased speed & loads before spinning it up!


      • #4
        I've got a 16"(18-1/2") CY Monarch, about the same vintage as your Sidney, that I increased the top end to 1100 RPM from 487 by changing the motor pulley. Monarch offered this machine with a top end up to 1000 RPM. I've had the lathe for close to 20 years, and I've only used the top end once. I usually stay under 700 RPM.
        I've also got 12"(14-1/2") CK Monarch that I doubled the top end to 1400, and have only used the top end once, and I usually stay under 800 RPM. Monarch offered this lathe with a top end up to 1200.
        I also increased the HP for both lathes, from 5 to 7-1/2 on the CY, and from 3 to 5 for the CK.
        Exercise caution in your speed selection for the top end. Running at the upper speeds has tendency for oil foaming.
        You should also consider what a speed change will do to the other speeds. I'm very tempted to drop the top end on the CK to 1200, as I would more usuable mid range speeds.
        Also, consider your chuck sizes.
        Last edited by beckley23; 01-18-2009, 04:24 PM.


        • #5
          Replace motor with one that turns 3450 Speed doubles.
          Every Mans Work Is A Portrait of Him Self


          • #6
            increase the spindle speed of a old Sidney Lathe

            Thanks or the input guys

            I think now is a good time for me to do the research on VFD ,I no nothing about them other than a bit I read on a google site tonight. I see now that changing the driven sheave will increase the top end, but will mess with the lower speed as well. I want to have it all, the low end, but I like the top end to hit 1200 to 1500 rpm. The one reply had mentioned the he changed out the motor pully but had uped the HP from 5 hp to 7 hp,,,now this raises a new question, Is RPM dependant on HP? To spin it up to say 1500 rpm,,do I need more HP to get atleast the same amount of torque. And with the factory 5hp motor that the lathe has, with a VFD installed, will there be a noticable loss in torque at the top end?



            • #7
              If the bearings get hot, slow down NOW\

              Pressure lubrication can sometimes help.

              One option is to make an adapter as detailed in recent HSM mag.


              • #8
                What type of bearings were used in these machines? That may be your limiting factor.


                • #9
                  RPM isn't dependant on HP, but torque is. I want the ability to move a lot metal fast, in other words large DOC, heavy feeds, and high speeds. The only limiting factor is dodging those big, hot chips.
                  IIRC, the headstock input RPM on my 12" CK is higher than the top speed, which means that the top speed has a bit more torque than the motor is supplying, and that torque keeps increasing as the speeds are lowered.
                  Personnally, I don't think you are going to have any issues with the 5 HP motor.


                  • #10
                    With higher speeds rigidity may become a big factor due to chatter beign a high speed problem.


                    • #11
                      Three choices as all mentioned above... Change shivs/pulleys easy to do but screws up the lower speeds. Go to a VFD in one of 2 ways, 1) just over speed your existing motor, not my favorite fix. 2) put a 3600 rpm motor on it and use the VFD to slow it down, this is my favorite. Now for cost, the shiv is the cheapest. The VFD is not high cost for a 3 ph x 3 ph drive. My approach to this would be to buy a VFD for the application. I would probably buy at least a 7.5 hp drive, this is why... if you run the existing motor at double speed there will be more Hp available. If the existing motor fails at the increased speed (which is very possible / likely) then just replace it with a 3600 rpm motor probably 7.5 Hp and reprogram the VFD and go. I say a 7.5 hp motor because running the motor slower will reduce the hp available.

                      So in summary.. I would recommend going to a 7.5 Hp VFD on your existing motor and setting the max frequency as is appropriate. This may last a lifetime for HSM use, but a motor failure is possible. If that happens replace the motor with a 3600 rpm motor and slow down the VFD. The end result is that you get the speeds you want and the money spent is recyclable into future changes.


                      Happily working on my second million Gave up on the first


                      • #12
                        I don't think with this lathe you will have any problem with rigidness, and I doubt he will be using the higher speeds for large work, however I'm sure carbide inserts may be one of the reasons, along with work with smaller diameter stock for the lust of higher speeds. I think looking into a VFD would be a great way to do this, and you would also get the benefit of dialing in the speed, once you get used to a VFD it spoils you fast.

                        If you go the VFD route, and it seems your interested in this type, if it were me I would look at getting a bigger pulley for the motor, I'm not sure of the setup on this lathe for transfer of power from motor to spindle, but instead of over speeding the motor you would be better off going with a bigger motor pulley to give your added speed by not over speeding so much. Just don't go to big, you want to keep plenty of power for the slower speeds, it may also be easy to change the pulley out, and if it's just a seldom needed thing for the fast, or slow speed you could keep a nice power band so to speak through out the entire range by having two pulleys.

                        My Clausing 4900 is set up with a VFD, and the motor has a step pulley on it, I rarely change the speed by the pulley, it saves me loads of time, and aggravation having a VFD.


                        • #13
                          Unless you have a money tree, I'd spend $50 for a 50% bigger moter pulley and forget the $500 vfd and $500 motor. Don't mean to be a buzz-kill, but you can swap pulleys in an hour. Figure two days to replace motor and install and program vfd.


                          • #14

                            He may not need a motor, just a VFD, and if he is frugal about it, he may come out around $150 or so. Just the benefit of VFD speed adjustment alone in my opinion is enough to pay for that, and while he is wanting to add speed to his lathe I think this will just be icing on the cake. However I do agree with the need for a larger pulley, it would save a lot of other problems, and may keep him from damaging the motor as well. Then again over speeding the motor may not hurt anything, I don't have enough experience over speeding motors to give any advice here, but from reading most motors of this type are built the same as far as bearing etc for 1750 RPM or 3600 RPM, not sure if it will damage the electrical components of the motor.

                            A pulley change to increase the speed before you dump any more money into it would however give you a hands on example that will let you see if this is what you want to do, how the lathe, cutting tools, etc react to the increase of speed etc.


                            • #15
                              "its a big monster 14 swing x 32 centres..."

                              Thats funny, must be the smallest Sidney ever made, and its a monster!!
                              James Kilroy