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small vertical mill speed range recomendation

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  • small vertical mill speed range recomendation

    I have a Tom senior vertical mill with a MT2 spindle, with a four speed belt pulley, driven by a single phase 220volts, 3/4 hp, 1725 rpm motor which gives a speed range of 480- 6133 rpm range at the spindle. I would like to drop the minimum speed down to about 100 rpm, so that I can machine some steel without burning the cutting edge of my end mills.
    Here is what I found out so far.

    -single phase can't be controlled using a electronic speed control. I tried and the centrifugal switch didn't like it and the motor did not sound right.
    -The slowest single phase 220 volts with a 56 frame electrical motor I could find was 900rpm and that would bring the speed range to 253- 3200 rpm not slow enough, I think to machine ferrous stuff. Price was $225
    - Found this gear reducer which is a direct fit to my motor, just need to make an adapter plate to fit the mill and make a 5/8" shaft to mount the 4 speed pulley. It would now give me a range of 98- 1250rpm. https://www.emotorsdirect.ca/item/ku...&tab=specs-tab
    and the price is reasonable at $160.

    Does the gear reducer sounds like a good idea. Would this speed range be adequate for my MT2 spindle to machine ferrous and non ferrous material.
    Any help or guidance would be appreciated
    Thanks!
    Phil


  • #2
    I have recently refurbished one of these TS mills using a VFD and a 6 pole three phase motor. The motor I used is 1hp, but because I converted the spindle to R8 and yours is MT2, I would recommend 1/2hp. The 6 pole motor allows a speed between 174 and 2900 rpm with the frequency of the VFD between 25 and 75 hz. That is using the available belt pulley combinations. The motor is safe to 100hz, but I am not that brave. The total cost of the new motor and a Schneider Altivar VFD was £250, but the smaller setup would be less.
    You can check out the website www.model-engineer.com.uk for lots of info on the Tom Senior mills.
    Having a relatively small spindle size, it would be better to retain the higher speeds compatible with smaller size cutters.
    Last edited by old mart; 08-25-2020, 12:37 PM.

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    • #3
      My Millrite has a low speed of 350rpm and I use it (the mill, not the low speed) 95% of the time on steel, even 4340, S-7 and others. I use endmills up to 1 1/4", drills to1" and taps to 1/2-13 without issue. But... being 3-phase I do have instant reverse for the tapping and I use mist coolant for milling and drilling.
      Last edited by chipmaker4130; 09-14-2020, 09:05 PM.
      Southwest Utah

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      • #4
        that speed reducer would probably work, but for that amount of work and money I'd look into a 3 phase motor and VFD which will give you much more useable speeds between those steps. 480-6100rpm is a HUGE range - what are the other 2 speeds?

        Other options - see if you can change the motor pulley to something smaller, that will shift all your speeds down, but hopefully not screw up the belt tensioning. You could also look into an intermediate pulley. My Walker Turner drill press has one and it helps fill in the ratio gaps quite nicely.

        Then again, all my machines have treadmill motors on them so I typically leave them in one belt and use the dial to vary speed, unless I'm working real slow (50-150rpm) or real fast (2000rpm+).

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        • #5
          480 rpm should be good for HSS cutters up to 3/4". I can't imagine you're using much larger on an MT2 mill. Carbide cutters these day can be had pretty cheap as well and will last longer in steel. You may also fine that with the rigidity of your machine you can run a smaller EM faster and actually remove material faster than with a larger cutter running slower.

          That being said, with on 4 speeds in that range a 3ph motor and VFD would be my first choice as well over the gearbox.

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          • #6
            That speed range of 480-6133 rpm with a Tom Senior light vertical seems wrong to me, the limited space for the pulleys in the one I worked on at the museum gave a 2.0:1 top gear ratio, which with 1725 rpm motor gives 3450 rpm.

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            • #7
              Thanks you all for taking the time to reply.

              Unfortunately I don't have three phase power at my residence.Variable speed at the tip of my fingers would be nice.

              I used a website pulley speed calculator to calculate my low and high speeds. The motor is 1725RPM, the two 4 step pulleys are identical the small end measures 1.125" and the large end is 4". I have a dial meter for rpm, I will stick it on the spindle tonight and see what I get.

              On the low speed of 480rpm, I am able to machine steel but I find the machine struggles, the chip are tan color which is good but sometimes blue (spindle is too fast or dull cutter). I don't have mist or flood coolant setup, I have an IV bag drip system and "don't laugh" a manual spray bottle or a brush. I find the Bridgeport at work cutting steel so much smoother at speeds of 80, 135 and 210. I understand that the BP is much more rigid and can take heavier cuts. But the Tom senior Major weight about 600lbs, so not bad. My gibs are snug and the spindle has no play, the cutter are new, so I thought the spindle speed was my issue. Chipmaker is doing good, so maybe I should be looking at a different type of cutter style for this lighter machine. I buy my hss cutter from accurite. I have tried a banggood 4 inserts carbide mill design for steel, and I could only take small cut of maybe a .002" it would struggle and not be smooth finish. But the same cutter on aluminum was fine and left a nice finish.

              Note: I am a self thought homeshop tinkerer not a machinist, just looking for a solution to be able to cut steel reasonably well.

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              • #8
                you don't need 3ph power to use a 3ph motor, that's what a VFD (variable frequency device) does. For motors less than 1 1/2hp you can even get VFDs that convert 110V single phase to 220V 3 phase, so no need for a 220V outlet for your mill if you stick witha smaller motor.

                Although you can get where you want to get with extra pulleys and the like, variable speed really is a boon. For a motor sized for that mill (3/4-1hp) a 3ph motor + VFD will run you ~US$200. You can also get nice 3/4hp DC Consew motors that have an included speed control and run off 110V, several people on here have used them successfully. Or be a tight wad like me and drag an unwanted treadmill home and build your own for $40-50.

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                • #9
                  Get yourself some solid carbide cutters, then run them flat out dry on steel. Also get a 1/2", or 12mm twin insert indexable cutter that takes APMT or APHT inserts. The latest Chinese offerings are very good. An er25 by MT2 collet which goes up to 16mm, 5/8" with only the size collets neded for the cutters you intend to use.
                  Anything over 1/2hp is asking for trouble with MT2, its as flexible as a wet noodle.

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                  • #10
                    Do you use 'roughing' endmills (sometimes called 'corncob')? These greatly reduce the cutting force and allow even a small machine to take good size cuts. They leave a textured surface that is often fine for many jobs, and if not it takes only a light skim pass with a conventional tool to smooth it all out.
                    Southwest Utah

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                    • #11
                      This machine has a 7 1/2 hp spindle motor, no mechanical speed reduction just the VFD. Running the spindle slow enough for a 1" diameter hss twist drill will stall it. The spindle drive is virtually silent when running, the cooling fan inside the spindle enclosure is quite loud however.
                      Last edited by Bented; 08-25-2020, 10:03 PM.

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                      • #12
                        I had a Tom Senior Mill , speed range was 60-1660
                        It wouldnt handle 6133 RPM
                        Beaver County Alberta Canada

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                        • #13
                          Used my rpm dial indicator and stuck it on the end of the rotating shaft and got the following speed 800, 1350, 2100 and 3680 RPM. Interesting , using the WEB pulley speed calculator, I got 435,1028,1999 and 4021 which I believe is closer to the actual speed. I will look into purchasing some solid carbide and the roughing corncob cutter and give it a go. I think I was expecting to much out of this MT2 spindle and reducing the spindle speed won't really help. Thanks all for your help and advice,it save me money and time I would of wasted installing the gear reducer.

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                          • #14
                            Originally posted by fixerup View Post
                            Used my rpm dial indicator and stuck it on the end of the rotating shaft and got the following speed 800, 1350, 2100 and 3680 RPM. Interesting , using the WEB pulley speed calculator, I got 435,1028,1999 and 4021 which I believe is closer to the actual speed. I will look into purchasing some solid carbide and the roughing corncob cutter and give it a go. I think I was expecting to much out of this MT2 spindle and reducing the spindle speed won't really help. Thanks all for your help and advice,it save me money and time I would of wasted installing the gear reducer.
                            Seniors do have a Hi and Lo range.
                            Beaver County Alberta Canada

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                            • #15
                              I bought one of these cheap optical rev counters on ebay a couple of years ago, the only recomendation I can think about it is to take the battery out if it is not going to be used for a while. Ebay no. 353062688315

                              Last edited by old mart; 08-26-2020, 02:46 PM.

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