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Thread: Reducing Shaft Diameter Without a Lathe

  1. #1
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    Reducing Shaft Diameter Without a Lathe

    Starting to work out a plan to make the old bench grinder into a belt sander. First hurdle - the motor shaft size. Currently it is 0.98" diameter (with no keyway), and all the belt grinder pulleys have 7/8" a bore. I want to bring the shaft down to 7/8" so any pulley will work rather than try to concentrically drill out a hub - that just won't happen.


    Since the motor will obviously spin the shaft, the question I have is what to use to grind the shaft down.

    • A flat file on a rest
    • Square edged grinding stone of some sort on a rest
    • Angle grinder/flap disk and a steady hand
    • Any other ideas

    The pulleys all have set screws so a flat on the finished shaft should secure it well enough.

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    Re: Reducing Shaft Diameter Without a Lathe

    Mill?

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    Re: Reducing Shaft Diameter Without a Lathe

    Use flat coarse file with a light touch and a pair of dial calipers to measure progress. Use a sharpie marker to mark the high spots that need to be filed down. Not rocket science, just be patient and measure every so often as you remove metal. Unless you go for a long period of time without stopping or measuring I don't know how you could screw it up.

    When you get close to the measurement you need you could bust out some sanding paper and "shoe shine" it to the final dimension.

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    Re: Reducing Shaft Diameter Without a Lathe

    I believe you will not get a truly round shaft using your suggestions. I think drilling out a pulley hub would be the best method. The drill hole should be 1/64" small than 1" drill, as drills tend to drill over size. Then you could use an adjustable reamer to get to the .998" bore size.
    Last edited by milomilo; 12-07-2021 at 11:57 PM.
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    Re: Reducing Shaft Diameter Without a Lathe

    Angle grinder to about 1/32 TIR then a file on a rest. If you can file up like a chainsaw gauge then you can tame the high spots by slowly lowering the rest.

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    Re: Reducing Shaft Diameter Without a Lathe

    Quote Originally Posted by Mac's Crew View Post
    Mill?
    A mill would be my choice,, run the mill, run the motor, an end mill in the mill would result in an accurate shaft diameter.

    Heck, I would bet that a drill press could do it,, also,,

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    Re: Reducing Shaft Diameter Without a Lathe

    I was envisioning the motor running "as is" while reducing the shaft?

    If you take it apart, then have somebody else turn it to size.
    Last edited by tapwelder; 12-08-2021 at 02:14 AM.

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    Re: Reducing Shaft Diameter Without a Lathe

    Problems you will have. Going to be about impossible to keep concentric. Keyway will be an issue as depth will not be deep enough. Boring and rebroaching the keway on the pulleys is a much better and easier option. Much cheaper to possibly ruin a pulley than most definitely ruin a motor shaft.

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    Re: Reducing Shaft Diameter Without a Lathe

    I would take motor shaft out and turn on lathe or bore the pulley

    Dave

    Quote Originally Posted by Shootr View Post
    Starting to work out a plan to make the old bench grinder into a belt sander. First hurdle - the motor shaft size. Currently it is 0.98" diameter (with no keyway), and all the belt grinder pulleys have 7/8" a bore. I want to bring the shaft down to 7/8" so any pulley will work rather than try to concentrically drill out a hub - that just won't happen.


    Since the motor will obviously spin the shaft, the question I have is what to use to grind the shaft down.

    • A flat file on a rest
    • Square edged grinding stone of some sort on a rest
    • Angle grinder/flap disk and a steady hand
    • Any other ideas

    The pulleys all have set screws so a flat on the finished shaft should secure it well enough.

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    Re: Reducing Shaft Diameter Without a Lathe

    If you would have said the shaft is 0.984" ,, I would conclude that the shaft is actually 25mm ,

    Is there any chance that there is a metric 25mm bore pulley that would fit your needs??

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    Re: Reducing Shaft Diameter Without a Lathe

    Thanks for all the input, I appreciate it. To clarify a couple things brought up:

    I definitely don't want to disassemble the motor. This thing is decades old and runs great - I'm not going to mess with a good thing lol.

    All the pulleys I'm considering already have a keyway in the bore. I know my chinese drill press doesn't have the tolerance to keep a bit from wandering off center towards the keyway.

    I don't see a lack of keyway on the shaft a big deal. A flat on it should be plenty to resist slippage with the pulley set screw driven against it.

    Taking it to a machine shop isn't economical. I can buy a whole new motor for what someone would charge to do the work.

    Andre and Tapwelder are where I want to go. I believe with the shaft spinning at 3600rpm +/-, shaving .05" off of it should be in the capabilities of a flat file, emory cloth, etc.

    Other plusses for changing the shaft vs pulley:
    * Any 7/8" pulley will be able to be used, in case pulley diameter needs to be adjusted/changed.
    * Having a shoulder on the shaft would be nice for the pulley to push up against.
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    Re: Reducing Shaft Diameter Without a Lathe

    https://www.ebay.com/itm/113925034958

    Hmmmmmmmmm,, it seems that 25mm is a VERY common size belt grinder pulley,, on eBay,,

    https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313&_nkw= 25mm++Contact+Wheel+Belt+Grinder&_sacat=0

    Some drive pulleys are available at 25mm for less than $20, delivered,,

    https://www.ebay.com/itm/16339492471...UAAOSwIJVgrONS

    That might be the best option,,

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    Re: Reducing Shaft Diameter Without a Lathe

    Be safe. No loose fitting gloves or clothing. A partner would be nice to monitor kill switch

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    Re: Reducing Shaft Diameter Without a Lathe

    Quote Originally Posted by tapwelder View Post
    Be safe. No loose fitting gloves or clothing. A partner would be nice to monitor kill switch
    I showed my wife a video of guys in India making brass items, using casting, lathes, and buffing,,

    The men were ALL wearing long sleeve, VERY loose fitting clothes around the rotating equipment,

    Well, her career had been an Industrial Engineer, and for over a decade, she managed a 150 man machine shop.
    When she saw the video, her first comment was about the long sleeves, and loose fitting clothes,,

    She then went nuts when she saw them pouring molten brass,, while wearing sandals,,,

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    Re: Reducing Shaft Diameter Without a Lathe

    I don't trust the chinese to provide accurate measurements. Every single ad always says something like "please allow 1-2mm in measurements". Plenty of American made pulleys I'll be using, and they aren't contact wheels, true belt pulleys.

    I'm pretty careful about the shop, especially since cutting the tip of a finger off years back when.
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  25. #16
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    Re: Reducing Shaft Diameter Without a Lathe

    If you feel the best bet is to reduce the shaft diameter......................

    Get ahold of a single cut lathe file, and gently run it away from you, against the shaft, as it's spinning. The shaft should be spinning towards you. Don't let the file sit still, keep stroking it like you would if the shaft weren't spinning.

    https://www.ebay.com/itm/11318073687...kAAOSw519bYwz5

    https://www.mcmaster.com/lathe-files/

    I'd suggest buying a cheeeeeep mic, but you may not want to. A mic will be handy to measure progress, and to insure that you don't taper the shaft too much.

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    Re: Reducing Shaft Diameter Without a Lathe

    So how much will it set you back when trying to file the shaft round fails?

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    Re: Reducing Shaft Diameter Without a Lathe

    I just snagged the first video I came across. It's ok.



    No way that motor will grab you, unless you get clothing wrapped around the shaft, or your fingers underneath the file. It's a far safer bit of work than it would be on a regular lathe.

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    Re: Reducing Shaft Diameter Without a Lathe

    Quote Originally Posted by lars66 View Post
    So how much will it set you back when trying to file the shaft round fails?
    Good point.

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    Re: Reducing Shaft Diameter Without a Lathe

    Such a simple job for a lathe owner.
    Remove motor bolts, ease off the end caps. Pull the armature toward the pulley end. Be careful to not scuff.

    Place the armature on a lathe, between centers.

    Use lathe operator skills to fix shaft diameter.



    In answer: all your efforts to avoid a machinist are futile. The job only gets bigger, or results get unusable.

    I once ruined a motor taking advice from a know it all, using a file.

    I regularly struggle removing a pulley, or replacing a motor where it almost fits. I've used plumber's cloth, or crocus cloth while running the motor.I'm changing diameter by .001 or.002". Attempting to reduce shaft size would work, but you'll get a tapered, off centered, or tweaked shaft. 1725 RPM it'll be unusable. 3450, don't even try, it'll cause an earthquake.
    Last edited by Willie B; 12-08-2021 at 06:21 PM.
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  31. #21
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    Re: Reducing Shaft Diameter Without a Lathe

    Yeah, I think you guys are probably right. You'd just mess up the shaft with anything other than a lathe.

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    Re: Reducing Shaft Diameter Without a Lathe

    Think about what that file will do when it hits the keyway? It's going to take that area, basically a flat spot, and dig in even more.

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    Re: Reducing Shaft Diameter Without a Lathe

    I think he said that the keyways are all in the pulleys, none on the shaft. That brings up another question in my mind... are those pulleys milled slightly off center to center them as the key way is tightened?
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    Re: Reducing Shaft Diameter Without a Lathe

    MJD I don't think there is a keyway in the shaft. But hey, everybody needs a lathe now shootr has an excuse to get one.
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    Re: Reducing Shaft Diameter Without a Lathe

    If that motor shaft has a key way then it will be impossible to keep it round with your method, 3600 RPM will smoke a file really quick if you're not careful, although at that diameter the surface speed won't be horrible. I wouldn't worry about disassembling the motor, they're pretty simple. Take it apart & take it to a machine shop where they can put the shaft on centers & drive it with a lathe dog, you will be much happier in the end. What MJD said about the file & the keyway IS spot on.
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