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Thread: Mounting blower to motor with different shaft sizes - is this safe / correct?

  1. #1

    Mounting blower to motor with different shaft sizes - is this safe / correct?

    I found a 5HP, 1ph, 3450rpm motor that I was considering building a dust collector with. It has a 5/8" shaft.

    I also found a 15.5" diameter backwards-inclined impeller. Based on what I've read, this would likely be approximately appropriate for a 5HP motor. However, it has a 1 5/8" bore.

    I'm considering building a blower housing (based on Bill Pentz's plans) and a "pull-through" cyclone (the impeller is "closed" - plates on top and bottom - so I understand it shouldn't be used to convey "dirty" air, so it will go on the "clean" side of the filter).

    My concern is: how do I safely/correctly mount the impeller (with 1 5/8" bore) onto the 5/8" motor shaft? It looks like a "D" series QD bushing would work, but would I need to drill/tap holes in the impeller for the bolts? Is there another way to make this connection? Is there any concern with a bushing this large causing the impeller to become unbalanced?
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  2. #2
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    I would see if they make a taper lock bushing with those sizes. A one piece bushing will have to make allowances for the keyway size changes. It has to be stepped on two sides so it remains geometrically correct or there has to be a angled step.
    Bill D.

  3. #3
    Thanks, Bill. I believe this split bushing would work? https://www.mcmaster.com/6086K197

  4. #4
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    The QD and taper lock bushings require the proper taper in the impeller. Fenner makes an adapter that will go on parallel shafts.
    Confidence: The feeling you experience before you fully understand the situation

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    Quote Originally Posted by Dan Friedrichs View Post
    Thanks, Bill. I believe this split bushing would work? https://www.mcmaster.com/6086K197
    Quote Originally Posted by Jerry Bruette View Post
    The QD and taper lock bushings require the proper taper in the impeller. Fenner makes an adapter that will go on parallel shafts.
    Hard to tell from the pic, but I believe Jerry is correct. The impeller doesn't look like a tapered bore to me (highly doubtful they would taper AND cut a keyway). If not tapered, you'll need the parallel adapter.

    Or if the impeller hub has sufficient mass, perhaps take it to machine shop and bore for suitable taper-lock..??
    Molann an obair an saor.

    If Heaven ain't alot like Texas, I don't wanna go. - Hank Jr.

  6. #6
    Thanks, Jerry and Malcolm. You're correct - it's not tapered.

    Those Fenner bushings are cool, but I can't seem to find one that will do 5/8 to 1 5/8...

  7. #7
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    Just looked at your pictures at home on the big screen and not my phone. I notice that the hub in the impeller is bolted in. Maybe you could unbolt it and have a new one made at a local machine shop with the 5/8 bore and keyway you need.

    I'd check the weight of the impeller too, might be a bit heavy for a 5/8 shaft. A little out of balance and it could wreak havoc with shaft strength and/or bearings.
    Confidence: The feeling you experience before you fully understand the situation

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    Quote Originally Posted by Jerry Bruette View Post
    Just looked at your pictures at home on the big screen and not my phone. I notice that the hub in the impeller is bolted in. Maybe you could unbolt it and have a new one made at a local machine shop with the 5/8 bore and keyway you need.
    Or a 5/8" hub may be readily available. The local electric motor/fan/pump emporium carries impellers sans hubs & you select the hub that fits your motor.

  9. #9
    Quote Originally Posted by Frank Pratt View Post
    Or a 5/8" hub may be readily available. The local electric motor/fan/pump emporium carries impellers sans hubs & you select the hub that fits your motor.

    A true five HP motor seldom has a 5/8" shaft, usually in the 1" - 1 1/8" range. Maybe as small as 7/8", or 22 MM. I double that motor actually produces five HP.

  10. #10
    Quote Originally Posted by Bruce Wrenn View Post
    A true five HP motor seldom has a 5/8" shaft, usually in the 1" - 1 1/8" range. Maybe as small as 7/8", or 22 MM. I double that motor actually produces five HP.
    Hmm... I agree that I was surprised by that. But it's a WEG motor, compressor duty: https://www.amazon.com/Weg-Electric-.../dp/B07BQDJZBT

    What do you think? Would you guys trust that to hold a 30lb impeller? Or should I find a 5HP motor with a bigger shaft?

  11. #11
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    I'd go bigger.
    Confidence: The feeling you experience before you fully understand the situation

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    Quote Originally Posted by Dan Friedrichs View Post
    Hmm... I agree that I was surprised by that. But it's a WEG motor, compressor duty: https://www.amazon.com/Weg-Electric-.../dp/B07BQDJZBT

    What do you think? Would you guys trust that to hold a 30lb impeller? Or should I find a 5HP motor with a bigger shaft?
    Since it’s not a c-face motor (unless I missed something in pics), you will have to imagineer some means of fixturing the motor to the blower housing. Could you use a belt drive with suitable sheave on motor, mount the impeller on a jack shaft, with a driven sheave on opposite end of jack shaft?? ...It would ‘extend’ the motor mount away from blower housing.

    Might get a bit complicated, but if the motor was a screaming deal... might be worth it. And less risk of overwhelming the 5/8” motor shaft with a 30 lb load at 3600 rpm.
    Last edited by Malcolm McLeod; 05-21-2020 at 9:48 PM.
    Molann an obair an saor.

    If Heaven ain't alot like Texas, I don't wanna go. - Hank Jr.

  13. #13
    Thanks, guys. The motor was, indeed, a screaming deal (as was the impeller), but sounds like a more optimal solution (for both) could be found. I'll keep looking...

  14. #14
    Key words "COMPRESSOR DUTY." Compressor duty has nothing to do with real HP ratings. Kind of like my 120 volt 6.5 HP shop vac. If it were truly 6.5 HP. it would require over 40 amps to run, but the plug fits into a 15 amp receptical.

  15. #15
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    Quote Originally Posted by Bruce Wrenn View Post
    Key words "COMPRESSOR DUTY." Compressor duty has nothing to do with real HP ratings. Kind of like my 120 volt 6.5 HP shop vac. If it were truly 6.5 HP. it would require over 40 amps to run, but the plug fits into a 15 amp receptical.
    No, that's not correct. Compressor duty has to do with it's duty cycle, not the power it produces. You are confusing this with how universal motors are rated, such as those in routers & vacuums. Look at the FLA and the HP ratings on the label & do the math. When motor efficiency is allowed for, it works out to 5 HP.

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