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  1. #1
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    Default Need advice making a small part

    Hi all,

    Planning to go camping for 10 days in January. I mentioned this at a family get together and now it looks like most of the fam are keen to come too!
    I have had a small project sitting and waiting to be made and now seems a good time since it may come in handy for the up coming trip. Some years ago I purchased one of those dreadful GMC 2 stroke 750W generators. As a generator it is less than useless, it hunts and surges and is never stable enough to trust it to even the cheapest of electrical items.

    Anyway, to cut a long story short, I have decided (for ####s and giggles) to rip out the generator guts and replace with an car alternator so I can use it as a rough & ready battery charger. After some butchering and hacking using brute force and ignorance I now have a bare bones 2 stroke motor with a tapered output shaft. I need to make a coupling to couple the alternator to the tapered shaft. The alternator has a parallel 15mm shaft. The question is:

    After turning the taper on the lathe, how do I then bore out the 15mm hole at the other end without loosing concentricity? The small end of the taper is less than 15mm so I cannot do it from the same end. Once I remove the shaft from the chuck I loose concentric. I know I can put it in the 4 jaw but the part is only going to be about 50mm long, I can't imagine my 4 jaw is so good that it will hold the part extremely parallel to the bed and so if I dial the other end in, it will only be dialled in at that point.

    I want the alternator to be a direct drive set up so as to keep it compact, hence no belts etc. There are several M10 threaded holes around the output shaft on the motor, I plan on making an adapter plate to mount the alternator body to the motor. Do I have to accept that the adapter sleeve won't be perfect and use a spider coupler?

    Was hoping this would be a quick and easy project (I'm in the middle of another bigger project and needed a rest!), maybe even a bit of a cake walk but it's starting to challenge me!

    Any ideas?

    Cheers,

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  2. #2
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    I may have answered my own question.

    If I started with a piece of parallel stock and used an er collet to hold it, would this produce sufficient & repeatable results if removed and turned around?

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  3. #3
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    Probably be ok.

    Have you considered making a tapered mandrel and then just boring the other end of your tapered bush.

  4. #4
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    Default

    I think I'd be using a coupling.

    Another problem that you have, even if you do make a fully concentric adapter, is how to mount the motor and alternator so that the concentricity and linear alignment of their 2 shafts is as good as that of the adaptor.

  5. #5
    Metmachmad is offline Turning useful pieces of steel into scrap metal.
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    Yes a flexible coupling is the way to go here. You need to have a little flexibility as they correct any small amount of mis-alignment. Check some of the couplings available at the site below. You can bore each half to suit whatever shaft sizes or tapers that need to be married. - HRC-Couplings - F W Hercus Pty. Ltd - Hercus Gear Cutting - Adelaide
    Turning useful pieces of steel into scrap metal.

  6. #6
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    Perhaps make up a sleeve, conical to suit the shaft and an OD to suit the coupling.

    Michael

  7. #7
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    Default

    Thanks guys.

    Hi PC, at the risk of sounding dumb, what is and how does a tapered mandrel work?

    WRT the flexible coupling, I was hoping to firstly mount the alternator on the shaft and then drill the mounting holes. Also was thinking of some rubber between the alternator and the mounting bracket. Maybe a bit dodgy but I don't want to turn this thing into an engineering feat. Want it to work though….

    I'll have a look at those couplings.

    Cheers & thanks all,

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  8. #8
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    What I would call a typical standard tapered mandrel has a very shallow taper over its working length and come in a vast array of diameters.

    Abratool has shown previously tapered mandrels that he has made.

    In this case with your adaptor my reference to a tapered mandrel was not one as previously described but a tapered mandrel (shaft) with the same taper as your motor output shaft.

    After you cut the internal tapered bore, mount another suitable piece of material and turn a taper on the OD then mount your tapered adaptor on this and finish your parallel bore,depending on the angle of taper you may need to use a grub screw or similar to hold it to the mandrel if the taper is not self locking.

    I call anything that I need to mount jobs to in a lathe chuck or similar for 2nd operations a mandrel.

  9. #9
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    Just a small note about car alternators. They have a relatively narrow speed range where they make there rated power, and a direct drive may not match it. On a car they are typically geared up around 1.8:1 to 2:1 by the belt drive and reach rated power with the engine running around the 2K mark, so alternator at around 3.5-4K. Once there get revved far beyond that range, the inductance of the windings and the high operating frequency limit the output current to their rated output.

    On the other hand, you 750W generator motor would have been struggling to make 1HP output at about 3000RPM for 50Hz output, so is probably too slow, and possibly way underpowered to spin a car alternator. I figure that you will get something, but 14V 15A would probably be the limit. Remember also that the alternator will need an external sourced current of up to 5A to energise the armature to generate that so your total output could be fairly low.

    Don't know about the GMC unit but a lot of the toy gensets had a 12V charger winding built in that was rated for 5-10A. You might not have a significant improvement on that.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  10. #10
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    Quote Originally Posted by malb View Post
    Just a small note about car alternators. They have a relatively narrow speed range where they make there rated power, and a direct drive may not match it. On a car they are typically geared up around 1.8:1 to 2:1 by the belt drive and reach rated power with the engine running around the 2K mark, so alternator at around 3.5-4K. Once there get revved far beyond that range, the inductance of the windings and the high operating frequency limit the output current to their rated output.

    On the other hand, you 750W generator motor would have been struggling to make 1HP output at about 3000RPM for 50Hz output, so is probably too slow, and possibly way underpowered to spin a car alternator. I figure that you will get something, but 14V 15A would probably be the limit. Remember also that the alternator will need an external sourced current of up to 5A to energise the armature to generate that so your total output could be fairly low.

    Don't know about the GMC unit but a lot of the toy gensets had a 12V charger winding built in that was rated for 5-10A. You might not have a significant improvement on that.
    The one I have has a 12 volt battery charger built in , that's all I use it for , as an emergency battery charger. Anyway you don't need to rip it apart just buy a plug in 240 v battery charger and run it straight off the 240 socket .
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.

  11. #11
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    Hi there,

    Yes, I could use the generator to produce (very dirty) 240V and then plug in a charger to convert it back to 12 by using a battery charger, however this requires extra equipment and further expense. Further, a good battery charger may only give say 20A. An alternator (well, this one) is a 65A alternator so I have cut out the middle and still ahead. Also means running it for much less time. The 240V generator was never a very good or clean source so I would be really annoyed if I destroyed a $300 3 stage battery charger on a $100 generator!

    WRT the generator not being suitable, maybe, maybe not. After some thought, I figured it was worth a look. The 2 stroke motor is rated to 2 HP @ 3600 rpm so that seems in the range for an automotive generator. At 60 amps @ 12.5V it's about 750W which is what the generator was rated to. In any case, the battery would not accept 60A unless it was close to being completely drained which I don't plan on doing. 40A initial charge probably being more realistic. So, I can't see why it would not work in this regard.

    Sure, the generator had an 8A 12V socket but that would require me running it 5 hours + to put 40AH (ignoring efficiency losses) into a 100 AH battery. Why do that if I can run it for 1-2 hours?

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  12. #12
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    Quote Originally Posted by simonl View Post
    Sure, the generator had an 8A 12V socket but that would require me running it 5 hours + to put 40AH (ignoring efficiency losses) into a 100 AH battery. Why do that if I can run it for 1-2 hours?
    Coz it would make less noise. The engine will last longer. It might not use much more fuel.

    That aside, one other problem could be that you no longer have much of a flywheel which can make starting tricky.
    Also make sure you wire it up so you can turn the field off.

    I made a real butcher* one of these before I had the tools. Seemed to work pretty well even at low revs. If memory serves, 40 odd amps into an N200. Now maybe doing that uses the brushes up faster??


    Stuart



    *think hex bolt into the crankshaft, a short length of hex key into the hex in the end of the alt shaft......... didnt last very long, I assume the changing rpm of the motor during each rotation flogged the hex in short order lol

  13. #13
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    Quote Originally Posted by Stustoys View Post
    Coz it would make less noise. The engine will last longer. It might not use much more fuel.

    That aside, one other problem could be that you no longer have much of a flywheel which can make starting tricky.
    Also make sure you wire it up so you can turn the field off.

    I made a real butcher* one of these before I had the tools. Seemed to work pretty well even at low revs. If memory serves, 40 odd amps into an N200. Now maybe doing that uses the brushes up faster??


    Stuart



    *think hex bolt into the crankshaft, a short length of hex key into the hex in the end of the alt shaft......... didnt last very long, I assume the changing rpm of the motor during each rotation flogged the hex in short order lol
    Hi Stuart,

    I have since had the motor running with nothing on the shaft. It runs OK, better than I thought it would actually. The stator (is that it's name) is a little less mass than the generator stator thingy but should be OK.

    A hex key eh? Boy you are dodgy! That makes me laugh. You are so pedantic with other things and then you come out with that little gem!

    PS I would rather put up with a little more noise for hour or 2 than 2 stroke fumes for 5 hours!


    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  14. #14
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    I cannot say definitely without some checking but just thinking about the diameter of my cars harmonic balancer pulley and the pulley on the alternator I would imagine that the increase ratio would be more than 2:1. The diameter of alternator pulley's these days is much smaller than they used to be.

    Dean

  15. #15
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    I am thinking that Hercus may be expensive for that type of flexible coupling

    shop around at "power transmission" places..even blackwoods would have them or be able to get them

    Alternative is "flex type" but these are expensive

    there are thomas rex and plenty of others to choose from

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