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Thread: Bridgeport Mill

  1. #26
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    Default Re: Bridgeport Mill

    Quote Originally Posted by John Morton View Post
    If it's three phase, use this: http://www.factorymation.com/s.nl/it....f?category=32

    John
    I've tried a few VFD drives similar to that, but never found one I could really use. Maybe technology has gotten better, but those that I've tried put out what seemed to be a square wave - motor startup was tricky to dial in, and when they did run the motors were noisy as hell, and sounded like they were being painfully tortured.

    I'm lucky to have 3 phase in my shop, but those I know without it all seem to prefer rotary converters over digital. There are ways to make your own fairly easily if you can find a 3 phase motor just above the horsepower you'll be driving, and use it as a generator. I'd love to find a good VFD drive that's compatible with all 3 phase motors, as most of my tools run on it and I would love to have the convenience of digital speed control on some. Of course the two I've tried were probably 15 or more years old, and maybe the technology is better now.

  2. #27
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    Default Re: Bridgeport Mill

    Quote Originally Posted by grandcanyonminstrel View Post
    The one I'm looking at is pretty simple and in good condition. No digital readout and it has the round ram head, not the dovetail ('think I got the nomenclature correct), 1/2 hp single phase, and the step pulleys for speed adjustment along with a LOT of tooling and accessories; pretty much plug 'n ' play once I set it up- even the finish is in nice condition. One thing I already figured out is that I know I'll want to pair it up with an old South Bend lathe right next to it to really have nice machinihg capabilities...
    ...

  3. #28

    Default Re: Bridgeport Mill

    VFD's have come a long way and the price has also come down, They are pretty much plug an play, just get one suited to you horsepower. If its a one horse motor you can get one that will do very nicely for around $200. I would recommend the rotary if you have more than one piece of equipment. Although you can run two different motors on the same vfd but it is a bit more tricky. The one thing to keep in mind as you lower frequency you also loose horsepower, So at half rpm you also loose around half the HP. Most people can work the speed control to their advantage. I have three of them and also a 5 hp rotary. The rotary runs a hardinge horizontal and and 3hp gear drill press. One vfd on a belt sander and one on a wood lathe. hope this helps. kevin

  4. #29

    Default Re: Bridgeport Mill

    anything you could ever want to know about both the vfd and the roatry can be found on
    http://www.practicalmachinist.com/vb...onverters-vfd/

  5. #30
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    Default Re: Bridgeport Mill

    VFD's have come a long way in 15 yrs. In fact the quality of their output is such that new CNC machines are offered that accept either single or three phase power. I guess the VFD is part of the electrical panel. There is good discussion on these matters on the forums at http://www.cnczone.com/forums/index.php? Look for the one entitled "Phase Converters and VFD".

    The current wisdom seems to be that phase conversion using a large 3 phase motor is optimal for a shop with several large 3 phase machines (which may be used simultaneously). Such a unit might run all the time for convenience in starting tools, so noise is a factor. Substantial 3 phase motors are efficient and can be amazingly cheap. You might spend quite a bit on wire with a central converter, 4 conductors to each machine.

    A VFD can only run one machine, but it's cheap, and quiet except for a slight high freq. chirp. Even the cheap ones let you program acceleration/deceleration, forward/reverse and continuously variable speed using a dial. I didn't know what machines I would have when I started out, and I wound up with 4 VFD's. The 3 hp lathe has a variable speed control; the 2 hp Bridgeport has instant reverse (great for tapping!) but I use the mechanical speed change because it needs occasional exercise; the 1.5 hp buffer has a variable speed control. Looking back I think I did the right thing - I'm out about $600 in VFD's and I didn't have to change my wiring.

    The VFD must be the only thing between the power source and the motor. Any switching, reversal, speed control etc. has to be done using 5 volt terminals in the VFD. If you want to use the original controls, you have to disconnect them from the power and connect them to the appropriate terminals.

    John

  6. #31
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    Default Re: Bridgeport Mill

    Man, those phase converters have gotten cheap?

    First one I saw was a homemade version using a large three phase "idler motor" being started up rotating by a single phase motor; the late Jim Rickard had it in his home shop in Connecticut. The second start up motor may not be necessary.

    Here's an article on how to do it: http://www.metalwebnews.com/howto/ph-conv/ph-conv.html

  7. #32
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    Default Re: Bridgeport Mill

    Quote Originally Posted by man dough nollij View Post
    ...
    Thanks Lee - I guess I should learn to read a bit more thoroughly.

    Rick, the machinist I bought my Rusnok head from used a similar idler motor, but rather than a start up motor or capacitor start, he just wraps a rope around the shaft and gives it a pull-start. Seems crude, and I'm not sure how balanced the voltages are, but he say's it's worked just fine on his tools for the past few decades.

  8. #33

    Default Re: Bridgeport Mill

    John you probably know more about this, but I did read several articles on running more than one motor on a vfd, Off hand I don't remember the procedure but if you look at the link I put up and search "more than one motor" you will see what I saw.

    I have gotten used to one motor one vfd, because its so much easier, you don't have to even program the vfd's anymore,unless you want to do more than start/stop and change speed on the controller. The handy thing about freak drives is that you can do remote control wiring very easily. thanks for the info.

  9. #34
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    Default Re: Bridgeport Mill

    In my shop the air compressor, dust collector, spray fan, table saw, milling machine, belt/disc sander, thickness sander, and two grinders all run off 3 phase, so converting would be quite a burden if I ever had to. The milling machine and spray fan are probably the only things I would like to have VFD's for, but honestly I'm probably fine just sticking with the belt speeds on my mill. When I tried one on my spray fan I got much more than a high frequency chirp. It was a nasty loud chirp, and aside from being loud, sounded like it couldn't be good for the motor. I don't recall what make it was, but as I said, it was an older model. As cheap as they seem to be these days though, I may be willing to give another try if they can deliver a smoother power.

    Do you know if any of these new VFD's will work fine with a standard 3 phase motor, and not require an inverter-specific motor to run smooth?

  10. #35
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    Default Re: Bridgeport Mill

    I don't want to convey the impression that I know a lot about this. I just got an education from the machine tool forums, enough to answer my specific questions. The one motor/one vfd admonition is something I read somewhere. As with many rules, you can probably circumvent this once you know exactly why there is a rule. Just offhand, it might be that the vfd can't handle the changing load characteristics as you change the number of motors that are running.

    David, I see no reason to convert the whole shop away from a 3 phase line, unless that power costs a lot more (which it does in some places). You could put vfd's on the mill and fan, if the control features make it worthwhile. The Teco units I have are available in 3ph in/3ph out versions for about the same price. I read the discussion about inverter-duty motors, and decided I could safely ignore the warnings about voltage spikes or whatever. I was reassured by what I read, and by a number of case histories for Bridgeport conversions. My vfd's have a parameter setting which gives you 6 choices of carrier frequency. I shopped through them all to find the one which was least offensive, and got used to that pretty quickly.

    saintjohnbarleycorn, the power curve is also discussed in the forums. I can't remember specifics, but I think that the torque/speed relationship is not as unfavorable as you describe. I have not noticed any loss of torque myself, nor have I seen mention of the problem in the Bridgeport conversion stories. I could be wrong, let us know if you learn otherwise.

    John

  11. #36
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    Default Re: Bridgeport Mill

    Thanks John - I would never consider moving away from 3 phase, but it would just be a concern if I ever moved my shop. Sounds like it may be worth giving the VFD's a try again for my spray fan, with new and hopefully better technology. I'll start looking around.

  12. #37
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    Default Re: Bridgeport Mill

    One thing that's amazing about high voltage 3 phase (I've got 480 volts and 220 or so in 3 phase) is how small the wires can be. Also the spindle motor on my CNC machine, a 5 hp automatic tool changing type, runs quieter than a Dremel. Of course it gets noisy when the vacuum pump and dust collector are going!

  13. #38
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    Default Re: Bridgeport Mill

    Well...it looks like I missed out on the Bridgeport due to delays from three different transport folks....Needless to say I'm a bit dissappointed by it, but the proces taught me so much about having a nice mill that I'm actively searching for another and expect to have one in the shop by years end.

    I've used a bunch of different three phase converters over the years. The old Rube Goldberg things where you had a couple of giant motors that you had to fire up and the jump back and hope the whole thing didn't explode in your face and burn the shop down were a reckless nightmare. The newer VFD boxes are pretty amazing and work great. You don't really need to modify much of the system and you get power conversion and instant variable speed for under $200 a machine. They have to be one of the greatest assest to the small shop builder in a long time. Suddenly all of that amazing old iron from the last century - names like Oliver and Yates and such are completely accessable to folks who couldn't use it or it required major modifications in the past.

    If you head over to OWWM.com- old woodworking machinery, there is a wealth of information on old machinery and conversion systems. On the surface, some of them can be VERY crusty old crumudgeons ('never happens around here!), but I've also learned a lot from them and met a lot of good people. They have their own variation on Loarfest- "Arnfest", which is very cool.

    j.
    www.condino.com

  14. #39

    Default Re: Bridgeport Mill

    Maybe I am not using the correct terminology, what happens is when you dial down the drive to slower rpm i have on my belt sander
    1. lets say at 30hz you can load the belt and stop it
    2. on my lathe I have worked at low rpm and set off the overlaod

    in my mind you loose the torque at slower rpms, I know there is a setting on the parameters that gives you full torque through all speeds and I think I did program that in. So I am probably misunderstanding the torque curve and I tend to think in simple terms, if it had the same HP at slower rpms I shouldn't be able to slow the belt down as if it was on a gear drive. In reality it doesn't do that but what the proper terminology is I don't know. In the end you learn to work with it and on the wood lathe It is a variable speed (mechanical) so I keep the rpms up most of the time. If I need very slow rpm and know I am not going to load it such as sanding, I will use the vfd. I hope this all makes sense.

  15. #40
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    Default Re: Bridgeport Mill

    As to the torque question, I have an Ulery lathe. I believe the man that made it is now deceased. He was in Washington state. And if I'm wrong, he may still be! This thing is a monster and can turn 26" diameter up to almost 48" long. Take the long bed off for bowl turning and the like (short bed) and it can go to about 36" diameter, 8" thick. Enough to kill you if something goes bad. It has step pulleys and a base made by me with 700 pounds of sand in it. It doesn't vibrate!

    In any case, I think I'm running on 115 V, perhaps 220, single phase (I'd have to check on the voltage). But here's the deal: it has a converter that moves it from AC to DC and the motor that actually runs the lathe is DC. And an electronic speed controller. When you go to DC it is my understanding and it seems to be from experience that you don't loose any torque by going to slower speeds. And there's a switch wherewith (aye, mate) that I can reverse the direction of rotation which is very handy in fine sanding wood turnings. I shall now say the word "mandolin" just to make sure I have mandolin related content in here.

  16. #41

    Default Re: Bridgeport Mill

    dc is a very good variable speed/ torque motor. Vfds try to be like them, but I don't believe that they have to torque/hp at the lower speeds like dc does.

  17. #42
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    Default Re: Bridgeport Mill

    Thinking it over, I have to say I have not made a practical test of my vfd's at low speed. My tools which require low speed torque all have gearboxes to help with that. There are constant torque vfd's available, but they are expensive. Machine tools that require power at low speed do generally have gearboxes, even those that use DC motors with speed control. The marvelous Monarch EE toolroom lathe uses a system as Dale describes: a motor-generator set that uses AC to generate DC, running to a DC motor. But that machine has gear reduction for low speed. In the machine shop, low speed means <100 rpm

    John

  18. #43
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    Default Re: Bridgeport Mill

    I think, but haven't measured, that I can run somewhere around 30 rpm and still have enough power to hurt myself. I do know this- I can't stall or stop it. I really should install some sort of guards around the power train.

  19. #44
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    Default Re: Bridgeport Mill

    Torque at low speed and start-up is exactly why railroad locomotives couple diesel engines to generators to DC electric motors to drive the wheels. It's also why the new breed of electric drag racing cars and motorcycles are blowing the doors off of gasoline powered cars.

  20. #45

    Default Re: Bridgeport Mill

    I used to work for Electro-Motive division of GM at a repair shop. We rebuilt generators, alternators & traction motors, etc., heavy duty doesn't even begin to describe the power these thing are capable of. Quite often I tore down traction motors that had a six inch steel shaft twisted off between a pinion gear and the frame of the motor. Incredible torque. Plus, I learned quite clearly never try to beat a train. Sorry to get so far off the subject, but even in a much smaller machine, there is still a lot of power.

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