Re: [CAD_CAM_EDM_DRO] Re: hi-freq motors[perske etc]

machines@... wrote:

> >--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> >
> > What???!!!!! You are going to take a standard, 3450 RPM motor and
> > run it at 12000 RPM? Are you familiar with the construction of
> >blast
> > shields? Have you calculated the first critical speed of that
> >rotor?
> > I have a strong suspicion it is probably in the range of 7500-10000
> > RPM. Are you aware of what happens when rotating machinery
> > is operated near the critical speed? Where are you located?
> > (Hopefully not near me!) Is the motor shop going to try it for you?
> > Just replacing the bearings isn't going to hold this motor together!
> >
> Jon,
> The answer in a nutshell is YES.
> The motor rewinders have done this many times but without changing
> the end bearings. I aim to do this to handle the side loads.
> Over here in the UK we have a big woodworking concern called Wadkins.
> For years they made routers with fixed head motors i.e. the motor
> housing was part of the frame. They used to take standard Brooks
> motors and use the rotor and stator.
> The rotor had a collet chuck built in and the stator was rewound for
> them.
> By modern standards these were huge rotors but other than usual motor
> misuse problems they ran for years.
> I have rebuild loads of them.
> I must state here that I do a *lot* of mechanical work on motor
> repairs, probably to the extent of 35 to 40K per year.
> Another thing to bear in mind Jon, is that the UK / European motors
> being made now are far smaller than your American series. I had to
> mod a 2Hp motor to fit an American framed machine a while ago. I got
> the mounting specs off Baldor and the nearest motor I could get off
> the shelf was a 3Hp model. Our 2Hp was tiny compared to the Baldor.
> The rotor on this 1/2hp motor is way way less in size and mass than
> the 2Hp Bosch router I have and is far more sturdy that the skimpy
> wound armature that is in the Bosch spinning at 20,000
>
> John S.

Yikes! This is pretty scary. There are still some other things to look
at. The thickness of the laminations is determined by the eddy losses,
and that needs to be made thinner for higher frequencies. You did note
this was a fairly small motor, so it is a little less likely to go boom.
The motor shop may have selected a motor that had a more robust
design than some others. Unless they have made it to run at much lower
flux levels (lower torque, too) than the original motor, I can't see how
they can get away with such a large frequency increase without smoking
the stator. I just worry that something bad is going to happen someday,
and somebody is going to get hurt. Even a piece of the integral fan
flying off could be lethal.

Jon