On D.C. Motors;

[Pete Wass]

I have noticed a number of folks switching to D.C. Motors on their lathes on other forums. If they are "better", why don't manufacturers use them in the first place? What is the appeal to those converting? I don't belong to any of the forums so am asking here to see what you lads think.

Thanks,


Pete

 

[brickeyee]

Speed adjustment is easier.

AC induction motors require VFD to alter speed.
Motor speed is based on cycles per second of the AC waveform.

'Universal' (brush type) motors can often use voltage adjustment.
They are often higher RPM lower power type motors though.


Either Variac or (for some) Thyristor or other 'magnetic dimmers'.

 

[Pete Wass]

Soooooo,

Speed adjustment is easier.

AC induction motors require VFD to alter speed.
Motor speed is based on cycles per second of the AC waveform.

'Universal' (brush type) motors can often use voltage adjustment.
They are often higher RPM lower power type motors though.


Either Variac or (for some) Thyristor or other 'magnetic dimmers'.

Is one to infir that a higher hp motor would be needed to provide enough torque to be as useful as an ac motor ?

P

 

[GeneT]

A torque converter is often used to get torque at the low speeds. I believe the Monarch 10EE used DC to drive the spindle (it used AC to produce the DC, all inside the machine).

GsT

 

[R Stiner]

Pete

If you have an old hand {AC} powered hand drill pull the trigger as light as you can to make the chuck turn at its slowest speed you will hear and feel the difference as you would doing it with a battery {DC} powered hand drill.

Remember the old ceiling fans when on low they had that rhythmic hum......

That's the reason old lathes have different size pulleys to change spindle speeds. the AC motor is always turning approximately 1750 rpms the pulleys or gear reduction is what gives you different speeds and torque!

It's quicker to turn a dial {DC Motor}to change speeds than it is to change belts and pulleys {AC Motor} to change speeds.

Advantage of a DC motor.

Russ

 

[jackie schmidt]

A torque converter is often used to get torque at the low speeds. I believe the Monarch 10EE used DC to drive the spindle (it used AC to produce the DC, all inside the machine).

GsT

Our Monarch EE originally was one of the self contained DC power units. When it started giving us trouble, we came up with our own solution, rather than converting it to the modern all electronic controled drives that refurbished machines employ.

We took the armature out of the main drive motor, and replaced it with a solid shaft with fits sticking out from each end. We then mounted a variable speed drive, (CVT), in line with that at the back of the lathe, with a u-jointed drive shaft connecting it.

The main reason we did this was we could do it all in house, and, more or less, made the lathe a total mechanical unit.

http://benchrest.com/attachment.php?attachmentid=18730&stc=1&d=1481725003

http://benchrest.com/attachment.php?attachmentid=18731&stc=1&d=1481725116

http://benchrest.com/attachment.php?attachmentid=18732&stc=1&d=1481725228

 

[Pete Wass]

So, say

A lad would want to make a .075" cut @ 70 rpm's, would he need a 4 horse motor instead of a 2 to not bog the spindle down?

It sure is a lot easier to turn a dial than to shift belts so I can see the why but if the dern motor has no power when going slow; I think this is where we are here, no?

P

 

[Woodhunter]

A lad would want to make a .075" cut @ 70 rpm's, would he need a 4 horse motor instead of a 2 to not bog the spindle down?

It sure is a lot easier to turn a dial than to shift belts so I can see the why but if the dern motor has no power when going slow; I think this is where we are here, no?

P

I have a 2 hp DC motor on one of my lathes. That cut in your quote is easy for the DC motor.

DC Motors have high torque at slow speed.

The reason we do not see DC on lathes from the manufacturers is the high cost of a DC motor and drive.

Sorry I do not have a photo of the lathe with the DC motor but my vertical mill in the photo below is DC motor equipped. I love it! Change speed while under a cut. This is a 2 hp DC motor with a Reliance solid state drive: Start/stop, forward, Reverse, Jog and variable speed.

The black box on the wall is the Reliance controller. Actual speed dial and other motor controls are mounted on the left side of the mill head in the silver box..

This mill has the step pulley head with back gear, combined with the DC motor the speeds range is infinite.

I have two more lathes in the shop with AC motors, and I have DC motors and drives for them: More winter projects!

 

[Pete Wass]

Thanks for the reply,

I am thinking about replacing my AC motor with a D.C. Reversible as they seem to be a lot more versatile. It would be nice if someone would put together some kits for those of us who are electrical and electronic lacking , I must say.

That's a nice looking controls box you have there, by the way. To paraphrase Jimmy Carter, I lust in my heart for a mill like yours. I bought one of those smaller Grizzlies and wish now I had one that would actually CUT metal instead of worrying it off. I really enjoy watching machines that mow metal off.

Pete

 

[GeneT]

Our Monarch EE originally was one of the self contained DC power units. When it started giving us trouble, we came up with our own solution, rather than converting it to the modern all electronic controled drives that refurbished machines employ.

We took the armature out of the main drive motor, and replaced it with a solid shaft with fits sticking out from each end. We then mounted a variable speed drive, (CVT), in line with that at the back of the lathe, with a u-jointed drive shaft connecting it.

The main reason we did this was we could do it all in house, and, more or less, made the lathe a total mechanical unit.

http://benchrest.com/attachment.php?attachmentid=18730&stc=1&d=1481725003

http://benchrest.com/attachment.php?attachmentid=18731&stc=1&d=1481725116

http://benchrest.com/attachment.php?attachmentid=18732&stc=1&d=1481725228

Well done! I've seen a few gutted and converted to VFD's, but that's a first!

GsT