Clausing 12x40 DC motor conversion

[BrassBuilder]

I am in the process of converting an old Clausing 100 mk3a lathe over to CNC. The current motor has the following specs:

1/2 hp
1750 rpm
115 volt AC motor.

While I was CNCing the lathe, I thought it would be nice to get a variable speed DC motor on it. I've been looking at treadmill motors on ebay and found one with these specs:

2.5 hp
4500 rpm
130 volts/10amps

I would then run a DC controller to run the motor and have variable speed.

The motor that I am looking at runs CCW. The current motor runs CW. Since I need to make a new mount anyway, I was just going to mount the motor reverse of the current motor.

The lathe tops out at around 800 rpm. I want to get a little higher...maybe around the 1500-2000 rpm. The headstock already has Timken bearings, so it should handle the faster rotation. I am replacing the bearings just to be safe.

Is this a viable plan? I thought of putting a 3 ph motor on with a VFD, but the cost is a lot higher. I may look at doing that later.

Thanks
Mike

[BrassBuilder]

NO ONE has any words of advice on this?

I'd like some idea if I am going in the right direction.

Mike

[Al_The_Man]

Should be feasible, You could use one of the KB/Baldor DC drives, these give either 90v off 120ac or 180v off 240vac.
The 90vdc version should work.
Al.

[BrassBuilder]

Originally Posted by Al_The_Man Should be feasible, You could use one of the KB/Baldor DC drives, these give either 90v off 120ac or 180v off 240vac. The 90vdc version should work. Al.

I was hoping to keep everything 120...someone did one of these conversions to a 9x20 and recommended using a 120v DC motor. Those are hard to find, but I come across the 90v often. I was not sure the same basic motor was going to be big enough for the 12" lathe.

I've been sort of looking at servos too....not sure whether the DC motor or the AC servo has more potential.

My eventual goal is to have Mach3 run the spindle too.

Mike

[Al_The_Man]

With the DC motor , servo or otherwise, the drive is not so much of a problem.
You can use anything from a common SCR drive to a servo drive, the AC servo motor requires more matching due to electronic commutation required.
Also using a DC servo motor, you can often find ones with a Tach, this also offers more precise speed control.
Al.

[BrassBuilder]

Originally Posted by Al_The_Man With the DC motor , servo or otherwise, the drive is not so much of a problem. You can use anything from a common SCR drive to a servo drive, the AC servo motor requires more matching due to electronic commutation required. Also using a DC servo motor, you can often find ones with a Tach, this also offers more precise speed control. Al.

I'm still looking for likely candidates....if you happen to see any potential candidates on ebay, let me know. Here is one condender:

http://cgi.ebay.com/treadmill-motor-...d=p3286.c0.m14

Wish the motor was bigger on this one. A package deal:

http://cgi.ebay.com/Dayton-3-4HP-PM-...d=p3286.c0.m14

And if someone buys it out from under me....I'll find another one...

Mike

[BrassBuilder]

Originally Posted by BrassBuilder I'm still looking for likely candidates....if you happen to see any potential candidates on ebay, let me know. Here is one condender: http://cgi.ebay.com/treadmill-motor-...d=p3286.c0.m14

I decided to go ahead and buy the above motor. For $60 and a few bucks for shipping, I figured I could use the motor for something if it does not work on the lathe. I'l have to see what I get....

Mike

[Al_The_Man]

That motor shows up to 150vdc so you could use one of the KB/Baldor 180 v drives that run off 240vac.
You could easily limit the max rpm by a resistor in series with the pot, or by the signal in, if using CNC control by S value.
Al.

[BrassBuilder]

Originally Posted by Al_The_Man That motor shows up to 150vdc so you could use one of the KB/Baldor 180 v drives that run off 240vac. You could easily limit the max rpm by a resistor in series with the pot, or by the signal in, if using CNC control by S value. Al.

I eventually want to control the spindle speed through Mach 3, but for now I was just going to use a DC motor controller. I'll look at the KB/Baldor drives too.
Thanks
Mike

[BrassBuilder]

Update!

I bought a Dart Controls 253G-200E DC controller on ebay. The specs:

Input: 120VAC
Output: 0 - 90VDC
HP: 1/8 - 1

Input 240VAC
Output: 0-180VDC
HP: 1/4 -2

The control has directions on adding a dynamic brake resistor into the system. This helps to slow the motor down after shutting it off.

I was looking through ebay today and found a KB Electronics KBCC-125R that looks like it would have been even better. The KB already has the brake resistor built in and it had a few other features that would have made it worth the almost double price. If the Dart does not work, I'll splurge for the KB.

My DC motor showed up today too. It is heavier and bigger than what I expected. There is also a tach hookup on the back, but I need to figure out how to wire it.

Mike

[Al_The_Man]

Originally Posted by BrassBuilder My DC motor showed up today too. It is heavier and bigger than what I expected. There is also a tach hookup on the back, but I need to figure out how to wire it. Mike

If its a DC tach then there is only two wires, with most drive that take DC tach input, you just need to scale it to the speed pot/control input.
If you have the polarity wrong it will usually run away at switch on.
Al.

[BrassBuilder]

I have another question...

How do I figure up how big of a pulley I need on the motor? Just for an example, let's say my motor tops out at 4000 rpm and I have a pulley on the spindle that is 5" in diameter. I was shooting for around a 2000 rpm max rotation on the spindle. I figure the headstock should handle it as it already has bearing installed and I was going to replace them with new ones once I started taking this apart. Anyway....I have the following info:

Motor RPM: 4000
Spindle Pulley: 5"
Motor Pulley: ???

I am just guessing a 2.5" pulley would do it since a 5" pulley would give the ratio as 1:1. The spindle would turn at the same pace as the motor. If I put a pulley half the size on the motor, that should cut the RPMs in half...

Is there a "magic" formula for this?

Mike

EDIT: Never mind...a short google search gave me the info I needed. It is easy beans!
Mike