Servo vs 3 phase for mill spindle?

[coolidge]

I think the go/no go decision will be made when I'm able to inspect the spindle side of the head. I think the timing belt disintegrated, there are a bunch of belt corpses in the housing. I also found a new timing belt in the toolbox that came with it. If that side of the Reeves is too shot to repair then I may convert over to direct drive. That would solve the motor issue. The direct drive motor version of the mill in the parts manual has a much shorter shaft, a cogged timing belt type pulley and another of the same diameter on the spindle. While the Reaves drive is removed (the sliding pulleys) the direct drive still has the lower unit back gear, high/low range, brake drum and brake shoes the same as the Reeves.

 

[mattthemuppet2]

There's not much that goes wrong with 3ph motors, they're pretty simple.

 

[pontiac428]

Duty cycle at rated power at rated rpm would be paramount in my mind for a spindle motor. Most of what you find in 3ph will be continuous duty. I dunno about new servos, but I'm skeptical you'll match the price or performance of the head motor you already have. The VFD will give you the extra high range you want. Sometimes the obvious choice is the best choice- Occam's Razor, principle of parsimony, and all that.

 

[mksj]

If you look at retrofit motor-VFD kits for many mills like those sold by Servo as well as others, they all use direct drive and use an inverter style motor. The inverter type motors tend to have a wider operating speed range with constant torque below the base speed (typically 10:1) and constant Hp to ~2X the base speed. You are limited at the extreme speed ranges if a TEFC motor. Typical operating range might be 20-150Hz, although performance drops off around 2X the base speed. A vector motor/typically those designed to run off of a VFD, have constant torques pretty much down to 0 speed (1000:1 constant torque or more), the TENV type do not have cooling issues at speed extremes, and typically are designed to operate to around 3X their base speed for their 4P motors (~6,000 RPM) with full Hp. The newer Marathon BlackMax (Y543A 5 HP) series also have an aluminum housing so much lighter then their cast iron counterparts like the BlueMax and Baldor IDNM, ZDNM types. They also have provisions for an encoder for positional control. Using an encoder requires a compataible VFD and tuning, as well as interfacing with the CNC system. Altenrative maybe a BLDC with controller.

Marathon Motors 184THTY7726 5 HP 3600 RPM Max Speed 230/460VAC Vector Motor | eBay

This is a Marathon Motors vector motor. Item Vector Motor. Speed 3,600 RPM. Duty Cycle Continuous. We have inspected this item and we do not have the capability to fully test it. This unit needs to be hardwired and should be installed by a professional.

www.ebay.com

Using a Reeves drive of this type, you loose power/heat in the drive and will see accelerated wear, can't say I have seen any modern CNC mill system that use them.

 

[coolidge]

If you look at retrofit motor-VFD kits for many mills like those sold by Servo as well as others, they all use direct drive and use an inverter style motor. The inverter type motors tend to have a wider operating speed range with constant torque below the base speed (typically 10:1) and constant Hp to ~2X the base speed. You are limited at the extreme speed ranges if a TEFC motor. Typical operating range might be 20-150Hz, although performance drops off around 2X the base speed. A vector motor/typically those designed to run off of a VFD, have constant torques pretty much down to 0 speed (1000:1 constant torque or more), the TENV type do not have cooling issues at speed extremes, and typically are designed to operate to around 3X their base speed for their 4P motors (~6,000 RPM) with full Hp. The newer Marathon BlackMax (Y543A 5 HP) series also have an aluminum housing so much lighter then their cast iron counterparts like the BlueMax and Baldor IDNM, ZDNM types. They also have provisions for an encoder for positional control. Using an encoder requires a compataible VFD and tuning, as well as interfacing with the CNC system. Altenrative maybe a BLDC with controller.

Marathon Motors 184THTY7726 5 HP 3600 RPM Max Speed 230/460VAC Vector Motor | eBay

This is a Marathon Motors vector motor. Item Vector Motor. Speed 3,600 RPM. Duty Cycle Continuous. We have inspected this item and we do not have the capability to fully test it. This unit needs to be hardwired and should be installed by a professional.

www.ebay.com

Using a Reeves drive of this type, you loose power/heat in the drive and will see accelerated wear, can't say I have seen any modern CNC mill system that use them.

First, very informative thank you for taking the time to help.

You touched on a couple of things I have to watch out for...

1. Weight. The original 5hp motor is surprisingly light. It bolts to an aluminum housing hanging in mid-air to the rear of the spindle. I'm not sure that housing will take a big heavy cast iron motor.

On a side note, in the category of things that make no sense to me...how is a 5hp motor lighter (significantly) than a 2hp motor? The original 5hp motor has a thick aluminum housing but still, I was surprised how much lighter it was. Though it's 3 phase vs the 2hp is single phase.

Next was a Clearpath servo 4.5 kW motor I was looking at. It's quite small dimension wise at 7x7x8 inches. Then I looked at the weight, 58 lbs gawd what is it made of lead? Shocked it was that heavy.

Motors are not my strong suit I need some learning in this area.

2. I took a look at the motor you linked to. One other thing I'm dealing with is the factory motor has a large flange. I could machine a custom plate for the motor you mentioned, but that would consume some of the shaft length.

 

[mksj]

Agree that a cast iron motor would be significantly heavier and more momentum/mass to deal with for the CNC drive.

If you were to switch the motor to a vector or servo type, you would just use a V or cogged belt for direct drive, no practical reason to keep the Reeves drive with these types of motors because they can be run up to ~6,000 RPM. Many of the newer knee mills like the Acer E-mills no longer use Reeves drives. Belt direct drive is also much quieter drive system, and use back gear for any low speed application. The marathon motor indicated may be able to be stepped down into a mounting plate (mounting face bolt circle is smaller than the frame), I helped another person with the a similar situation and that is what worked well. If direct belt drive it becomes a non-issue, you just need to adapt a pulley for the type of belt to the spindle end.

e-mill – Springwood Industrial, Inc.

 

[matthewsx]

Quick, possibly irrelevant question.

How viable would this be on a non/CNC mill? I have a baby Bridgeport with a Reeves drive that maxes out RPM before it gets to top speed. Eventually I'll have to tear into it and am wondering if just ditching the Reeves is a ton more work than rebuilding it.

John

 

[matthewsx]

Okay, found this thread.

Thread 'Mill Spindle Direct Drive Conversion'

Jul 29, 2016

Just a little teaser, I got the rest of the parts in today for the vari-drive to direct drive conversion on my mill. I have a bearing failing in the existing drive and I'm getting tired of listening to the noise it makes even with new bearings in it. This conversion will also allow a max speed of 6000 RPM as opposed to the current 4200 RPM.

I'll get started on this in the next few days, I need to get some other work done first and I have a couple of small mill jobs that have to get out the door before I can have it down for a week.

So watch this space

• JimDawson
• Replies: 40
• Forum: JIM DAWSON

• 

 

[coolidge]

Agree that a cast iron motor would be significantly heavier and more momentum/mass to deal with for the CNC drive.

If you were to switch the motor to a vector or servo type, you would just use a V or cogged belt for direct drive, no practical reason to keep the Reeves drive with these types of motors because they can be run up to ~6,000 RPM. Many of the newer knee mills like the Acer E-mills no longer use Reeves drives. Belt direct drive is also much quieter drive system, and use back gear for any low speed application. The marathon motor indicated may be able to be stepped down into a mounting plate (mounting face bolt circle is smaller than the frame), I helped another person with the a similar situation and that is what worked well. If direct belt drive it becomes a non-issue, you just need to adapt a pulley for the type of belt to the spindle end.

e-mill – Springwood Industrial, Inc.

Removed more parts from the head last night. That's one big diameter shaft close to 2 inches where the pulley would need to go. I don't think the Marathon would be any trouble at all fitting an adapter plate. I would need to machine some means of adjusting the belt tightness anyway e.g. some slots.

I ordered all the bearings, I'm good to 9,500 rpm throughout bearing wise.

 

[coolidge]

Quick, possibly irrelevant question.

How viable would this be on a non/CNC mill? I have a baby Bridgeport with a Reeves drive that maxes out RPM before it gets to top speed. Eventually I'll have to tear into it and am wondering if just ditching the Reeves is a ton more work than rebuilding it.

John

It would be just as viable, this is power transmission so CNC vs manual mill. Obviously you would need to mount a pot control and RPM electronic indicator for adjusting your spindle speed. All sorts of manual machines with electronic variable speed have this now.

I am leaning towards ditching the Reeves if for no other reason than the tilt plate mechanism is pretty funky. MKSJ made a good point on heat generation as well, especially if I'm going to run at or above the rated max 4,000 rpm.