All,

I'm planning to upgrade/change my mill's spindle motor and am seeking input from the CNCZone braintrust having reached my wits end searching for just the right motor...

I currently have a Marathon Blackmax Y551 2HP induction motor on my mill with a Hitachi WJ200 VFD. Motor has an encoder for speed mode feedback to the VFD. Running a 1.5:1 pulley and limiting the top spindle speed to 7500RPM to save my bearings and motor a bit of wear.

Two issues are driving the planned motor change.

First, the motor is extremely heavy and the cast-iron case means it has a very large OD for the rated HP. The large OD means I cannot use a standard 3-4 stage air cylinder for a PDB (R8 spindle w/TTS system) - the air cylinder simply won't fit centered over the spindle without raising it up about 15 inches on some kludgy riser. I currently have a home-made hydraulic intensifier installed on the spindle and an off-set air cylinder with a rocker-arm mechanism pushing down on the drawbar (with Belleville stack). This mechanism is not reliable - the fluid weeps out and after about 30-50 tool changes there isn't enough stroke left to reliably release the tools.

Clearly, I don't have the tools or skills to make a high-quality hydraulic intensifier that doesn't leak a little.

Second, the slow-speed performance is not very good - below about 500RPM the motor is very erratic. The VFD + encoder combo should give excellent performance down low. It's possible that my PWM source (PMDX-107 daughter board) is sending erratic 0-10V signals, but this is a minor gripe.

The Marathon motor is otherwise performing very well. No bogging, overheating, or other performance issues. However, as I'm getting more paying work recently, the need to stop and fiddle with the hydraulic PDB for an hour in the middle of a job is just not going to cut it. Plus there's no way I could build/buy an ATC without a reliable PDB.

I have 230v single phase, 30 amps available. I do not plan to invest in a significantly larger electrical supply or a 3ph converter. Besides, my mill isn't rigid enough to take advantage of more than 2-3HP. Also need a motor w/encoder (or provisions for same) so I can continue rigid tapping.

So...

I'm looking for a suitable spindle motor in the 2-3HP range that can achieve 5000-6000RPM. I can try a smaller-cased induction motor with a decent CT ratio such as this:

https://www.ebay.com/itm/Gator-Stain...kAAOSwp1RZgKUB

This appears to be a 145-frame 3HP motor with a 10:1 CT ratio and a smaller OD than the Blackmax. I could pull the fan to fit an encoder and put an external electric fan on it. Price is decent, and my current VFD should run it fine. Downside is that it weighs almost as much as my current motor and doesn't gain my a whole lot of space. Some, but not a ton.


The alternate is to find an actual AC spindle-servo motor and drive. My somewhat limited experience shows that a PM motor should be physically smaller than a comparable induction motor of the same HP rating - meaning I could finally fit a reliable PDB mechanism on my mill.

This would be preferable as I could (hopefully) run a 1:1 belt drive and still have 7k+ RPM top end. I know, these are expensive, and hard to find single-phase drives in the 2kw range.

All of the Fanuc/Mitsubishi/Yaskawa/AB/Baldor/etc. servo spindle motors I've seen have built-in fans for continuous use. They do not appear to be re-purposed 'standard' axis servos, given the RPM range on the nameplates.

Installing a DMM Tech 1.8kw servo was my first thought, but the 3kRPM top end means I'd have to give up a ton of low-speed grunt with the pulley ratios needed to get to 7500RPM. And I really don't want to drop my top spindle speed any lower than it already is.

I'm not willing to spend $3k (and up) for a new motor/drive, but I am willing to spend well over the $500 for an induction motor if the soulution is easy. I found a Alibaba vendor selling just the thing (2.2kw, 1-Ph 6kRPM spindle servo), but I'm unwilling to spend $1200 if the vendor won't even send me a datasheet/drive manual in English.

Nor do I have the expertise to troll eBay and find just the right servo and determine what an appropriate drive would be from the squillions of surplus items.

Does anyone have a suggestion on an appropriate spindle motor and/or drive? Weighs less than 65lbs, wide RPM range & torque curve, smaller than the Y551 Blackmax, and doesn't require 3-phase?

Thanks,
Ralph