New member - Wrestling with mill conversion to CNC

[tgarson]

Hello,

I joined cnczone last year, but this is my first post.

Several months ago, I acquired a Husky branded 8x30 pedestal type knee mill built in Taiwan by AIC in 1981. (Could be a predecessor to the Grizzly G0678?) It's really a stout "little" machine and in surprisingly good condition, considering how much gunk, grime and old grease full of ground up chips I removed from its cavities, bearings and gears. It has its share of wounds, but nothing to prevent it from becoming the tool I want it to be. I attribute at least part of the lack of serious wear to the gutless little 1/3HP 120VAC motor it sported.

What I am doing is converting the Husky to CNC.

Step #1 is done:
It's now got a dandy new 1.5HP Emerson/US motors 208V 3 phase spindle motor with a VFD.

I've just about completed Step #2:
The transition from acme lead screws to ball screws. This entailed machining (by hand on the Husky) some custom blocks with which to attach the ball nuts plus some hired out machine work on the saddle to accommodate the much larger size of the X-axis ball nut over the original acme nut. I found a surplus Warner double race ball nut with ground screw for the X-axis, and that works real sweet with less than .005" lash. I bought a Roton LH rolled thread setup for the Y-Axis ('cause it was cheap, of course!). The Roton will be OK after I add a second ball nut to it to trim out the .015" of lash. (If necessary, I have a second ball nut for the Warner to make it zero lash as well, but that will require a lot more effort, due to requiring more extensive modifications to the saddle.)

I'm in the middle of step #3:
Get the spindle feed in shape for a motor: It's obvious that the designers of these small mills (and large ones, too?) don't have as much respect for precision in the quill feed. There is noticeable lash in the main quill rack and spur gears, and no way to adjust it out. I am machining a replacement bearing block for the left hand end of the quill feed drive shaft whose hole will be slightly off center, so I can rotate it until I get optimum mesh of the rack and spur gears. I am also adding needle bearings to that block. Further upstream, there is a ball thrust bearing on the front of the the quill vernier worm shaft, but only a large steel waster on the back, so I decided to add a rear thrust ball bearing. While I have it apart, I am going to install needle bearings on the worm shaft as well. The reason for all of this is I don't want to have to count on just the recoil of the quills return spring to keep it from bouncing around.

I'm beginning to accumulate the stuff needed for step #4:
I've ordered three 3/4HP (12A x 70V for 3450 r.p.m.) NEMA42 brushed DC motors and have to devise mounts for them. These are premium quality "Old Stock" servo motors, but have tachs rather than sine-cosine encoders, so I figure that I'll need to convert them. How should I couple these motors to the screws. I see a lot of timing belts in use. My screws are 1" dia. x .25" lead, single start. Should I use belts and step the motors down or will these motors work well driving the screws directly?

Step 3.5 (Power):
Got that covered. I've been hoarding a USA built Triad Industrial power transformer for just such an occasion. It's continuous output rating is 62 VAC with a 20 Amp load. Once rectified, I will be able to pull DC current in excess of 30 Amps from an 88 Volt supply to run my 70 Volt motors. (Yes, I will need to use very stout rectifiers and a BIG capacitor.)

Step four is still up in the air:
What drives do I get (I'm leaning towards the Viper 100)? Do I need a BOB (I think so)? What make, model? What features? Where do I get limit switches? etc.... Questions and more questions.

I've got plenty of software, including an Alibre Expert level license that includes their CAM software. I currently use Alibre for my 3D CAD work, so their CAM extension is especially appealing.

I welcome any (constructive ;-)) suggestions on methods, components, vendors, etc. that anyone might wish to offer. I have an extensive electronics background, but am just getting into machine control, so I have a LOT to learn.

Thanks and a good day to all,
Tom Garson
Aural Technology, Ashland, Or.