Newbie- Scratch building - request opinions/ideas

[erikjgreen]

Hey all... I posted this request in the general forum a week ago, but I've updated my plans a bit since then and I'll try again here.

I have been using a mini mill and mini lathe for about four years, and I acquired a Grizzly G4000 lathe two years ago. I still have all three. I've run into the limitations of my current machines and I've decided to build a small CNC mill. Originally I was going to convert my X2 mill, but I decided it would be better and cheaper to scratch build, not to mention more fun and a better learning experience.

So far I've decided to make it a bit larger workspace wise than the X2, partly due to the parts I've found. I'll be using it for CNC milling aluminum, plastic, and some steel, although I realize steel cutting will be limited in some ways.

Here are the parts I've collected so far:

• 2x Universal thread lead screws, X grade, with nuts - new
• 1 THK "caged" ball screw/rail combination, I think model "SK" - brand new
• Two Superior Slo-Syn stepper motors, 300 oz-in, 8 wire - used
• two "unknown" round steppers, probably 100-150 oz-in
• Four sections of Schneeberger rail, new, no carriages/trucks
• 5 feet (!) of thomson 1 inch round linear rail with bearing carts
• Lots of stainless steel plate and parts from a lab machine
• a Hobbycnc controller (not gonna use probably)
• A 1.5 HP DC treadmill motor
• A DC motor controller rated to 1.5HP
• A spare 2 ghz computer to run Mach3
• Plenty of electronic parts... switches, wire, etc.

So far the plan is to form a base and column, potentially from stainless steel. I have a part of a lab machine that could be cut to form a 9 inch square base (to attach to a heavier base plate) that has a 3 inch by 6 inch stainless steel column welded to at a right angle. The tube is made from 1/4 inch wall tubing. It's very stiff as-is and could be made stiffer and reinforced. Pretty much a ready-made column with an attachment plate.

If I take that and reinforce it (fill with cement and attach more bracing?), then attach the 1 inch rails and their mounting bar to it vertically, I'll have a very stiff vertical axis. I'll attach the base plate of the column to maybe a polymer concrete block about 16x24x4 inches (I have a lot of spare boatbuilding epoxy).

The vertical motion (Y) will come from one of the Universal lead screws, which should give me about 12 inches of vertical run. I'll counterweight the head with a simple pulley and use a large stepper, probably with belting to increase torque, for motion.

The Z axis will run on a pair of the Schneeberger rails (I have to find some trucks for those yet) using the second Universal lead screw. That should give me about 10 inches of travel in that direction. Motive power is one of the Slo-syn steppers.

The third axis will use the nice, compact THK rail/ballscrew combo. It's got a bracket for a stepper at one end that I may use as-is or replace.. it looks made for a NEMA23, but I did check the capacity of the whole unit and it looks like it can handle up to several hundred lbs of dynamic load, and can be mounted in any orientation.

I'm thinking of buying a keling power supply, 20A at about 80 volts, to run the steppers using Gecko 203V drives open loop (for now). Probably a USB stepper controller to ensure no missed steps and to give me connections for buttons/etc.

The spindle I'm trying to think of a good solution. If nothing else I can get another X2 head and belt drive it from the treadmill motor.

I'm thinking I'll build a flood cooling system from a fountain pump (which will require an enclosure).

Construction material will likely be aluminum plate (haven't got yet) stainless steel plate (got quite a bit of this), bolted and welded together. I'm not taking parts from the lathes or mill so I can use those while I build this.

So far does this sound reasonable? Should I not use any of this, or will using three different rail mechanisms cause problems? Any issues with the Slo-syn motors, or motor sizing?

I'll see if I can get some drawings together soon. Part of this exercise is to give me an excuse to learn CAD, so I need to hunt up a good free CAD program.

Comments/suggestions welcome.

Thanks,
Erik

[stewi]

You may need to review the stepper motors, operating at 80 Volts? Why USB not supposed to loose steps is new to me. If the stepper motors are unknown, it will be quite difficult to hook them up correctly.
However, I started out pretty much like you, but then found out, it is less expensive to buy new hardware, which works out of the box than fiddling with used and unknown parts.

[erikjgreen]

I actually gave up on this a while ago, and saved to buy a full size mill, which I'm now getting operational.

Erik