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X2 MINI MILL

CNC CONVERSION WITH STOCK SCREWS
The goal of this section is to convert the X2 to reliable CNC for low-cost. This section will detail a low-cost method to mount motors onto stock screws and still get reasonably good resolution and rapids. There are OTHER reasons for doing this besides cost. Sometimes you just need to get CNCd as quickly as possible. And you can CNC the mill in stages:

1. CNC WITH STOCK SCREWS using the manual mill to make the CNC parts.
         This design will be modular. Many parts from present stage will be reused in following stages.
          First stage will also include column stiffening  built-in.
2. Increase travels with Acme screws.
3. Upgrade to Ball screws--or not.
4. Mobile VMC stand.
5. Flood Cooling enclosure and mechanics.
6. Head counterweight.


I won't stint on the electronics--I believe the G540 already IS the lowest cost reliable driver.
ELECTRONICS: 
$289 G540 http://geckodrive.com/product.aspx?c=3&i=14469
$147 Three $49 KL23H2100-35-4B 381 oz motors for X, Y & Z
$060 One KL-350-48 48V/7.3A power supply.
-------
$496.00
 
All of this is available from Keling:
 
http://kelinginc.net/

MOTOR DRIVE CONNECTORS:

There are basically two ways to connect the motors to the axes:

1) Direct Drive:
With this method, a coupling is attached directly to the end of the lead screw--usually where the crank handle was--and the motor is attached to the coupling. This requires a hollow mount that contains the coupling.
In my opinion, the only good direct connection is with a helical connector. Sure, some connectors are almost as good, but the helical is the best. Good Helicals (and you DON"T want to use cheap ones) cost upwards of $30 each. One drawback to direct connections, however, is that they add considerably (by extending motor and coupling straight out)  to the working envelope for an enclosure. We are designing with an eye to a compact flood enclosure so want to keep dimensions tight. Another drawback is that some thrust, or back and forth pressure is applied to the motor. Stepper motors have radial bearings--They expect SIDE loads--so any thrust load is detrimental to them.

In this exercise we will use the second method:

2) Pulley drive.
We will connect a pulley to the end of the lead screw, and a timing belt (toothed) to the pulley that runs to another pulley attached to the motor. Now the motor load will definitely be applied radially, or to the side. The cost of pulleys and timing belt about equals the cost of good helical couplings, and the backlash of tight timing belts is virtually zero. This allows the motors to tuck out of the way without using envelope space.

Z AXIS:
The X2 is unlike most other mills in that it uses a rack and pinion drive for the head and HAS no stock drive screw for the Z axis. We will have to provide one. In order to use a stock screw, I propose to purchase a stock X axis lead screw plus nut and use them for Z. These are readily available both from Grizzly and Little Machine Shop.

X AND Y AXES: We will try to keep the motors tucked out of the way, while mounting pulleys to the ends of the stock screws. We will swap out the axis thrust bearings and install good radial bearings.

So there is the operating plan: Design cheap motor mounts and a new stock Z drive.


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