Mayday! Time to get some progress and self serving industriousness laid out, and resume paving the path to the future.

Forging a bit of progress on the CNC project. Smoothing out nicks and surface irregularities of the structural material through a gentle file hone and fitting the bearings onto the screws as outlined following.


In preparation I stuck the screws in the freezer for the afternoon, and the bearings in an oven (initially at 250 f) for ten minutes. I forget the actual room temperature dimensions, as they were compared at ODD a while back, but it did amount to an interference fit. The hope here was that between thermal expansion and contraction a fit could be made without the necessity of an actual press.


Note the frosty condensation at left offset by the heated metal at right, the metal cylinder was the bearing race "anvil" to alleviate hammer shock from being transmitted through the bearing itself. The first two involved hammering at the coupling end. This wasn't a huge concern as the coupling end is not a super critical precision surface as it will be floating to allow drift from minor misalignments to be taken up at the coupler as opposed to premature wear on the bearing surfaces (no mushrooming occurred).

The second bearing was a bit more resistant to installation, probably due to the cooling of the bearings during the first installation; so the third bearing was heated at 350 for five additional minutes. Additional heat was the key, as the third bearing required no hammering at all.


Installed, ready to move on to structural plotting, based on actual measurements of installed screws.

It took me a week to execute a simple task. Referring back to the interference fit for the Z axis screw, my planned fix involved cleaning the threads on both parts and filing down the folded thread on the screw.


My initial mock up here, in which I've placed a knife in the channel between threads to act as a protective barrier between my filing work and good threads, proved cumbersome. In the end I simply held the file as I would a pencil and exerted more care than slop.


Success! Sometimes the fastest fixes are the most satisfying.

Next phase of the CNC project entails getting metal milled for the gantry. Once the gantry is solidly defined I'll build the frame on which it connects to the table, most likely out of wood since my budget is wearing thin. I reason that the framework is a bolt in layer, that can be upgraded if wood proves inconsistent in dimension.

It also looks like my initially just hoped for feature of a spindle RPM control for the Porter Cable 75192 fixed speed 3 1/4 HP router motor is achievable with the Super-PID closed loop controller. I think I would have easily burned up more than twice the cost of that trying to engineer something myself.

Inching forward with the CNC project, my screws and some hardware have arrived.


Here's a quick mock-up of my X axis, well, hardly a mock-up, but I digress. Framework and data handling aside, these are the important parts.

X axis is to ride on THK linear bearings, driven by a Pacific Scientific Powermax II stacked stepper turning a screw, powered through a GeckoDrive G201X which will receive commands ala dedicated desktop PC running Ubuntu/EMC2. Having all these components laid out in front of me means I really need to address the power supply sooner than later (now).


Front and center sits 112 pounds of power supply, waiting for me to lug it to the bench.


It's only after executing that little juggling operation that I remember this is the unit with a faulty breaker on the DC side and what I'm really after is the 107 pound power supply that was sitting next to it.


After a brief inspection confirming that the power transformer is strapped for 120 volts and nothing is visibly leaking, bulging or dead inside the case, I fire it up. The hum of operation borders on a buzz, but no smoke or sparks thus far... good.


There's a standard cassette tape at upper right for scale.

There's a point of concern with this PSU, the DC breaker. I've gathered that it's inadvisable to to switch the DC side of the power at the drivers, as they will face back EMF from the motors which can burn them up, setting me back replacement costs on up to four G201X, which isn't something I'm interested in.

The supplies are also tailored to battery charging, which has a different set of operational parameters than driving motors. My Y axis will have two motors working in hard sync to move each leg of the gantry, the two stacks of each motor are going to be wired in parallel, offering a path rated at 7 amps per motor. So the last thing I want is some battery configured current sniffer to crowbar output voltage when I most need it.

In short, I came to the realization last night that my best tactic is to gut the logic/regulator portion of the power supply, reconfiguring it into a primitive rectified DC beast, which, as I understand it, is best for this brute force application to begin with. I guess I could have stayed with the heavier supply after all.