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The Assembly - Making the Parts

I have virtually no tools with which to make the parts needed for this drilling machine, however, my brother and his friends do. If you needed your electronics stuff worked on then, I'm your man... I'm just a little short on lathes, saws and milling machines. I asked them to fabricate the parts needed using the model and drawings I made with AutoCAD. With the workshops they have for building and maintaining their racing and custom cars, fabricating a few simple parts like these should be no problem.

I would like to give special thanks to Jim Stephens, Corvin Latus and Bob Carter for actually making the parts of this CNC PCB Drill project. These guys took time out of their busy schedules to fabricate these prototype parts saving me a lot of money over the commercial alternative, thanks guys, great job.

There is also some additional thanks due to David Parkyn and Daniel Valdes (not pictured) for getting the computer in shape. Dave and Dan are my employees, so they didn't have much choice in the matter... I guess I will have to give them a candy bar or something. :-)

The Assembly - Fitting the Parts

A quick test fit of the major parts shows no big alignment problems so it all goes into a box and is shipped to me in Los Angeles for final assembly, calibration and use.

There were a few changes from the original design, Guide Blocks(502-3008) and the Screw Block(502-3009) were fabricated out of aluminum instead of delrin. The frame bottom(502-4001) is made out of 2 pieces of aluminum instead of one continuous piece.

The one problem area of the design is the plate body(502-3010). These were fabricated out of .035" thick cold rolled steel instead out of .047" thick aluminum. There is a dimensional stability problem with the parts not being exactly square. The thickness or material have nothing to do with this problem, it is instead in how the parts were fabricated which was by hand with a manual bending break. If we had an NC bender available, we could have made the parts more accurately, It's no big deal, the design is pretty tolerant of misalignments like this.

When these pans are affixed to the machine base, they straighten out nicely and the alignment problem goes away. The X axis however poses a problem where the pan is designed to support itself and being dimensionally ambiguous, this causes binding of the guide rods causing motor stalls. The simple fix for this problem was to add a 12" X 4" X .25" thick piece of aluminum plate under the X axis to support and align the pan. This provides a strong base to fasten the X axis pan assembly.

Several small details were left to this point in the project so they could be added as needed. Holes for the limit switch wires were drilled and test fitted with rubber grommets. The home or zero switch assemblies were fabricated and tested, electronic equipment mounting holes were drilled and in general the cnc_drill was rough assembled and tested.

The Assembly - Testing the Parts

The real big milestone was however, plugging it all in and making the machine move under software control, which it did, kind of. See the "Plugs-In Test" Movie (MP3 - 12.04Mb)

To achieve this momentous goal the TurboCNC software had to first be configured to reflect the machines architecture. Let's do a little review, it's a 3 linear axis (X,Y and Z) machine with limit and home switches on all axis, it has motors with 200 steps per revolution, it has 13 threads per inch on the leadscrews and... that's about it, right?

To make a long story short, I configured the axis interactively, making sure to set the jog directions as well as the program directions and units. Below are the settings I made for the 3 axis or control:

NOTE: By now, I hope you realize that you can click any of the pictures in this article to see a larger version.

There was one thing however which I still have not figured out. Seeing that the motors are directly coupled to the leadscrews without any gear reduction or increase, I assumed the gear ratio should be 1:1. In fact when moving an axis at that setting I get 2" of travel on the software for 1" of travel on the machine. Setting the gear ratio to 2:1 fixes this problem but leaves me wondering why.

I also set-up the limit switches and home switches by editing the turbocnc.ini file directly. You can do this from the user interface, I just decided to do it directly using a text editor. You should note that there is one more ActiveHigh=NO at the end of the code in the picture, it just would not fit on the screen at the same time.

The main thing is to get the right pins on the motors and limit switches talking to the right pins on the controller board. Now that this is all set and saved away we can get onto the landmark Plugs-in test.