Introduction

This project started off when I loaded up a nice freeware pcb layout program (FREEPCB). Many years ago I did PC board work for aerospace companies up until around 1984 when PC CAD systems were just coming into being. Since then I have been computing and wound up owning a couple ISP's and an amusements company dealing with vintage arcade video games. These vintage games brought back memories of my earlier electronics technician jobs in the early 70's.

This prompted me to layout some simple boards like audio amplifiers and converters. These projects were very home brew, breadboard or simple single sided boards, limited quantities. I came across one design however that would need a lot of vias and two layers, and this is where things get going.

Send questions or comments to: wstephen@sowhatsoftware.com

I could of course, send some gerber files to (PCBEXPRESS) or (PCBPRO) online and have them make the PC boards, but I'm a DIY type of person and would rather spend the money giving myself the capability. In order to homebrew two sided plated through circuit boards, I would need to do some good registration, Electroplating copper and in general, make the board the same way the professionals do. In analyzing the pcb fabrication process at (THINK & TINKER) it became clear that before I could electroplate the through holes, I need to have the holes drilled and only after plating could I actually etch the copper patterns. Immediately I knew I first needed a CNC PC Drill.

You can shop around and find a nice one for about $5,000.00 to $10,000.00 which have way more capability than you would need... remember, you're only drilling holes. or... you can find homebrew CNC milling projects online like (THE BRUTE). As I said, I'm very DIY and although the BRUTE plans were available for a few bucks, I decided to take a cursory look at a few hobby machines and set out to design and build my own.

I have a lot a lattitude in the design of this mill because it's really only going to be used to drill holes in circuit boards. It does not have to be real strong and can afford a little sloppiness although not too much. If I make it out of lightweight materials, and keep the axis travel fairly short I should be able to hit these ideals with ease.

Control Electronics - The Motors and Controller

Before we get into the design we need to select the electronics. You can find stepper or servo motors and controllers many places but I found that the package offered by (HOBBY CNC) a good value, and it's a kit too!!! The 3AUPC uses one Allegro Microsystems SLA7062MLF2102 Unipolar Stepper Motor Translator/Drivers for each axis of control simplifying the circuit board considerably.

3AUPC Kit + (3) 80oz-in, 6v, 1.2A, Dual Shaft Steppers


Assembling the 3AUPC was easy and straight forward following the instructions provided with the kit. I have a 40 amp lab power supply which I use to calibrate the board which provides extremely clean DC power. After wiring up the motors to the board terminals and hooking up the power supply, the motor shafts locked in place, just like they should.

Control Electronics - The Power Supply

I do not intend to use this expensive power supply for this project, instead, I will be using an ATX power supply from an old computer. These power supplies have several voltages available but you need to modify it a bit for use as the supply for the stepper motors.



What you do is open up the power supply and remove all the outgoing wires except for a red 5 volt, yellow 12 volt, green enable and two black grounds. Put two 8 ohm 20 watt resistors on the 5V/GND lines mounting them near the fan(large white components in picture) , ground the enable line and run the 12V/GND pair out the grommet to supply the stepper driver. Click here for detailed instructions.

After making these modifications and powering-up the controller board I got the same results as with the lab supply except that I now heard the stepper motors "singing or buzzing". This is probably due to the lower power capacity of the ATX power supply. All that's needed now is 4 holes to mount the case to the machine frame, but let's defer that until we have a frame to use as a pattern. Another nice thing to add is an ON-OFF switch... you know, one of those red button switches that you need to pull on to turn the power on and all you have to do is press the switch to kill the entire system... an emergency stop switch.

Control Electronics - The Computer

Probably the most difficult part of this project so far is getting together the computer to run this thing. This should have been the easiest seeing that I have a few dozen computers at my disposal, but none of them had DOS. I have UNIX, LINUX, OSX, and even an XP or two but no DOS machines. Microsoft does not sell DOS anymore and the software I have chosen, (TURBOCNC) works in DOS. Most of the CNC software runs in DOS... it has something to do with bus timing. I tried an XP machine by making a boot disk as they recommend and I got an "internal error 0222" for my effort, I don't have time for this type of stuff... on to effort #2

I next started off with a SUSE LINUX machine and eventually turned it into a Windows 95 machine setup to boot into DOS mode... that's about as close as I can get to a DOS machine these days. This is not to say that somehow I could have made a pure DOS 6.22 machine or something like that, it's just that I want to get this thing done in some sort of reasonable timeframe. I also want a little "connectivity" on the machine for uploading and downloading data and Windows 95 makes that pretty easy. Of course I would never put this thing directly online because of the highly exploitative nature of such an old operating system. Instead, it will be shared through a Mac.



Control Electronics - The Wiring

Installing and setting-up TURBOCNC was quite easy and I was jogging my motors in no time. I hooked up the limit, home and e-stop switches and gave them a test as well, all seems to work as expected at this point. Below is the wiring diagram for the cnc drilling machine.



Click here to watch the "Jog The Motors" movie (MP3 - 16.50Mb)
The Design - The Big Idea

I started off the mechanical design part of this project with the motor shaft diameter which is 1/4". Ideally and typically most people use 1/4-20 threaded rod for the leadscrew. A little math shows that the motor has 200 steps per revolution and the screw needs to be revolved 20 times to get 1" of linear travel, so there are 200*20 or 4000 steps per inch which equates to 0.00025" per step. I wanted it to move a little faster so I sacrificed some power and accuracy by deciding on a 1/2-13 threaded rod instead... a little more math shows 200*13 or 2600 steps per inch which equates to 0.00038" per step. A theoretical four ten thousanths of an inch accuracy is fine with me, that is as long as I have no backlash in my axis drive. I'm actually hoping for a few thousandths accuracy when all is said and done. This leaves me a factor of 10 yet for any slop that is added into the design.

The Design - The Linear Axis

One nice thing about this design is that once you have designed an axis, you have designed them all! Each axis mechanism is identical. This cuts down on the different types of parts that need to be fabricated.

502-3005.pdf : PLATE, END - CNC MILL 502-3006.pdf : SCREW, LEAD - CNC MILL 502-3007.pdf : ROD, GUIDE - CNC MILL 502-3008.pdf : BLOCK, GUIDE - CNC MILL 502-3009.pdf : BLOCK, SCREW - CNC MILL 502-3010.pdf : PLATE, BODY - CNC MILL PURCHASED PARTS Steel Ball Bearing -- ABEC-1, Open Bearing No. R6 For 3/8" Shaft Dia, 7/8" Od (Mcmaster ref:60355K14) Sae 841 Bronze Flanged Bearing, For 3/8" Shaft Diameter, 1/2" Od, 3/4" Length (Mcmaster ref:6338K416)

NOTE: the drawings and parts presented in the body of this document are "initial" design components. The final design may or may not incorporate modifications to these parts. Use this information as reference only.

Above is a 3D rendering (in false color) of an axis and all the part drawings in acrobat format. The purple part is the stepper motor, the green plates(502_3005) are 1/4" aluminum, the tan body(502_3010) is .06 aluminum plate, the orange blocks(502_3008) are delrin 500, the darker orange block(502_3009) is also delrin 500, the light blue rods(502_3007) are hardened and anodized aluminum and the golden rod(502_3009) is a 1/2-13 aluminum threaded rod. The end of the threaded rod rides inside of a standard ball bearing and the guide rods (light blue) have bronze bearings in the guide rod blocks. Just make 3 of these linear axis and 90% of the construction is done.

What's not shown here are the limit and home switches (Omron VX-56-1A3). Microswitch mounting holes are provided on the BLOCK, GUIDE - CNC MILL parts for mounting these switches.

The Design - The Machine Frame

There are several ways to tackle this part of the design, John Kleinbauer's BRUTE mill uses a piece of plywood and some water pipe. All that's needed here is to provide places to mount the X-Y axis stack, the Z axis, the power supply and the stepper controller along with some terminal strips. This part could be made from 3/4" plywood and be more than sturdy enough for this machine however, it would grow and shrink a bit depending on the humidity. I decided to make this part out of 1/4" aluminum plate... less prone to growing and shrinking. The parts for this frame can either be fastened with screws or the whole thing could be welded.

502-4001_1.pdf : BASE, BOTTOM - CNC MILL 502-4001_2.pdf : BASE, BOTTOM - CNC MILL

NOTE: the drawings and parts presented in the body of this document are "initial" design components. The final design may or may not incorporate modifications to these parts. Use this information as reference only.

Additional features such as mounting holes and tie downs need to be added but these are best left to assembly time to determine the optimum location for these features.

The Design - The Tool Holder

Oh yeah, I have not mentioned what drill motor I intend to use, well, it's the old reliable hobby workhorse, the Dremel® Tool. Actually, it's a Model 395 Dremel® MultiPro. This Dremel® tool is fitted with the Dremel® Chuck #4486 which will hold even the smallest drills.

I have a drill press(Dremel® #212) for this tool and considered cutting off the mounting bracket and reworking it to fasten to my CNC drills Z-axis but that would be too easy (maybe). I decided instead to design some parts that mimmic the drill press mount, saving my drill press from destruction.

502-3020.pdf : PLATE, DREMEL MOUNT 502-3021.pdf : BASE, DREMEL MOUNT 502-3022.pdf : SUPPORT, DREMEL MOUNT 502-3024.pdf : RETAINER, DREMEL MOUNT

NOTE: the drawings and parts presented in the body of this document are "initial" design components. The final design may or may not incorporate modifications to these parts. Use this information as reference only.

The yellow bent rod is a #4-40 threaded rod bent in a horseshoe shape. I will probably be a good idea to heat up this rod before bending it around a mandril to minimize snapping or kinking it.

The tool has 10 speed positions ranging from 5,000 to 35,000 RPM which roughly lays out like this:

1	5,000 RPM	2	8,000 RPM	3	11,000 RPM	4	14,000 RPM	5	17,000 RPM
6	21,000 RPM	7	24,000 RPM	8	27,000 RPM	9	31,000 RPM	10	35,000 RPM

It would be nice to set the speed via software control but this would necessitate that I disassemble and modify the Dremel® tool with some sort of switching electronics or yet another servo. Seeing that I will not be able to automatically change the drill bits (tool change), I see no reason to go to these lengths to fully automate the drill motor. I will have to start-set-stop the tool manually... small price to pay.

The Design - The Table

This part of the design is the least critical of all the parts of the cnc drilling machine. I will start off with a piece of 1/2" MDF 8-1/2" square fastened dead center on the X-axis. To be more precise, it will actually be a piece of 3/8" MDF with a 1/2" border of 1/8" spruce fastened to it to hold a 1/8" thick piece of spruce as the table top backing material. This way, as I drill holes I will gradually chew up this backing material and I can easily replace this part of the table as need dictates.



The machine is designed to accomodate many tables from this bare bones "setup" table to a yet to be designed vacuum base table.

Download the entire 3D layout (DWG - 2.36Mb)


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.


The Assembly - Taking it all apart

Now that the Plugs-in test is complete and the machine has been adjusted, filed, drilled and tweaked, it's time to take the whole thing apart in order to get paint on some of the parts, especially the steel ones.

Painting raw aluminum or raw steel for that matter requires some preparation. The first thing is to degrease and clean the parts by washing them with detergent and hot water. After rinsing and drying the parts, I need to deoxidate and roughen up the surfaces which is accomplished by a thorough rubbing with Scotchbrite pads. Another quick cleaning and drying gets the parts ready for a nice coat of Self Etching Metal Primer. It should be noted that all this is done wearing rubber gloves, the acids on your hands will ruin the surface cleanliness.

I kept the pan and end plates assembled for alignment purposes so the end plates need to be masked with some tape prior to any painting, also, I put scrap screws in all the threaded holes in the parts to keep them free from paint. Once this is done I primed the parts with steady even strokes and like that. I let the primer dry completely and then applied a nice topcoat of Hunter Green Satin Enamel. In deciding on the color, I tinted some shots of the cnc_drill in progress with Photoshop to see what color would look best. Well, I don't know if my choice is best or not, I like it however.
The Assembly - Putting it all back together again

Now that the paint is on and everything has been fabricated and test fitted I can put the thing together for real this time. When putting in screws I apply a bit of Locktite 242® Threadlocker to the threads of the screw. This helps prevent the screws from working their way back out from vibration.

When the machine goes together this time special care needs to be taken so that everything is square and perpindicular. The Y axis is the first axis to be attached to the frame. I aligned the Y axis perpindicular (90 degrees) to the Z axis mounting surface using some precision flats and a right angle square. I tried to keep this angle while keeping the axis in the center of the frame, this is not ultra critical, the angle however is. Once I have the axis exactly positioned I fastened it down, Locktit-ing the screws.



The X axis must be aligned perpendicular to the Y axis using much the same tools as before. It should be noted here that these alignment techniques are not a good precision method but they are good enough. Precision setup would require digital or dial indicators and some precision supports and flats, not to mention the precision granite block. Seeing that this is just a drilling machine and not a milling machine, a carefully measured visual alignment should suffice.

Continuing on with the assembly, I attach the table to the X axis and align it parallel to the X axis guide rods. This completes the X-Y table assembly. The last alignment job is to install the Z axis and align it perpendicular to the table top. This needs to be done in 2 planes to make sure the tool is square to the table top. This is kind of important especially if you do not want to break the fine drills used for PCB fabrication.

This is also where I seriously wire the machine. Up to this time most of the wiring was temporary and in many cases nothing but test clip leads. With a little figuring I determined that a 10 circuit, 20 screw terminal strip would buss all the sensor wiring using no more than two wires per terminal. I also decided to use jacketed 18 gage 2 wire cable for each limit switch pair and each home switch making a total of 6 sensor cables.

I opted for a looser more free form of wiring rather than the tightly routed wiring of most commercial products. This allows me to work on the circuits if needed because the room for the electronics and wire terminations is tight. I soldered all connections to the microswitches and put crimp lug terminals on the terminal block end of the cables. I did this because putting wires directly under the screws of a terminal block just has no class. A few tie wraps here and there to neaten up things a bit, connecting the motors, power and the limit switch leads to the controller and the final assembly of the CNC Drill is complete.

The Assembly - the Damages

Total elapsed time: 8 weeks from conception(10/12/04) to this point. This may be a long time in your estimation but I spent 2 weeks on the computer making solids models and in general designing the parts and then, all my parts were fabricated 2,400 miles away from me and there was a bit of shipping and receiving involved to make this project happen. If you have the machine tools locally available, then your time would be far less.

Total cost: Less than $1,000.00. I don't have accurate figures because I did not keep accurate records of the little trips to the hardware or electronics store. I do know that $500.00 of this cost was for machine part fabrication, which I consider a deal taking into account all the parts that needed to be fabricated. The motors and controller cost $130.00 and I splurged and bought a new flat panel monitor for the computer that cost another $200.00. I also got some things for free like the power supply and computer to name a few.


The Assembly - So... are we done?

Although the CNC Drill is fully assembled it is only partially set-up. All the home switch positions still need to be set and the speed and feed parameters need to be figured out, this will take a bit of trial and error. Aside from those little tid-bits, I need some drills, routing cutters, board fixtures and drilling substrate. I am not going to get away without some programming as well seeing that this is a computer controlled machine, so you could say that the CNC drill is done, if you wish to ignore these other realities.
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