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RAPID PROTOTYPING at HOME

"Rapid Prototyping" is a method of producing actual samples from design concepts in a short period of time.

I realized early on in my stereo photography adventures that I needed a quick, repeatable and accurate way of turning my design ideas for stereo photography products into actual samples to test and develop.

When I started in stereo photography 10 years ago I only had a saw and a drill for prototyping product designs. While you can actually built something with this equipment (and many people do) the result is not satisfactory for developing a product for sale to the public. I felt that I needed a way to construct a sample of any design concept I had, and the sample had to be of the quality necessary to offer as a product for sale.

This led me into an area that I never thought I would be involved in: CNC (Computer Numerical Control) machining. After studying the available methods for rapid prototyping I realized that the only one that was affordable and practical for the average person at home was CNC machining.

But the catch: I did not know anything about CNC machining. I had seen it in action in industry and always was impressed by the process, but I never thought it was something that could be done by anyone at home.

I was wrong. It is not only very easy to do at home, but it is affordable. And it is incredible! It is amazing what you can make just from a design on "paper" in a very short amount of time.

I get asked at stereo photo shows how I make some of my projects, and how my products are prototyped. I have decided to present this topic on "rapid prototyping at home" in order to interest others in the concept and to take some of the mystery out of it. I would enjoy sharing ideas and stories on CNC machining with other stereo photo hackers.

Before you get discouraged from trying this yourself remember; I did not know anything at all about stepper motors, control boards, or G-code

$Description: C:\Users\Lewismain\Pictures\My Pictures\3-d Website\proto\mach.jpg$ programming. But I did know how to use a CAD drawing program, AutoCad.

This is my rapid prototyping area at home. A bench milling machine and a router controlled by stepper motors attached to a 233MHz Pentium computer. The parallel port is used for program and motor control signals.

What you need for CNC machine control:

A machine to control (It doesn't have to already be a CNC machine)
A computer (many machines can be controlled by a 386 computer, sometimes a 286)
A motion control program (to send the proper signals to the parallel port and then to the motor control unit)
Motor control unit (this converts the parallel port signals to motor control signals, and supplies the motors with their electrical power and control)
Motors (most people use "stepper" motors to move the machine slides)
A CAD drawing program to make the design drawing (AutoCad or Intellicad for example)
A code generator for making the machine code that is used to convert the drawing into machine movements. The code generator (I use G-code) is quite often built into the motion control program you use.

The machine can be any kind of machine, the most common being a milling machine, router or lathe. A milling machine and router usually require a 3 axis control system, and a lathe only 2 axis.

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The first machine that I bought is a Sherline Bench Milling Machine. I bought the machine without any CNC controls on it. The first CNC conversion package I bought was the MaxNC basic kit using small 70 oz-in. motors and the small MaxNC controller. I built my own motor plates for fastening to the machine. I used a 386SX computer for control.

The machine resolution is .000125"/step.

This photo is the current setup using SuperCam control program, SuperTech motor drivers, and Sanyo-Denki 180 oz-in stepper motors.

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This is the original MaxNC controller and motors that I first used on the Sherline milling machine. The controller has a 1 amp capacity and uses 24Volts. The motors are surplus Sanyo-Denki 70 oz-in. stepper motors. It worked wonderfully, very precise and smooth. But it was slow. The maximum rapid traverse speed is 8"/min. The stepper motors are easy to stall if you take too large a cut depth or cut speed. This setup served me well for 5 years. I learned all my CNC G-code using the MaxNC software and this

$Description: C:\Users\Lewismain\Pictures\My Pictures\3-d Website\proto\sherlin2.jpg$ motor setup. This is a great bargain!

I have since switched the motors to these much stronger Sanyo-Denki Unipolar 180 oz-in. steppers. I can't use the MaxNC motor controller because it doesn't have enough amp capacity for these motors.

I am using the Super-Tech 5 amp motor control boards that are on my CNC router. These are unipolar controllers. I share the motor control boards between the router and the mill. With this setup I can get a rapid traverse speed of 12"/min., and I won't be stalling these motors.

You can still buy the basic motor/controller/software setup that I started with from MaxNC. Using it you can start with your home based CNC adventures using the Sherline Mill for less than $1,000!

There are now many other complete milling machine turnkey setups using the Sherline or the Taig or the MaxNC milling machine. A turnkey bench sized milling machine setup will cost between $1200 and $2500.

The milling machine was great for small sized, super precise machining. But I also needed a faster machine that could cut plastic and wood more efficiently. A CNC router is the thing to use.

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This is a Mini-Robo CNC router/engraving machine from Super-Tech. At the time it was the least expensive 8" x 12" table machine available.

Unlike the milling machine, this machine is built for speed as well as accuracy. Using Pac-Sci 100 oz-in. unipolar motors and a 1" pitch lead screw it will rapid traverse at up to 120"/min.! Using the half-step motor controllers the machine resolution is .0025" per step.

The original Mini-Robo machine I bought was designed for engraving using a Dremel Tool. I replaced the Dremel with a Ryobi trimming router head for routing hardwood and acrylic. Eventually I replaced the X-axis and Z-axis mechanism with a Sherline lathe dovetail rail (steel) and a lathe compound for the Z-axis. This made for a much stronger machine for routing.

WHAT CAN YOU DO WITH THIS STUFF?

Here's an example of a project I did using the Sherline milling machine with the MaxNC controller and the small stepping motors (using an old 386SX computer):

I designed a conceptual prototype of a ViewMaster cutting die for the Personal Camera and Reels in AutoCad. The machine G-code was generated in the MaxNC program.

$Description: C:\Users\Lewismain\Pictures\My Pictures\3-d Website\proto\vmjig1.jpg$ This jig required a precise cut for three mating parts: The cutting die, the pressure plate, and the cutting punch. The die necessary for cutting the tiny ViewMaster film chips has to be very precise.

O-1 flat ground stock was used for the plate material and the punch.

I measured the VM film chips cut from the "official" cutter and made an AutoCad drawing of it. I used these dimensions for the cutting die portion of the jig, and sized the punch outline by offsetting the AutoCad drawing by .0025" to give the die clearance.

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This is the punch for the jig. The punch dimensions must be identical to the die dimensions except for a constant .0025" clearance all around, or else the cutting jig would not cut. The edge must also be sharp.

I used a 1/8" diameter 4 flute end mill with a cutting speed of 1"/min., but only cutting .015" deep per pass. The smaller stepper motors require a shallow cutting depth so multiple cutting passes are needed.

The milling machine was able to repeat the cutting path multiple times without any measurable difference in dimensions between cuts.

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This photo shows how the jig cuts on a piece of blank film strip. What I am testing is the ability of the cutting jig to make a precise enough cut to leave the extremely thin cutting edge along the film perforation edges as well as between cutouts (as you can see in the photo the cutout comes very close to tearing through to the film perforations but does not cut through the perfs.). This shows a good cut.

I was very impressed with the cutting precision of my Sherline mill/ MaxNC CNC setup! This is a very tough test of any machine!

WHAT'S NEXT FOR "HOME CNC"?

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I now use this Larken Camtool 2424 dual head router.

I no longer use G-code programming. I use the Larken software that imports .dxf files and writes and edits the cutting tool paths. It is much easier than writing G-code.

USEFUL CNC LINKS

MaxNC

Super-Tech

CNC link page