MANY of you guys have sent me emails regarding the 4 axis CNC hot-wire cutter that I have been working on.  Rather than answering the same questions over and over again, I've decided to write this little article so that  I can share the info I've accumulated with everyone. When I have everything in place and my machine is finished, I may write a construction article that will be significantly more detailed than this text. :)

Yo, Crash! What is a CNC Hot-Wire Machine?

A CNC hot-wire machine is a CNC machine that allows one to cut foam accurately using a heated wire. The best way to imagine this is to picture TWO separate machines (towers, if you will) where a single point on each machine may be actuated on a Z and X plane simultaneously. Now, picture a wire strung between these two machine's single points and you have what I'm talking about. A blank of foam is placed in between the two towers, the wire is heated with electrical current, and a program is run thus moving the heated wire into the foam to cut shapes. Four axes of motion (2 on each tower) are required since often times, when we cut our foam wings, we want something more than just a constant chord, rectangular-shaped wing. Separate control over each tower's 2 axes allows one to design and cut wings of various shapes (i.e.,swept wings, tapered wings, double tapers, wash-in, wash-out, etc.). A computer program is required to precisely move each tower to meet specific numerical criteria to produce the intended final product - CNC (computerized numerical control).

Of course, it's very easy to gather the necessary materials to cut your wings WITHOUT a CNC machine, but if you're like me, you'll soon realize that doing it the "manual" way requires a partner to help, LOTS of practice with that partner to get the process right, the fabrication of templates to guide your wire, and lots of foam to waste with fine-tuning your process. As well, you will find that repeatability (the ability to accurately reproduce the same thing over and over) is low and waste is high. There are "manual" systems that allow you to do all of this with pulleys and fixtures so you don't have to rely on a skilled partner, but those systems cost almost as much as a CNC machine to buy them, and quite frankly, I don't want to invest the time in making a system of my own (figuring the pulley positions, etc.) when I can just build a CNC machine (something that I already fully understand) to do all the work for me. :)

What kind of wire do you use for cutting foam?

This is an easy question to answer! I have experimented with several different types of wire (guitar strings, NiChrome wire, Stainless Steel Fishing Leader wire, etc.). I have found all of them to work favorably, but they all present the same problem in a production environment - they stretch and break! Dennis (Dorsal) turned me on to a new wire and I hafta say, this is the ONLY wire I will be using from here on out:

Rene Wire

Thirty-six bucks will get a 50 ft. spool of this stuff shipped to your door, and it will probably be the last wire you will ever need to buy! I've strung both of my "manual" bows (30" and 52") with this wire and have yet to break it. When you are done cutting, crank of the juice and watch the foam remnants burn away - all without breaking the wire! This is the wire that the commercial cutters use when they cut the large blanks of foam down to smaller, more manageable pieces.

What Power Supply do you use to heat the wire?

This is an area where I have to admit to being no expert at, as my electrical skills don't go much beyond being able to solder and read the simplest of wiring diagrams. When I first got into hot-wire cutting, I used my friend's (Max Blose of B&P Associates and Waco Hobby Stop fame) equipment. He heated his wires with a VariAc. I started looking for one of these things and quickly realized that it was WAY out of my price range (often $200 and higher!). I ended up with two much lesser expensive power supplies that fir my budget much better:

SMALL, INEXPENSIVE UNIT - I followed these instructions and built this power supply for less than $20. I have found that it works really well for bow lengths of about 30", or less.

LARGER, MUCH MORE CAPABLE UNIT - This power supply will probably have you looking for a friend with professional electronics skills, if you are like me. My buddy, Ron Stubblefield, helped me on this one (he bought all the components and built the thing - I just payed him LOL). This unit works really well for small AND large bows. I have used it with my 52" bow with no issues whatsoever.

Where did you get the plans for your machine?

I looked all around for plans detailing a machine like this and I found many! The problem, as most of you know, is that I wanted to build a machine on a budget. This not only applies to the cost of a good set of comprehensive plans, but of the build, too. When I came across the link below, I couldn't resist!

FOAM CNC CUTTER FOR YOUR HOME

If you had any difficulty in picturing what a CNC Hot-Wire Cutter might look like, then the pics on this site should help you to understand.

You will need to use PayPal to order your plans, and after the purchase is complete, you should be given a link to download the PDF file for the plans. In my case, I didn't get the link. No worries, though - I checked my receipt in PayPal and got the phone number for the people selling the plans, rang them up, and they took care of me right away (it turned out that the email through my ISP, also my PayPal address, had recently added some new SPAM protection and this inhibited me from getting the PDF plans).

The plans are VERY easy to follow and require pretty much no knowledge of this type of machine to pull off a good build. The plans were cheap and the materials to build the final product would not break my wallet. :)

What Stepper Motors are YOU using?

The shroud of mystery regarding stepper motors was pulled away from my eyes by the PhlatBoyZ. After building their Original PhlatPrinter (MKI) and PhlatPrinter MKII CNC machines, I learned so much about CNC principles, and this journey resulted in some spare parts in my inventory. LOL The PhlatBoyZ recommend stepper motors and driver cards from a company called Easy-CNC. I found that the stepper motors that Easy-CNC offered in their package were a bit weak for my MKI machine and were quite overpriced. In fact, when I started my MKII build, I elected to NOT use these stepper motors and sourced another motor for that build. Just before I started the build of my MKII, I scored a great deal on some better stepper motors for my MKI machine, so I upgraded to them and pitched the old motors in a box - these are the motors that I plan to use on my 4 axis CNC Hot-Wire Machine. I only had 3 motors, but found other PhlatPrinter customers had upgraded their "stock" motors, so obtaining a fourth motor to match what I already had was fairly easy.

If YOU don't have motors on hand like I did, then I can recommend a good and inexpensive motor for you.The truth is, if I didn't already have steppers that could be used, and had to purchase four new stepper motors, I would have just bought four of these steppers:

Vexta Stepper Motor

I have three of these in my PhlatPrinter MKII and they are working flawlessly. Keep in mind, the torque requirement for the stepper motors in this application is only like 30 oz-in and these motors provide something like 4 times that amount, but they would fit the bill just fine.

So what kind of driver card will you use to run your steppers?

I have a very unique opportunity here. If you've read about my new overhead-gantry CNC machine, you already know that I am driving the stepper motors on that machine with a Gecko 540 driver card. This card is a top of the line driver card and handles current regulation in a very cool way - you choose a resistor of a certain value to correspond to the highest amount of current you wish to drive through the stepper. That resistor is soldered in to two of the pins in the DB9 connector plug that connects the stepper motor to the drive card. I plan to mount my Hot-Wire CNC towers to my overhead-gantry CNC's table and will be unplugging the three DB9 connectors for the big machine's steppers from the card so that I can plug in the four DB9 connectors for the Hot-Wire CNC's steppers. Cool, eh? This approach is keeping me from having to buy a new 4 axis driver card and power supply (not to mention the parallel connector and PC!) for this new machine. ;)

There are two other options that I considered before the realization that I could get double-use out of the Gecko drive, and these are options that I'll suggest yo you guys:

1. BUILD YOUR OWN CARD -  This Hobby CNC card is an ideal solution for you if you have experience with soldering components onto boards, or have a friend that can help you out. For a 4 axis card kit, it will set you back $99, but lots of people have used these kits without any problems and they have a very good reputation amongst CNC hobbyists the world over. Keep in mind, though, that this card can only supply power to your stepper motors in a "unipolar" fashion, which means (in most cases) that you'll not realize the full holding power advertised for most stepper motors (most motors achieve max holding torque when wired in a "Bipolar" fashion), but in this application it will be just fine. Remember, you only really need about 30 oz-in of torque to build one of these machines.

2. EASY-CNC CARD -  This card is made by the same manufacturer as most of us PhlatPrinter customers are running in our PhlatPrinter CNC's. The cool thing about these cards is that if you blow a component (usually the IC chips go out if you short something), the whole card is set up as "Plug and Play", so you can just replace the faulty component(s) yourself instead of having to buy a whole new card! PhlatPrinter owners that have blown out IC's on their boards have been able to buy new chips for about $6! I personally LOVE these cards! PRO TIP: If you buy one of these cards from the Easy-CNC website (and live in the USA), the current pricing is $189 shipped. The guy that owns this company has an ebay store and often puts these cards up as "Buy It Now", or for auction. Either way, you can obtain one of these cards much cheaper from his eBay Store. His username is Autohec.

What Power Supply do I need to power up my driver card?

Whichever driver card you choose, you should look at it's requirements as specified by the manufacturer. In the case of the two cards that I have recommended above, they'll both work dandy with the Power Supply that I have been using on my Easy-CNC cards:

24 Volt, 6.5 Amp Power Supply

Another little "PRO TIP" you might consider is that old computer power supplies can be used to supply the power to your driver card (if it will accept a minimum voltage of 12v like the two I've suggested will). Often times people will have an old PC just sitting in a closet somewhere because they can't bring themselves to dispose of them properly. If you search the interwebs for "pc power supply conversion" , you'll get all kinds of DIY articles for converting your old supply into a "Lab Power Supply". The 12 volt rails can easily carry enough amperage to keep your driver card happy. Just BE CAREFUL and follow the instructions CAREFULLY when doing the conversion - you could get hurt badly (the capacitors in these power supplies can hold a serious amount of juice!)! 

What software are you going to use for your machine?

This is a very good question. I've searched all over for the software to run the machine and have found some very nice options (some even FREE!), but I have elected to use the FoamWorks software offered by Designed Computing Systems. I have played with their demo copy and have found that it's very easy to use and should suit me fine. Plus, my friend Randy uses it, and if he likes it I'm certain I'll like it, too.

Well, that's it! I imagine that you can now see why I've elected to write this article ONCE rather than reply over and over to everyone's emailed questions.  A special thanks for your kind patience for those of you that have been waiting a bit for this information. :)

Good luck with your build, and if you have any questions, just shoot me an email!