CNC Build or Buy
To build or to buy, the eternal question. In the end we bought a used machine. However the research into building a machine made it easy to understand what we where looking at when we went to buy our machine.
We found really good quality machine with all of the parts, but which was not in working order in a business that had gone under. Unfortunately there are lots of people that try starting CNC wood or plasma businesses and it's got to be horrible to try and compete with garage owners that will do the same work with almost no overhead and little concern for making much money. Think long and hard about it, if you are thinking you can make a living from your CNC work.
By the way, buying used is the best way to get a sailboat too, yet we are building one. So if you have your heat set to build, then build it.
What You Need to Know
Hands down the best site to start researching CNC is www.cnczone.com. It is also the most overwhelming. This might be the best place to start: www.cnczone.com/forums/forumdisplay.php?f=251&order=desc
Most hobby and lots of commercial CNC machines use Mach3 software to do the job of actual controlling the machine because their software is capable and very well supported. I found their web site; www.machsupport.com and forum very educational, especially the tutorial videos.
Bottom line is capabilities of a CNC should be dictated by "form follows function". It would be nice to have a CNC that could cut large plates for boat building, but having build the sub, I know that 90% of complex the parts are less than 2 sq feet, so a 4x4 table is ample. I also know few things I build needed to be very accurate. Most of my cuts were only within 1/32 inch, however the few parts that do need to be accurate, like gears of winches and rudders are very expensive to buy. I am not going to mass produce parts so speed is not an issue, and 45 to 140 ipm is the optimum cutting speed for the Hypertherm when working on plate that is 3/8 to 1/8 inch thick.
The requirement for a router is two fold. I'd like to do relief carvings in acrylic and foam that will then be epoxy coated in order to produce decorative works, and then I'd like to be able to foam carvings that will be used for lost foam casting. Toward that end I'd like a Z-axis of travel of at least 5 inches.
I also will only use this machine one or two days a
month so it needs to be able to be broken down and stored without
too much effort and its cost should be in keeping with it output,
which is to say; cheap. It needs to tolerate being at sea too,
since this is one tool we plan to take with us. So aluminum is our
A portable CNC is a great idea for how we plan to use our machine. It can be setup in the cargo hold or on deck or moved ashore. During the build, it can be moved into the shop during bad weather or carried out to the steel under the gantries so that moving the steel is not so difficult a task.
SteelTailor and it's knock offs are the design that I think will work best for our needs which is plasma cutting larger steel plate parts for a boat and routing foam. Routing wood in not something we plan to do and that's good because I doubt the arm could support much of a router.
The problem with the StealTailor type of design is that it is not going to support the tork needed for a router to work on acrylic. However routing foam would not be an issue.
I like that the material does not need to fit into the dimensions of the table. You could easily set the unit down on top of a 1/4 plate of steel that is on a welding table or even already part of the boat and have it cut a perfect hatch opening.
I have not yet seen it done, but I can see any reason that a 3x3 CNC table can't be built without legs or a bottom. That would again give it an advantages of portability and being able to work on a sheet of material that is far too large for even the large tables and far too large to move into the shop.
Drivers and Motors
Kits and Packages
Torch Height Control (THC)
Heavy plate steel when plasma cut will just lay there, but thin steel will flex and bend. The THC automatically raises and lowers the torch over the bumps by monitoring the voltage of the arc. This prevents the torch from crashing into the metal and keeping it the correct height for cutting. www.CandCNC.com sells THC and control packages.
Motors: Stepper or Servo
Servo motors are more susceptible line noise and there rpm is much higher so they need to be geared down. Stepper motors are slow but more common, especially on router tables. Count on about 500 rpm from a stepper motor. A router needs slower speeds and a plasma needs to do 100 ipm on 3/16" steel.
Rails and Drive Options
All thread. - Cheap, Best for small 3 x 3
machines. Problems keeping them clean.
CNC Table Links
solsylva.com - Plans for router tables and good explanations.