Frequently Asked QuestionsClick questions for long answers. |
| Machine
Construction How much do the tables cost to build? $350 to $1300+ How long will it take to build? Half day to a week What tools are required? Home shop tools What are the tables made of? Hardware store parts and standard components from online suppliers. |
Machine Capabilities
Can the machines cut metal? Not well How accurate are they. What is the resolution? Accuracy 0.003" Resolution 0.0007" and better |
| Software
and Computer Do the plans cover any of the electronics or software? No, but this site gives links and info. What kind of computer is required? Ancient 486 and up. What software do I need? What is its cost? Freeware, shareware and up. What is the difference between Mach3 and TurboCNC? Price and features ;-) |
| International
Do you ship outside of the United States? Yes I live outside of the USA, finding parts may be a problem; what are the sizes of the materials used? List given, substitutions possible. |
| Miscellaneous Do you sell a parts kit or an assembled table? No Do you give refunds? Certainly |
|
Hacksaw |
Machine Capabilities Can the machines cut metal? Only soft metals and it must be done slowly. Machines built of wood and thin aluminum lack the mass and rigidity to cut metal well. The 25 x 25 and rack/leadscrew machines have been used to cut aluminum, but the depth of cut has to be kept very shallow. For small metal work a micro or mini-mill retrofit is the route I would choose. A retrofitted bench or knee mill would be a better choice if the primary jobs will be heavier metal work. Expect to spend thousands of dollars, not hundreds. Here is a picture showing the difference between a steel cutting mill's servo and these machines' steppers. How accurate are they? What is the resolution? Accuracy (tolerance) and resolution are often confused. Accuracy relates to the slop and play in the actual machine. Resolution relates to the software and the smallest distance the table can be commanded to move. High resolution without good accuracy is useless. (Measure with a micrometer, cut with an ax.) With hardware store threaded rod as leadscrews, backlash will be between 3/1000" and 10/1000". This range is the thickness of one to three sheets of paper. The photos on the Work Examples page show what this accuracy can and can't accomplish. Acme rods with anti-backlash leadnuts will improve performance. Resolution is in the software, computer, motors and gearing. This number is determined by the speed of the computer and capability of the drives and steppers along with the number of threads in the leadscrew and/or teeth in the pulleys. For the leadscrew tables with 200 steps per revolution steppers, the worst resolution on an old DOS computer is: 200 steps/rotation with ½ step micro-stepping and 18 threads/inch leadscrew with direct drive = 1/(200 x 2 x18 ) or 0.0001389 inch per step. This number can be made better (even smaller) with a faster computer and 1/8 or smaller micro stepping. This may give smoother stepper operation but otherwise there is likely no benefit since the accuracy of the leadscrews is the limiting factor, also the smaller microstepping can adversely affect stepper performance. The accuracy of the 25 x 25 and rack/leadscrew machine will vary according to the quality of components used. They were designed to permit a number of options from hardware store parts to commercial components. |
Software and Computer Do the plans cover any of the electronics or software? The plans go as far as stepper installation, but do not cover the setup of the drives and software. The tables were designed to use products from HobbyCNC and Xylotex because these two companies work with the Do It Yourself market and offer support and documentation. There are now other suppliers who offer similar products and support, and their drives and steppers can also be used. The plans do include directions for determining the Steps per Unit value required by the software. There is more information on the Drive & Stepper and Power Supply pages. There are a number of software choices though most prefer Mach3. This product also offers excellent documentation, support, and tutorials. What kind of computer is required? TurboCNC controller software can use an old 486, and Mach3 requires Windows XP or later. An entry level Compaq 3000+ AMD Sempron with 256 MB SDRAM is used here with Mach2 and it works fine. This is mentioned because there was once the concern of computers having the processing capacity for CNC work. Now a basic computer is fast enough. This answer deals with these two popular software options and the required computers. The computer used for the CAD and CAM work can be a different unit than the one used to control the table; the type of computer used here too can vary. I have used old CAD programs on an old 486 which worked well enough, and have also used a basic P4 with contemporary software. Often a better computer is kept in the safe home environment for design work, and a hand-me-down computer is used to run the machine in the dust of the shop. The files can be transferred by memory stick or even floppy disk if the shop computer is not networked. Here is a note about protecting the computer's parallel port.
What software do I need? The software required for 2 or 2.5 D work shown here can be downloaded for free or low cost. In a nutshell, three distinct types of programs are needed. Some software combines the functions and others just do one aspect. The three functions are:
To create the drawing on the computer a CAD program is needed. A9CAD is a 2D program that is free. Older versions of Corel Draw can be found for $25 ± ; this program is used rather than Paint Shop Pro, for example, because it can export DXF files. DXF is a standard format used to transfer files among different programs. (DXF=Drawing eXchange Format) Once the file has been drawn it needs to be converted into G-Code which is what the machine's controlling program understands. A free G-Code generator or converter is ACE Converter, it only does 2.5D which means the Z axis is either up or down, like a plotter pen, (no 3D), but the price is certainly right. It takes a DXF file and converts it to G-Code. Since ACE only converts DXF files it is important that the CAD program be able to export in DXF. Once the CAD drawing has been converted to G-Code, the G-Code is given to the computer which controls the actual CNC machine. TurboCNC and Mach3 are popular controller programs. (See the next question for details.) These tell the drives how to move the steppers. 3D work requires more expensive programs for the CAD and CAM components and for the most part begin in the over $1000 realm. RhinoCAM and VisualMill are popular choices. MeshCAM is a low cost option in the $150 range but it is limited in 3D. Fortunately for the pocketbook, both TurboCNC and Mach3 can work in 3D so no extra controller software is needed to switch up to 3D. It is possible to use 2D software to cut material that is thicker than the single pass that the 2D program creates. Mach3 includes the option in its software.
What is the difference between Mach3 and TurboCNC? TurboCNC is a shareware application with an unlimited free trial; it has a $60 registration fee and the source code is available to registered users; therefore customization is possible. It is DOS based which has advantages and disadvantages. On the plus side it can be used on a very old 486 computer; the down side is the user interface is not as easy as point and click. Another disadvantage with TurboCNC is it does not have a constant contour/velocity function. CAM software frequently codes many arcs and curves so they are a long series of very short line segments. Without constant velocity in the controlling software, the router ramps up and decelerates for each tiny line; this causes jerky motion which can telegraph through to the work causing the edges to be scalloped. Mach3 is Windows based software and requires Windows XP or newer. It costs $175 and is considered to be one of the best software values available. It uses a mouse interface, has a dynamic display of the work as it is being cut, and has constant contour. It is a much more feature rich product in ways too numerous to list here. It offers a free trial version as well, but the trial version is limited to only 500 lines of code. (This sign was 6500 lines of G-Code.) In my opinion, if the newer computer and higher price can be afforded, Mach3 is definitely the software to use. At the same time, TurboCNC can get you into the game for very low cost.
A note about desktop computer protection. An inexpensive ounce of prevention is installing a second parallel port card inside the desktop computer to connect to the drives. If something fails, the problem will likely cook the second parallel port card before the current reaches the other components of the computer. Since parallel ports are frequently integrated into the motherboard, damaging the original parallel port could be catastrophic. |
Below is a list of the home center parts used in the other machines.
|
Miscellaneous Do you sell a parts kit or an assembled table? No, a parts kit has been considered, however the shop time drives the price beyond an acceptable level. This is why it seemed that there would be an interest in these plans. The final product is of respectable quality, and the price is very reasonable when the labor is supplied by the end user. Do you give refunds? Of course! You must be satisfied. I'll proudly put these plans and the machines against any comparably priced product out there. |
