Question On Cnc Router

[js15]

I have almost all the materials to build my cnc router but have two questions. I will be using acme stainles lead screws 1/2 inch 2 start and 8 threads per inch. The stupid question is how far does the machine know its moving with the stepper motors. I mean since you can use diffirent thread sizes on the lead screws a finer thread will move slower while a more course will move faster per revolution how does the machine know how many thousandths it has moved. The other question is what cnc program would you reccomed for wood plastic and picture engraving

thank you

[jeffs555]

Most all cnc controller programs have configuration settings for the distance moved per step of the stepper.

[ger21]

Mach3 will control your machine, and it can also do picture carving. You'll need a CAD and CAM program to do other things.

[CJL5585]

I will try to answer your questions.

You will need to purchase a program such as recommended by Gerry (Mach3) in order to do photos, etc.

Usually the programs have several menus which allow you to input data for your leadscrew, any microstepping, steps per revolution of your motors. All programs (I have seen) will calculate this distance and enter the value per step of the system. In most cases this value can be entered manually also.

This program sends out direction and step information that it has received from a g-code program thru the computer printer (Parallel) point to a breakout board. The outputs of the breakout board go to the various inputs on the drives (Gecko, OMC, Centent, etc). The drives take the step and direction signals and move the various Axis to the correct coordinates to recreate in the material the image or part that was created in a CAD or graphics package that is compatable with the control program.

Hope this explains a couple of your questions.
Jerry

[spalm]

Think of your screw as 4 turns per inch (8 turns / 2 start). Your steppers have a number of steps per revolution (many are 200 steps per rev). Most hardware controller boards drive the steppers with micro-steps to get smoother movement (4, 8, or 16 usually jumper selectable). So you multiply these three numbers together and enter that number into the controller software.

So with your screw and if your motors are 200 steps per rev and you want to run with 16 micro steps:
4 * 200 * 16 = 12,800
Now enter 12,800 to tell the software how many pulses it should generate to move 1 inch.

You will also have the option to tell the software how fast to send these pulses. The object is to send them as fast as your machine can take them, but no faster.

There are endless combinations; some of the hardware controllers generate the micro-steps by themselves.

Same concept when using metric.

Steve

[ger21]

Originally Posted by spalm You will also have the option to tell the software how fast to send these pulses. The object is to send them as fast as your machine can take them, but no faster.

A better (imo) way to describe this, is that you tell the software the maximum speed the motors can spin reliably without losing steps (found out through trial and error). This maximum speed is used when you're machine is positioning the tool, and are called rapids.

Actual cutting speeds are called out in the g-code file with an F.
F20.0 would mean cut at 20 ipm.

[js15]

thank you for the information. I have just a couple more questions for you if you dont mind. Where can I purchase Mach3 and what computer requirements will it require. Whas other software do you reccomed to run with it for designing, cutting out and routing wood and plastic. I was looking at the kits that www.lowcostcncretrofits.com sells what kit do you think will operate a 36'' X36'' aluminum router. I also notice that some of the kits come with a jog remote what is jogging a machine.

Thank You for all of your information. I will try to start building the machine at the end of this mounth and will try to post pictures.

[ger21]

Get Mach3 at http://www.artofcnc.ca

You can download the demo and try it out before you buy. It's limited to 1000 lines of gcode. It need Win2K or XP, and 1Ghz is the recommended minimum, but it works for some on as low as a 500Mhz PC.