Beginners CNC Advice

[UKRobotics]

I'm planning to build a CNC mill/router. I have a rough idea of what I want to do, and if someone who has more experience with building these things could answer my questions it would help me a great deal and I'd really appreciate it.

My plan is to build a CNC Mill/Router based on this design -http://www.suregrave.co.uk/images/cipher2516.gif which is what we have at college but I’ll make the table slightly larger (about 1 sq metre).

One motor moves the table for the Y axis, another motor moves the spindle motor along the X axis and also mounted on that rail is the 3rd motor to lift the spindle motor up and down for the Z axis movement.

I intend to use servo motors for the axes and a 1.2HP S1 Rated 24VDC Bosch motor for the spindle motor.


Now for some questions …..


The gecko drive controllers that lots of people seem to use look ideal, but what is the difference between the G320 and the G340?

Also, the whole of the electronics/computer stuff is still confusing me somewhat. I draw something in cad …. – Then what do I have to do to get the CNC mill to cut it out?

Do the gecko drives all connect to the computers parallel port?

What happens about data storage – do the gecko drives have internal memory or is the data streamed off the computer as and when it’s needed?

How does 3D CNC milling work? Is there software that can import a standard JPG/BMP file and convert it into something that the CNC machine would understand?

I noticed the threaded rod used in the college CNC mill is very different to the standard threaded rod available in DIY stores – the thread is much flatter and there’s a wider gap between each thread. Question is, is standard threaded rod ok, or should I try to obtain some of this special stuff?

Something else I noticed is the motors in the college CNC mill are directly connected to the threaded rods for the axes, but a lot of the home built machines I’ve seen on the internet use a belt drive & reduction to connect the motor to the threaded rod. In your opinion which method is better & why?

I was also intending to use a normal drill chuck to hold the cutters. Would this be acceptable, or should I use something different?

Finally, can you recommend some servo motors to uses for the axes? Ideally I’d like something which is both fast and powerful.

Apologies for the large number of questions but it would help me immensely if anyone could spare the time to reply.


Regards

Dominic


http://www.ukrobotics.com

[sol]

Lots of questions; I take a shot at a few.

"I draw something in CAD ..Then what do I have to do to get the CNC mill to cut it out? "
This is a basic query that seems to stump everyone at first and then once understood seems too obvious, or vague, to answer...in part because different software packages go about it differently...
But for low up front cost...
Draw something in CAD
Convert it to DXF in the CAD program
Use ACEConverter (2.5D)(free) to convert the DXF file to Gcode
Use TurboCNC ($20) to send the Gcode to the Geckos

The Geckos connect to the printer port of the computer. Two wires/connections (step,direction) per Gecko.
For a basic set up you only need to pull three pairs (X-2,3 Y-4,5 Z-6,7) out of the printer cable. The computer via TurboCNC streams the data to the Geckos.
TurboCNC is DOS based and can be run on an ancient 486...so you do not have to put your nice CAD computer next to the dusty router. If using two computers transfer the ACE-Converted gcode file via floppy to the 486 which has TurboCNC installed.

Vextractor (free logo infested trial version) can convert BMP, Jpeg and others to DXF which can be cleaned up in CAD and then sent to ACEConverter.
There also is the ACME profiler for $20 which is a neat toy that converts greyscale to gcode and is sort of "2.75 D" in that it works from a plane but has more than just up/down in Z.

Regarding the threaded rod... do a search on this site for Acme thread, lead-screw, ball-screw...tons of info...
For a cheap machine, hardware store threaded rod will work...I'd have used it when I was a penniless student, but it is of low quality, resolution and durability will suffer.

Enough for now

[onthemarc]

Can you use a USB port to hook up to the controller instead of the parallel port? Have heard USB is faster and more reliable.

onthemarc

[Chagrin]

"Normal drill chucks" aren't the best choice for this type of application; they don't have the grip that a proper collet would and the morse/jacobs tapers that they normally connect with aren't designed for the side stresses they'd see on a CNC router.

[abasir]

onthemarc,
Most 'hobby' cnc controller are parallel port based because it is easier to make and parallel port works in all OS (Windows, DOS, linux, etc). With USB you need to develop other codes just to talk through it. The speed at which most hobby CNC operates (normally less than 50kHz pulses) is lower than most parallel port limits.

[vineyard]

New address for acme profiler:
http://www.gunstar1.com/scispec/scispec.htm