A Little Advice

[Carson89]

Well, this is my first thread after spending a few hours browsing through CNC router designs and what people have done when making their own. I have now convinced myself that i should try and build one of my own.

Now, whilst i know the basic principle of how a CNC router works, i am unfamiliar with exactly whats needed to drive each axis. I know that I need a ballscrew, or rack and pinion and a stepper motor for each axis, but what i dont know is exactly what i need for each axis for best operation (ie. the kind of ballscrew, stepper motor, etc).

I have drawn up a complete, to scale, model in Google Sketchup (i know its not great but it does the job) and have decided that i'd like to build a CNC Router which has roughly 2000mm movement in the x-axis, 1500mm movement in the y-axis and 150mm in the z-axis. This should be big enough for anything i may need it for.

I am a student who will be going to university this year and so, the cheaper i can make it without compromising on quality, the better. I also only have access to a basic power tools (pillar drill, grinder, welder, etc) and a large selecting of hand tools, so this will have to be taken into consideration as well.

I would be very grateful for any advice that you think i may need to build this.

Cheers,

Carson

P.S. Here is the model I created. The middle (slightly smaller one) pole on each axis is a ball screw, and the white tubes on the side of the model is conduit for wires.

[Al_The_Man]

There are many disiplines involved with designing a CNC system from scratch, to speed up the process, decide first what you want to do with the table, work wise, with this in mind see if you can see some tables already doing this kind of work, especially industrial types, to get an idea of design concepts.
This will decide the mechanics, rigidity etc, once you have a rough design for this you should have an idea of the weight of the moving parts and this, coupled with the rate of accel/decel and any side forces etc will determine the size of stepper/servo's.
To get a feel of what is involved here, load your designed system into a sizing program like Kollmorgen one etc.
This will give you an inkling into how load inertia at different speeds and acceleration rates affect the size of the motor.
Due to the different characteristics between steppers and servo's, they both require a slightly different approach due to speed/torque limitations when using stepper motors.
Al.

[Oldmanandhistoy]

Hi Carson,

As always Al The Man is on the money. It will be well worth your while doing as much research as possible as mistakes can be costly.
Find as much information as you can then ask specific question on detail you are unsure about; you will get some very knowledgeable answers from some of the expert members on this site.

Good luck with your build,

John

[Carson89]

Thanks for the advice so far, much appreciated.

I am aiming for a fairly versatile machine, which is capable of handling most materials up to metals such as aluminium (maybe some steel). I will be using the machine to perform simple milling, engraving, cutting out parts for projects and anything else I may need the machine for.

As for rigidity, i'd like to build something that will be simple yet very rigid and strong enough to support anything i may decide to put on it. Im the kinda guy that wants to make sure that i won't be pushing the machine with what i throw at it.

Speed wise im not bothered, as long as it is capable of doing what i ask it to do (but without taking days over a task), then this is fine. Being quick is just a bonus.

Weight. Well, i am planning on building the table out of square steel tubing welded together to give a strong and rigid platform to work off. The gantry any everything else that moves will ideally be made from aluminium in order to minimise weight in the moving parts.


Hopefully, the above information will have explained in more detail what i'd like to get out of this machine, etc.


Thanks again,

Carson