[UKRobotics]

I am going to start building a CNC machine this year, have done quite a lot of research so far and for the electronic side of things and I intend to use 3 gecko drive controllers, servo motors and this http://www.campbelldesigns.com/breakout_board_plus.htm interface board.

The thought that is troubling me now is whether to build a CNC router, or CNC mill. The only CNC machine i've had experiece using is http://www.suregrave.co.uk/2516.htm <--- this router which they have at my school. I have got used to using this machine now, so I wouldnt want the thing I build to have a lower spec than this.

Somthing I like very much about this router is the size of the table (25" x 16") - (my machine would have to have a work area at least as big as this) but the thing I dislike with the school machine is the speed, - the top speed of 3"/sec is not very fast, and when milling hard plastics like polycarbonate I can only run it at about 1.5 inch/s @ 0.5mm per pass. It is not very powerful and cant do more than 1mm per pass even in soft plastic. I'm guessing that this is because it has rather weedy stepper motors but I could be wrong.

The types of materials I want to be able to CNC will be mainly plastics such as HDPE and Polycarbonate, composites like carbon fibre, and 6061 or 7075 T6 ali.

It is unlikley I will need to machine steel or similar metals.

I suppose my question is, If a built a CNC router based on this design - http://www.suregrave.co.uk/images/cipher2516.gif and used a decent sized servo motors on each axis, would I be able to machine aluminium with it and would I be able to machine plastics faster than I can do at the moment on the school machine ?

As for the depth/thickness of the materials, I will not need to machine any materials thicker than 30mm.


So..... should I go for a router or a mill?


Any thoughts, comments, opinions etc on this topic would be apricieated.



Dominic

http://www.ukrobotics.com

[InventIt]

You could build a router but just make it heavy duty with good thk linear slides or large supported rods. This way you'll enjoy the best of both routing and milling. If you want to mill alum you'll need to make the machine heavier then if you only intend to do plastic or wood. Build the machine according to the work you intend to do with it. There are alot of machines on here that can mill alum. Check them out. As for speed, your headed in the right direction with the Geckos and Servo motors. You can also get good speed 350IPM+ with steppers using the right leadscrew.

[ESjaavik]

Me too!
I was looking for the right forum to post, and it seems I did. I don't even have to start a thread myself. :-)

I want to build a mill for higher speed milling in aluminum. After much pondering I guess the gantry type is the best for low space requirement and light weight of moveable components. But most of what i've seen looks like not much thought went into making it rigid but still not heavy. Placing the ball slide carriages at max distance from each other will oppose the gantry's tendency to "wag" under acceleration. But where do I put the ballscrew for the gantry? Not on one side, that will create a moment skewing the gantry under acceleration and cutting forces. One on each side? Expensive, and more rotating mass. Under the table? More mass in the connection to the gantry slides.

And how to construct the gantry. A spaceframe construction would be light and stiff. Any disadvantages?

Did anyone here study the different possibilities and their pro's and con's?

[Stevie]

AS a machinest and tool and diemaker with 35yrs behind me i'd say stick with a regular mill layout; the only Gantry machines i've seen out in moldmaking had many problems with both ridgity and alinement
I'm in the design stage of the mill I want; see this thread http://www.cnczone.com/forums/showth...&threadid=3071
I'm looking at several sizes right now; I'll finalize the design after the Lathe project is fully working; see this thread http://www.cnczone.com/forums/showth...&threadid=3029
It's all a case of what you need and the best way to make it; if your background will allow you to make good close tolerance parts for your project then thats the way to go; however if your a newcomer to machining and just want to try CNC then I'd suggest a simpler and cheaper alternative; plus the use of the project has to be taken into account; mine will be to help me finish a 1/48th scale Battleship (Yamato) to museum standards

Look at your useage and your ablities to build to guide you

[IndHobby]

If you make(convert) the CNC mill first you can use it to make a CNC router, when it comes to machining metal there is no substitute for mass of cast iron. this way you will have two machines that do each a task very well, vs. one machine that does two tasks ok.

two cents.

Thanks