my first homemade CNC

[valenti]

Hello. Well this is my first try on homemade CNC and i try to designe it the way it will cut aluminium without problems. My main concern is that Y-axis bridge isn't strong enough, about main cage ridgity, i can add more vertical aluminium extrusions to make it more ridgit. All the additional parts are made from aluminium. So please comment/critic the design.

In the link there is the Solidworks 2010 assembly.
http://dl.dropbox.com/u/24846288/Cnc2.rar

[KOC62]

I'm an "armchair" critic - meaning I have not built a cnc for cutting aluminum.

What strikes me is that your machine stands on "toothpick" legs. I see no triangular braces, only parallelograms - a weak structure. I also don't know what forces you will face when cutting aluminum.

Perhaps you could look for design ideas used by successful working units on this forum.

[valenti]

yes, thats true, but i can easily add some more legs at the end of the build(also im using some extra strong brackets, so thaht shouldn't be a problem

[KOC62]

I suppose that you will know what you need to beef up after you build it.

It wasn't only the legs but also the flexing potentional and the lack of corner bracing of your X-axis (long side). And maybe the Y-axis too?

But it does have a clean look to it. Keep going.

[valenti]

on the model, there are not any brackets given, but in real i use strong one. If you mean flex under self weight? no there wont be any, and if any, those vertical legs will hopefully fix it. About Y-axis flex, i agree, it could be a problem, but since linear bearings are preety much apart it wont be a problem, but in the end, if the flex of Y-axis bridge will be a problem, i can still add second aluminium extrusion aside. My main concern is if this design is ready to make some aluminium extrusion, or should i change design before finishing it(since now i hace built main cage, so X-axis, and some part of Y-axis bridge)

[T.W.O.]

What do you understand under "cutting aluminium without problems" and what are the dimensions of your machine.
As i look at your design i think you can only engrave alu with it, but milling alu will be difficult.

i have a simple rule: a machine must be stronger than the material of the workpiece.

greetings

[T.W.O.]

on the model, there are not any brackets given, but in real i use strong one.

If it's possible post a picture of your machine just as you gonna build it.
It is very difficult to give comment on a drawing that is not finished.

greetings

[valenti]

dimensions are x=1580mm y=1200mm z=68mm -those are main cage outer gabarits
about unfinished model. Model is exactly the same as it will be in the end(if u guys will tell me that this can cut aluminium), except on this model, there is no brackets on the main cage(main cage aluminium extrusion will be connected with strong brackets-only that is missing)
also about "cutting aluminium without problem", i meant more like, could this design cut aluminum? or does it have any potential of cuting aluminium

[KOC62]

Still hard to say. It looks too light to me.
What spindle size are you thinking of?

This video shows a smaller machine cutting aluminum. http://www.youtube.com/watch?v=n5ESjVZ4vQI]DIY homebuilt 3 axis CNC router, CUTTING ALUMINUM - YouTube

[valenti]

well i have nothing specific yet for spindle, but im thinking for some dewalt modified tool. Well yes i know its hard to tell if that will work, so i think the best idea is to finish current design to the end, and than see what's going on
thanks

[T.W.O.]

Hello there.

Damn, that a big machine. Do you really need i to be so big?
I think your design have some possibilities. It depends on what you are planning to do with it? Just engraving with a 1mm endmill or facemilling with a 100mm facemill?
I see your planning on using 40x80mm alu extrusions. For such a big machine i suggest you to use at least 80x160 alu extrusions and more beams to support it.
You also need more beams to support your working table.
Work in triangles in stead of rectangles. A triangle is the strongest geometric figure. It's impossible to disform them without bending a side.
Keep in mind that there are not only cutting forces but also acceleration and braking forces and there is also the weight of the machine itself.
Also i should use fully supported rails or even square rails (hiwin or equal).
What i do like on your design is the raised sides of the base so your gantry is a straight beam and not a wobbly bridge contruction.
The only problem: Do you have acces to your working table to place and fasten your workpiece?
The fact that you are planning to use 2 motors and ballscrews to move the gantry is also a must.

Here is a picture of a frame of a machine. Dimensions are approx. 1000x600x200mm.
Compare it with your drawing.

Here is the complete drawing of it.

I "stole" the pictures from Desmond and Winters from the cncworld.nl forum. So a big thx to them.

greetings & success with the build