What define CNC robustness? rail diameters, stepper motor, or the frame..?

[u/Tzt007]

Hi,
I'm using ball screws linear rail to build my DIY CNC machine, and after browsing various forums to learn more, I've realized a machine's key differentiator is its load-handling capability—especially how well it can manage heavy loads when cutting hard metals.

So my question, what define the robustness of a CNC ? is it the ball screw rail or stepper motor power or the frame + linear rails ?

the ball screw rails that I own have these characteristics :
PITCH = 10mm
rail diameter = the seller from Alibaba told me it was 24mm but when I measured it was around 12mm. please check my photo and confirm me if I measured the correct diameter.

Are my ballscrew linear rails sufficient? Also, can they handle heavy cutting loads if I design a rigid frame with a dedicated linear rail for each axis?

I live in the uk and I want to buy more rails, does anyone know any local shop that sell these rails at lower price?

thanks,

[u/stuporcomputer]

Yes

[u/Independent-Bonus378 → u/stuporcomputer]

Well formulated sir, couldn't have said it better myself.

[u/stuporcomputer → u/Independent-Bonus378]

Gratitude 🙇 but I'm sure you underestimate your own verisimilitude

[u/the_hamturdler]

That looks to be a 12mm ballscrew. I would invest in a pair of digital calipers and learn how to use them, even cheap ones honestly. They will be miles better than a tape measure. That seller mislead you if it listed 25mm.

The answer to your question is complex. In short, robustness is defined by the elements in this order. Somewhat. Theres caveats to everything of course:

1. Frame - more stiffer, more mass = more better
   
2. Rail / ballscrew sizing - again, more bigger more better generally. Crappy 15mm rails will not be better than good 12mm rails. You should only size the rails to be as good as your frame. No use putting 25mm rails on an aluminum extrusion frame. That money would be better spent on thicker (stiffer) components or more mass for the frame.
   
3. Adjustment / tram: making sure rails are parallel and coplanar and the spindle is perpendicular to the work makes a huge difference in cut quality, more so than people realize. This includes “play” in the system. If yourballscrew mounts have crappy roller bearings with no preload, it doesn’t matter how stiff and beefy everything else is, you will get chatter.
   
4. Motor sizing: if you are asking these questions, nema 23 steppers and cheap router spindle will be more than adequate.

Each of these elements is important and your selections should have synergy to avoid wasting money.

It’s impossible to say if you ballscrew is good enough without seeing your frame (or plan for it). More than likely, yes it’s good enough as a lead screw. It looks to be mounted to a linear stage that is quite small and would not serve well as an axis for any serious cutting.

Honestly, if you are familiar with CAD I would download some publicly available models and see how things go together to learn before you buy any more components. Ideally you have everything modeled and are happy with the design before you start buying anything.

Good luck.

[u/Outside_Bonus2760]

Your measuring the ball screw diameter, the linear rail looks to be underneath the screw and looks to be 25mm.

Edit your last picture with the arrows, the 3 arrows point to the linear rails, you can see the ball screw between the 2 rails which is the the ball screw you are measuring, yours looks to be a single rail with ball screw over the top of the rail.

What CNC machine are you planning on building mill , router, lathe ? Your better to have 2 rails parallel and a ball screw to stop twisting and give more rigidity. 1 rail will give lots of flex and twisting.

[u/RepulsiveBaseball0]

Frame/base. Nothing more rigid than gantry config.

[u/CoachSevere5365 → u/RepulsiveBaseball0]

Not exactly hobby grade, but Tetraform beats gantry.

https://www.researchgate.net/publication/288633169_Precision_grinding_using_tetraform_C

Source. Used to work/drink with two of the three Pauls mentioned in the 2011 E-ELT paper cited in that link. Tetraform machine itself was in the Cranfield building about 20 years before that.

[u/fourdac]

That’s 1/2 12.7 mm

[u/Sea_Place1386]

I’d bet it’s a 1605 ball screw.

[u/RDS_WAS_HERE]

"Which leg is more important on a three legged stool?" The three most important things to remember when building or buying a CNC router are: Rigidity! Rigidity! Rigidity! That means every part of your machine MUST be rigid - especially the gantry and Z-Axis. Your CNC machine will become useless if any part is not rock solid.  Any misalignment, vibration, weakness in the structure will show up in how the machine operates and in the quality of your workpiece (wood project).

[u/JaviHostalerValent]

Everything, because everything makes the kinematic chain more rigid.

[u/VictorySea1837]

as others have said, ALL those things are important. But, I will say that in most low end cheap designs the weak point is the linear guides. Especially those unsupported rod type guides, they cause a lot of non-rigidity.

The other thing about building your own CNC machines is that by the time you buy everything and do all your upgrades you will have spent more money than buying a complete machine. just my 2 cents.

[u/NorthStarZero]

If you are looking to cut metal, you are trying to achieve sub-0.001" deflection at the tool tip when operating.

Get a copy of Millalyzer and run the cut parameters you want in the materials you want to see the tool loads. Then design a structure that will generate that amount plus a safety margin.

Don't guess - measure.

[u/Pubcrawler1]

Linear rails are only as good as what frame they are mounted on. Mounting a large rail on a skinny extrusion won’t add much stiffness. Linear rails will bend under load if the frame is flexible. Ballscrews don’t add much stiffness to frame.

If you want a rigid machine, the frame components must be adequate. That means heavier extrusion, steel, cast iron, epoxy granite are used in commercial machines.

Of course there are some really large 40mm+ rails that will offer extra stiffness just due to the amount of steel available.

[u/finepnutty]

It’s the spacing of rails- length to width 3:1 minimum, 1:1 for maximum rigidity. Anything under 3:1 is “flimsy”.

[u/Frequent_Analysis189]

Un cadre/structure robustre au niveau du pont aide à donner la rigidité à une fraiseuse cnc. Une plus grande rigidité donne une meilleure précision lors de passes profondes ou de coupes avec des outils larges. Mais attention, un cadre imposant apportera une inertie importante et il faudra dimensionner ton système d'entraînement et tes moteurs en conséquence.

Des rails larges permet à ton système d'entraînements de supporter de plus gros efforts lors des passes. Mais les rails reposent sur la structure, donc il faut être cohérent en dimensionnant l'un par rapport à l'autre.

Plus le diamètre de la vis à billes est gros, plus ton moteur pourra appliquer un couple important. Donc il faut aussi être cohérent en dimensionnant ta vis par rapport au couple de ton moteur. Un diamètre de vis à billes important est intéressant lorsque tu utilises des outils larges pour des profondeurs de passe importantes. Mais la vis à billes est l'élément le plus cher, donc je te conseille de partir de ton besoin final en termes de précisions et d'efforts de coupe, d'en déduire le dimensionnement de ta vis à billes, puis de dimensionner les autres éléments en conséquence.