moving gantery CNC sturdiness

[JAZZCNC]

And the base matirial i was thinking of was steel rectangle tubes (50*100mm with wall thickness 3.2mm) mainly cause it is massive and should vibrate less and it is can fit into my budget

No it's not massive and is barely just thick enough if your wanting a strong machine with low resonance. Even 5mm wall is only just good enough and will only give average vibration dampening. 3mm wall resonates like a tin can.

And the first question that was on my mind is how to connect all the parts of the frame?
I think i will not be welding because i dont think i have the skills to make it precise enough
So the alternative is having the steel cut precisly at the store, connecting with bolts that way i have option to compencate most errors with shims and a file
(If you have any thoughts or tips for me it will be very helpfull)

Precision doesn't come from welding it comes from setup and alignment, strength comes from welding. You don't need to be a welder to build a strong CNC machine and a grinder hides all sins. Many good CNC machines have been built and welded by people who had never touched a welder before so don't be put off from welding.
That said bolting as it's place because it does allow easy adjustments, like wise it easily gets knocked out of adjustment and isn't always easy to keep the precision you worked hard to achieve when setting up.
My advise is to do a mixture of both and I've said it many times, build in as much adjustment as possible into the design, then look again to see how you can add more adjustment. Because like you not many people have the equipment to machine parts to high or tight tolerences so you need other ways to achieve this and building in adjustments allows you to do this. However you have to think about how you can lock those adjustments so they hold fast.
It can take days, weeks or months to fine tune a machine and it's not something you want to be doing very often.

The second thought i wanted to run by you is : i was thinking of geting the two ribs under the linear rails from thicker steel (3.2mm 50×100mm tube) and the other two ribs of the frame from thinner (40×40mm 1.5mm thick steel profile) below the first two ribs

Nope waste of money and time. As I explained above 3.2mm is not thick and 40x40 x 1.5mm is about as strong as wet spaghetti.

[RonVais]

No it's not massive and is barely just thick enough if your wanting a strong machine with low resonance. Even 5mm wall is only just good enough and will only give average vibration dampening. 3mm wall resonates like a tin can.



Precision doesn't come from welding it comes from setup and alignment, strength comes from welding. You don't need to be a welder to build a strong CNC machine and a grinder hides all sins. Many good CNC machines have been built and welded by people who had never touched a welder before so don't be put off from welding.
That said bolting as it's place because it does allow easy adjustments, like wise it easily gets knocked out of adjustment and isn't always easy to keep the precision you worked hard to achieve when setting up.
My advise is to do a mixture of both and I've said it many times, build in as much adjustment as possible into the design, then look again to see how you can add more adjustment. Because like you not many people have the equipment to machine parts to high or tight tolerences so you need other ways to achieve this and building in adjustments allows you to do this. However you have to think about how you can lock those adjustments so they hold fast.
It can take days, weeks or months to fine tune a machine and it's not something you want to be doing very often.





Nope waste of money and time. As I explained above 3.2mm is not thick and 40x40 x 1.5mm is about as strong as wet spaghetti.

You got me a be confused i have seen over the internet lots of builders use aluminium profiles with trapezoidal connections and reach good longjevity without calibration
Wouldnt five M10 s with proper washers and some locktite give same result?


Do you have some examples of build logs - of what you would define as a good mix of welding and proper adjastments?

[Neale]

My router (about 1500x750 cutting area) is all steel, welded. I have only used bolts where I fix to aluminum mounting plates for motors, etc. I was also a first-time welder on this project (using MIG) and an angle grinder fixes many problems

Aluminium profile is bolted because you cannot weld it (at last, not many of us can, or have the kit to do so). It's probably a good choice for smaller machines but as the size goes up, the balance shifts towards steel. Cost becomes a strong argument then. I guess that if you are going to need to break it down for transport, say, bolting might be an option but you are going to end up fabricating brackets, welding on flanges for bolting, etc, so welding the lot is less work. All these things are a balance, a compromise, but it's probably easier to cut and reweld something that went in the wrong place than to move a set of bolt holes!

I can only emphasise a couple of points Jazz has made - if something might need adjusting, make sure that you allow plenty for it. Even the steel box you buy is not straight or flat and by the time you have welded it, it will be worse! That's the place for bolted, movable, joints - for setting-up tweaking, not the basic structure. And I can tell you from my own experience, 50x50x3 really does resonate - there's no mass damping worth talking about. I'm doing some cutting in steel at the moment with my machine, making some fiddly little bits that would be a pain on my manual mill. I never expected to be able to do that when I built it - it was intended for wood - but it can just about handle it. I do wish I had gone up a size or two in wall thickness, though, just for better resonance control. Search for "AVOR" for my write-up to see more of my mistakes...

Plan carefully - it's too easy, especially on the Z-axis, to paint yourself into a corner in the sense that you can't get to half the bolts to assemble it. 3D CAD, if you can use it (and it's worth learning), can be a lifesaver. For example, my Z platform has a couple of critical bolts that hold the ballnut in place and need tightening only when everything is assembled and adjusted but with good planning I made sure that I had already added a couple of access holes for the Allen key in advance.

Have fun - it's a frustrating game and there'll be lots of sometimes conflicting advice but it's great when you start cutting on your own machine!