moving gantery CNC sturdiness

Hey
I want to build CNC router mainly for wood processing (MDF + Plywood up to 30mm thick) I need the machine to cut/drill the pannels with less then 0.5 mm (or 20 mil) resolution.
and sometimes i intend to cut/drill aluminium profiles on the machine (it doesnt has to to that fast and i can go at minimal feeds)
also the CNC will be 1500*1500mm (and i need 1300*1300 effective working area)
also the budget is about 1000euro for everything

Im alittle affraid the machine will be not sturdy enough and will resonate and get bad surface finish or will not be accurate enough

I have already ordered :
steel 100*50mm tube profile (with 3.2mm wall thikness) - for the frame and gantery
2.2KW chinees spindle
Nema23 steppers 2.2N/m

now i want to buy all the moving parts:
* linear rails: i was thinking about HGR20 (4*1500mm and 2*300mm)
* ball screw screw 2005 due to the lengh (3*1500 and 1*300mm) - will 20mm thick ball screw be ok- or the ball screw will bend?

as a kit from aliexpress - to save some money
https://www.aliexpress.com/item/4001230601992.html?spm=a2g0o.cart.0.0.5d4a3c00Mas6 rE&mp=1


what do you think about that? do you have any recomendations for me?

Hi RonVais
Welcome to the forum, rule number one DON'T buy any kit until you have your design sorted,if possible cancel your order until your design is finalised. your best option is to read the build logs on the forum to get an idea of the actual build process.
Regards
Mike

Ron, Mike is correct you have made cardinal Sin #1 by buying before the design is finalized. STOP and cancel if possible because you are heading for a dissapointment.

Some of those parts are a bad choice for a router and will affect performance badly. For instance, 5mm pitch is too slow for a router, 10mm is much better and will allow you to reach the feeds you'll require for cutting MDF/Ply correctly. With 5mm pitch, esp with those motors, you won't get any where near the correct feeds which will mean poor finish and excess tool wear.

Next those 2.2Nm motors are too small for 20mm screws and you don't mention the most important part which is the drives and their Max voltage. The voltage you run steppers at makes a huge difference to performance, like wise the spec of the motor plays a big role in how much voltage is required for best performance. The Nm rating is only one aspect of selecting the motor, the inductance rating of the motor is very important and plays a big part in how well it will perform at a given voltage. High inductance will require more volts to get the same RPM as a Low inductance Motor with less volts.
So if you have High inductance motors paired with Low voltage drives then you cripple the RPM which if combined with low pitch screws cripples the machine so badly it's impossible to reach the feeds required for cutting correctly.
It's a common mistake to think you can cut at any speed you like, the tool and material dictate the feeds you'll require, run them too low and you'll wreck tools and leave a poor finish.

I suggest you take step back and do some more research. Start a build thread and ask all your questions in that thread, this way you can look back in weeks or month's time and find any info which may have been given.

It's not difficult to build a great machine but it's very easy to get it wrong if you go blindly buying parts without knowing what or why your using that part. Look around see what others have used and then ask if your not sure about anything, then ask again before clicking BUY.

The 'kits' are usually not any cheaper.

Ask any decent seller (BST Automation is my go to) and they will put together exactly what you want and give you a good price.

Thank you everyone for your fast response !

I'm currently designing the machine in cad but i need to choose my components for the design- so dont worry choosing the compontent doesnt mean that Ill buy the component tomorow before compliting the design

As for the items i have bought are pretty much general use - exept for the spindle that i have seen lots of builds with (also as far as i know plywood usualy is cut at high speeds and those chineese spindle do fine at and dont loss to much torque at high speeds) and for the other parts i just had them already (steppers and steel tube profiles)

The main tree questions for now are:
* Will 50*100*3.2mm steel frame (not welded frame) will be sturdy enough and not vibrate? (as I sayed earlier I intend to build moving gantery configuration CNC with the dimentions 1500*1500*300mm of the frame)

* Can i get off with the kit mentioned in the original post? it includes HGR20 rail and HGH15CA carts
and a 2005 ball screw ( i understand the 2010 will be faster though i can compensate with driving the steppers at higher speeds to reach 100mm/Sec)
a kit with 2010 ball screw at aliexpress is about 250 euro more exprensive

* Will a ball screw at such length unsupported be sagging? and what can i do about it? (i dont want to use the rack and pinnion systems cause they are more expensive )

Thanks!

Not to crash your dreams, but I think you can forget about this. You will need at least 3-4 times that much money even if you buy everything cheapest. I think under 2500€ you can't even make a smaller one. Mine is fixed gantry and considerably smaller but still in the 3000€ region.

Quote:

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Originally Posted by RonVais

The main tree questions for now are:
* Will 50*100*3.2mm steel frame (not welded frame) will be sturdy enough and not vibrate? (as I sayed earlier I intend to build moving gantery configuration CNC with the dimentions 1500*1500*300mm of the frame)

* Can i get off with the kit mentioned in the original post? it includes HGR20 rail and HGH15CA carts
and a 2005 ball screw ( i understand the 2010 will be faster though i can compensate with driving the steppers at higher speeds to reach 100mm/Sec)
a kit with 2010 ball screw at aliexpress is about 250 euro more exprensive

* Will a ball screw at such length unsupported be sagging? and what can i do about it? (i dont want to use the rack and pinnion systems cause they are more expensive )

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#1 Yes it will vibrate for sure, the question is how much and this we can't answer because too many variables involved. However, your needs cutting plywood are not taxing so it will probably easily fullfill your main needs, Cutting aluminium on the other hand is different and here it could struggle with vibrations leaving a poor finish.

#2 It's not that simple I'm afraid which is what I was trying to tell you before in my post about the motors.
You can't simply increase the speed of the steppers because as the RPM increases torque drops and because you are using a 5mm pitch you'll need 1200rpm to reach 100mm/sec which those motors won't provide enough torque at those speeds to turn 20mm screws. There are other factors due to resonance and whip which will also come into play and make it not happen.
Again I'll say it because it's VERY important, the Drives and the voltage you run the motors at make a big difference to performance and they need to match to get the best from them.

#3 Pay the extra and get 10mm pitch or even 20mm. You think your saving money by buying 5mm but what your actualy going to do is waste money because you'll soon realise after it's too late you can't reach the feeds you'll need and then you'll be stuck with them.

Now the reason why a larger pitch is better is two fold,
#1 Is obvious in that It gives you the feeds you require
#2 It means you can reach the feeds at a lower RPM which means you have higher torque as the motor is operating lower down the speed curve while cutting and the screw speed is lower so less chance of whip.

These Kits are false economy and nearly always made up of cheap components or poorly matched components. DONT DO IT is my advise, buy separate components that are better matched.

Also Like A_Camera says and I failed to spot first time you have NO CHANCE of building this for 1000 euro's, you'll need at least twice this to make it worth the time and effort.

well guys you are right i need to start designing before thinking about anything else so i started modeling and planing the project and some questions came up:

My main limitation is i dont have access to any milling machine or any metalworking precision tools.
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

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)

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


By the way i was thinking to try and simulate the vibrations of the machine - the fundumental as i understand is 3.3khz for two flute at 10,000rpm
What would you emphasize on in the simulation?

Quote:

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Originally Posted by RonVais

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

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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.

Quote:

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Originally Posted by RonVais

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)

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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.

Quote:

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Originally Posted by RonVais

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

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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.

My first time welding, using a stick welder that cost a fraction of the price I was quoted for the aluminium profile I had planned to use just for the gantry, was very ugly but completely effective. But it will not be dead accurate and as Jazz says you will need to design in adjustment for everything. One thing to be careful of is to design the machine so that you can actually access all the nuts and bolts you will have to get at once the whole thing is assembled.

Quote:

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Originally Posted by JAZZCNC

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.

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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?

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 :smile:

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!

Neale, if the 50x50x3 tubes resonate why not drill a hole and fill it with sand? It should increase the mass and reduce resonance.

Hey guys
Wood has some good dumping qualities so i was thinking - why havent i saw any designs of steel/aluminium with wood base ?

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Originally Posted by RonVais

Hey guys
Wood has some good dumping qualities so i was thinking - why haven't i saw any designs of steel/aluminium with wood base ?

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Few top builder here gave you great tips, probably saved you money and definitely disappointment and you still asking same questions, instead of reading related posts.
In my place 8 ton machine separated from floor only because of rapid feed - inertia. How the hell wooden frame can hold anything. I am building metal frame bed as wood can not last my banging:hysterical: