[sky99]

Hi all, i'm new to the CNC routers domain, although i'm familiar with 3D printing and the construction of a 3D printer.
I'd like to build a CNC, and i've been looking around for some time now. I was considering a shapeoko3, but the surface area for the price did not satisy me, i'd like to make a CNC either cheaper,
or at this price bigger.

So i looked around online and started thinking about stuff.

I'd like to build a CNC with a work area of approximately 50x50cm, and at minimum 30x30cm.
I don't have very specific materials to cut, so i'd say plastics, wood, and aluminium.

As of now, i'm thinking about the linear motion axis.
I've considered 3 options :

1. C-beams, V-beams, openbeans and the like;
2. supported bearings like SBR12 or SBR16
3. linear rails like MGN12H

I read that the third option is the best one, with little to no backlash, but requires accurate positioning, and is the most expansive.
Supported rails come second in accuracy, but are a bit more forgiving, and cheaper.
At last, the C-beams with rollers and things like that are the lest precise,but really modular, easy to work with, and can be the frame of the machine, unlike the other solutions that require to be bolted on something.

i'm leaning towards option 3, because although it's more expensive per item, it's also less heavy than supported rails, and it shows on shipping.
In my researches on aliexpress, i managed to find this kit of 2 800mm MGN12 rails with 2 MGN12H carriages, for 96$, free shipping, so that's less than 50$ per rail.

In comparison, for SBR rails, i can get 600mm SBR12 rails at 23$ a piece, but with 15$ shipping, so that's almost 40$ for a lesser length, and less precise system. It may not be the case for you, but as i'm in Guadeloupe, shipping costs can be expensive, and i have to take them into account.

The way for it to be cheaper is if i settle for even shorter supports, with this 500mm SBR12 coming at 24$, with free shipping.

So, what do you think about my reflexion on the axis so far?

have i overlooked something? is there an obvious solution that i missed?
Should i build a smaller machine first, using the SBR12 500mm rails first? Or should i put extra money and go for the cool 800 mm MGN12 rails right away?

I don't fear too much buying stuff and later on replace those with other stuff, since rails or motors that i may replace later on will find use in other machines, at least in a 3D printer

As for motors, i'd like to stick to nema17 (i can get 5 for aprox 50-60$), since they are cheap, plentiful, compatible with a DRV8825 ramps board, etc. So it would be parts that could go in a 3D printer as well as in a CNC if they suffice. I don't mind, later on, buying a few nema23 if needs be, the nema17 will always find some use elsewhere.

In order to transmit the motion, i'm considering two options :
a ball-screw system, such a this one, that are the top notch no backash solution from what i understand, or classic timing belts, that i've seen used in many CNCs, and are cheap, available to great lengths, cheap to ship, with good enough precision.
I think i'l probably use the ballscrew for the Z axis anyway, since it's short travel, but i'm considering both choices for X and Y.
Any thoughts on that ?

Many thanks in advance!

[Jon.N.CNC]

what do you expect to be cutting? nema 17 wont be up to anything more than foam. Aside from the motors you have pretty much described something like a chinese 6040. which are pretty pants unless you replace motors and drivers and bob and then the supported round rail carriages open up and you get play in the gantry.

If you want quality then use square rail and carriage. If you can get your hands on a 6040 without electronics but has ball screws, swap out the supported round rail for square rail and get some descent mosfet drivers (wantai would be a good example) with some efficient high torque nema 23's , descent motion control, 1.5kw spindle minimum and it may just pass for a good cnc router.

Cnc routing if you dont use quality parts you dont produce quality parts and being cross compatible with 3d printing gear is really the wrong direction to be looking in.

[Louis_Cannell]

I picked up two sets of 1000 600 300 20mm supported rails 1605 ballscrews and all fittings except ballscrew brackets from Rattm on aliexpress with my 10% discount cost me under £300 shop around bargains are there I only brought two sets to get two 1000mm screws, rest will come in usefull at some point.

[fretman_2]

For a machine with a 500mmX500mm work area you could drive the machine using belts like the SO3. I've got a belt driven NEMA 17 Shapeoko2 and it'll easily cut more than foam. The issue I'm having with the SO2 isn't the belt drive...the issue with the SO3, and somewhat with the SO3, is inherent flex. My current build, which is under way, uses the Chinese SBR16 rails. Although I haven't finished the machine and put it to use, I'm happy with those rails. Once the pre-loading is done on each truck, they're very tight. Keep reading on here and asking questions...you'll zero in on the right way to proceed.

[awerby]

To have any hope of cutting aluminum, go with the square profile rails, not the round SBR type. As Jon says, NEMA 17 motors aren't strong enough for a machine the size you're talking about or the materials you say you want to cut. Your ballscrew link didn't resolve for me, but beware of cheap ballscrews; they're not accurate at all. They can also have significant backlash; to get rid of it you need to preload them with larger balls or double nuts. An acme screw that costs the same will generally work better. Timing belts are good for transmitting motion to screws, but only 3D printers use them as a drive mechanism with any success. From what you've shared, it sounds like you're planning on building something a lot like a 3D printer, and hoping it will somehow cut aluminum. But printers don't have any cutting loads to work against, and cutting vibrations aren't a problem for them; mostly they have to be fast. Routers need to be a lot more rigid, but they can run slower.

[Jon.N.CNC]

I picked up two sets of 1000 600 300 20mm supported rails 1605 ballscrews and all fittings except ballscrew brackets from Rattm on aliexpress with my 10% discount cost me under £300 shop around bargains are there I only brought two sets to get two 1000mm screws, rest will come in usefull at some point.

The supported round rail carriages will inevitably open up and get sloppy if its used for cutting and as of such should be classed as disposable imo. Pay not a huge amount more and get hiwin and at least you dont have that concern.

[sky99]

Hi all,
thanks for your inputs!
I considered supported round rails carriage, but as i mentioned in my first post, they are cheaper by themselves, but more expensive with shipping to where i live.
The rails i was aiming are those that you call square profile rails, as i've seen that they are the most precise and reliable.

I don't mean to build a CNC like a 3D printer, i'm well aware of the problems with the prusa-like chassis woble that would make it inneficient for a CNC.
If anything, it would be the other way around, i want to build my 3D printers as CNC, with a rigid frame

What i meant by swapping parts in and out was that if you guys consider that it's too ambitious to go for a full build, i could go for a smaller scale CNC for starters,
knowing that nothing would be lost afterwards!

I take good note of your warnings about ball screws , and it's a shame, since it seemed so nice!

I also take note about the nema17. I wanted to use those since i have seen many CNC builds using those (and even machining aluminium), but if they're too weak, i'll order nema23.

Are nema 23 enough?

When i mean cutting aluminium, i mean that i'd like to be able to do it, not that i need a machine that eats thick aluminium sheets all day. In fact, i have no plan to cut aluminium in a near future.
However, i'd like to have this option so that at least, i can make motor mounts, chariots, or other stuff to make the next CNC or improve this one later on!

So about the linear motion, would two rails suffice for the X axis?
I've seen a design with a fixed gantry that i liked a lot, because it seemed strong and stable.
I was planing a moving gantry at first (and it's not out of the table), but it seems more complex to do.
If the design can be kept simple, this is less failure points, right?

So for now, i would go with rails like those : 3D print parts cnc Kossel Mini MGN12 12mm miniature linear rail slide 1 Set=3pcs 12mm L 800mm rail+3pcs MGN12H carriage-in Linear Guides from Industry & Business on Aliexpress.com | Alibaba Group

I've found two good deals : one pair at 96$ with free shipping, or a set of 3 at 130$ including shipping.
So if i order those 2 times, i'd end up with 6 bars, and 12 chariots for around 260$, shipped.

If those sliders are confirmed as good as i've read, this is the first stuff i'd order.
With 6, i'd feel more confortable with a moving gantry : i'd use 2 per "foot" of the gantry, but perhaps this is overkill?

I've also seen those : HIWIN Taiwan made 2pcs HGR20 L 1000 mm 20 mm linear guide rail with 4pcs HGH20CA or HGW20CA narrow sliding block cnc part-in Linear Guides from Industry & Business on Aliexpress.com | Alibaba Group
They are based on the same concept, but seems much beefier, and 1m long. But it would cost me 300$ for just a pair (150+150$ shipping!). I think i'll keep those in mind for a later build?



Then about the cutting bit, i'll probably start with a router. the dewalt model that everyone is using will probably be my choice. The machine will use linuxCNC, because i want it open source and open hardware as much as possible.

About the ballscrews here's another link : BallScrew 1605 C7 SFU1605 Length600mm Rolled Ball screw with single Ballnut for CNC parts BK/BF12 standard end machined-in Ball Screws from Industry & Business on Aliexpress.com | Alibaba Group
Another question about those : if there are bad quality ballscrews, won't there be equally bad acme threaded rods?

I understand that this is a vital part of the system, so i don't want to screw up (no pun inteded ^^)

[Jon.N.CNC]

Hi all,
thanks for your inputs!
I considered supported round rails carriage, but as i mentioned in my first post, they are cheaper by themselves, but more expensive with shipping to where i live.
The rails i was aiming are those that you call square profile rails, as i've seen that they are the most precise and reliable.

I don't mean to build a CNC like a 3D printer, i'm well aware of the problems with the prusa-like chassis woble that would make it inneficient for a CNC.
If anything, it would be the other way around, i want to build my 3D printers as CNC, with a rigid frame

What i meant by swapping parts in and out was that if you guys consider that it's too ambitious to go for a full build, i could go for a smaller scale CNC for starters,
knowing that nothing would be lost afterwards!

I take good note of your warnings about ball screws , and it's a shame, since it seemed so nice!

I also take note about the nema17. I wanted to use those since i have seen many CNC builds using those (and even machining aluminium), but if they're too weak, i'll order nema23.

Are nema 23 enough?

When i mean cutting aluminium, i mean that i'd like to be able to do it, not that i need a machine that eats thick aluminium sheets all day. In fact, i have no plan to cut aluminium in a near future.
However, i'd like to have this option so that at least, i can make motor mounts, chariots, or other stuff to make the next CNC or improve this one later on!

So about the linear motion, would two rails suffice for the X axis?
I've seen a design with a fixed gantry that i liked a lot, because it seemed strong and stable.
I was planing a moving gantry at first (and it's not out of the table), but it seems more complex to do.
If the design can be kept simple, this is less failure points, right?

So for now, i would go with rails like those : 3D print parts cnc Kossel Mini MGN12 12mm miniature linear rail slide 1 Set=3pcs 12mm L 800mm rail+3pcs MGN12H carriage-in Linear Guides from Industry & Business on Aliexpress.com | Alibaba Group

I've found two good deals : one pair at 96$ with free shipping, or a set of 3 at 130$ including shipping.
So if i order those 2 times, i'd end up with 6 bars, and 12 chariots for around 260$, shipped.

If those sliders are confirmed as good as i've read, this is the first stuff i'd order.
With 6, i'd feel more confortable with a moving gantry : i'd use 2 per "foot" of the gantry, but perhaps this is overkill?

I've also seen those : HIWIN Taiwan made 2pcs HGR20 L 1000 mm 20 mm linear guide rail with 4pcs HGH20CA or HGW20CA narrow sliding block cnc part-in Linear Guides from Industry & Business on Aliexpress.com | Alibaba Group
They are based on the same concept, but seems much beefier, and 1m long. But it would cost me 300$ for just a pair (150+150$ shipping!). I think i'll keep those in mind for a later build?



Then about the cutting bit, i'll probably start with a router. the dewalt model that everyone is using will probably be my choice. The machine will use linuxCNC, because i want it open source and open hardware as much as possible.

About the ballscrews here's another link : BallScrew 1605 C7 SFU1605 Length600mm Rolled Ball screw with single Ballnut for CNC parts BK/BF12 standard end machined-in Ball Screws from Industry & Business on Aliexpress.com | Alibaba Group
Another question about those : if there are bad quality ballscrews, won't there be equally bad acme threaded rods?

I understand that this is a vital part of the system, so i don't want to screw up (no pun inteded ^^)

Nema 23 with planatary gearboxes yes fine. I can imagine anyone cutting aluminium with nema 17's is having a hell of a time with it. I have a self built 200kg moving gantry on square rails. 2.2kw spindle, twice as rigid as any kit available and that just meets the requirements for aluminium. Planatary gearboxes, dsp drivers. And it's ok at it, the spindle for one thing is not powerful enough really.

And in all honesty there isn't a cnc kit out there that's really upto the task of Aluminium. Firstly you want a fixed gantry moving bed to stand a better chance.

A fixed gantry moving bed will do aluminium woods and plastics but a moving gantry generally gives you a larger cutting envelope so suits woods and plastics better as parts are generally larger.

[pippin88]

Virtually all Aliexpress and ebay sellers will do custom deals - number of rails and length etc.

If the seller won't, find another. Don't design your machine around 'sets' or end up with bits that are not suitable.

[sky99]

Nema 23 with planatary gearboxes yes fine. I can imagine anyone cutting aluminium with nema 17's is having a hell of a time with it. I have a self built 200kg moving gantry on square rails. 2.2kw spindle, twice as rigid as any kit available and that just meets the requirements for aluminium. Planatary gearboxes, dsp drivers. And it's ok at it, the spindle for one thing is not powerful enough really.

And in all honesty there isn't a cnc kit out there that's really upto the task of Aluminium. Firstly you want a fixed gantry moving bed to stand a better chance.

A fixed gantry moving bed will do aluminium woods and plastics but a moving gantry generally gives you a larger cutting envelope so suits woods and plastics better as parts are generally larger.

Wow, so Nema 23 are not enough, and require a gearbox? i was really far off!
So what torque should i look for? Or should i just watch for 3A stepper?
if a gearbox is required, should i look for nema34, or is it better to have smaller steppers with a gearbox?

I think i was really not realizing the difference of scale...

If aluminium is too difficult, maybe i should drop it for a first build?

Indeed, i'm interested in milling metals, but mostly very thin sheets, that i'm able to cut with scisors, to make neat faceplates for various projects...
The only exception would be what i mentioned earlier, for making parts for another later CNC.

But perhaps that since i'm investing some time and money in this project, i may as well go further and go for reasonable aluminium cutting performances?

[sky99]

Virtually all Aliexpress and ebay sellers will do custom deals - number of rails and length etc.

If the seller won't, find another. Don't design your machine around 'sets' or end up with bits that are not suitable.

interesting, i was not aware of that. There are so many things on aliexpress that i never asked for customization.

However, as of now, i don't have specs for my machine, i don't have size requirements.
I don't want to build a too small one, but other than that, i don't have much requirements...

The bars i found, at 800mm seemed a reasonable size, considering that i'll probably lose some of this length due to the chariot size.

Anyway, this is a great adventure starting, i'm as excited as the first time that i had my 3D printer!

[Jon.N.CNC]

Are you experienced in Cad? Finding a fixed gantry design and having a steel frame fabricated if you dont weld, that you would just need to drill and tap for square rail, is not as expensive as you may think and can work out cheaper than aluminium. Use resin to level under the square rail.

something like this:Steel Frame CNC Router | OpenBuilds

But use square rail and dont leave the lower x rail unsupported like they have :s. also wants some additional 45 degree supports for gantry legs and some cross bracing in base frame.

[Louis_Cannell]

The supported round rail carriages will inevitably open up and get sloppy if its used for cutting and as of such should be classed as disposable imo. Pay not a huge amount more and get hiwin and at least you dont have that concern.

Pay treble minimum (4 x1000mm 4x 600mm 4x300mm Rails with 24 bearings) (2x300 2x600 2x1000 Ballscrews with all fittings) shipping vat and duties included supplied from europe under £300.
Show me anywhere equivelant with H-Win for little more i.e. less than double and I will buy at least a container full and start a third business, for a pro machine I would have used HWin for a hobby machine if bearings spread with hobby use I have a complete set of spares, also a complete set of rails and half a set of ballscrews. Quality tools for my work is a no brainer I pay for the best, for a hobby I get to play with a few hours a week because of work I choose adequate quality that do the job.

For those that say Supported Round rails SBR won't cut Aluminium
I slipped up the other day cutting Aluminium and left DOC set for MDF test piece 6mm 2 Flute 3mm DOC and 1000mm FR and it was not as good a finish than more conservative cuts would be, but cut without problem sounded under pressure it was, but to say these rails won't cut aluminium is Male cow excrement.

[Jon.N.CNC]

Pay treble minimum (4 x1000mm 4x 600mm 4x300mm Rails with 24 bearings) (2x300 2x600 2x1000 Ballscrews with all fittings) shipping vat and duties included supplied from europe under £300.
Show me anywhere equivelant with H-Win for little more i.e. less than double and I will buy at least a container full and start a third business, for a pro machine I would have used HWin for a hobby machine if bearings spread with hobby use I have a complete set of spares, also a complete set of rails and half a set of ballscrews. Quality tools for my work is a no brainer I pay for the best, for a hobby I get to play with a few hours a week because of work I choose adequate quality that do the job.

For those that say Supported Round rails SBR won't cut Aluminium
I slipped up the other day cutting Aluminium and left DOC set for MDF test piece 6mm 2 Flute 3mm DOC and 1000mm FR and it was not as good a finish than more conservative cuts would be, but cut without problem sounded under pressure it was, but to say these rails won't cut aluminium is Male cow excrement.

Yes they may do it for a bit. I have been given a 6040 which has these sbr rails. It has illegra drivers that are all of 1a if that, cheap nasty Chinese motors and you can stall it by putting your hand on it. Yet it still has caused its carriages to open up. It otherwise was well looked after I was told that this happened with a single jamming incident.

Another machine I know of having gone through multiple sbr carriages in just months, attempting aluminium has now had all rails replaced by square rail and now cuts aluminium well.

Even at a triple more. The difrence being you have 10 year carriages or you have 1 year or 1 incident carriages. Which is cheaper in long run, it's going to be square rail two or three fold.

[Louis_Cannell]

No doubt H Win are superior to SBR they are a professional quality item, but you price the package I paid £300 for and your talking at least 5 times the price in effect more than I paid for my whole machine and endmills for hobby use so effectively doubling the price and making it un affordable in scheme of things for a hobby. I could afford to buy the best I can buy whatever I want whenever I want and am fortunate in this way, but an open mind is required I pay a lot of money for my cycles and ridiculous amounts for computer software and hardware the tools of my trade, but a hobby needs to be affordable for most for me its what I am prepared to spend, for others what they can afford to spend. To argue that the best is the only option for all, or that the less affluent or tight! are wrong everytime for being poor is ridiculous, as professionals you should consider time, down time and use top quality to do other is false economy. As a hobby that may or may not continue why should people not use second best, SBR improvement on unsupported rails and worse than flat rails, people make decisions for many reasons, my hobby to experiment a little at £1000 is disposable income I do not drink or smoke but I also take care of my finances and some decisions are made to budgets I do not consider spending twice as much at this point in time to be beneficial to me. The SBR carriages may be less durable and I have 12 spare in my budget, the damage is maybe a lot to do with design many frames I see in DIY even retail designs would also twist beyond any future usefulness I leaned my budget to a solid frame.

[wizard]

You have a lot of good comments here but I think you need to step back and evaluate what your needs are and what you expect out of the machine. As others have said a machine suitable for machining aluminum must be far more rigid than one suitable for wood working. Rigid means a massive frame, ideally built from steel.

Even with aluminum we get into degrees of rigidity required. If all you want to do is engraving you can get by with a far lighter machine. If on the other hand you want to run end mills and use all the horse power in your spindle, you will need a very rigid machine. Actually the same applies to wood working, a light machine suitable for engraving will not do well running a 3/4" cutter.

In a nut shell what you expect a machine to do for you will dictate how it is built and how much it will cost.

This statement: "I don't have very specific materials to cut, so i'd say plastics, wood, and aluminum." is all well and good but it makes it difficult for people to zero in on an ideal machine design. What most people would think about when you mention aluminum puts you into a different class of machine. In this case a far more expensive machine.

Considering you are on an island you may have constraints the rest of us don't have. For example access to steel or aluminum suppliers and machine shops to help with material prep. I'd seriously look into what resources you have on the island or near by. In case it isn't obvious I don't know much about your island. However machine shops can be a huge advantage for a DIY build so I'd put a high priority on getting an inventory of resources on the island and near by.

I'm getting wishy washy indications as to what you really want to do here. Is it build a machine from the ground up or to assemble a kit? This might be a case where I would be OK with your buying a kit of T-Slotted extrusions that is ready to assemble. Generally I suggest steel as it is so cheap these days. {well it was until the tariffs increased} Steel has additional benefits including adding mass to the machines frame, easy weld ability and good strength. The problem in your case, with steel, is getting it there in good condition at a reasonable price. However for these sorts of machines I do believe steel is the best choice if you can handle it properly.

As for T-Slotted aluminum, I really don't like it for machine tool major structures, especially the three axis supports. Most of the T-Slots on the market are very light weight and the stuff that isn't is very expensive. You could look into plain old aluminum structural sections, again not cheap but maybe lighter. You would have to balance shipping costs against the increased material costs to determine if it is worthwhile to use aluminum.

[plcamp]

No doubt H Win are superior to SBR they are a professional quality item, but you price the package I paid £300 for and your talking at least 5 times the price in effect more than I paid for my whole machine and endmills for hobby use so effectively doubling the price and making it un affordable in scheme of things for a hobby. I could afford to buy the best I can buy whatever I want whenever I want and am fortunate in this way, but an open mind is required I pay a lot of money for my cycles and ridiculous amounts for computer software and hardware the tools of my trade, but a hobby needs to be affordable for most for me its what I am prepared to spend, for others what they can afford to spend. To argue that the best is the only option for all, or that the less affluent or tight! are wrong everytime for being poor is ridiculous, as professionals you should consider time, down time and use top quality to do other is false economy. As a hobby that may or may not continue why should people not use second best, SBR improvement on unsupported rails and worse than flat rails, people make decisions for many reasons, my hobby to experiment a little at £1000 is disposable income I do not drink or smoke but I also take care of my finances and some decisions are made to budgets I do not consider spending twice as much at this point in time to be beneficial to me. The SBR carriages may be less durable and I have 12 spare in my budget, the damage is maybe a lot to do with design many frames I see in DIY even retail designs would also twist beyond any future usefulness I leaned my budget to a solid frame.

Loius, please remember that the comments here are strictly individual preferences and intended for the most part to share 'ones' experiences both good and bad. True some components are superior to others, and I believe these comments are directed towards helping you make the best decision for your intended use and budget. Do not take it personally, as the more information you have of any subject the easier it is to make a proper decision suitable to your needs.

I recall going though this same process for my 'hobby' machine, which happens to be all wood and uses 'V-Groove' bearings riding on steel angle iron rails. When the day comes to replace the rails it's a simple task of bolting on new ones for a minimal cost. The machine has worked for me flawlessly for almost 2yrs. FYI, it will run and maintain accuracy of 0.006" (.15mm). The machine was not designed to cut aluminum, however, I should give it a 'test run' so see just what happens.

Design and build to your needs, at the end of the day the decision is yours.

[Louis_Cannell]

Don't get me wrong I do not take comments personally too long in the tooth for that, my point is to constantly shoot people down and tell them everything less than H win is rubbish to be avoided will put many people off seeing cost to produce a hobby kit. Its great fun and can be enjoyed on a relativley small budget, which may be all that can be afforded in lots of cases, the learning experience and the enjoyment of designing building using etc should not be restricted to those with ability or budget to acquire only the best and they should not be discouraged quite as much as they are. Personally I entered into the realm of CNC from a programming job, I did some work on 3D printing software for a medical research lab, built a 3d printer, printed a couple more and laser cutter engraver, then printed a CNC using no more than £50 worth of bearings nuts and bolts and electrical conduit it worked and got me interested. Now I have converted a micro mill and built a solid Router in a few years when I retire I may well have time to use these and decide to build a better model, the benefits of better quality can be stated without claims that the result will be wasted money and machine falling to pieces and the ability to cut little more than foam if lesser quality is used, not so long ago most were using MDF succesfully producing great work and enjoying it.

[fretman_2]

Nice machine!!!!

Loius, please remember that the comments here are strictly individual preferences and intended for the most part to share 'ones' experiences both good and bad. True some components are superior to others, and I believe these comments are directed towards helping you make the best decision for your intended use and budget. Do not take it personally, as the more information you have of any subject the easier it is to make a proper decision suitable to your needs.

I recall going though this same process for my 'hobby' machine, which happens to be all wood and uses 'V-Groove' bearings riding on steel angle iron rails. When the day comes to replace the rails it's a simple task of bolting on new ones for a minimal cost. The machine has worked for me flawlessly for almost 2yrs. FYI, it will run and maintain accuracy of 0.006" (.15mm). The machine was not designed to cut aluminum, however, I should give it a 'test run' so see just what happens.

Design and build to your needs, at the end of the day the decision is yours.

[sky99]

Are you experienced in Cad? Finding a fixed gantry design and having a steel frame fabricated if you dont weld, that you would just need to drill and tap for square rail, is not as expensive as you may think and can work out cheaper than aluminium. Use resin to level under the square rail.

something like this:Steel Frame CNC Router | OpenBuilds

But use square rail and dont leave the lower x rail unsupported like they have :s. also wants some additional 45 degree supports for gantry legs and some cross bracing in base frame.

Hello,
yes, i am able to use cad software. My software of choice is OpenScad.
I was considering such a frame, but i feared that the tolerences for such square tubes would not be good enough.
I bought a tube like that for a mast for my house. However, i dont' know if those square tubes are straight enough,
if the dimensions are coherent along the bar (i guess that they are, if they are extruded?, but are they
totally straight?)

I've read that h-rails require extremely precise positioning to work, and otherwise end up damaging themselves.
Then, assembling those bars, won't it be a problem? how do i ensure a precise positionning when whelding it?
Won't it deform under the heat?