Theorycraft +/ endgame project - cnc The Mischievious Brownie

[Anubite89]

First of all, Hello and welcome to my dream/nightmare of making a DIY CNC, any and all suggestions and opinions are very welcome.
Beforehand a little bit about me: Name is Atila, from Serbia, 28yrs old, working in a factory that gives an average paycheck around here but it is hard physical labour that optimistically would and should not last me for a lifetime. Since i love woodwork, mechatronics and assembly im thinking of trying to get into the woodwork with best leap and efficiency possible because of a Personal OCD for accuracy and efficiency, (measure 10times, cut once or throw into trash kind of thing)... so "enter the CNC"

- The Idea -
Making of a CNC machine that will do mostly soft materials - wood, foam, plastics but also can do aluminium and to super minimal degree steel/iron....(steel is most possibly non existant but option to minimally invest later to be able to do it..)
Core of the idea is to make addons or improvements either minimal or MAX or none at all... Budget would be optimistic 2.000 euros

- Current opinion on dimensions, materials and parts -
- working table dimensions: W (Y) 100cm x L (X) 140cm x H (Z)18cm - 3 working axis with possibility for upgrade for B axis as a turning lathe/cnc

- Material: - Full welded steel setup ( with my available tools it is much easier to work with steel than it would be with aluminium)
- Linear motion : - HIWIN rails and carriages for Y and Z axis, Guide rail and ball bearing - back to back setup for X axis,
- some good spindle with up to 300e in cost ( I've realised that working with steel is far fetched dream but the main point stays, if i do make some additional money i dont mind investing in a pro spindle for that purpose.(ofcourse waterpump for spindle)
----------------------------------------- still in consideration ----------------------------------------------------------------
Linear movement: "rack and pinion" or "belt and pulley" system for Y and X axis(though id rather put ball bearing and lead screws for X and Z) - would need some dire advice on theese and their implementation
3 axis control: NEMA23 3A 2.8Nm x3 -> but because of importance(in theory at the moment) if there is some way of adding a lathe like axis in "ground" level by swapping out table for some cnc lathing for which
Im thinking of using a stronger motor for Y axis so i can separate it onto both outer sides of gantry or just 1+1slave for Y for more safety.

corresponding drivers for motors and a 6axis UC300ETH - 5LPT board that supports mach or other software.

Thought on motors and use of gear transmission to lessen the speed and improve torque/precision(dunno actually)

a possibility for swaping out spindle for 3dprinting head, ive seen that it is possible to swap cnc onto 3dprinting ability with right parts if machine is accurate enough (planing to do the resin leveling allso)

A vacuum/pressure pump for makeshift residue removal / cooling of workpiece



That is my idea so far. Since getting the budget will be a slow process ( maybe 2 years untill i start full assembly/getting parts) i am learning to work in Inventor and gobbling applied knowledge from all the people on this forum. before i start planning a layout, can someone explain to me the importance of shape of gantry sides? the most i see are leaning onto the back a bit

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[wizard]

Im not sure i follow everything described however the number one thing here is that it is extremely difficult to bud a machine capable of handling steel well and being a cost effective wood router. To put it another way you will not be able to machine steel even like a light weight milling machine (Bridgeport for example).

Im a bit confused as to which axis is which in your description however unless this machine is huge i generally see ball leadscrews as the most cost effective axis motion solution. Like wise you will want to use linear rails on all three axis. Done right it is fairly easy to get a machine that can do wood, some composites and aluminum well. To machine steel even modestly requires a very stiff machine.

By the way machining steel means different things to different people. If you are thinking engraving size tools you might get acceptable results. You will not get a router to replace a general purpode milling machine. At least not for 2,000 Euros.

[Anubite89]

Thank you for replying. I will hopefully manage to explain a bit better here:

- My thought on steel was ( if it can do steel.. it could do everything else like butter....) but since then i've realised that machining steel with home cnc is super hard so i will just stick with woods, artificial wood and softer metals - alloys ( if someone could tell me what would be possible and what not.. as im seeing a plethora of others designs and stuff thats adding even more clusterf... to my "ideal" design.. engraving is also a valid option to add more touch to the projects ofcourse, if whole cnc is made of steel(except the gantry that im thinking to make from 20mm 7075 Aluminium alloy plates(if it would weigh less than steel construction for same job to lessen the burden on rails/ball leadscrews)
- worktable dimensions should be in the ballpark of 1500mm length(X?), 800(Y?)mm width, and at least 150mm height(Z?) of workable space (still racking my brain on those for ideal size to decrease shaking, stress and load onto shafts and rails)

[wizard]

Thank you for replying. I will hopefully manage to explain a bit better here:

- My thought on steel was ( if it can do steel.. it could do everything else like butter....) but since then i've realised that machining steel with home cnc is super hard so i will just stick with woods, artificial wood and softer metals - alloys

This shouldnt be a problem! To do aluminum it benefits from a stiffer machine than is acceptable for just wood. It is not a huge problem though

( if someone could tell me what would be possible and what not.. as im seeing a plethora of others designs and stuff thats adding even more clusterf... to my "ideal" design.. engraving is also a valid option to add more touch to the projects ofcourse,

If it can be imagined it can be built. The question then becomes will it work? The good thing with CNC routers is that the basic arraingement of components is well understood or accepted. An ideal design is one that fits your needs and budget, this is where you come into play to nail down what is acceptable.

if whole cnc is made of steel(except the gantry that im thinking to make from 20mm 7075 Aluminium alloy plates(if it would weigh less than steel construction for same job to lessen the burden on rails/ball leadscrews)

I would completely disagree with this approach as i see the gantry being the place with the highest pay off for going with steel. It is an inexpensive way to get the strength that a gantry needs.

Unless you weld those plates into a rigid box beam i dont even see them coming close to a square beam in stiffness. The problem with welding is distirtion and the likely need for post welding machining and heat treat. At that point you might as well look into a steel beam to save on material costs with machining expenses being a wash.

By the way i realize that in theory aluminum can produce a lighter and stiffer beam. However the material costs generally blow it out of the water for a DIY machine. This especially square extrusions of the same wall thickness as steel.

I mentioned wall thickness because its importance in both cases here isne so much structural, though that is important, but rather screw holding ability. That is you dont want to strip out the threads for the linear rail mounting screws.

There is the option of threaded linear rails allowing for thinner walls in your tube but that isnt a "normal" approach.

In any event the concern here is that many gantries are a machines weak link often by a wide margin. As such it pays to put a lot of thought into the design. Your concerns about bearing liads is good but the trick here isnt to compromise the gantrys design but rather too arrainge the bearings such that they are running with acceptable loads.

- worktable dimensions should be in the ballpark of 1500mm length(X?), 800(Y?)mm width, and at least 150mm height(Z?) of workable space (still racking my brain on those for ideal size to decrease shaking, stress and load onto shafts and rails)

This is a very doable size for a homebuilt DIY router. There are somethings to consider though. With the Z axis make sure the Z has enough vertical travel to clear the tools you intend to use. That might mean more travel than the 150mm clearance. Dont foget that your working areas implies axises that are considerably longer than the 1500 x 800 mm specified. The Y (gantry) needs to be able to clear that tool on both sides. Likewise the X needs to be able to clear the tool and more importantly accomodate the gantry support bearings. So on the X you may need linear bearings 200mm or more longer than that 1500mm spec.

I bring up the size issue because people at times underestimate how big a machine will be to contain their ideal work space. Once they realize this we often see bad engineering such as bearings to close together on the gantry supports or gantry saddle. In any event you are rightly concerned about bearing loads, i just dont see making a light gantry as the best approach here. You are better off selecting the right bearings for the application and making sure they are mounted correctly for the loads applied.

[skrubol]

Do you have the ability to stress relieve the weldments? What about getting the mounting surfaces milled/ground flat?
Unless you've got a cheap supply for the aluminum I'd recommend sticking to steel as well. Aluminum is quite a bit more expensive, and you've got to get it fastened together into some sort of box arrangement for it to have as good strength to weight as steel box section, plus its thermal coefficient of expansion is much higher than steel, so if it's not in a temperature controlled room it will affect your accuracy, and possibly put stress on your rails.