wood cnc machines?

[vivi-d]

Hi I'm curious about the cnc machines on this site: https://www.bobscnc.com/

They claim wood is a good material to make the machines out of. How could wood be better than metal? Are these overpriced?

[TimFox]

Note that their products are to fabricate and shape wood objects, using routers and other woodworking tools.

[ataradov]

It is not better. It is just good enough for their application. Plywood is dimensionally stable and easy to work with especially if you already have woodworking CNC. The machines are pretty light duty, so you don't need them to be really strong.

Unless you buy a pre-cut kit or have a CNC anlready, typical aluminum extrusion would be much easier to use.

[Roehrenonkel]

Hi,
 
wood will shrink and expand depending on humidity.
Metal will do the same with temperature.
Real "stone-solid" CNCs are made from granite:

CNC machine made out of granite - part1:

Another Granite-CNC:
https://www.flyingfoxcam.com/cnc
....if one can affort it. :-(

Ciao4now

[Coordonnée_chromatique]

Is anymone knows how this material is handling the mechanical stress and the gradients of temperature within time ?

[Jackster]

It is a router bed made with slotted plywood and screws holding it together with small rubber belts for movement.
It just limits you to how much stress you can put onto the machine (speed, feeds and depth of cut).

My 3D printer made from 20x20 aluminum extrusion would have more rigidity that any of those "CNC machines" to put it into perspective.


Wood is in no way better than metal for this type of application.

If you want a kit build CNC machine that looks pretty and can do light work for hobby use, then it is fine.
But if you actually want to cut some material or do anything more than some light hobby projects, you would be better off finding a used metal router.

[johansen]

Is anymone knows how this material is handling the mechanical stress and the gradients of temperature withing time ?

because the cutting forces needed to cut wood with a 20,000 rpm 1/4 hp router is just not much. a few pounds of force.

If the wood body of their cnc router was twice as thick, and a square closed box section instead of open I beam sections, you could put a 1hp router with nema 34 steppers.

the next thing to upgrade would be the rails and rollers, for just regular cheap 20mm linear rail. then the next thing to upgrade is ballscrews instead of a belt. but all that costs money.

1500$ for a complete system that can do intricate carvings (they just take a long time) can pay for itself in 1 day if you have a customer base. 

[Doctorandus_P]

Wood is not better then metal, unless ease of use and cost are the main driving factors for your equation. Even with wood routers, the stiffness of the construction is a major factor, and there is quite a lot of flexibility in wood. As a result you have to make more and shallower passes and use a slower feedrate. Another problem already mentioned is movement with humidity changes. Painting the wood really good helps with stabilizing here. But it is possible to make such a router from wood and then be able to make products with them.

A quite nice design is:
https://www.instructables.com/LOW-COST-DIY-500-CNC-MILL/

First it uses the square MGN rails, which are supported over their length and overall of better quality than anything with round guides or wheels. Second, it uses simple aluminium extrusions to stiffen up the rails. The rest of the construction is made of wood to keep the cost down and make it easy to manufacture with simple tools. It is also an adaptation of the routers made by Sorotec. But Sorotec is all aluminium, more presice / stiff but also much higher in price.

The version from "Bootec" (below) is also very similar, but it uses a bit too much wood to my liking.



If you want to improve these designs, the first thing is to make a box section out of the gantry itself. Ideally you take 4 pieces of angle steel and put those in the corners of a box made of 4 slabs of wood. Or you only put two pieces of steel on the backside, as the front already has the two steel rails.

Next improvement will be to stiffen up the vertical legs of the gantry. Just gluing two slabs of wood together quadruples the stiffness, but better is to add steel or aluminium strips. Just gluing steel or aluminium strips vertically over the legs (both inside and outside) Aluminium is about 1/3 the weight of wood, but Youngs modulus of Aluminium is also 1/3 of that of wood.

Next improvement would be to add some concrete inside the bottom box. Filling the whole box would make it heavy, But pouring a "beam" around the perimeter, and adding a diagonal or some slanted cross beams is a good compromise. You can use UHPC or Epoxy granite, but even regular concrete will work almost as well. But with regular concrete, do add some rebar in it, just as is normally done with any foundation.