Portal CNC question

[TimmiAlias]

Hi everyone. Recently started thinking about why there are more routers with z axis assembly moving along the y axis, then routers with y moving up/down along z.
They cost about the same to buid, same weight, same dynamics...

So, ppl with experience, share your thoughts on the subj

Thanks

Similar Threads:

• Mass Portal 3D-printer form Finland
• New Machine Build- Yet another 5 axis - 500mm cube portal
• portal milling machine - construction - mineral casting
• CNC-Portal Milling Machine Construction with 3D Turbocad 11 Prof.

[Andreiir]

Interesting point , but how is the cost the same?
U need 2 motors , 2 screws , 2 nuts , 2 drivers , the weight is more , because u move both z and y axys , wich is more weight .
The dinamics of course is better if u move z and y same , low vibration .

[TimmiAlias]

Well, you can use just one stepper, just slighly bigger or geared a bit more.
And you can have one 600mm screw + one 300mm (horizontal setup), or two 300mm and one 600mm (vertical setup)
so the screw and the motor just a little bit more... +/- USD100 compared to 2-3K for the whole thing, is unnoticeable

[coherent]

You not only have racking issues because when the z is off center the forces of the router put more stress on one slide/motor vs the other, but most importantly, the Z would have to lift and lower the entire gantry vs only the spindle and mounting plates. On a standard Z the slides are very close together allowing a single screw and motor. Not just cheaper but more efficient and less parts to keep aligned or replace.

[TimmiAlias]

Good point: - being off center, puts more stress on one side.
On the other hand, isnt the same thing happening when you lower the z to the lowest position on a standard setup?
the example pic in the first post is a bad example, because the z axis assy stays at the same height

Alignment issue... the master alignment is done once, then you check and adjust, which doesnt take much time

more weight to lift and more weight on the screws, it is a good point too, which can be addressed at design stage, its just a "more money on parts" issue

The price diff is obvious, besides the prices what are the reasons?

[A_Camera]

Hi everyone. Recently started thinking about why there are more routers with z axis assembly moving along the y axis, then routers with y moving up/down along z.
They cost about the same to buid, same weight, same dynamics...

So, ppl with experience, share your thoughts on the subj

Thanks

The mass you have to move up and down is considerably more and is more difficult than moving the same mass sideways. It is easier to keep a high speed and acceleration than if you move the whole beam with the Z up and down.

[TimmiAlias]

The mass you have to move up and down is considerably more and is more difficult than moving the same mass sideways. It is easier to keep a high speed and acceleration than if you move the whole beam with the Z up and down.

Yeah i agree with that, the greater mass has more momentum to it, and has to be taken into consideration.

After throwing some numbers in to the calculator and looking on the net, i came to the following conclusion:
The moving or stationary Y axis setup can do the same job with same results, but the moving Y setup, because of the extra weight and momentum, has to be a size bigger (16mm screw instead of 14, 30mm rods/rails instead of 25....)
Yes it costs more, but not much more, my cnc costed me around 2k to setup, if i redo it to moving Y, the price diff would be around $230 which is 1% of the whole thing.

I can have a stationary Y and spend less, and itll be easier to setup, or i can have a moving Y, which will cost a bit more, be more complex to setup...

Probably the right question would be - what is the benefit of using a moving Y setup?
Are there any people here with moving Y setup, that can share the exp with us?

[A_Camera]

200 is 10% of 2k, not 1% and 230 is 13%, which is a lot, even if you don't consider it that way. Spending money on rigidity is good, but I'd spend mine elsewhere.

Honestly, I don't think it is a good idea. I think there are many other disadvantages as well with that design. OK for 3D printer with low mass and constantly balanced load, even if the Z is moved out to the extreme end and doing it's work there and than moved to the other extreme end to do some other work.

Never the less, I am curious, so if you ever make this machine I'd be very interested in following up the experiment.

[TimmiAlias]

200 is 10% of 2k, not 1% and 230 is 13%,

True, my bad bad maths, need to go back to school

if ill end up doing this setup ill post it here.
I ll c if i can disassemble one router to convert it to moving Y setup

found this:
Mill

[gizmo333]

Hi, guys, i am thinking the exact thing to move the whole z up and down.
I'm designing a machine 900x750x500 ( working area 400x400x210) if I'm honest my friend is designing it I'm just giving my opinions and money for the material.
The machine will be made out of 3 welded baked to release the tension and then the parts will be machined on a CNC milling machine. Will show some pictures when the machine is out of design.

I have now a homemade CNC machine on aluminum profiles with a combination of metal linear rails and ball screws. It is powered by stepper motors 8,2Nm and a 2,2kw Chinese spindle ER20. The working area is about 890x400x210. It is ok, I'm using it for engraving in metal materials and the machine is pretty accurate regardless of how it is constructed and build. And on this machine i have z-axis assembly moving along the y-axis.


Best regards