[levathar]

Hello guys, I am new here, but I am not completely unfamiliar with CNC machines.

It was almost 20 years ago I had the chance to work with a CNC mill, it was barelly powerful to deal with 600 HB hard steel, if I recall right.

Now I am sinking in this passion of mine, after having completely lost contact with such world.

I want to build a 3 axis mill that can work from aluminum to steel. I do know that I will have to make a first attempt far from this standard, but I want to start working right away in the main goal.

Here is some prntscn of the google sketch I did the drawing.

Some considerations:
After looking at many designs, I felt that the X axis would be limited, so I made a table sliding on top of another.
I consider using SBR20 line rail and bearings, supported, and 16 anti backslash ballscrew, and direct drive on X and Y, and pulley reduction on Z 2:1, using NEMA 34 3,4Ncm (481,5oz.in) stepper motors with 3 x Leadshine M542 stepper motor driver, these I can get as a kit.

The construction would be on 50x50x2 mm steel profile, should I go stainless steel? I was thinking about 304.
On the side panels would be 20 mm plating, and wherever looks thinner will be 20mm plates.

It do looks very robust because I am scared of structure deformation affecting the quality of production.
But I guess it will be very heavy?

The chassis have been designed around this values:

Y axis rail length (Base rail): 1000 mm, separated by 600 mm, bearing position would allow 550 mm travel.

X axis rail length (on top of the other): 1500 mm, separated by 450 mm; bearings position would allow 950 mm travel. full length of table structure 1700 mm

Measuring Z I conclude that I got the rails too short, because I have 580 mm between bottom of Z table (spindle support)
z rails length: 500 mm
Z movement range: 200 mm

Because I want a long large spindle shaft, like the one I tried 20 years ago.

With these results in following machine measures (Excluding support table):
Depth - 1320 mm
Height - 1550 mm
Width - 700 mm

Forgive my first rough approach, can you help me getting started?
Is the structure too much? I haven't yet considered costs, I want to get to a effective design first.
Are the stepper motors strong enough?

Thanks to everyone for the input, much appreciated!

Lev

[underthetire]

It's going to chatter like crazy with those rails and that X axis "frame". Don't use stainless, steel has better dampening properties. The entire head looks like formed/welded sheet metal? Going to cause a lot of vibration, and no where close enough stiffness for steel cutting.

[levathar]

Mr. Underthetire, thanks for the input.
I will be looking forward to work the debilities of the design with you and the guys

Yes, the design would be like single piece sheet 20mm thick (I am not yet sure if I can get someone to cut it for me) left and right, welded together on the middle by same 20mm sheet steel. Should I work a thinner body to increase stiffness? Or should I go into a crew and bolt solution? What do you think?

To reduce chatter, what kind of rails would you recommed?

Thanks in advance!

Edit: SBR20 rails are fully supported, I did not put in drawing but its bolted in 150mm spacing.
Does it make a difference?

[underthetire]

Oh, from the drawing it looked like thin sheet, 20MM would be much stiffer. As far as rails, you need something more like
NSK Linear Bearings | NSK

Still think you will need to enclose that X axis, not going to be stiff enough like that.

[levathar]

(EDIT: Trashed previous sketch and decided to try again - Need your input to correct this. I am starting with the chassis. All in 20mm steel plating. Thickness is ok? General measures are the same as posted before)

Mr. Underthetire, thanks once again!

I think I do understand what you mean.
I had put the X,Y,Z rails mounted on 50x50x2mm square profile (2mm wall thickness) and probably that lead you to think it was thin metal sheet.
I considered using the square profile for ease of mounting the rails. Should I replace the square profile (hollow) for thick plate?

I had previously seen those rails, they look much stronger indeed.
SBR20 use roughly 50x50x40mm sliders, and this condition the area of support, and the
HA25AN would have a slider of 147mm long. Two of these per rail would do fine?

I don't know these range of rails very well, and how easy I can get a full set, but will look into it!
As you recommend these kind of rails, what model would fit better such application (cnc mill)?

Regarding X axys I will change it, will use the steel plates. That will raise the momentum of inertia (sorry if the word is not correctly translated to english) "I" that will act in the ability to get the structure deformed.

I am very eager about all this, if I had a Inventor Pro licence I could see the 3D model bend!
I am very excited as you can see

Glad to be changing ideas and learning with you guys

Lev