need your opinion :) 2500x1500

[toskata]

hi to all
i'm new to this forum
after long hours of watching homemade cnc ,reading forums
i have decided to make my own, using sketchup make some drawings.
I want to use it for wood ,aluminum , and granite - marble milling 2500x1500x200
yes many of you will say go with r&p for that size
but i want big tough precise machine with ballscrews
on which machine later maybe i will upgrade with a rotating ballnut for
2500mm axe long and increase the critical speed
it should be like this
z axe
1605 ballscrew
16mm l 250mm linear rail 11143rpm

y axe

2010 ballscrew with ballnut 888rpm
15bk/bf support
20mm linear rail l 1500mm

x axe 484rpm (1078rpm rotating ballnut)
2 x 2510 ballscrew
20mm linear rail 2500mm
BF/BK15 end support


spindle 3kw air cooled
4 NEMA 34 step motors 878oz with motor drive DM860A


rpm's are calculated with nook calculator for critical speed
max speed should be aprox 5m in minute(hope it's not too slow for cutting aluminum and marble)
geared 1:1 with 30t 5m f20

please share your opinion,missing something will it works

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[louieatienza]

If your goal is to mill harder materials, I would stay away from that round rail, and use profile rail. It's about 10x stronger than round rail for the given size series, and can receive the same load in all four directions. Unlike round rail, whose load rating depends on its orientation.

You may have not drawn it in yet, but some triangulation I feel is necessary, especially wit the heavier workpieces on the machine. I'd also consider using at least 32mm or 35mm screw on the X to prevent sag. Some way to protect your ballscrews and LM guides from marble dust/slurry.

[toskata]

yes i want to mill harder materials and i will take that on mind
dust protection isn't drawn yet because i am not still decided
for the size of the ball screw and as you said the linear rails.
i know that 32 or 35 mm ballscrews are better but little bit expensive for me at the moment,
i have seen people whose cnc's are milling steel with 25mm dia ballscrew and i m hoping that two bawwscrews on same axe will help against sag.
THANKS a lot for your opinion and your time
best regards

[hanermo]

You need to massively increase section sizes, and hugely upgrade all components, to route harder materials, not mill.
By about 20x in stiffness.

TO mill, another 20x in stiffness.

The problem, like always, is NOT strength it is stiffness.
A 20mm ballscrew will mill, well, when it is only out 5x-10x the D or diameter, == 200 mm (max, bit long, 5xD is better).
At 2500 mm, it is 2500 / 20 = 120D diameters out.
This is 120 / 20 = 6 times more.

Siffness = rigidity.
Rigidity is length cubed.
6 x 6 x 6 = 216 times less stiff.

Look at old HAAS routers on the net for inspiration.
That is what You are proposing to do.

[louieatienza]

yes i want to mill harder materials and i will take that on mind
dust protection isn't drawn yet because i am not still decided
for the size of the ball screw and as you said the linear rails.
i know that 32 or 35 mm ballscrews are better but little bit expensive for me at the moment,
i have seen people whose cnc's are milling steel with 25mm dia ballscrew and i m hoping that two bawwscrews on same axe will help against sag.
THANKS a lot for your opinion and your time
best regards

Having four 25mm won't help, because it will sag from its own weight. Then again, even 32mm may sag also. And it's about 40% heavier, so you'd need larger steppers.

I think you'll find on eBay 25mm profile LM rail from HiWin, or TBI, or PMI, or HSAC, which are not much more than round rail.

[toskata]

You need to massively increase section sizes, and hugely upgrade all components, to route harder materials, not mill.
By about 20x in stiffness.

TO mill, another 20x in stiffness.

The problem, like always, is NOT strength it is stiffness.
A 20mm ballscrew will mill, well, when it is only out 5x-10x the D or diameter, == 200 mm (max, bit long, 5xD is better).
At 2500 mm, it is 2500 / 20 = 120D diameters out.
This is 120 / 20 = 6 times more.

Siffness = rigidity.
Rigidity is length cubed.
6 x 6 x 6 = 216 times less stiff.

Look at old HAAS routers on the net for inspiration.
That is what You are proposing to do.

so according to this, what sizes of the ball screw would you choose for this
size of the machine, and yes you're right about stiffness and the rigidity
thanks in advance

[ger21]

I don't see how you can cut granite with this machine. Granite requires a powerful, low speed spindle, and a LOT of water.

You probably want a 3232 screw with a rotating nut for the long length.

[toskata]

let's say that i will redraw my scetchup plan,
use stronger tubes reinforced with 10mm plate(to get more on rigidity,siffness as Hanermo said)
will use one3232 with rottating ballnut on x axe 2500mm long
with two 20mm hiwin hgw rails
y axe one 3210 ballscrew
with nema 34 878oz with two 20mm hiwin hgw rails
the spindle should be 4 kw(air cooled)or more with a lot of water to
cooling the carbide cutter working on a slower feed rates.
What do you guys think,will it works?

& how much load can be put on one 20mm hiwin rail with two hgw blocks?

[wizard]

let's say that i will redraw my scetchup plan,
use stronger tubes reinforced with 10mm plate(to get more on rigidity,siffness as Hanermo said)

The issue is the desire to machine granite. Most of my experience with stone comes from using a hand drill in impact mode and frankly that stuff can be very hard. Obviously this doesn't translate directly into machine requirements but the need for stiffness here is going to require more engineering than the run of the mill build here. If you can visit a plant that processes granite to get an idea of what commercial machines look like. Actually you probably can find something on youtube as there is a video of almost everything there.

will use one3232 with rottating ballnut on x axe 2500mm long
with two 20mm hiwin hgw rails
y axe one 3210 ballscrew
with nema 34 878oz with two 20mm hiwin hgw rails
the spindle should be 4 kw(air cooled)or more with a lot of water to
cooling the carbide cutter working on a slower feed rates.

How will you handle waste water collection?

What do you guys think,will it works?

I really doubt it will handle granite/marble, but the rest of your stuff listed will be OK.

& how much load can be put on one 20mm hiwin rail with two hgw blocks?

What you might try to do is to find a carbide cutter supplier that supplies to the granite industry and ask them for info on machining parameters and expected reaction forces. From there you can estimate deflections expected. It probably would be worth asking what do you expect to do with the granites it machining in a general sense or something more like engraving? Engraving would be far easier to handle if you use very small cutters to do the job.

[RCaffin]

Granite: basically you are talking about a lot of water and diamond tooling.

Visit a monumental stone mason for an education. (They make tombstones.)

Cheers
Roger

[louieatienza]

What you might try to do is to find a carbide cutter supplier that supplies to the granite industry and ask them for info on machining parameters and expected reaction forces. From there you can estimate deflections expected. It probably would be worth asking what do you expect to do with the granites it machining in a general sense or something more like engraving? Engraving would be far easier to handle if you use very small cutters to do the job.

I think with granite, it's going to be some form of diamond tooling... which in total would probably cost as much as the machine.

[toskata]

well i think that it worth it,
a machine like that to buy it it cost a little fortune
but to build it with a little help from you(i'm watching ebay prices for the parts) good planing,it would be an
affordable price