DIY Marble - Metal Machining 3 axis CNC Router

Greetings gentleman,

Here I would like to post my new welded construction 3 axis cnc router design.
X axis : 3.000 mm
Y axis : 2.200 mm
Z axis : 600 mm

It is now on design stage.
Material to be machined will be marble and carbon steels.
First post will be about Bridge - Saddle - Ram Design.

At first i started with one linear rail on each side of bridge (X axis) and one ball screw.
Afterwards I increased the linear rails on each side to 2 in second and thirth designs.
Difference between second and thirth design is,linear carriage mounted bridge supports on each side is 300 mm for second 200 mm for thirth.
Center distances of linear carriages is 170 mm for both second and thirth design.

Total 3 designs. I would like to hear what is your choosing among 3.

Linear rails are roller bearing type for higher load capacity.
Linear guide rail Size : 35 mm
Quantity on right side : 2
Quantitiy on left side : 2
Ball screw size : 40x8 mm

For Y axis 3 linear guides . One of the linear guide rail is located on top with a different direction.
This will improve the strength of the bridge %20 higher according to studies.
Linear guid rail size : 35 mm.
Ball screw size : 32x5 mm

For Z axis; there are 4 linear guide rails. 2 at rear 2 at sides.
Linear guide rail size : 28 mm
Ball Screw Size : 32x4 mm (may be this size will get smaller)

Mass :

Ram : 240 kg Saddle : 240 kg Bridge : 1.200 kg Bed Frame : 4.800 kg

Y and Z axiss will have 1 kW servo motor - 3000 rpm drive, directly assembled to ball screw via coupling.
X axiss will have 2 piece of 1 kW servo motor directly assembled to ball screw.

There will be 2 counter weight pneumatic or hydraulic cylinders located on Z axis saddle for balancing the Z axis Ram.
This will improve Z axis servo performance.

You may see rail lock and carriage lock units at every axis.

Here are self leveling chocks and my standard leveling blocks for bed frame.

Very nice. Double or triple linear rails on one axis require very high mounting precision .
On your Y axis i would move the ball screw lower, to be "closer" to the tool.

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Originally Posted by stonix

Very nice. Double or triple linear rails on one axis require very high mounting precision .
On your Y axis i would move the ball screw lower, to be "closer" to the tool.

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Good idea for Y axis ball screw location ! Noted.
to get closer to saddle center of gravity, and the tool itself.

I would like to talk about the geometry of the bridge and placement of 3 rails.This design is called "ladder design". Instead of a complete flat front of bridge you must have triangle shape at front.You can use one flat plate and one plate with 30-45 degree or complete one plate with a relevant degree.
With 2 or 3 rails, you must have ladder shape. This makes saddle center closer to bridge, and inproves bending strength capacity of linear rails drastically.

Spindle -1ES793 - H6161H1060

Spindle -2
ES796 - H6161H0916

I think i will choose spindle-2 due to connection flange location. I can use 1 bolted plate to bottom of ram.
There fore it will be easier.

Is there any specific requirement to cut marble ? So you need a big spindle and expensive one ...

[QUOTE=asuratman;2188796]Is there any specific requirement to cut marble ? So you need a big spindle and expensive one ...[/QUOTE

For cutting marble you need higher speed spindle than required for metal and less kW for the same feed rate and cutting depth.

spindle kW for marble in the market is 15-40 kW with minimum 12.000 rpm
Actually for marble machining 9-12 kW is just fine, 15 kW is required if you gonna use 600-800 mm diameter saw. Some machines are capable of using 1.200 diameter saws therefore you need higher kW.
Power depends on you tool diameter mostly.

Min spindle kW for metal machining in the market is 15-20 kW - 6.000 rpm

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Originally Posted by Halbmond

Good idea for Y axis ball screw location ! Noted.
to get closer to saddle center of gravity, and the tool itself.

I would like to talk about the geometry of the bridge and placement of 3 rails.This design is called "ladder design".

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As alluded to by another poster the big problem with this design is manufacturability. If you have the machine shop tools and personel to do the machining then you may be sucessful. My big fear is that you wont hit the require precision and as a result will put the linear bearings under an excessive load.

This makes me wonder if you have considered a big tubular beam for the gantry with internal bracing? You should be able to reduce fabrication costs and end up with the same stiffness. Plus you reduce rail usage by one.

The concerns above with the closely spaced linear rails also applies to the Z axis. The smaller axis does make machining somewhat easier but you still need to obtain a rather high level of precision. This especially if no means to mechanically adjust linear rail positions is provided.

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Instead of a complete flat front of bridge you must have triangle shape at front.You can use one flat plate and one plate with 30-45 degree or complete one plate with a relevant degree.

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This does seem like a hard way to get to a level of stiffness. No matter how the gantry is created those plates will require post fabrication maching. The maching isn't a huge problem if you have the linear bearings in plane but with this arraingement i see a far more difficukt task for the builders.

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With 2 or 3 rails, you must have ladder shape. This makes saddle center closer to bridge, and inproves bending strength capacity of linear rails drastically.

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Im not sure i follow the above. For one are you refering gantry beam twist when talking about linear rail bending? My big problem, especially with the three rail design, is with being actually able to build the machine and to be able to maintain it. There is good reason for the common practice of a master rail and a slave rail with the master registered against a locating shoulder and the slave rail left free to align properly. With over constrained designs something ends up binding leading to linear bearing failure or less than desirable assembly practices.

In any event don't let my concerns stop you, im always interested in new designs.

Good solid designs. Are you planning on using water with the diamond tools?

I also don't quite understand the purpose of the middle rail on the Y. It doesn't seem to contribute much, as it's near the axis the carriage would want to rotate on.
Any reason for doubling up rails on the X rather than going with larger rails?
Similar concern on the Z, getting those outside rails aligned properly is not going to be easy.