Metal CNC Machine

[johnansaro]

Hi there a friend of mine has asked me to build him a Metal Cutting/milling 3 axis CNC machine. I know in principals it is similar to a wood cutting CNC machine, But i know I have the
Following Challenges: I should mention that this is a 1200*900*700 mm Machine

• What material to use for my Chassis, I would say It should be I beam of some sort?
• What would I select for my rail and wagon, Is it similar to Wood or some thing else?
• what would the better choice Step Motors or Servos? is step motor a possible choice generally speaking?
• Moving System, I believe should be Ball and Screw? Do I need to Install 2 Motors on the sides of me table for my Y Axis or One in the middle is recommended?
• and any recommendation on how to build the protective Structure is greatly appreciated.

also is milling Possible with lets say a laser cutting machine? Or laser CNC machine are basically a 2 axis Machines, and one just can not control it in Z direction?
otherwise is a process like are clearance possible with laser CNC Machine?



Regards
jhonansaro

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[awerby]

While mills and routers are somewhat similar in how they work, they aren't built the same way. Mills are usually much heavier in construction, with a solid overhanging arm that holds the spindle.

Cast iron is the preferred material for building mills.

Dovetail slides and box ways are traditional, but some use heavy-duty profile rails.

Step motors or servos can be used, but most large professionally-built mills use servos.

Ball screws are usually the preferred method of transferring force from the motors. Since the Y travel on a mill is generally much shorter than X, they are commonly driven with a single screw.

Enclosures for milling machines are usually built from steel and glass, with doors that have an interlock which cuts power when it's opened.

Lasers are not used for milling. There are laser cutters and laser etching machines, but I've never seen them combined with mills - they are entirely separate tools.

[wizard]

Hi there a friend of mine has asked me to build him a Metal Cutting/milling 3 axis CNC machine.

What type of metal and what type of usage? Anything beyond aluminum you are likely barking up the wrong tree.

I know in principals it is similar to a wood cutting CNC machine, But i know I have the
Following Challenges: I should mention that this is a 1200*900*700 mm Machine

The large Z can be a problem in a machine design due to the lever arm it represents.

• What material to use for my Chassis, I would say It should be I beam of some sort?
  

• Steel.
  

• What would I select for my rail and wagon, Is it similar to Wood or some thing else?

[johnansaro]

Hi awerby, wizard

Thanks a lot for your replies, It has been most useful, greatly appreciated.

regards
jhonansaro

[genixia]

How much do you value your friendship, and what is the budget? I suspect from the nature of your questions that one or both of you will be disappointed by the end of this project and that will test the friendship. Are you looking to buy parts at a true business cost or bargain-hunt ebay and the like. What is your time worth?

Please don't take that the wrong way - it's just that the questions that you have asked suggest that you have little experience building CNC machines, yet the machine you are looking to build is very ambitious. The machining envelope is large in 3 dimensions so you will need a heavy rigid frame in order to cut metal. That will require fairly large linear rails and ballscrews. You will also need appropriately large steppers or servos to drive them, in turn needed appropriately large motor drives. The costs will add up quickly, and expectations with them.

Don't feel bad - we'd all like a 1m^3 work envelope machine capable of cutting steel (preferably with a laser head etching add-on) for only a few thousand dollars. At some point dreams meet reality.

You need to make some tough decisions and properly define the scope of this machine. Halving either Y or Z (or thereabouts) would leave you with either a vertical mill or a gantry mill design. Both of those designs are widespread because they can be made to work. You haven't talked about spindles, or whether a toolchanger is needed. It would be daft to spend several thousand dollars on a machine to then put a $200 spindle on it. You haven't defined what precision you need to hold, nor travel speeds. Both will have a large effect on ballscrew and motor/drive costs. Rule of thumb - ballscrews should be sized about the same as the rails.

eg.
450mm * 200 mm * 300 mm - Vertical mill design, 15mm profile rails and 16mm ballscrews would work. You can buy rolled C5 ballscrews of that size relatively cheaply (Gten, TBI Motion), or easily found T7 rolled ballscrews which aren't really supposed to be used for positioning but many hobbyists do.
1200mm * 900 mm * 300mm - Gantry design. You'd probably need 25mm rails and ballscrews on the X because of the gantry weight required to span 900mm and to minimise screw whip with a 1200mm long screw. Y and Z would depend on spindle weight, but I'm guessing 20mm on Y. Those ballscrews are almost certainly going to be ground, and expensive.

[johnansaro]

Hi genixia

Thanks for the reply.
This is a good friend, and basically from now on, If I ever decided to built a CNC machine I would chose only from the best possible material, But more importantly the Right part.
The size must be 1200*900*700, the rail system I believe, as awerby Suggested I will go with Dovetail slides and box ways. spindle must be a ATC capable with Highest possible Power.
But on the issue movement of the axis what is the better choice:
1: X,Y Table moving system, basically with spindle fixed in X,and Y Position? or
2: like a traditional router with axis moving and not the table, basically the spindle moving in all 3 axis?

Regards
jhonansaro

[genixia]

If you're absolutely set on that size than a gantry router style would be better.

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[skrubol]

For a machine that size, if you want much productivity out of it, you're probably looking at a mass of 3-10 tons. 700mm is very tall for a router, but 900mm of y is quite long for a mill. If you go with a gantry router, it seems for metalworking stationary gantry with moving table are the preferred arrangement rather than a moving gantry stationary table that most wood routers are. I think for a taller router that is another argument for the stationary gantry (it's going to need to be a tall gantry.)
Do you have a budget? Thoughts on how to get the weldments created? What sort of power are you thinking?

[skrubol]

One point of clarification, is the 1200x900x700 size the outside or the machinable volume of the machine (X, Y, Z travels)?

[Third-Gen]

looking at building something this size, youre gonna need to start with either a large slab of granite and bolt guides onto it, or build a large metal base and pour concrete into it. Moving gantry will get you the smallest footprint vs travel, but if you want better ridgidity do a sliding table, with just Y and Z on the gentry. tool change spindles for the "hobbyist" level arent cheap. Youre also gonna be looking at doing a servo drive control system, steppers arent gonna cut it. I would highly suggest buying a used machine. Haas or even an old Gantry mill. My neighbor just took a large gantry mill to scrap, 12' long, 6' wide, 2' in Z, 30hp, with drawbar spindle.