[eMTea]

Hi!I'm dreaming of my own CNC machine, stable and accurate enough to also work with steel.I've understood that a solid gantry type machine will be the best way to go for most accuracy and stability with harder metals.It's not intended to be machining hundreds of kg of steel, but I want a big work area, for oil pan, valve cover mods, flanges also for inline 6 engines. I will probably use LM (flat square) rails, but just for the design, I had these already in my library.I'd like you to comment my design.

[awerby]

I don't want to disturb your dreams or anything, but I don't see that design as working very well for steel (or anything else, for that matter). Where does the part you're machining on fit? You've got the spindle assembly attached to that red box, and unless the vise is attached to the bottom of the box, the tool won't reach it. But although the box can move around, there's no way the spindle can move in relation to a workpiece, which is what milling is all about. At best, this would be able to drill a hole in something. You'd have to refixture your workpiece to drill another hole.

To change this into something with a chance of working, you need to eliminate that red box, and attach your Z axis to a big "G"-shaped iron casting, or the equivalent in heavy welded steel plate. Put that assembly of moving stages on the horizontal part of the "G" and you've got an approximation of a milling machine. How well it would cut steel would depend on how rigid you could make it, among other things like the accuracy of the slides and screws, and the construction of the spindle.

[eMTea]

I don't want to disturb your dreams or anything, but I don't see that design as working very well for steel (or anything else, for that matter). Where does the part you're machining on fit? You've got the spindle assembly attached to that red box, and unless the vise is attached to the bottom of the box, the tool won't reach it. But although the box can move around, there's no way the spindle can move in relation to a workpiece, which is what milling is all about. At best, this would be able to drill a hole in something. You'd have to refixture your workpiece to drill another hole.

To change this into something with a chance of working, you need to eliminate that red box, and attach your Z axis to a big "G"-shaped iron casting, or the equivalent in heavy welded steel plate. Put that assembly of moving stages on the horizontal part of the "G" and you've got an approximation of a milling machine. How well it would cut steel would depend on how rigid you could make it, among other things like the accuracy of the slides and screws, and the construction of the spindle.

The red box is an illustration of the work area.

Z-axis is not finished planning wise, I just want to have 250mm of vertical travel, is all i know for now.

[awerby]

Okay, that makes things a little clearer. But it still looks like the column is attached to the sliding plate that moves front-to-back, or is occupying the same space. You need to make the front-to-back dimension of that plate shorter so it doesn't interfere with the column.

[eMTea]

As you see from the location of the rails/bearing blocks and the illustration of the work area, the Y-axis is in the inmost position now, will not move any closer to the colomn, only 400mm travel AWAY from the colomn.

[LeeWay]

What you have there is your basic wet noodle design. I do no see anything in that design that I would actually use. Even if everything shown is ground steel, there is just not enough structure and too much weight for the table to be efficient. More along the lines of something like this.



The rails in the design are really not rigid enough for steel. While they may be able to handle a little, the lack of rigidity will cost you a fortune in broken and chipped tools. I really think you should look around at existing milling machine designs and pick a better starting point that this one.

[kawazuki]

Judging but the input monitor ....................thats gotta bigger envelope than the OP's proposal? LOL
But, I would imagine the concept could be 'scaled down' to a degree, atleast until the lack of rigidity becomes
an issue when machining ferrous although coping with aluminium perfectly adequately?

[LeeWay]

Just an example of the design layout. There are other examples that would work as well. The size envelope require's either a very large machine or one specifically designed to do the task. You won't accomplish that with parts and a design that may be questionable when cutting wood, much less steel.

The reality is that to build a machine like this on a budget, first increase the budget.

Then you have to get very creative with the design and material procurement. I am speaking from experience here. I did design and build my own much smaller milling machine using non standard materials. While some of it was aluminum, it was basically covered in steel and cast iron to achieve the results that I got. It has been upgraded several times in different areas. It is a great little mill and has paid for itself, however I could have bought one larger ready to go for less money.

[eMTea]

Ok, so basically you would define it as a waste of time? If i let go of the wish to machine steel parts, will it still be waste, and would a gantry type table be better?

[RCaffin]

Hi Lee

Bit of steel there ...
What is the brand? I can make out 'NC' but not the rest.

EDIT: figured it out. Um - bigger than mine ... :-)

Cheers
Roger

[LeeWay]

Ok, so basically you would define it as a waste of time? If i let go of the wish to machine steel parts, will it still be waste, and would a gantry type table be better?

Building a machine is never a waste of time. The experience you gain will be useful for further projects and will allow you to recommend outrageously huge machines in the future.

Honestly the original design will be able to cut something. Just not sold that it will cut anything well. To start with, there is usually no need to have double rails in one axis. One set of proper size and type would do. That means that you need structure on top of those rails to carry a machining load.
Next, most of the machining in that format will take place over an unsupported area. Supported yes, but not directly. If it is stiffer or thicker, then the rails will pick up support for this. As it is now, it will not be solid and will break tools. Minute flex is very bad for end mills. Router bits don't like it much either. My best suggestion is to look around the zone at router builds and mill builds to see the differences. Then the outcome. I would strongly urge you to pick a better starting platform to have any hope of machining steel with any kind of decent finish. It may not be a waste of time, but could certainly wind up being a waste of money if it doesn't meet your needs.