new build opinions required

[george uk]

Again, very usfull stuff in there.

Am using motors as i can easly get the resloution i need and if i make a mistake i can change them reletivly cheeply,

Nor you can wear Hiwin bearings if properly mounted. When you have them in your hands you will see why. They will be probably that last element in a machine to fail.

You not considering the difference in wear when using stone, Its not just the heavy use on the machine parts, your basicaly air-rating grinding paste. allthough the powder feels fine and soft, on a particulate level, its rock hard and sharpe. vacuums and covers can pre-long bearing wear, but, you are going to wear rails and bearings when cutting or surfacing stone. Then think that large beds are hardly every fully utilised, everybody's got there own favourite sweet spot on there machine were most of the smaller jobs get done, so you get uneaven wear.

If you then want to surface a large bit of stone, 1500mm by 800mm, you would see the wear patterns in the surfacing as the rails and screws go between the commonly used area and the less used area.

There are other considerations as to why it might be a good idea to have the bearings as the failure points. Re=straightening a frame, or gantry, is quite a long and complex job, that involves building a jig, usualy into a thick concrete floor, and gooing through a heating,cooling and tighnening routines, then when its in shape, heat it and cool it to even the stresses.

8/10 times, it would be cheaper to just remake the gantry, and salvage the unbent parts.

whereas, if you specifically design your frame for the bearing to be the week point, servicing is easier, serviced periods are calculable and variable depending on machine use. and as long as your bearings will fail, beyond the maximum cutting forces your machine will exert, then you could consider it a safety feature.

[JAZZCNC]

whereas, if you specifically design your frame for the bearing to be the week point, servicing is easier, serviced periods are calculable and variable depending on machine use. and as long as your bearings will fail, beyond the maximum cutting forces your machine will exert, then you could consider it a safety feature.

Your correct about stone being grinding paste but don't agree that you will be designing in the rails to be a fail point.?. . . . They will naturaly be a fail point because they are moving components, has will the be ballscrews and nut.
So instead of designing in what will happen anyway put all your design efforts into the best way to limit or avoid this.

Best why I know off is to cover and conseal so get them either up high out the way or under neith and under cover.!! . . . . Now Remember you'll be using Mass's of water which tends to run down hill, also gravity brings droplets down eventually so personally I'd be looking to get the rails higher rather than lower and still under cover has much possible.

Then you have the Ballscrew or R&P debate.? At 3mtr length then the Only way I'd use ballscrews is if they used rotating ballnuts. Which would actually help with reducing the number of rotating parts and be much easier to cover and conseal.
To use rotating ballscrews at 3mtr length would require at least 25mm Dia screws which then takes you into large Stepper motors/ drives etc added to this the fact your gantry will be heavy anyway means even larger motors or going with servo motors and all that comes with them.!
This is why ballscrews and long machines don't match perfectly well and if you find any long machine that use's Ballscrews you'll see they often have large diameter screws with a Large pitch thats geared with ratio to keep the rotation speed down and whip from happening. They also have servos on the ends because steppers can't handle the torque required to Accel and Slow from traveling a heavy gantry with large rotating mass.!

R&P is there foreoften used when accurecy isn't the prime concern because it's less expensive and has less rotating Mass. Down side is it's less efficeint and more exposed and prone to interference from debris getting into the workings so again needs careful placement and consealment.!!

Which I'd use would depend on machine design and my budget.? Probably Ballscrew because I prefer them but 100% it would be a rotating nut and up high out the way along with the rails. This is where all my design efforts would be concentrated and even if it cost extra money to put up high and under cover because of building in the extra strength required I would do it to save on the down time which would come from replacing worn components.

Machine setup can take many hours or days and even weeks at DIY level if your after close tolerances so anything to reduce this or limit having to disturb the finely setup machine would be my prime concern along with strength and accuracy.

Now I'm going to honest and blunt here George.!! . . . . I think you are going to waste an awful lot of time and money plus dissapointed with results because what your wanting to have is Large machine that is all things to all materials but haven't got a clue to just how hard that is to achive or make happen.
When you go large even with machine designed just for one main purpose the design and build process takes you to new levels, expensive levels well above the average DIY build. SO to try and build a machine to be ALL THINGS to ALL MATERAILS with advanced features like 4th & 5th axis etc is a BIG BIG BIG under taking that would make even the most experienced DIY builder like Jonathan or Me sit down and think very very very carefully.? . . . . . To take a project like this on with NO experience is a recipey for wasting money and time .!
My advice is don't do it and build smaller or focus at one machine designed for that main task, which at this size will still be a very very big challenge for some new.!!