Stell frame cnc 1500X1000. Adjustable table your opinion please

[JAZZCNC]

Hello Vagelis,

Following your PM I did see this thread and forgot to post Sorry.

First Agree with Silyavski that your double I-beam design is bad idea and would drop it like hot potato.

Also agree that a fully welded Bed is slightly stronger but it doesn't allow easy adjustment if you need large items and having raising platforms like suggested can be inconvenient and take up space for storage.!

To decide which best suits your needs then you'll have to consider closely what your cutting needs are.? . .If you only plan to raise the bed to say just cut Aluminium so bringing table surface closer to spindle a fixed amount every time then go with the fixed bed and build raising platform to suit. (If you have room to store it.!!)

But if you what to cut a range of material thickness's then adjustable bed is the better option. If designed correctly and built strong then the strength difference is negligible for most cutting conditions except really heavy duty or very hard materials, In which case you have probably built the wrong design machine.!!

Now regards the table Bed and getting it parallel to the cutter then don't worry this is not a problem.? Because every time you move the bed or in Fixed bed case Add the raiser block you MUST surface the table to be sure it's parallel to Cutter.
This also means it doesn't matter if the adjustable table isn't perfectly level or even in twist because after being surfaced it will be parallel to cutter and thats all that matters.

NOW what is VERY VERY important is that the X axis~(long axis) rails are on the same plane and not in twist.!! This is where all your efforts need to be concentrated on getting correct. The Bed could be Banana shaped and slopping at an angle it doesn't matter because after surfacing it will be flat and parallel to cutter BUT ONLY if the X axis rails are on the same plane. Any errors in this department affect the whole machine.

Several ways to ensure this but really only 2 that are realistic to the DIY builder. These are Epoxy levelling or adjustable top rail and careful measurement.
Epoxy is probably the easiest because it doesn't require accurate straight edges or equipment.! It's just more time consuming because of prep to surface to ensure clean and setting up dam walls and bridge etc . . .Plus it's messy and requires clean up afterwards!.

Thou For first time builder then I'd probably suggest taking Epoxy route has it's easier to ensure rails are on same plane and doesn't require machines to ensure top rail is surfaced flat.

- between 80x80x3 and 4mm, the best choice is or 80x80x3 or 100x100x3 .
Why?
80x80x3 1m=7.17kg/m
80x80x4 1m=9.47kg/m
100x100x3 1m=9.02kg/m

Now regards this Silyavski then there's little more to it than just weight.? The thicker material will lessen resonance and resonance affects the quality of cut, it can also affect motor performance to some degree and I recommend Digital drives with good resonance damping built in if building from steel. Also fill the Tubes with sand for best affect.

Some times it's better having less speed but Stiffer machine with less vibrations than trying to save weight. Again this depends on what your doing with machine.

Let me say for cutting anything below Aluminium these steel built machines are massive overkill and would need huge spindle power to achieve the Depths of cut and feed rates that would stress the frame or make it become the weak point.

For Cutting aluminium or harder materials correctly to high standard requires a certain attention to design and detail that is very hard to Achieve, just look at Jonathans latest post about his friends excellent machine to get an idea of what's needed to do it correctly and I'd even say this is a minimum requirement if high standard of finish and feed/DOC rate is needed.
This is just medium sized machine and with every 100mm wider or longer the level of engineering gets more and more important and harder to achieve accuracy.

So my Advise is THINK CAREFULLY about your cutting needs and be REALISTIC about feeds/DOC etc you expect to achieve.
No point using a Sledge hammer to crack a nut and same goes with cutting wood, Machines built to this level are Sledge hammers to wood.!! . . . . Build it just stronger than needed for the Job it's doing, any more is waste.

If you need to mainly cut aluminium and correctly then build a different machine designed to do the job correctly.!!

If you want one large machine to do all jobs then it will have weak spots in every area, it CANNOT Excel at cutting every material just impossible to achieve realisticly.!!