New CNC router 8x4 For Cutting Multiple Materials

[JAZZCNC]

Hi Richard,

This design is really only suitable for Wood/plastic cutting. While it will cut aluminium the finish won't be very good and the cutting conditions regards DOC and feeds speeds will be far less than ideal.
After our conversation and knowing your intentions to cut Ali to high finish standard then machine is all wrong. Even at half length it's all wrong.
Again knowing your needs better then a dedicated small fixed gantry machine using profiled rails matched and ballscrews along with either high flood coolant or blown air/mist system will be far better.

Regards this machine then I'd use supported round rail on X & Y for convenience and Budget, they will be more than good enough for just cutting wood/plastic.
Personally I don't like R&P and would use 2010 screws on a rotating ballnut if much over 1800mm. Below this then standard connection is fine.
That said I have used R&P in the past on large machines and it works OK but find it needs more maintenance and critical to keep free from debris. Needs much larger motors with matching drives with high ratio gearing to achieve decent resolution which together make it more costly than ballscrews with far less accuracy and efficiency.

For the Z axis even with R&P I'd still use profiled rails and ballscrew. The Z axis is the single most important part of the machine that takes all the cutting forces directly, it also directly affects cut quality finish and if it's weak or poorly designed or uses cheap components then it will show in finish or wear and perform badly.

The gantry design looks a little on the flimsy side regards it's sides and Box section for the gantry will be very resonant which is less than ideal and could directly affect cut quality and even motor performance if bad. If your using Aluminium box then it will need to be thick walled stuff 3 or 4mm won't be enough.
Don't be afraid of weight when it comes to the gantry, often folks believe and go out there way to make the gantry has light as possible thinking it improves the machine when in reality it compromises the machine where it matters which is when cutting.!
Mass helps significantly with cutting and damping resonance, light gantry only really helps regards allowing higher rapid speeds which come much lower down the pecking order of desirable requirements.

If you want an all round machine then really this design isn't the way to go. In my experience for a successful all round moving Gantry machine then the frame/gantry needs to be different with the gantry mounted directly on the X axis bearings with no gantry sides to speak of. The distance from bed to cutter or put another way Z extension needs to kept to a minimum for harder materials like Aluminium. This requirement is often restrictive to the requirement to cut softer often bulkier materials like wood.!
So away to accommodate both needs to be found.? You could just raise the material to the cutter for hard materials and keep the high gantry side design but this is less than ideal has the very high sides are weak area and allow flex and resonance that will show in the finish of harder materials like Aluminium. . . . Fine for wood plastics etc that need to hold less tolerance or finish.

To do this we get rid of the the gantry sides and mount direct to bearings by raising the frame sides.
Now we still need to accommodate the high clearance for bulky materials while still keeping the rigidity by not having the Z axis extend all the way down to the bed when cutting thinner Aluminium but at the same time we don't want to be messing around with Blocks to raise material.
To get round this we make the bed adjustable, doing this takes away all cutting restrictions meaning you can keep maximum rigidity for all materials with much higher clearance if required.
In real world use you will seldom move the bed and find a position that suits most of your requirements but for the times when MAX strength or large materials need to be worked on then you can and the whole machine is very configurable for ALL ROUND uses.
All you have to remember is that it will always be a Jack of all trades and master of none but will still do a bloody good job.!

hope this helps.

Look around the forum for Z axis examples I've posted several examples with pictures of them in pieces and complete.