Ok well it's plenty strong enough but I would use 2 x ballscrews on the Gantry with this wide Y axis design to stop any racking affect but connect with timing belts using one motor.
I would use 20mm diameter and 20mm pitch screws at this length with a ratio applied. This will give more torque allow lower screw speed and still maintain decent rapid speeds.
Regards the motors then be aware that large nema 34 motors spin slower and require high power drives. So for this reason I'd go with 6Nm or no more than 8Nm motors as they will spinn slightly faster but still will require high power drives to get the best from them.
20mm linear rails will be more than enough.
With this wide gantry design you make it more stable/stiff but your making life hard regards the Z axis and you'll need to work on this area because that simple frame won't be enough. To be honest I'm not a Fan of this style of gantry design because it makes life harder than really needs to be and for not much more gain really. If your just cutting wood then you need to ask your self do you really need this complexity and my answer would be No.
Also to take advantage of the extra stiffness the gantry allows you need to have a powerful spindle so again not much point if your just using a plane old router or 2.2Kw spindle as a conventional gantry design built strong will be more than good enough.!!
Thanks Jazz. I will change the design to incorporate the twin screws with belts in my next drawing. I could change the motor to whatever you recommend though, it doesn't have to stay at a Nema 34?
The frame for the Z axis is just a starting point, the actual Z will mount to the box section but wont be relying solely on the box. It will be a solid construction all round and will cut every material possible. The main material I will be cutting will be 6082 aluminium so the stiffness will hopefully provide me with a great finish on the cutting surface, rather than the opportunity of mounting a monster spindle. i will stick to the 2.2Kw items most people use.
I know it may be overkill, but I think it will be great to have the best machine you can build and afford, rather than something you know you could have improved and done better on, that would just bug me.
If there are any other changes I need to make, please comment.
Thanks as always for the quick replies, really appreciate it!
Ok well lets see the rest of the design for Z axis and work from that.
My suggestion for nema 34 on 2020 screws was mostly for the long (X)axis to keep screw speed down to reduce whip and still maintain 10mm pitch speeds but I've just noticed it looks like your intending to use rotating ballnuts which if correct then you could use nema 23 motors on 10mm pitch.
That said 20mm pitch would allow a ratio to increase torque and have a lower nut speed for same speed as 10mm pitch which if using 20mm dia screws (which I would use at this length) may be better with the larger nut on smaller motors.
This doesn't help the Y axis thou which will still need nema34 motor if you use twin screws on single motor. That said Mixing motor sizes isn't a problem if you use High powered drives because they run from mains AC so don't have a mix matched DC power supply which would be needed for the lower voltage DC drives running the nema23 motors.
What you miss with this gantry design is that the rails must be as low as possible, at least one of them. Otherwise is pointless. Now you are just making a big lever.
As it is now is weaker than normal gantry.
The big+++ of this design is eliminating overhang and stiffening at the bearing blocks and lowering the assembly and eliminate gantry twist.
But as i see it you just lengthened the lever and didn't eliminate twist. Ok, square z casing will be stronger but will push more the gantry beams and bearings.
Ideally 3 rails at the gantry will be perfect as i see it with this design.
But adding third couple of bearing blocks on a normal gantry Z will do the same, its easier and cheaper. And 2 beams soldered together will be stronger than 2 separate beams as is your case.
So, try to lower one of the rails.
The point being here is that this design needs to be done correctly cause it will allow high speed machining or deeper dig, but you will need as i see it at least 3kw spindle, or it will become the weak point. As Dean said before.
Also just to clarify, the Z axis will be inside the boxed section, not on the front, overhanging it, so the loads will be evenly spread across the frame as far as I can see?
Running a 3kw spindle would be nice, but to begin with I think I would opt for the 2.2kw as I can find out the limitations of the machine with that and then start to push things later on in the process. The option of quicker cuts would be nice, but quality is my first concern to begin with.
I mean- to lower one rail at least on the gantry. To be nearer to the bed. Not on top like its now. I know- more difficult.
My point is that if you don't lower the gantry rails like Jonathan's friend machine, you gain nothing with this gantry design.
Yes, i get- the Z will be enclosed and strong, but long...so bearing blocks will be the weak spot.
Jonathan's design is great but changing this and that can make it weaker and not worth it or opposite, better it.
Obviously you haven't seen 2.2kw and 3kw spindles. There is 1hp difference, which could be quite important at low revolutions where there is not enough power. Also the bearings are bigger if i remember correctly.
A 100€ difference including VFD, which i believe is worth investing into.
Ok question whilst Im back to the drawing board.... Can I run profiled rails upside down, as in, on the base of my gantry box section? If not I will have to build the Y axis completely differently to the way I intended and therefore the Z too.
Also I have seen the difference between the 2.2kw and 3kw spindles and am aware of the differences, also the diameters are different 80mm vs 100mm I recall? I will use the 3kw at some point, but as with everything, budget has to come in somewhere.
Thanks, makes it a lot easier. Will that put the twisting/leverage issue right?
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