My first CNC Router *PAULIC* (the machine)

[WandrinAndy]

Keep posting.. beauty of the internet is even though you think your talking to yourself, your not!

Ditto..... And to add to the defence's case in mitigation .....

+ This forum is often quiet over weekends
+ Some of us are too inexperienced to offer advice
+ It's mostly only Jonathan who has specific experience of the rotating ballnut design?

Seriously though Paulus, whilst you have have obviously put a great deal of effort into your drawings, I think some of our minds have been spolit and brainwashed with 3D!

Your design looks good to this newbie.... Keep posting....

Andy

[paulus.v]

Thank you all for the replies,

What drive mechanism are you planning on using for the B/C axes? Either way the gantry needs to be *much* stronger.

I will try to build something like this. My concerns are about the gantry twisting from the long distance between Y rails and spindle. But if/when I will upgrade to servos I will be able to add more weight to the gantry and double/triple the profile/stiffness.

You should run the motors on about 70V - drivers are around £35 each from China, which will be far superior to the TB6xxx ones.

Yes I know. With 7A/80V I’ll get easy 600-800 IPM but this will be for the future upgrade. I cannot find on ebay any 70V drives at £35. Anyway I’ll enjoy soldering the components to build my drives :)

Z is fine with RM1605, Y is best with RM1610. No point using a rotating nut on Y or Z as it's not near the critical speed of the screw.

With X you're on the borderline for using RM1610. If your maximum travel is 1350mm, then you should be able to use a 1450mm screw quite comfortably which would be fine with RM1610 without the rotating nut. If you want it to be a bit longer, then the rotating nut with RM1610 will work very well.

I chose RM2005 for my long Z axis (20kg+spindle) to have a smaller thread angle and the rotating ball nut to avoid the motor weight added up to moving Z part. Do you think RM1605 will be fine? I do not want the spindle to fall when I turn off the power. It will be easier to make all the rotating nuts the same size. For Y I will consider rotating the screw but not sure if the RM1610 or RM2510 and for Z definitely RM1610 with rotating nut.

Putting both pulleys on to get 2:1 and 1:2 is a nice idea, the problem is it doubles (ish) the moment of inertia, which will greatly affect the acceleration you get. For that reason I would stick with just the one pulley and make the shaft as short/lightweight as you can.

I completely missed to consider the moment of inertia of the rotating nut assembly. Never thought it could be greater than the 1.25m steel screw. But after calculations it is actually three times greater with both pair of pulleys and equal to the gantry inertia, (0.75 vs. 2.3 kgcm2). I can reduce it at least to half by profiling or drilling the pulleys. Thanks again for enlightening me about this important aspect.

Everybody who joins here, including me. Says, "I want a machine that can do everything!. Foam through to ali"

Yes I wasn’t clear in my description. I want to be able to cut ali only occasionally. Maybe better not to mention ali at all. The main materials will be wood up to about 10-15cm thick and foam up to 65cm. This is why I’m trying now to design a removable/adjustable table to be able to put the hard material as close to the gantry as possible.

Seriously though Paulus, whilst you have have obviously put a great deal of effort into your drawings, I think some of our minds have been spolit and brainwashed with 3D!

I’ll make a simple 3D model if I have the time but I will rely on my accurate drawing for all the dimensions I need. I work better in 2D :)