Design Help Pt2 Required for CNC design/Build

[MikeyC38]

Thanks everyone for the very kind and useful advice. Here are the revised plans with most of the stuff hopefully taken into account:

1. Revised Z axis with bearing blocks fixed to the Z plate against the gantry
2. Gantry sides beefed up to 200mm width to reduce racking . 20mm thickness
3. More detail added in drawings

The endplates will be extended to allow for a future upgrade to twin ballscrews as everyone is suggesting! and belt driven to avoid synchronisation issues as discussed earlier.

Thanks for the guidance on sources of aluminium plate.

For the eagle-eyed viewers you may notice that the y-axis bearings are floating... this is not deliberate but something I realised that a 750mm ballscrew is the total length, not the threadlength and as I want to bolt the BF/BK blocks to the gantry sides then I will have to reduce the length of the y-axis round rail and support. Question here - is it best to dismantle the supported round rail then cut the rail and support seperately and re-assemble? or try to cut it all in one go?

I'm really getting into the 3D solid CAD in a big way - it really does help you work out how things need to fit together and how on a 300mm ball screw, the maximum travel you can get on the Z axis using supported round rails would be no more than 150mm at best!

Thanks again everyone!

[JAZZCNC]

Question here - is it best to dismantle the supported round rail then cut the rail and support seperately and re-assemble? or try to cut it all in one go?

Cut it in one go. . . . I do it by first cutting the round rail using 1mm thin disc in the angle grinder, cuts like hot knife thru butter then finish Alu base using mechanical hacksaw but hand held will work just same.

[Jonathan]

The distance measured parallel to the Y-axis between the spindle and the Y-axis ballnut/screw is currently quite large. This will cause the cutter to deflect parallel to Y as the rails offer little support in that direction. Between the Y-axis rails is a good place, hence why a lot of people mount them on separate pieces of extrusion.

[routercnc]

The vertical plate on the back of the Z axis (to which the Y axis ballscrew is attached) is trapped between the small top and bottom plates. This means it needs to be machined accurately to ensure the Y axis bearings sit correctly. It would be better to make this plate full height and have narrower top and bottom plates so that everything can be set before tightening the bolts.

[MikeyC38]

Thanks Jazzcnc, Jonathan and routercnc for the comments on the Y and Z axis. Re-design in process to include using smaller seperate extrusions to reduce
alignment issues and enable the Y axis ballscrew and nut to be located under the Y axis rails and reduce the distance to the Z axis assembly.

Talking about the alignment of the axes for a CNC, I had the idea to buy a large thick piece of float glass (10mm x 1500 x 1000) to provide my "flat" surface from
which I could then make accurate measurements using a dial micrometer. By measuring the surface first, one could reasonably then account for the variations in the surface when measuring...

Regards
Mike

[MikeyC38]

Hi Guys

Been busy at work but have re-worked the Y-axis gantry design, taking into account all your comments. Have shifted the Y axis ballscrew closer to the Z axis gantry and used seperate extrusions to allow this and maintain torsional stiffness I think. I guess the main issue is the use of supported round rails - profiled rails would reduce the height and thickness. However given my other constraints of time, budget etc..lets see. The other approach is to use the extrusions in a L-shape as per Jazzcnc's photos. This has the advantage of mounting the BF and BK blocks on the Y-axis and not having to cut the rails. Will probably work up that design as well and make a decision. Now I just need some more money for the ali, steppers and electronics!

Regards
Mike

[MikeyC38]

Hi Guys

Been busy at work but have re-worked the Y-axis gantry design, taking into account all your comments. Have shifted the Y axis ballscrew closer to the Z axis gantry and used seperate extrusions to allow this and maintain torsional stiffness I think. I guess the main issue is the use of supported round rails - profiled rails would reduce the height and thickness. However given my other constraints of time, budget etc..lets see. The other approach is to use the extrusions in a L-shape as per Jazzcnc's photos. This has the advantage of mounting the BF and BK blocks on the Y-axis and not having to cut the rails. Will probably work up that design as well and make a decision. Now I just need some more money for the ali, steppers and electronics!

Regards
Mike

Well finally after all this time, I plan to start my build in August. Attached is the final design. I got all the bits now (Plate, extrusion, Zapp Stepper kit 1, ballscrews) so watch the build log for pics and progress. Again many thanks to all especially Jazz for the redesign. Here goes!